Transmission Retarder & Air Pressure

[Big Al]

Why does the using the transmission retarder use air from the front brake
air tank? On a recent trip while using the transmission retarder I coasted
into a wayside and my front brake air supply went way way down
and the low air alarm came on. The rear brake air tank was still above 100 psi.
When I stopped the front air tank built up pressure.

When ever I use the retarder I always see the front air pressure drop.
Is there a problem here or is this normal?
When I don't turn on the transmission retarder my brake air pressure stays up.
Is there away to keep air pressure up while using the transmission retarder?
Thanks for your help.

[sfedeli]

Your retarder uses air to modulate the degree of braking force. It would appear to me that you have a pretty significant leak in that system for you to be losing air at such a rapid rate. If the leak is not occurring at the brake lever near the dash, I suggest getting the coach over a pit, fulling airing up the chassis and then deploying the retarder (engine running, in drive with parking brake set) to see if they can hear air escaping from under the coach somewhere.

[Big Al]

Originally Posted by sfedeli

Your retarder uses air to modulate the degree of braking force. It would appear to me that you have a pretty significant leak in that system for you to be losing air at such a rapid rate. If the leak is not occurring at the brake lever near the dash, I suggest getting the coach over a pit, fulling airing up the chassis and then deploying the retarder (engine running, in drive with parking brake set) to see if they can hear air escaping from under the coach somewhere.

Thanks Shane
I don’t think it’s leaking by the lever but I will look and I don’t know anyone with a pit
So I may have to take it in.
Thanks

[Randy Dupree]

I know for sure on the 93 retarder it uses a small air cylinder on the trans,but i'm thinking your model is different.
Shane?

[sfedeli]

All I know is there's an airline going to the retarder head on the trans... Fortunately, I have not "had to" investigate that component yet! A few years back, I had the local Allison shop rebuild my retarder module for a paltry sum. At that time, it needed a modulator of some sort that had a broken internal spring. My guess is that there's a chafe somewhere in the air line or on a fitting connection.

[Dieselbird01]

My 91 WB has a small air cylinder like the 93 WB Randy mentioned but since Alan's coach has a retarder hand control it should be more like what Shane described.

Attached is some retarder info from the 88 WB owner's manual - it shows several items that could leak air. With luck it could be as simple as a stop light pressure switch or an Allenair Solenoid.

[Randy Dupree]

Tanks John,i have never worked on that system.
But if i were,i would get a shop compressor hooked up and use it to check for leaks,it should be easy to find.

[Big Al]

Originally Posted by Dieselbird01

My 91 WB has a small air cylinder like the 93 WB Randy mentioned but since Alan's coach has a retarder hand control it should be more like what Shane described.

Attached is some retarder info from the 88 WB owner's manual - it shows several items that could leak air. With luck it could be as simple as a stop light pressure switch or an Allenair Solenoid.

John,
Thanks for the information that will help.

Originally Posted by Randy Dupree

Tanks John,i have never worked on that system.
But if i were,i would get a shop compressor hooked up and use it to check for leaks,it should be easy to find.

Randy,
Will hooking it to shop air make it leak? Or do I need to have the engine running with the retarder on like Shane mentioned to make it leak.
Thanks

[Randy Dupree]

I'm not sure if shop air will make it leak or not,i bet it will make some components leak.
first thing i would check in the spring brake cans,i think i see them in the drawing,

[Big Al]

Originally Posted by sfedeli

Your retarder uses air to modulate the degree of braking force. It would appear to me that you have a pretty significant leak in that system for you to be losing air at such a rapid rate. If the leak is not occurring at the brake lever near the dash, I suggest getting the coach over a pit, fulling airing up the chassis and then deploying the retarder (engine running, in drive with parking brake set) to see if they can hear air escaping from under the coach somewhere.

I aired up the coach via shop air and the way Shane suggested. I did not
find an air leak. Do you need to be moving for the retarder system to leak air?
If so then how do you find out whats leaking?
Maybe I'm not using it correctly......... I have been using it to slow me down
and bring me to a stop. Is this the normal way to use it?
Should I use it to first slow me down, turn it off and then use the brake to
stop me the rest of the way?