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Topic: Retarder only works with brake application not when lifting foot off gas (Read 634 times) previous topic - next topic

Retarder only works with brake application not when lifting foot off gas

Wondering if anyone has run into this, we have a long trip through New Mexico, Colorado and Wyoming in the coming months and would like the aid of the retarder on the trip.

Last weekend on a short trip the retarder would not engage regardless of joystick position when releasing the accelerator pedal.  It functions perfectly with application of the brake.  I figure is a small electrical issue but would like to have some pointers on trouble shooting it.  Has anyone experienced this and do you have any suggestions on how or where to start?

We have a 2000 U320 with the 450 Cummins

Thanks,
Dave

Re: Retarder only works with brake application not when lifting foot off gas

Reply #1 –
Was your cruise control on when doing this?  Retarder won't engage if cruise is set on mine.  And cruise won't set or engage if retarder is on (meaning the joystick is clicked back one or more)

Re: Retarder only works with brake application not when lifting foot off gas

Reply #2 –
I would first try and spray some deox-it on all the connectors. Joy stick, Retarder on-off and the big Allison connector in the luggage area. On my 1998 M11 that connector is on the rear wall drivers side. But yours might differ.
My coach will use the retarder while in cruise to hold the speed to the set speed on down grades.

Re: Retarder only works with brake application not when lifting foot off gas

Reply #3 –
Quote from: folivier –
Was your cruise control on when doing this?  Retarder won't engage if cruise is set on mine.  And cruise won't set or engage if retarder is on (meaning the joystick is clicked back one or more)

I believe cruise was on but not engaged.  It operated in this condition before this trip.  I believe previously when cruise was engaged on a down grade the retarder would activate when the cruise let out of the gas.  The cruise saw this as braking and would deactivate the cruise setting.

Re: Retarder only works with brake application not when lifting foot off gas

Reply #4 –
Dave,

The retarder, cruse, and brake interface can be set up either 5 or 6 different ways as to how it operates. So ours may not be set up like the next coach that came down the line.

Your problem could be the rheostat is failing or, the wiring connection at the rheostat has come loose, or where that wiring harness hooks into the retarder control box under the dash has come loose. If the retarder is working with the brake then that makes the control box good and the problem is most likely in the other leg that feeds it.(the rheostat side)

Mike

Re: Retarder only works with brake application not when lifting foot off gas

Reply #5 –
Quote from: Pamela & Mike –
Dave,

The retarder, cruse, and brake interface can be set up either 5 or 6 different ways as to how it operates. So ours may not be set up like the next coach that came down the line.

Your problem could be the rheostat is failing or, the wiring connection at the rheostat has come loose, or where that wiring harness hooks into the retarder control box under the dash has come loose. If the retarder is working with the brake then that makes the control box good and the problem is most likely in the other leg that feeds it.(the rheostat side)

Mike

Can you give me an idea of the control box location?  I had recently had my camera updated so the tech was in the dash behind the gauges and the center box near the audit system.  Wondering if something got knocked loose.
 

Re: Retarder only works with brake application not when lifting foot off gas

Reply #6 –
Quote from: druehlman –
1. Can you give me an idea of the control box location?
2.  Wondering if something got knocked loose.

Dave,

1. I have seen them behind the removable kick panel beside your left foot. If your coach is new enough that you don't have the carpeted kick panel then I have seen the control box ty wrapped to the back side of the steering column. You may have to remove the console were the retarder rheostat is mounted and look and see if it is just hanging by the wiring. (yep have seen that also)  I don't have a pic of what you are looking for right at the present but will try and locate one without taking my kick panel off. Look up Allison # 295-11306 and it should bring up what you are looking for.

2. Sure

Mike