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Mack rearends, no power divider?, Marc S, 29. Apr 2006 20:54


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By Eddy Lucast - Sunday, February 10, 2008 4:35 AM
Mack rearends, no power divider?, Marc S, 29. Apr 2006 20:54
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Just how does that work anyway? The truck in question is a 89' R tractor. Also, should you preselect a Mack 9 speed? I think the model number is T2090. Oh, and why in the hell did they put the heater unit right in front of the throttle pedal?

Thanks
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Re: Mack rearends, no power divider?, Lmackattack, 29. Apr 2006 21:59
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Mack rears I belive come standard with the automatic powere divider , It should automaticly actavate the power divider when wheel slip is detected. some times they wear out and it does not work properly. one trick was to stab the breaks when you were stuck to put resitance on the spinning wheel(s) and transfer power to the not spinning wheels(s). some thimes this helped kick in the power divider. Its hard to explain how it mechinicaly works with out seeing it taken apart. Lots of parts inside that make it work, thats one reason they wear out and dont work like new after 15 years LOL

The T2090 from my experince the pattern is
L,1,2,3,4 pre select to high range,5,6,7,8

revisions were made at some time and the gear pattern was L,1,2,3,preselect to high range, back to the low hole slot "4",5,6,7,8

I say preselect because I flip up the range select button in 4th just before I let off the pedal and make the move to high range 5th, hope that makes sence

Heater box..LOL hows your right shin feel after a full day trying to stretch your legs in the cab LOL. One think I liked about the long hood R models was that the gear shift levers come thru the floor under the heater box and give you more foot room.

Trent
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Re: Mack rearends, no power divider?, jim k tomer, 29. Apr 2006 22:07
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drawin from my very limited experiances......marc s

1.....how does a no pwr div mack rear work???.......;;;very poorly;;;

2..... should one preselect a 9 spd???.......;;;dunno why anyone would select one in the first place;;;;;

3 ...why is the heater positioned where it is????......in case ya get ;;cold feet;;;


......LOL.......HEHE....jim k tomer ...the altar boy
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Re: Mack rearends, no power divider?, Marc S, 29. Apr 2006 22:59
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The plaque on the dash says the pattern goes from 4th to 5th. Maybe the different pattern would be for an overdrive tranny? I think this one is direct. It shifts equally well whether I preselect or not but I was told once that some transmissions shouldn't be preselected so I got in the habit of not doing it. I just move into neutral before changing ranges, never had any problems but I had an old timer ride with me last week and he said he'd never seen anyone shift like that before.

The power divider thing is interesting. Never had to use it yet I just noticed there wasn't a switch on the dash.

Hopefully over time my leg will develop a callous. If it don't I'll just find a big hammer and move it over 2".

I visited my old trainer and mentioned I've been bitten by the Mack bug. He suggested that's like chasing after a fat, ugly, and mean woman. Good laughs aside he explained that with a Mack you are stuck with Mack dealer prices due to them not having aftermarket competition. Is this a valid complaint?
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Re: Mack rearends, no power divider?, Lmackattack, 29. Apr 2006 23:26
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Mark, I just checked the T2090 book and it says to "select Hi range wile in 4th (lowrange) and move through neutral into 5th" i.e preselect. The T2090 is a OD trans with a .71 ratio many times you will find high 4.xx or 5.xx rear end ratios. thats why the road speed still may feel like a direct drive trans. I have a spare 9 speed trans that I intend to use with 4.17 rears in my RS700, kinda tall gearing for off road use but she will move down the highway with the best of them. Some sware by the T2090 some hate them. some people had problems with the clutch pack for the HI-Lo range selector. I have driven a few 9 spd that had this issue. It makes a harsh grind from Lo- Hi

you wont know if the power divider is working unless you are in the mudd or slick surface and can see the tires spin then stop then all 4 get traction. sometimes you can "feel" the powere transfer through the truck as it actavates. something to get a feel for I guess.

As far as dealership prices I guess thats true for new mack trucks but there are a few afermarket vendors that sell knock off parts. Some stuff is still cheeper at my Mack so I always shop around for expencive parts just to make shure I get a good deal.
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Re: Mack rearends, no power divider?, Bill Donnelly, 30. Apr 2006 20:51
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Marc Mack dealer prices for R Model stuff are very reasonable, but PAI is very reputable aftermarket Mack parts company. They make engine, trim, transmission and rearend parts.
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Re: Mack rearends, no power divider?, John Costley, 30. Apr 2006 03:38
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Marc,
I always pre-select everything, never had a problem,just go smooth and steady.Mack power dividers are a little different than everyone elses.Like Trent said, when they wear out they just dont work as well anymore.Eaton and rockwell pass power to one rear under normal conditions, until you throw the switch and you lock "in" the divider and get power at both rears.The power still follows the path of least resistance and usually only spins one wheel end on each axle, unless you have side to side air operated diff locks, which usually have another switch to lock them in.Mack power dividers throw power back and forth from front to back under normal conditions, like a front to back posi trac.If a Mack has a power divider switch its to lock the power divider "out" so that power goes eqauly to both rears.Power still takes the path of least resistance from side to side, unless the rears have the optional " inter wheel dividers " which are basically detroit lockers, or posi tracs, for Macks.Mack doesnt offer the air operated lockers like eaton and rockwell, just the interwheel lockers.Like Jim said, the heater placement is to make sure youre feet dont get cold, a common problem on old trucks.Works real well in july and august,lol.John

Attachments
MACK POWER DIVIDER.jpg (172.76 KB)
MACK POWER DIVIDER 2.jpg (184.28 KB)
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Re: Mack rearends, no power divider?, Freightrain, 30. Apr 2006 04:47
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How's it go..............A Pete has a heated steering wheel..........so the drivers hands don't get cold waiting for the tow truck LMAO!!!!!

Larry
1959 B61 15 gears of twin stick, black smoke huff'n fun
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Re: Mack rearends, no power divider?, Geoff Weeks, 30. Apr 2006 04:59
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Eaton and rockwell pass power to one
> rear under normal conditions, until you throw the switch and you lock "in" the
> divider and get power at both rears.
This is a common mis-conception, there is a differential in the powerdivider that shares the load between both front and rear axles, BOTH recieve power at all times, when the power divider is locked, the diff side gears are locked to the case and it turns as one unit locking the foward axle to the back, so both must have a wheel spinning to keep you from moveing.
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Re: Mack rearends, no power divider?, Marc S, 30. Apr 2006 05:05
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So if you were to run the power divider locked on dry pavement the rearends wouldn't fight each other? Interesting. I know my 2.5 suplus military truck (M35A2C) doesn't have a power divider, the axles are driven at all times. Not a big problem as long as I place the tires accordingly. However on long trips I'll take the interaxle driveshaft off thus driving only the front (rear) axle. I'll see a .5 mpg gain.

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Re: Mack rearends, no power divider?, Geoff Weeks, 30. Apr 2006 05:54
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yes they would if you left it locked, un-locked the interaxle diff adjusts the power to each so binding will not occur
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Re: Mack rearends, no power divider?, Jim Rose, 30. Apr 2006 14:46
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Goeff;
You are correct about the so called "power divider" driving both rearends. I have often wondered how myth of only driving one rearend, unless the powerdivider is locked, got started.The power divider is an inter-axel differencial that can be locked manually. It is the same as saying only one wheel on your car does all the work.
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Re: Mack rearends, no power divider?, Geoff Weeks, 30. Apr 2006 15:21
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It might come from refering to the "primary Drive axle" when talking about chain laws, or a throw back to the days of the belt drive tags.
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Re: Mack rearends, no power divider?, John Costley, 1. May 2006 03:21
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Geoff,
So if I read that correctly, that would mean every tractor Ive run over the last twenty years ( except the Macks ) has had a worn out power divider, even the new low mileage ones, because they would all only spin one tire on the back axle in mud,snow,or ice unless you locked in the power divider, then they would spin one tire on each axle.That means all this time, all those tractors should have been spinning one tire on each axle at all times without throwing the switch, like all the Macks Ive driven did.Guess those Eaton and Rockwell power divider wear out REAL quick compared to Mack.John
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Re: Mack rearends, no power divider?, Geoff Weeks, 1. May 2006 04:33
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No, you miss understand, There is a diff in the power divider, both are powered but, like a normal diff, if one looses traction it gets the power, when you lock in the powerdivider you are locking the interaxle diff. But as you point out it only take two wheels spinning to keep you from moveing. Thats where full locking diffs are handy
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 03:21
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on 1. May 2006 04:33 Geoff Weeks wrote:
> No, you miss understand, There is a diff in the power divider, both are powered but, like a normal diff, if
> one looses traction it gets the power, when you lock in the powerdivider you are locking the interaxle diff.
> But as you point out it only take two wheels spinning to keep you from moveing. Thats where full locking diffs
> are handy

Geoff;
You are wasting your time trying to convince the "only one rear end drives without the power divider locked crowd", which is probably 75% of the truck drivers, that both rears pull at the same time. They will not be confused by facts, manufactures brochures, diagrams or any other information you may present to them. One truck driver told another and he told ten others and they all beleive that only one rear pulls without the power divider locked and nothing is going to change what they think. If they were to talk to the engineer that designed the rears they would tell him that he is wrong also.
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Re: Mack rearends, no power divider?, John Costley, 2. May 2006 03:47
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Jim,
Since Im on dirt on a daily basis,and whenever my rear axle is unloaded by backing or driving over a smal ridge, or thru mud,sand, or snow, it will simply spin, with the front axle doing absolutly nothing to move the truck until I lock in the divider, yes I would have to tell the man who designed it that he screwed up.Every tractor Ive ever had with eatons or rockwells has been like this,even when they were almost new ( never had a brand new one ).If the rear axle loses traction, nothing happens until you throw the switch.They may have wanted it to work like a Mack, but it doesnt.I dont really care about what the diagrams show, I care about how it really works in the real world.John
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Re: Mack rearends, no power divider?, Jim Herriot, 2. May 2006 15:43
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John: I am confused now.......... The front diff is always driving the gear set, but I have found it won't move the truck. I have a 25000# drive on hoist, the on ramp is 10" tall, 32" long, If you get the front drives on the ramp, and the rears off the ground,forward motion stops, rear axle wheels spin........... Lock the power divider, and bingo ,drive on up...........much like the real world........ So I am amongst the 75 %ers(probably closer to 95 %ers) that believes the old wives tale about the "rear axle on a twin screw does the driving most of the time"............. Jim
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 16:01
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Jim H.
Try backing the truck on the ramp and getting the front rear off the ground and "Bingo" one or both wheels will turn and the truck will not move until you lock the powerdivider. It there is no power to the front axle until the powerdivider is locked, why do the wheels turn on the front rear axle when you get the load off them without the powerdivider locked? They surely would not turn unless they had some power to them. Anyhow stay in the 75% as you do not need to know how it works as long as you know enough to lock the power divider.
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Re: Mack rearends, no power divider?, Jim Herriot, 2. May 2006 16:29
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Jim R; on occasion we have to do that, back it on, most often when the power divider does not engage, and it works every time, as long as the rear drive has contact, it will move.......... Jim.
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 16:45
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on 2. May 2006 16:29 Jim Herriot wrote:
> Jim R; on occasion we have to do that, back it on, most often when the power divider does not engage, and it works every time, as long
> as the rear drive has contact, it will move.......... Jim.

The front axle has the have contact with the ground with the powerdivider un locked or the truck will not move.
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 15:45
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on 2. May 2006 03:47 John Costley wrote:
> Jim,
> Since Im on dirt on a daily basis,and whenever my rear axle is unloaded by backing or driving over a smal ridge, or
> thru mud,sand, or snow, it will simply spin, with the front axle doing absolutly nothing to move the truck until I lock
> in the divider, yes I would have to tell the man who designed it that he screwed up.Every tractor Ive ever had with
> eatons or rockwells has been like this,even when they were almost new ( never had a brand new one ).If the rear axle
> loses traction, nothing happens until you throw the switch.They may have wanted it to work like a Mack, but it doesnt.I
> dont really care about what the diagrams show, I care about how it really works in the real world.John

John;
You make my point and anything I tell you will not change your opinion. will you say that damm back rearend has quit pulling if you jack up one wheel on the front rear and it spins and the truck will not move until you lock the power divider? Also put the rear axle on the same ridge and watch at least one wheel on the front axle spin until the powerdivider is locked. Anyhow that is your opinion and you are sticking with it. Do not let the facts confuse you.
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Re: Mack rearends, no power divider?, John Costley, 3. May 2006 02:09
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Jim,
Okay, youre right.The front axle is getting power, maybe somewhere around 5 %.If it cant move the truck, does it really count as putting power to the ground ?.John.
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Re: Mack rearends, no power divider?, Jim Rose, 3. May 2006 20:12
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on 3. May 2006 02:09 John Costley wrote:
> Jim,
> Okay, youre right.The front axle is getting power, maybe somewhere around 5 %.If it cant move the truck, does it really count as
> putting power to the ground ?.John.

John;
Its not that the axle is not getting power, it is traction that is missing. Do not worry more than a few people think that one wheel on their car does all the pulling. I would suggest getting the front rear from an old SQHD, taking it apart and studying how the power flows. If that does not convince you then you are beyond help.
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Re: Mack rearends, no power divider?, Bill Donnelly, 4. May 2006 07:35
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Jim how about a little diplomacy in your replies. John is not dumb. This is a great thread but let's keep it friendly.

I remember this saying I picked up from a fellow employee at Vought Aircraft, "Diplomacy is the art of telling someone to go to Hell in a way that they look forward to the trip".
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Re: Mack rearends, no power divider?, Jim Rose, 4. May 2006 12:29
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Bill D;
In no way did I want to insult him with my reply and I apologise if he was insulted. It seems that the majority of truckers cannot understand or do not want to understand how the power divider works. I will have to admit that I enjoy being involved in the controversal discussions on this site.
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Re: Mack rearends, no power divider?, John Costley, 5. May 2006 04:14
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Bill,
Thanks.
Jim,
It seems to be more about the proportion of power than actual traction conditions.Mack and Eaton/Rockwell use the same terminoligy, but the engineering and actual function are like comparing apples and oranges.The Macks seem to throw more EVEN power to all four wheel ends regardless of terrain or individual wheel traction.In a typical scenario, if one rear/rear wheel breaks traction on a Mack, its not as noticible because the front/rear is still recieving a full 50 % of the power and pulls the truck thru.On an E/R set up, if one rear/rear tire breaks traction the truck will stop and spin until the switch is engaged because the front/rear is not recieving a full 50% of the availible power.The E/R set up only seems to throw 5-10% of the availible power to the front/rear which isnt enough to pull the truck thru.Generally, if the front/rear falls into a low spot the rear/rear will push the truck thru without a large enough pause to notice any wheel spin on the front/rear.This is probably the biggest reason for the majority of folks saying that power only goes to the rear/rear on an E/R set up.The proportioning is so uneven that it might as well only be going to the rear/ rear when compared to a Mack.Thats not to say the Mack set up is better in all things,its just better in a switchless scenario.Its not that E/R didnt try, its just hard to design a better mousetrap when the first guy allready holds the patent rights.Its kind of like this.Youre on LEVEL ground, but its greasy brown mud or slushy snow with hard whitepac underneath.A Mack and a truck with an E/R set up are side by side.They let the clutches up and the Mack spins a tire on both axles, then maybe one stops while the other spins,then they might switch again, but its trying to dig in and its starting to move.The E/R Breaks loose as soon as the clutch comes up,usually just the right rear, and the truck wont move.While the Macks gaining a little ground and maybe starting to even out on spinning because its starting to get a little momentum going, the E/R driver clutches down and brakes to stop his spinning wheel,throws the switch, clutches up and now has a wheel spinning on each axle at pretty much the same speed.He tips in a little throttle and catches the Mack pretty easily, if the Mack tries to throttle up to stay ahead instead of holding the throttle steady then he might go back to alternate spinning wheels and actually lose ground.Now,if the E/R driver was smart he would have engagded the switch before he ever let the clutch out, knowing from experiance that he would be wasting his time if he didnt,and he would probably already be ahead of the Mack.The Mack driver probably wouldnt have a switch because his boss was too cheap to order that option, mostly because the salesman went to great lengths explaining to the boss how well the Mack power divider worked and trying to talk him out of it so the salesman wouldnt have to worry about a warrantee claim if the boss's drivers didnt use it right.Of course, if they are both late model trucks, and the owners had spent time in the mud themselves, they would be ordered with the Power divider lockout switch and interwheel power dividers in the Mack, and four way lockers in the E/R set up, and they would both perform pretty evenly or they just shouldnt be in the mud anyway.But,its not a perfect world and options are expensive, so you try to get by with what you have.If both trucks never left the asphalt they would never notice the differance anyway.John.
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Re: Mack rearends, no power divider?, Frank Surber, 5. May 2006 09:28
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Several years ago a company called Gleason Torsion developed a diferintal that would actually suply 50% of the power to both wheels at the same time even if one was sitting on ice and the other on dry concrete.
it used a complex gear set of 8 helical type gears mounted 90 deg to each other. instead of spider gears. It was susposed to become the ultimate 4x4 drive system but As far as I know most of their technology was bought up for Military testing And I have no Idea what has become of that.
The sample cutaway display that I saw looked promissing. you could turn the hand crank on the input andtry to hold either of the out put shafts . I re peat TRY to hold the out put shaft.
But you could turn either output shaft ever so much faster that the other
Frank in Kuwait
f_s482000@yahoo.com
http://frankinkuwait.bravehost.com

Attachments
Torsen.jpg (35.27 KB)
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Re: Mack rearends, no power divider?, Ed Pruss, 5. May 2006 09:54
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I think Eaton recently bought TrueTrac.

Ed Pruss
Longmont, CO
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Re: Mack rearends, no power divider?, Frank Surber, 5. May 2006 10:07
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Heres a link to the torsen home page

http://www.torsen.com/
Here is a link to the POP SCI atricle
http://members.rennlist.org/951_racerx/PS84Gleason.html
Frank in Kuwait
f_s482000@yahoo.com
http://frankinkuwait.bravehost.com
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Re: Mack rearends, no power divider?, John Costley, 6. May 2006 05:26
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Frank,
The aftermarket ones that they make for pickups seem to work real well and have had good write ups and test results in the 4WD magazines.Supposed to be more asphalt freindly than detroit lockers and long lasting.Dont think they were ever a factory option on anything but the hummers.Too bad they dont (didnt) make a big truck model like detroit.Nice design,almost like having a planetary diff as far as gear streangth.I may be wrong, but I think detroit was the onlt one to ever make a mechanical posi unit for big truck rears, other than the Mack's interwheel power divider for their own rears.John
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Re: Mack rearends, no power divider?, MORGAN HEATON, 6. May 2006 17:19
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Frank,
They use the torison gleason locking diff in the ford F150 and ranger FX4 level II pickups. I don't think it can break. Morgan
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Re: Mack rearends, no power divider?, Lmackattack, 5. May 2006 19:45
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John, good example of the diffrence in axels. I had worked a job site, In a R model, that was covered in hard packed clay that was like melting butter. Safe to drive on with out getting stuck in deep mud but so slick that if you stopped it was difficult to get her rolling again. The mack rears worked just fine if you went slow and did not try to rev the gears out from a full stop. I rember they day because I had to use all 5 reverse gears just to get the truck to ware we were dumping...down shifting as speed decresed BACKING UP!!!! LOL
HA love telling that story!!
All the other trucks with Eaton or rockwells had to use the "diff lock" or power divider to get out. I do like the Diff lock option as it gives powere to both axels no BS about them. but like anything If the driver forgets to unlock it befor he hits pavement...well ytou know the rest
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Re: Mack rearends, no power divider?, Brian Kelly, 5. May 2006 05:44
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My mother once told me that the definition of diplomacy was that instead of telling someone that they have a face that would stop a clock, tell them "When I look at you time stands still."
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Re: Mack rearends, no power divider?, Bill Donnelly, 6. May 2006 19:53
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Good one Brian!
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Re: Mack rearends, no power divider?, Gary Van Rheenen, 2. May 2006 10:57
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Geoff, if there where no power divider at all would one set of duals spin while the rest stood still?
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 16:04
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on 2. May 2006 10:57 Gary Van Rheenen wrote:
> Geoff, if there where no power divider at all would one set of duals spin while the rest stood still?

Gary;
It would be as if the powerdivider was locked and one wheel on each axle would have to turn. Try jacking up one wheel on each axle and watch the truck not move, let one down and it will move.
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Re: Mack rearends, no power divider?, Geoff Weeks, 2. May 2006 18:21
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The rear drive is most often the one that is backed into the soft mud, so it is more common that it will spin. If the front axle is dropped into a hole, or if the rear is backed over a large curb to take enough weight off the front drive, it will spin. Without the powerdivider locked only ONE tire has to loose traction for the truck not to move, with the powerdivider lock only ONE tire on EACH axle has to loose traction for the truck not to move. If the truck is equiped with locking diffs and locking powerdivider ALL 4 wheel have to spin for the truck not to move. Old worm drive axles often did not have powerdivider and the tires had to be matched to prevent binding.
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Re: Mack rearends, no power divider?, John Hanson, 2. May 2006 19:08
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Then why do the rear drivers always wear and cup faster than the fronts?
JH
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Re: Mack rearends, no power divider?, Too_Krazy, 2. May 2006 19:28
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My guess would be weight transfer to the rear set when pulling hard. Figure the front driver axle as a fulcrum when the truck is pulling. The front end of the truck tries to lift from the torque and weight is transferred to the rear set. If you figure the rear set as the fulcrum the same thing happens as the truck body pivots on the rear set weight is taken off the front driver set. Equalizing suspensions only truly equalize the load when the frame is parallel to the road surface. Leverage can be helpful but sometimes can be a problem. Good guess?

DODGE is the perfect thing to put on the front of a truck.
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Re: Mack rearends, no power divider?, John Hanson, 2. May 2006 19:40
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My guess would be that then there would be more slippage on the front drivers then...so more wear, or at least more apt to cup... I'm tending to agree with John C... I've been there too many years to go with much else. I don't think the rear does all the driving, but the majority of it at least.
JH
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 21:31
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on 2. May 2006 19:08 John Hanson wrote:
> Then why do the rear drivers always wear and cup faster than the fronts?
> JH

John;
It is because a 3 axle truck pivots on the 2nd axle when making a turn, and the 3rd axle is the one that slides sideways. Watch the 3rd axle the next time you see a 3 axle tractor making a hard turn.
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Re: Mack rearends, no power divider?, Jim Rose, 2. May 2006 21:25
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Geoff;
You said it well but I am sure that you have not converted even one of the 75% beleiving otherwise. Oh well! there are a few that still beleive that the earth is flat.
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Re: Mack rearends, no power divider?, John Evans, 2. May 2006 21:32
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Yep Jim some still feel they will fall over the edge.

John Evans
Trucks and dogs are Expensive !!
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Re: Mack rearends, no power divider?, Joe Wyse, 3. May 2006 01:30
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A differential is an equalizer. The same amount of power will always be sent to both wheels or both axles. When a vehicle goes around a corner and each wheel is moving at a different speed, equal power is transferred to both wheels. When one wheel is spinning, the resistance that is against that wheel, no matter how small, is still transferred to the other wheel, on a tandem axle it will be transferred to the 3 other wheels. If it takes, say 100 foot pounds of torque to spin a wheel on a slippery surface, the other 3 wheels will also have 100 ft/lb of torque trying to turn them. The truck does not move because the combined torque is not enough to move it. There is equal torque to both axles.
It would be better for the tires, the driveline and fuel mileage if it WAS only one axle driving.
It could be done like on a 4 wheel drive truck with a shift on the fly inter axle lockout and lockout hubs on one axle. I am thinking it would not need a differential because the tandem drive would only be needed on slippery surfaces. The question is if the savings would be worth the cost.
How often does the average on-highway truck need both axles driving? Not very much I would think. Especially the ones that stay south of snow country.
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Re: Mack rearends, no power divider?, jim k tomer, 3. May 2006 02:26
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when goin north a fairbanks ......in the winter....[sometimes summer also]...for us
it is ...power divider locked in...[at all times]
516 miles north
516 miles south

....jim k tomer ...the altar boy





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Re: Mack rearends, no power divider?, Jim Rose, 3. May 2006 20:23
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Joe Wyse;
I wish I could have stated it as well as you have. When you said having only one drive axle would be easier on the tires, did you mean less wear on the drive tires? If so I dissagree with you on that point only. I hope you meant less cupping etc.
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Re: Mack rearends, no power divider?, Joe Wyse, 5. May 2006 00:33
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All hope is lost ...... you'll have to enlighten me.
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Re: Mack rearends, no power divider?, dan renovetz, 30. Apr 2006 20:28
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GEOFF W. You're absolutely right about the misconception. All one has to do is put a bottle jack under one side of front or rear axles, then put the truck in gear and try to move it . It wo'nt pull itself off the jack unless power divider is locked . The one wheel will spin and truck wont move.
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Re: Mack rearends, no power divider?, Lmackattack, 1. May 2006 07:17
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intresting.. I dont know much about the "off breed" diffs/rearends, but that makes sence. If you did that same test on a mack tandem the powere should go to a stoped wheel and it would move foward. If it did not actavate a simple tap on the brake pedal should kick it in
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Re: Mack rearends, no power divider?, Marc S, 30. Apr 2006 04:59
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Good info guys. Macks power divider system sounds like it would be good for less experienced drivers who wouldn't remember to unlock it. Sometimes I'll still forget to unlock the power divider in the quad axle milk truck I drive on occasion. Of course that isn't the end of the world as long as the tires are matched fairly close. One thing I've never forgot, thankfully, is to unlock the drive axles. With a full load on and dry pavement I doubt they would last too long if you forgot to unlock them. When the going gets slick I'd say the standard Rockwell setup sounds better. When I get the R stuck I'll let you know how it works then.
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Re: Mack rearends, no power divider?, jim k tomer, 3. May 2006 00:48
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was waitin for all the ;;fallout ;; from the conversation
...basicly on a ;;normal ;;;[not mack tandem]
if ya jack up ANY wheel on any of the 4 corners ....[providing the pwr div is not locked in ...and is not equipped with any sort of side ta side lockers]

the truck will not move off the jack... as .its a one wheel drive...
....with the pwr div ;;locked;;; its a 2 wheel drive......will now move[with the 1 jack under it]
but wont move with a jack[s] under each axle...[on what ever outher wheel end]
one drives per axle......[as said....least resistance]....ie ..the one most likely ta spin
.....[dont matter which wheels]

in the case of the mack power divider [suppossedly] automatic
the ;;nest has 2 cages ....if one overruns the other ..[from the input shaft of the front drive axle].......it ;;spits out ;;;
lugs...[like a bulldogs collor] and locks it [both rears together]

kinda like spinnin flywheel weights......[far from rocket science]

onna the problems with that is ....that the whole purpose of ;;lockin;; is ta never allow one wheel ta ever lose traction in the first place

by the time onna those ;;;automatic;; power dividers decide ta engage
...it may be too late......
.[onea the reasons they aint worth a S#%^( for nothin]

...been slidin backwards myself with all 4 positively locked in....
...on someathe ice covered grades of the ;;haul road;;;;

..[and thats after approachin the bottom of that 12 to 18 percent grade at at 70 mph at the bottom]

...as your ;;quiverin ;;; .....your thinkin ....damn ;;; ;;;wished i woulda chained it at the bottom;;;.....but once ya commit ...theres no turnin back....[cept when ya spin out and slide backwards]
...mosta my stuff has 4 way ..lockups...[either detroit lockers or air shift]
.....and your right ...geoff....jim r ....and john e
...been inta [rebuildin] many many rear diffs over the years....
got an idea how they work
.....but still learnin...though

....LOL.....jim k tomer ....the altar boy
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Re: Mack rearends, no power divider?, John Costley, 3. May 2006 02:54
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Jim,
As usual, you cut thru the BS pretty good.The whole start to this thread was that the Macks throw more EVEN power to both rears in normal use, WITHOUT A LOCKOUT SWITCH, than Rockwells or Eatons.It didnt start out as a " Whats Better " conversation, just a conversation about the differances.Myself, if I was looking for a used tractor I'd most likely pick one with Eaton or Rockwells just because most Macks arent ordered with the power divider lockout switch or the interwheel dividers ( posi tracs ) and adding them in is pretty pricy 'cause theyre hard to find used.If you can find a Mack with both those options, its a good off road set up and worth having, but the dealers had a habit of talking most buyers out of them.If you run an older tractor with Eatons or Rockwells,you know to throw the switch as soon as you hit the slop,because they arent going to go far if you dont. The 4 way lockers have gotten common enough that you can get them for a decent price at the junk yard.You cant swap a set of '90s 4 way pigs into '70s housing, but you can swap the whole housing easy enough if both tractors had the same suspension.For the guys who only operate in the world of smooth asphalt, its not a big issue and they'd never notice a big differance between any brand, heck, 95% of the highway freight dummys could probably get by with a single screw with a tag or pusher and never notice the differance.I guess it kinda seems like the Mack rears were designed for the big fleets, like alot of their products were.The Maxidyne engine could lug to 1,150 rpms and you didnt have to order the tractor with a pyro or worry about the driver burning a piston out of it.The 5 speed would let you put just about anyone behind the wheel and you wouldnt have to worry about their shifting ability.The Mack power divider made sure you dont have to worry about the driver throwing the switch while the wheels are spinning and scattering parts, 'cause there is no switch.In the normal asphalt world, I dont know that I would say ones better than the other, theyre just different, and thats were this thread started.John.
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Re: Mack rearends, no power divider?, Aaron, 3. May 2006 09:56
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Well you could cure lotsa problems with a set of Timkin worm drives, there always locked up, just keep plenty of tires on hand.
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Re: Mack rearends, no power divider?, Bill Donnelly, 3. May 2006 19:52
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Jim, the Mack interaxle power divider is available either auto lock or air shift. My R Model has an air switch on the dash for the power divider. I am not sure if it would work automatically if you lost traction and did not engage it from the dash or not. It is a normal Mack setup, but has an air shift on the side.
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Re: Mack rearends, no power divider?, Mike Harbison, 3. May 2006 20:19
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Bill,
Does your R model have something besides Camelback suspension?I know they used to recommend the air lock power divider when ordering a non-Mack suspension.My '58 B73 has Mack rears on Hendrickson suspension and it's equipped with the air shift power divider.
In later years,they recommended it for all air ride equipped trucks.I had a '91 CH with the Hendrickson based air suspension and Mack rears and it didn't have the air shift power divider.It was pretty helpless in sloppy farm lots.Kinda made me feel like I was driving a KW.
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Re: Mack rearends, no power divider?, Bill Donnelly, 4. May 2006 07:32
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It has camelback suspension Mike, but the build sheet shows it was ordered that way if I remember correctly. I will look at tonight.
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Re: Mack rearends, no power divider?, Ed Pruss, 4. May 2006 08:14
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On this thread about locking differentials, since I want to get a modern rear end(single axle) for my '49 GMC, what does a locking diff. look like? Obviously it needs some sort of control mechanism, I need to be able to identify one on the truck, either a single axle or a rear axle of a double axle truck. Any px or diagrams anyone could post?

Thank you,

Ed Pruss
Longmont, CO
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Re: Mack rearends, no power divider?, Charlie Hatfield, 4. May 2006 09:59
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How big a truck is the '49 gmc?
Charlie
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Re: Mack rearends, no power divider?, Ed Pruss, 4. May 2006 10:03
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Its a 752 w/ a 4-71, 10 hole motor wheels, 10x20 tires.

Ed Pruss
Longmont, CO
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Re: Mack rearends, no power divider?, John Hanson, 4. May 2006 11:33
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Not necessarily visible from the outside Ed. I have a locker (detroit) in the back driver on my KW... it's automatic. Some are air or electric, and I'd imagine you could see the control, but mine's just "there".. sure makes it get around alot better, though.... even if I don't know where the power is going to or coming from......hahhaa
JH
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Re: Mack rearends, no power divider?, Ed Pruss, 5. May 2006 09:55
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I 'll have to look around carefully for one, then. Thanks, John.

Ed Pruss
Longmont, CO
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Re: Mack rearends, no power divider?, John Costley, 5. May 2006 03:07
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Ed,
If youre going to be shopping at a junk yard,and youre looking for a single,Look at the ones still mounted first.A quick look in the cab will tell you if theres a switch for a crosslocker.Not sure how they labeled the switch in a single screw truck/tractor,but it would be the only switch besides a two speed switch that would pertain to the differential.As far as a mechanical locker, like a posi type, there is no external indicator unless you got lucky and found a tag.You can find some external pics on Meritor's and Eatons websites that show the actuator mounted to the outside of the diff.,the problem is that they look alot like a two speed actuator on the bigger rears were the two speed is air actuated.If I remember right, a locker actuator is usualy mounted at the lower drivers side of the pumpkin, a two speed actuator is usualy on the upper passengers side, but I could be misremembering it.Theres always the old standby four wheeler method.With one side jacked off the ground,see if you can turn a wheel.If the wheel thats off the ground turns its a peg leg, if it wont then its a posi ( or locked up junk,lol ).You can try the same trick with air applied to the actuator to see if its a two speed or a crosslocker.A two speed will peg leg like a standard rear.Vocational truck/tractors are more likely to have a locker than city delivery stuff.Good luck,John.
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Re: Mack rearends, no power divider?, dan renovetz, 5. May 2006 08:43
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JOHN --The most recent Consolidated Freightways tractors with Cat power have an air operated locker for the single drive axle . Helped local used truck dealer move 16 from Columbus and 8 from Buffalo , also did some trailer switching for him in his yard in mud and snow. That axle lock saved me a tow, i was impressed !! I believe they're Century models ?
DAN R.
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Re: Mack rearends, no power divider?, Ed Pruss, 5. May 2006 10:00
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Thanks, John. I wouldn't mind a 2 speed, but they aren't so common now.

Ed Pruss
Longmont, CO
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Re: Mack rearends, no power divider?, Bill Donnelly, 4. May 2006 16:59
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Mike I checked the Build sheet on my truck and item 2. is Power Divider Lockout.
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