Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 17, 2025 ...

Retarder shifting

November 21, 2022, 11:53:08 am

When I'm using the retarder the first click comes on fairly strong and then the second and third
click I'm not sure if it makes any difference. Then then it works better with the sixth one really that
pulls the coach down. Is this normal.

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Re: Retarder shifting

Reply #1 – November 21, 2022, 12:41:48 pm

Mine seems to be  progressive as I watch the retarder temp as I move through the ranges. When the stick is on the first through the third holding 230 deg. and I hit the brake pedal, the temp jumps. I am assuming ( we know what that means) that the brake activates the forth through the sixth position.

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Re: Retarder shifting

Reply #2 – November 21, 2022, 12:59:12 pm

And yesterday on the grapevine it seemed that whatever position the joystick was in, short hard braking Initiated more retardation and dropped a gear.
  But yes, with each notch on the joystick there should be a slight increase in retardation.

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Reply #3 – November 21, 2022, 05:08:02 pm

I'm going to do what Mike suggested and look at the Allison retarder air valve.

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Re: Retarder shifting

Reply #4 – November 21, 2022, 06:53:26 pm

Allison retarder utilizes a transmission fluid accumulator that fully dumps its contents with the first activation, either from brake pedal or joy-stick. We think of it as getting retarder action started. Retarding is just flowing transmission fluid into an empty chamber that has a rotating veined disk where more fluid in chamber increases retarding. So, it is important to quickly get some fluid into the chamber and then emptying chamber as retarding is called for and then turned off.

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Re: Retarder shifting

Reply #5 – November 22, 2022, 12:40:03 am

Barry,

I had understood that a chamber with rotating veined disks were involved but have never understood exactly how it works.  Your explanation was not really clear to me.  Could you please explain again with a little more detail?  That might really help.  Thanks.

Richard

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Re: Retarder shifting

Reply #6 – November 22, 2022, 07:23:38 am

Not Barry but...
I have always thought of it as using a boat paddle to stir a barrel of air vs a barrel of oil.... the more oil in the barrel the harder it is to stir. The paddle (veins) are connected to the output shaft of the transmission and are always spinning with the driveshaft.  The air valve and accumulator tank control the amount of fluid in the retarder.

Maybe Allison has a video of how exactly the retarder operates. That would be informative to watch. 👍

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Re: Retarder shifting

Reply #7 – November 22, 2022, 08:19:46 am

https://video.search.yahoo.com/search/video?fr=yfp-t-s&ei=UTF-8&p=transmission+retarder+youtube+videos#id=5&vid=34649fc7989e66bc885b17a6c4176959&action=view

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Re: Retarder shifting

Reply #8 – November 22, 2022, 01:50:47 pm

Here is another explanation from Barry Brideau's famous web site:

Retarder: Transmission Retarder Operation -How Does It Work? - All Things...

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Re: Retarder shifting

Reply #9 – November 22, 2022, 07:36:51 pm

I took the Allison retarder air valve valve apart and it looks fine. I can live with to way the retarder
works and I mostly use the Jake Brake.

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Re: Retarder shifting

Reply #10 – November 22, 2022, 07:44:16 pm

I have looked at new air switches and from the part numbers from  mine the new ones are 2 psi
4 psi and 7 psi. The 7 psi part number 29511308 and I change the 8 to a 9 and I got 10 psi. I think
I might be better going 4 psi, 7 psi and 10 psi. Any comments.

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Reply #11 – November 22, 2022, 08:12:01 pm

As I remember it, the more air pressure the greater the fluid movement to transmission.

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Re: Retarder shifting

Reply #12 – November 22, 2022, 08:23:54 pm

The psi is when the brakes communicate with the computer so the retarder works a little later.

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