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Topic: Retarder switch on 1990 U300 with Detroit 6V92 (Read 938 times) previous topic - next topic

Retarder switch on 1990 U300 with Detroit 6V92

I have the retarder switch on dash, but how does this operate the retarder? What is the procedure? I've never had to use it before and now I'm in the mountains in Virginia and would like to know if it works.
Jeff and Victoria Moses
1990 U300 40'

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #1 –
Jeff, I would expect when you turn the retarder on, and press the brake pedal, it would activate.  Of course you would need to be moving above about 15 mph (That is how mine operates on the 320 & ISM engine).
Brother had a 89 GV with retarder and 6V-92, he loved the retarder, so I would guess if you get on the road and start playing with it, it will work.
Mine has 3 steps when using the brake pedal, all at different brake pressure settings.
Would guess yours would also.
Surely, there is someone on board here who has the same model as yours and can offer better info.
Good luck.
Dave M

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #2 –
It may be a jake instead of a trans retarder. Foretravel should be able to tell you
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #3 –
Jeff,
If it's like mine, when the switch is on it will activate in conjunction with the brake pedal.  It will operate proportionally with brake pressure - no electronics involved like the 3000 and 4000 series transmissions.  You should see that switch illuminate when the retarder is actually retarding.  The retarder has about a 2 second delay.  If you apply brakes lightly you should feel the retarding after the delay.
Here's what I do for grades: shift into 3rd gear, keep speed between 50 and 55 mph by applying brake (with retarder switch on).  Watch the transmission temperature - I keep mine below about 280 F.  When I apply the brakes I do it lightly so the reader does most of the work.  If the transmission wants to go higher that means you need to slow down even more (say 45-50 mph).  Turn the retarder switch off ( to avoid overheating) and use only brakes only to bring the speed down.  By all means keep it slower until you get the feel of it.  If you're feeling uncomfortable, you're going too fast.
Hope this helps.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #4 –
my 1993 U300 with the 6V92 has same switch.
It is for the Jake brake.
It has two positions. One is for all six cylinders, the other is for only three cylinders.
It works great in the mountains. Two years ago, in the great northwest it was invaluable.
However, it does not appear to work on level ground, but it does. Takes a lot of rolling force to really show.
1993 U300, 6v92
build 4366
USAF retired, Flight Engineer, C124, C130
 ATP, A & E.  & ex AI

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #5 –
Bill is right on the money. If you have a Detroit I'm betting it is a Jake Brake even though my switch says Retarder, it's a Jake and it works great in the mountains.

It is not active when the cruise control is on. Touch the brake pedal to turn off the cruise and the Jake will kick in.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #6 –
Here's a 1990 spec sheet and it shows a retarder under the transmission section and in the engine section doesn't mention anything about a Jake.  Makes me believe the retarder was standard and the Jake optional.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #7 –
John, it is my understanding that the turbo Detroit 6V92 had too much torque for the transmission retarder and the six speed Allison transmission. The retarder in the early 90's could only be used with the Cummins or Cats. Are you saying you have a 91, U300 with a 6V92 that has a transmission retarder and six speed Allison? I see your point regarding the spec sheet but that goes against what I always thought I knew about our early 90's U300's.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #8 –
I previously owned 1988 U300 40 ft 6V92 4 speed it had both jake brake and retarder could only use one or other
95 U320 SE
07 GMC CANYON

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #9 –
Quote
Are you saying you have a 91, U300 with a 6V92 that has a transmission retarder and six speed Allison?
Kent,
Not exactly, I have everything above but it's a 4 speed transmission (with a transmission retarder: MTB-648).  I don't think the 6 speeds had come out yet.
The HP on mine is 300.  In '92 when they went to the 350 hp, they up the tranny to a 700 series - still a 4 speed.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Retarder switch on 1990 U300 with Detroit 6V92

Reply #10 –
I learn something new every day. Thanks John for the clarification.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback