Problem: I have a 2003 U320 with an Allison 4000MH tranny. The retarder started acting weird on our way to the Ladies Driving School that ended last week. The retarder use to work in this manner: toggle switch ON, hand lever pushed forward as far as it will go = retarder will not engage while decelerating or braking. Retarder works in this manner currently: Toggle switch ON, hand lever pushed forward as far as it will go = retarder engages while decelerating or braking. If I want to use the cruise control, I have to toggle switch OFF the retarder. While at FOT I had them check out the retarder. They plugged a "brain" gizmo into the wiring harness and drove the rig down the highway and verified that something was amiss with the retarder. Specifically the retarder will not disengage when decelerating/braking. FOT said they can't fix it and to take it to an Allison service center. Well the LDS ended and we motored to the DFW area where I called an Allison service center and described the problem with the retarder. Allison referred me to Stewart & Stevenson. I presume S&S makes the retarder. I called S&S and they said it appears to be a loose wire since the tranny wasn't displaying any error codes; that FOT should be able to diagnose and fix the problem since FOT has all the wiring schematics. I called FOT and they insisted that they can't fix the problem. Called S&S and relayed the info to them. S&S is still sticking to their original thoughts but said bring the rig in and they would call FOT for info on the coach wiring. However, S&S doesn't have any plugins to keep the house battery charged; refer going, etc. It might take days to figure out the problem.
Stewart & Stevenson is an Allison dealer, not a manufacturer.
Yes, I suspect you will need your coach wiring diagram handy for them (or get one from James Triana at Foretravel.
Allison makes the retarder. No codes is good, probably a loose wire like they said. Pretty easy to look under the coach back at the rear of the transmission where the retarder is. Perhaps others who have retarder coaches will chime in as far as problem solutions go. Have you looked at the Foreforum schematics here yet?
Pierce
Start the engine and check to see if your brake lights are on. I was having the same issue and it was the brake light switch.
Thanks to all for the info. I'll check the brake lights with the engine on. Always check the brake lights when preparing to travel, after hitching up the toad. Engine is usually off when checking the brakes. Not sure if I could identify the retarder if I crawled under the coach.
someone on the forum should be able to post a picture of the retarder that is on a U320.......
should be easy to locate.
Edit:
unfortunately I can't find a photo of ours right now..........
It could be one of the retarder control module sending units. Not sure as to the exact location on your age coach but ours is located behind the left hand kick panel at floor level. This is the one under the your left side console.
Mike
Video below shows a generic Allison 6-speed tranny and how it works. Fast forward to 2:50 for view of retarder location around output shaft.
https://www.youtube.com/watch?v=v4AJ2BvUMG4
I read some posts on loose connections between the ECU and the transmission shifter pad. Wondering if there is a loose connection between the ECU and the retarder joy stick? I gather the ECU is located under the service panel near the floor and steering wheel column? How does one remove the shifter pad and/or retarder joy stick?