Cat 7155 Transmission ---Need help diagnosing problem with leaking air at Xsnm shifter control Assby block

[Mark Buller]

Can anone help me with a problem I am having with leaking air (via the most forward--when mounted in the truck--air vent cap) on the rectangular shaped transmission shifter block, mounted on top of the 7155 Xsmn. Air is leaking profusely, immediately upon pushing in the (air supply) Xsmn engage knob on the side of the Cab Xsmn shifter/gear selector (of course after waiting until the truck has built up at least 100psi air pressure) Is this a stuck poppet valve or a faulty O-ring or? or? Most important is how and what must be done to "FIX" this problem? The post about mounting an additional oiler and pressure regulator on the rear of the outside air tank is... done to preclude such a problem? i.e. dry sticking poppet valves?

 

[Karl kostman]

Mark it could be any of the above issues causing your problem. The first thing I would do is get some air tool oil into the trans manifold assembly then I would disconnect the air line leading the to the shifter assembly and put a decent amount of air tool oil into both these locations, then I would let it sit for an hour or so and activate the air valve in the cab to charge the transmission and work the shifter to the side back and forth. I would also keep an eye on the block on the manifold your talking about also and see if it leaking or blowing any of this oil out of it, if so then that would tell me you have a bad O-Ring in that block. As far as the trans goes I would add this oil to both locations at least a couple times and see if you can get that air leak under control.
Good luck!

 

[NDT]

Rebuilding the manifold is no simple task:

CAT 7155 Manifold rebuild | SteelSoldiers

Mine is doing the exact same thing.

 

[Mark Buller]

Mark it could be any of the above issues causing your problem. The first thing I would do is get some air tool oil into the trans manifold assembly then I would disconnect the air line leading the to the shifter assembly and put a decent amount of air tool oil into both these locations, then I would let it sit for an hour or so and activate the air valve in the cab to charge the transmission and work the shifter to the side back and forth. I would also keep an eye on the block on the manifold your talking about also and see if it leaking or blowing any of this oil out of it, if so then that would tell me you have a bad O-Ring in that block. As far as the trans goes I would add this oil to both locations at least a couple times and see if you can get that air leak under control.
Good luck!

Hi, thanks for your suggestion. I"ll get right on it....This seems like a very good idea and a logical method to see if it is possibly a stuck (ie. not closed poppet valve); or if the oil then allows the poppet to close--stopping or greatly reducing the air leak but with the added air tool oil being expelled via the vent breather---then yes, probably a bad O-Ring. Most likely a bad O-Ring would probably still be associated with "some" leaking air and oil-assumming the popet valve is fully closed. What do you think? The following members comment about rebuilding the Xsmn Control Block/Manifold , being NO "easy task"---would you suggest replacing the entire manifold?

 

[Mark Buller]

Rebuilding the manifold is no simple task:

CAT 7155 Manifold rebuild | SteelSoldiers

Mine is doing the exact same thing.

Well, I suppose there is comfort knowing "Iam NOT alone" with this problem! Thanks for your input. So, replacing rather rebuilding the manifold is the preferable option?

 

[NDT]

Well, I suppose there is comfort knowing "Iam NOT alone" with this problem! Thanks for your input. So, replacing rather rebuilding the manifold is the preferable option?

That is a good question. The manifolds that are available ($$$) were surplussed out back in the GL days, which is like 10 years ago. Already getting old for O rings. And then figure Uncle had them on the shelf for ? years. So that opens up the “R Racing” rebuild scenario which appears to be a huge time suck. So is swapping in a manual transmission. Where is the crying emoji?

 

[Mark Buller]

Rebuilding the manifold is no simple task:

CAT 7155 Manifold rebuild | SteelSoldiers

Mine is doing the exact same thing.

Hello NDT, Well after running some air motor oil through everything (without resolving the air leak problem) I finally removed the Xsmn Manifold block and seperated the plates and IMMEDIATELY saw the problem! A broken O-ring (p/n 5P8942, $5 on ebay) and a completely deteriorated red color rubber part called a: Plug, rotary valve p/n 9N4115 ($15-on ebay). So cost of parts was not bad..JUST have to see if reassembling all won't be too "challenging" or problematic. I'll keep you updated. I'll try to upload the pictures of the problem.

 

[Mark Buller]

Hello NDT, Well after running some air motor oil through everything (without resolving the air leak problem) I finally removed the Xsmn Manifold block and seperated the plates and IMMEDIATELY saw the problem! A broken O-ring (p/n 5P8942, $5 on ebay) and a completely deteriorated red color rubber part called a: Plug, rotary valve p/n 9N4115 ($15-on ebay). So cost of parts was not bad..JUST have to see if reassembling all won't be too "challenging" or problematic. I'll keep you updated. I'll try to upload the pictures of the problem.

 

[NDT]

Wow. How difficult was it to unbolt this through the access hole in cab floor? How many labor hours in are you at this point? Do you think the rest of the plungers are at end of life as well? Thanks.

 

[Mark Buller]

Hi, thanks for your suggestion. I"ll get right on it....This seems like a very good idea and a logical method to see if it is possibly a stuck (ie. not closed poppet valve); or if the oil then allows the poppet to close--stopping or greatly reducing the air leak but with the added air tool oil being expelled via the vent breather---then yes, probably a bad O-Ring. Most likely a bad O-Ring would probably still be associated with "some" leaking air and oil-assumming the popet valve is fully closed. What do you think? The following members comment about rebuilding the Xsmn Control Block/Manifold , being NO "easy task"---would you suggest replacing the entire manifold?

Hi, Just to keep you updated on my Cat 7155 Tranny problem: Well I tried the airmotor oil....no luck, so I removed and disassembled the manifold control block plates and see my fotos and response to NDT. Hope to get it back together ok and WORKING! Mark

 

[Mark Buller]

Mark it could be any of the above issues causing your problem. The first thing I would do is get some air tool oil into the trans manifold assembly then I would disconnect the air line leading the to the shifter assembly and put a decent amount of air tool oil into both these locations, then I would let it sit for an hour or so and activate the air valve in the cab to charge the transmission and work the shifter to the side back and forth. I would also keep an eye on the block on the manifold your talking about also and see if it leaking or blowing any of this oil out of it, if so then that would tell me you have a bad O-Ring in that block. As far as the trans goes I would add this oil to both locations at least a couple times and see if you can get that air leak under control.
Good luck!

To keep you updated see my response to NDT below. Thanks again, Mark

 

[Mark Buller]

Wow. How difficult was it to unbolt this through the access hole in cab floor? How many labor hours in are you at this point? Do you think the rest of the plungers are at end of life as well? Thanks.

Hi NDT, Well it wasn't so "terrible" ...I removed the left side (wet) air tank to increase the available space. Got maybe 8-10 hrs work in it so far...but no good having a nice M920 that does not run!!!! So I continue to "march on"; ordered the parts and waiting for their arrival here in Poland. I'll keep everyone updated on how "well" things go from here-on.