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Topic: Big Air Leak Hydraulic Accumulator (Read 2523 times) previous topic - next topic

Big Air Leak Hydraulic Accumulator

Our departure from Smithville, MO, was delayed by a significant air leak. After considerable searching, I located the leak at the control valve for the hydraulic accumulator that charges the transmission retarder. I was able to correct the problem with "percussive adjustment." The hydraulic accumulator on our coach is on the passenger side, near the front of the transmission. It is accessible through the door that allows access to the chassis batteries.

In preparation to head for home, we drove from our campsite to the dump station. All was well. I tilted the coach to driver side to enhance drainage from the waste tanks. When we got ready to roll, the coach leveled, but the air pressure would not rise above 70 psi. Pressure for the HWH "Travel Mode" was marginal. I could hear an air leak, but had trouble locating it. There was noise of a leak at the rear and the front of the coach. The noise at the front was from the large volume of air going through a pressure accumulator tank on its way to being exhausted in the rear by a leak. I assumed that a valve may have stuck when I tilted the coach to facilitate emptying the waste tanks.

If I tried to raise the coach with the leveling system, the front bags would full inflate. The rear bags would not fully inflate from air pressure from the primary compressor. Air bags would hold air. I could inflate the rear bags a bit more with the DC compressor. The brake system pressure would quickly drop from 70 psi to around 35 psi when I shut down the engine. The leak would only last a minute or so after the engine was off. It was hard to isolate the leaking sound with the engine running.

I blocked the chassis and crawled under several times searching for the leak. Marilyn and I communicated via walkie-talkies to check that the brakes worked and were not leaking air. I could see movement in the brake mechanisms and could feel exhaust on release. I talked to James Triana about symptoms and he provided some suggestions. It seemed like an HWH issue.

I finally found the leak when I put my finger below the valve on the hydraulic accumulator. I could feel air escaping. I rapped the valve a couple of times with a rubber mallet. The air pressure quickly climbed to about 120 psi and the air dryer purged. Travel the rest of the day has been good.

I share the experience and symptoms because it might help someone else avoid a service call because of a sticky valve operating by a solenoid.

Re: Big Air Leak Hydraulic Accumulator

Reply #1 –
I had a leak there once too. I had the offending part replaced a year or so ago.  Never thought of a percussive adjustment but then again the leak was constant. Now I can sit all night and not lose much air at all.

Re: Big Air Leak Hydraulic Accumulator

Reply #2 –
JD, D...., those symptom are close to what I had going on a couple weeks ago.  Would not hold air and could not find a leak.  Mechanic friend came over and spent an hour looking with no results and there was no air leak.  Weekend trip was uneventful after that. 
Before next trip I'll take a close look at the accumulator, never entered my mind.
Thanks
Gary B

Re: Big Air Leak Hydraulic Accumulator

Reply #3 –
JD,
Thanks for the heads up (from the head down guy ;D ).

Re: Big Air Leak Hydraulic Accumulator

Reply #4 –
Quote from: J. D. Stevens –

I finally found the leak when I put my finger below the valve on the hydraulic accumulator. I could feel air escaping. I rapped the valve a couple of times with a rubber mallet. The air pressure quickly climbed to about 120 psi and the air dryer purged. Travel the rest of the day has been good.

I share the experience and symptoms because it might help someone else avoid a service call because of a sticky valve operating by a solenoid.

Do we have a p/n for the solenoid/valve on the retarder?  Ours is acting up (small air leak; stops if lightly tapped) and we will be replacing it in the next few weeks when we pull the coach out of storage. 

Re: Big Air Leak Hydraulic Accumulator

Reply #5 –
I can look thru my invoices and see if I can find it for us.  Otherwise I am sure we can get it from MOT  or FOT.

Re: Big Air Leak Hydraulic Accumulator

Reply #6 –
Barry Beams Foretravel Technical help page has a good writeup on the valve replacement with an Allison part# of 29552377.None on ebay now. But you can find them on line.Gam

Re: Big Air Leak Hydraulic Accumulator

Reply #7 –
Michelle, wonder if that is the valve assembly we just replaced. If so the the Allison part # is 29552377. Attached photo shows old and new. EBay $130.00 plus shipping and I needed a longer nipple to install it.

Re: Big Air Leak Hydraulic Accumulator

Reply #8 –
Quote from: Dick S –
Michelle, wonder if that is the valve assembly we just replaced. If so the the Allison part # is 29552377. Attached photo shows old and new. EBay $130.00 plus shipping and I needed a longer nipple to install it.

Yup - that's it. 

Thanks,

Michelle

Re: Big Air Leak Hydraulic Accumulator

Reply #9 –
Just checked ours, large bubble leak, will try the impact adjustment first.

nope adjustment failed.
ordered one off E-Bay  $175.00

Re: Big Air Leak Hydraulic Accumulator

Reply #10 –
Related ...
On a routine "walk around" I recently found that retarder solenoid hanging by the air line & electric wires! My extra long brass nipple had broken, leaving the threads inside the retarder. A steel one probably would not have broken.
To prevent this happening again, I bolted the solenoid to a nearby frame member. The electric connector was long enough, just needed a longer air line.

Re: Big Air Leak Hydraulic Accumulator

Reply #11 –
Dick,  What are using instead of your long nipple?  Would a remote solenoid with a flexible air line to the accumulator work?

Re: Big Air Leak Hydraulic Accumulator

Reply #12 –
That is exactly what I did. "Remote'ed" the solenoid.  ;)

Re: Big Air Leak Hydraulic Accumulator

Reply #13 –
Would the valve be the same for a 1998 U270?