M939A2 CTIS Front/ Rear Wheel Air Seals - manual glitch?

So, just going through the 5000-plus pages of the c.2012 maint manuals and parts books, and there's an anomaly. In the maint. manual it indicates that there are two different air seals with two different part numbers at each hub. When you go to the parts manual set, it says that the air seals for each front hub are both the same part number, and only those fitted to the *rear* are different part numbers. Anybody know which is correct? My front hub right side is venting CTIS pressure to atmosphere and I'm wondering if the wrong seal was used due to this potential error in the maint. pubs at time of rebuild.

Take the cover off and find out where the air is coming out of. Windex will help you. I have had to replace o-rings expecially where the feed comes out the hub.

I do know the rear hub center seal part #is 357974TAO I'm changing mine as of this writing.

I had a leak at one of the rears. It wasn't the seal particularly, but the plastic collar (called a sleeve) that separates them. It grendaded. My best guess would be that my spindle nut wasn't tight enough causing a bit of a wobble. The smaller (outer) nut came off with a large pair of pliers. It's supposed to be torqued to 250 to 400 ft/lbs. Who knows what they did when they rebuilt it. YMMV

I've had to deal with a number of M923 family hubs already and not *one* of those nuts has ever been torqued properly. In fact, one of my non-CTIS trucks had an inner oil seal failure rear which looked like it happened because the hub nut wasn't torqued properly (i.e. not enough torque) which caused enough wobble/eccentricity to spread the seal.

The one I'm having a problem with on my CTIS truck in the front also looks suspiciously recently-serviced vs. the others and I bet I'll find incorrect torque values there too which likely sped up air seal failure. As to that plastic sleeve, I dissassembled a spare CTIS hub from a torch-cut rear axle just to see how it all went together and found out the plastic sleeve looked as though it had degenerated/ deteriorated -- almost as though some grease or oil contaminant had started eating it and making it brittle. Hope that's not the case in *all* of them -- as in some future plague-level CTIS disease.

The air is definitely puking out from inside the hub. You can feel a nice breeze all around the hub/ backing plate. I made an airline to throw 60-70 psi at the front CTIS system only and it's a pretty obvious failure.

According to the parts TM, there should be two different air seals on the rear: 1) 357974TA0/ 5330-01-272-1147; and 2) A-1205-D-2162/ 5330-01-308-0175

According to the parts TM, the front should just use two of the 357974TA0 seal instead -- but the maint TM says the above ^^^

Since I'm guessing the sleeve will have deteriorated too (and it doesn't look as though you can disassemble everything non-destructively anyway), the maint TM shows:

SLEEVE: 2245-H-1022 / 3120-01-271-8353

I've seen the various seals advertised, but never the plastic sleeve. Anyone know who stocks them?

Its usually just a matter of adding a generic o ring here and there. If you find a problem that cannot be fixed with either tightening or adding an o ring post a pic I have repaired several of the front setups.
Will

Suprman said:

Its usually just a matter of adding a generic o ring here and there. If you find a problem that cannot be fixed with either tightening or adding an o ring post a pic I have repaired several of the front setups.
Will

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Will do. I'll have the truck back late next week. I noticed Ebay has basically everything for better prices than you find anywhere else...that I'm aware of anyway.

You can get some great deals on ebay but I have also gotten great deals on parts from other members too. The o-ring kits are 6 bucks at harbor freight.
Will

Fixed it. Pics later, but the inner air seal was somehow deformed on installation - probably by someone using a punch or similar to seat it during installation - or possibly because the lip of the seal contacted the outer edge of the spindle under weight when they were reinstalling it. Either way - it was buggered. It was also not seated properly. Both seals in the front hub are the same despite what the Maint. manual said (the parts manual is correct.) The inner plain seal also remained stuck to the spindle as opposed to coming off with the hub, which...I've never seen before. Replaced the whole works and it's holding air perfectly now.

One thing...and that's the wheel nut torque/ preload seemed to be just a bit more than finger tight - but not much. Manual specs 50 ft-lbs for the preload and 250 - 400 for the lock nut, and though the lock nut was right up there, I doubt there was 20 ft lbs on that main nut.

The last frustration is a rim o-ring leak on the intermediate d/s rear. AaaRRRgh. No wonder the CTIS system alarmed - trying to keep up with that front leak and the rim leak both. Now I understand 2 different o-rings were used in those rims (thin and thick) and you don't know which one you have until you pull it apart.