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Bendix Tru Flo - TF700 compressor - replace or rebuild or?
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By kblackav8or - Wednesday, August 03, 2011 6:49 PM
This compressor is on my spare soon to be primary Cummins 400.  Right now the PT pump is on it's way to Cummins for a checkup, new seals and to fix whatever is stuck in it.  Based on not running in over 10 years the seals are probably dried out and who knows when it was last apart.  At any rate too my question.  The compressor currently installed comes up as a 2 cyl Bendix TF700.  Probably overkill for an old non-air ride truck.  At any rate it is covered in gunk - grease and oil and the intake filter is saturated in oil.  The engine was pretty gunky too but I have traced that down to at least one valve cover gasket that is missing entirely.  When we ran it a couple times the road draft tube wasn't kicking anything of not out and there were no big leaks anywhere to speak of so I think valve covers are certainly contributing if not the cause of some of it.  No way to test the compressor to see if it is good bad or other.  While the pump is off I would prefer to deal with it now before it is in the truck and a bigger problem.  So options are - replace with a Bendix re-man, or an aftermarket re-man or buy some sort of rebuild kit?  My nearest decent parts dealer is pretty confident in the re-man outfit they are using so I am leaning that way but I suspect it is expensive.  Any other options or advice? 
By John_Costley - Wednesday, August 03, 2011 9:56 PM

They arent hard to rebuild.If you can rebuild a briggs and stratton you can rebuild a compressor.Heck, the compressor doesnt even have an ignition system to deal with, lol.If youre going to do a performamce build on youre Cummins some day then I would definatly rebuild that compressor myself and blueprint it in the proccess.All the standard hot rod tricks can be applied to the compressor.The compressor, or 7th cylinder, is the biggest horsepower and fuel mileage draw on any engine.John
By tundra - Wednesday, August 03, 2011 10:05 PM
id stay with the 700 ......has larger drives /etc ... than the smaller versions and is far better than the one lunger cumapart comp .......and ya  got the desireable acc drive already;;;;

jest leave it alone and see what it does [or doesent do]
By junkmandan - Thursday, August 04, 2011 4:39 AM
I thought compressors only drew about 7 HP, certainly only about a third of what a fan will draw . And the 700 series compressor has been the industry standard for years regardless of suspension .
By Geoff Weeks - Thursday, August 04, 2011 5:14 AM
The 500 or 501 has been std for years, the 700 or 701 has been the larger displacement optional. I have a 700 series I used on one of my trucks and it biuld much faster then the 500 series. Even with air start, the 500 series is enough for most applications. I've never liked the Cummins compressors (either single or duel piston) as they seamed to be more touble-prone then the Bendix or Midland designs.
By kblackav8or - Thursday, August 04, 2011 5:59 AM
My 270 has a 2 lunger compressor and it is much quieter and smoother then the 1 lunger that was on my 81 A model.  I always worried that compressor was on it's way to putting the rod outside as noisy as it was.  Also took forever to air up the 8 bag and 3 tanks.  As for this 700, no intent of going to another model.  Where might I locate a rebuild kit - my dealer seemed to be leading me to the already rebuilt option.  What would cause it to be throwing out that much oil?  Head gasket?  It is mostly oily on the sides and in the air filter.  I am not afraid of rebuilding it.  Trying to keep my costs down.  If an already rebuilt one with a warranty is only a little more then the parts or if I later get an unpleasant surprise I may lean that way.  It didn't make any unusual noises during my test start (not under a load obviously) nor was there any noticeable leakage. 

I presume it has to come off to rebuild - I could leave it and find out if it has a problem.  Now seems like the time while it is out of the truck and the PT pump is off. 
By Geoff Weeks - Thursday, August 04, 2011 6:33 AM
That series compressor uses a seperate front and rear "adaptor" or bearing retainer to fit the Cuumins drive. I have had gasket leaks from both these places as well as the bottom cover. I haven't had good luck sourseing the parts and gaskets... It seams the normal truck parts places would rather deal in complete units (likely because when atruck "shucks" a compressor, time is more inportant then price) and the rebiulders will not sell parts. Gaskets are easy to make, but rings and pistons can be hard to find.
By wayne graham - Thursday, August 04, 2011 10:13 AM
Kevin, Which ever way you choose to go remember you cannot core a 500 for a rebuilt 700. Your core is worth more money so don't get hustled on a trade. Personally I like bendix rebuilt units cause I don't have time to fool with it,and they have a warranty. just remember to core a 700 for 700. Wayne
By glenn akers - Thursday, August 04, 2011 1:50 PM
The real problem of over hauling a compressor is were are you going to get the parts and most rebuilt compressors are bored as for as the cylinders go and the crank can be turned like a engine plus many have a up date that i am sure you would have no way of knowing about untill you open a few of them up.I have rebuilt many or reringed many cummins compressors year ago but then i started to see over size cyl and undersize cranks. Were would you get the parts and how long would you have to wait.They may be nothen wrong with yours. I would clean it and give it a change.Many of these components are not repaired by the public on count of the tolls you will have to have and the parts avaibilty.But you can try and that is the quikest way to find out. Just call around and ask if any one can get you some parts.
By kblackav8or - Thursday, August 04, 2011 2:55 PM
My parts guy is inquiring about parts.  What would cause it to leak oil out of the air inlet?  Not 100% sure that is the source but it sure looks suspect.  If I can replace some gaskets at some point and do it without having to R&R the PT pump again, I am fine with waiting, especially when a recon is $390 + core. 
By glenn akers - Thursday, August 04, 2011 3:36 PM
kblackav8or (8/4/2011)
My parts guy is inquiring about parts.  What would cause it to leak oil out of the air inlet?  Not 100% sure that is the source but it sure looks suspect.  If I can replace some gaskets at some point and do it without having to R&R the PT pump again, I am fine with waiting, especially when a recon is $390 + core. 
         Leaking some oil from the intake is very normal.Put a intake hose on the compressor back to the after cooler and then you want see nothen but some seaping. Its called oil carry over and its from the oil slopper when in unloaded mode.It can be from the compressor being worn out.We had to do a card test when doing them on warranty.You would take the discharge line off and on a warm engine hold a white card two inches from the discharge fitting for two 1000 rpm. and watch the oil splatter.If so much you replaced the compressor and most the time the new compressore would pass some oil. 
By wayne graham - Saturday, August 06, 2011 4:31 AM
Kevin, none of my business but if that motor has set for several years I would pull the front cover and do new seals and check accessory drive bushing . then a rebuilt fuel pump and air compressor and you have eliminated a lot of trouble points on that motor. It is so much easier to do with motor out of truck. just me thinking. Wayne
By John_Costley - Saturday, August 06, 2011 2:15 PM
Everything you need to know about the 700  This will give you all youre part numbers, up to 30 thousandths over.   Anyone who sells Bendix can get you the parts, they just might not be smart enough to be able to read the catalog.The end drive pieces are usually engine manufacturer part numbers, not Bendix.

Spend $50 to get the reciprocating assembly balanced, just like a real engine, and you'll barely feel a difference between loaded and unloaded.After balancing, spend an extra $250 or so to send everything out for hard teflon coating before you assemble it and you'll never have to touch it again.    On a hobby truck that doesnt have to go to work on monday morning youve got time to do some extra.If it will always be for fun only then you dont need it.If you think you might want to work it a little, like shagging paper loads for you're brother, then do the extra now and you'll have peace of mind later.John
By PZ 1 - Sunday, August 07, 2011 7:17 PM
Some parts on eBay. You could probably find more with some other search words.