Retarder: Valve Assembly Installation

Allison Part # 29552377 (this replaces earlier part # 29547934) Replaced 3/13/13

The Foretravel shop reported our retarder valve assembly was leaking quite a lot of air. We decided not to replace it due to cost and advice from Alton that it probably was not necessary. The part, which they had in stock, was $500.03.

Later, we found 3 of these available on eBay. Buy it Now for $169.00 or Make Offer. Got one for $130 plus $6.85 shipping.

Prior to the removal of the old one, I raised the coach and let it settle on supports between the frame and axles. Then bled the air out of all tanks.

Removal is pretty easy; disconnect the air supply line and the electrical connector.

Then remove the valve from the retarder accumulator.

The hardest part was cleaning old pipe compounds from hardware threads.

The solenoid on the new assembly is a little wider than on the old one Part # 29522717. As a result, reusing the old nipple did not work. I had to get something longer. Found a 3/8” x 2” nipple at the local auto parts store, which worked fine.

I used a TFE thread sealer. Tested for leaks with a soapy solution; none found. Now we just have to confirm the normal operation of the retarder on our next trip in a couple of weeks.

We were able to find one on eBay for ~$136 (same place/seller as Dick told us about).

The only difference for me from what was posted it that I could not remove the old valve as it hit our transmission cooler when you tried to unscrew it. 

I opted to remove 3 of the 4 bolts that held the accumulator to its bracket and just loosen the 4th one. This allowed the accumulator assembly to rotate down (once you unplugged the wire and air line).

With the accumulator, the valve rotated I had all the clearance I needed and it allowed me to use all of the existing hardware with the new valve. Tighten all the fittings, rotate the accumulator back up and tighten the bracket bolts. by Steve Cook 2003 U320 40′

The retarder valve was leaking on my 1991 U300 and I replaced it while I was at Foretravel in Nacogdoches a while ago. They tried to look it up on the drawings but the retarder wasn’t even on the drawings. They said 1991 was the first year for the retarder and of course, Foretravel was the first manufacturer ever to offer a retarder and very few customers ordered retarders that the first year.

After thinking about it a couple of the guys at Foretravel said they remember my coach being built and they think it was the very first coach ever to have a retarder. Foretravel had to put their own valve on when they built my coach because Allison didn’t supply one yet so they used an expensive European valve instead.

They still use a similar valve on the pneumatic doorstep of the current Foretravels so that’s what they sold me and I installed it in their parking lot and it works! It probably won’t benefit anyone because I believe Allison started supplying retarder valves shortly after my coach was built so it’s doubtful many readers will have the weird European valve. Scott Cook 1991 U300 36′