Detroit/Allison Confusion

Topic: Detroit/Allison Confusion (Read 1053 times) previous topic - next topic

Detroit/Allison Confusion

July 06, 2018, 01:14:00 pm

I have been studying the posts for how to use my retarder; however, many posts raise the issue of whether my 1989 U300 GV has a "Retarder" or a Jake Brake. I am currently not aboard the coach and so cannot consult manuals on this. Any clarification will be appreciated!

Re: Detroit/Allison Confusion

Reply #1 – July 06, 2018, 01:58:07 pm

Foretravel makes it difficult as the switch on the dash is lableled "retarder" regardless of whether it has a transmission retarder or Jake brake. Yours probably has a retarder but the easy way even if not driving is to look at the valve covers. If the valve covers are not too tall and have Detroit in big black letters, there is no Jake as the installation requires a taller valve cover. Jake equipped engines also have wiring that goes under the valve cover.

Driving with the retarder switch in the on position on a Jake equipped coach will cause the typical Jake sound anytime you lift off the pedal. The Jake has two positions, just the right bank and both banks.

The spec sheet for the 1989 U300 does not say which system is used: 1989 GV Unihome 300 36-38-40

Pierce

Re: Detroit/Allison Confusion

Reply #2 – July 06, 2018, 02:02:24 pm

Quote

whether my 1989 U300 GV has a "Retarder" or a Jake Brake.

I think you could order them either way. For example, my 95 300 had a Jake and a one speed Jake at that (changed it to two). Also, some technical documents refer to all the supplementary brake systems as retarders. Regarding the noise that Chuck mentions, you have to listen closely when driving and you'll hear a change in the engine. If you hang your head out the window you'll hear it better but it is still pretty quiet. At least that's the way it was with my M11.
jor

Re: Detroit/Allison Confusion

Reply #3 – July 06, 2018, 02:54:27 pm

Thanks! It appears that I will need to determine this when I get to the coach tomorrow.

Re: Detroit/Allison Confusion

Reply #4 – July 06, 2018, 06:07:21 pm

Normal 89 u300 has a brake only operated when on hydraulic Allison transmission retarder.

Sure would see how and if a hand controller wand could be fit to the coach.

Re: Detroit/Allison Confusion

Reply #5 – July 06, 2018, 06:42:52 pm

I have not worked on any of the 4 speed Allisons, so interested in learning.

On the 3000 and 4000 series Allisons, there is an embossed plate with transmission number on it. Makes it VERY easy to verify exactly what transmission/what functions it has (R vs no R).

So, would be interested to know if the earlier transmissions had the same plate/info.

Re: Detroit/Allison Confusion

Reply #6 – July 06, 2018, 07:44:22 pm

Randall,
I'm quite sure you have the same power train system I have: 6V92, 300 HP, rear radiator, MTB648 Allison transmission.
I believe the B stands for retarder. Attached is the owner's manual with photo descriptions and the brochure. You only need to open either of the bay doors behind the rear tires to see the retarder and compare images in the owner's manual. I also attached a photo of the placard for Brett. It's a good idea to have a photo on file in case it gets knocked off for some reason.

Caflashbob is right. No joystick for our retarders; it's controlled with an air pressure line at the top of the retarder housing.
The dash switch only enables the retarder to work with the brakes:
Dash switch ON = retarder operates proportional with the brakes. The dash switch will light up when the retarder is working.
Dash switch OFF = no retarder at all, even if you apply the brakes.

With the dash switch on, and the brakes very lightly applied, you will feel the retarder kick in (i.e. feel the coach slowing) after about 1 or 2 seconds. This is the time for the fluid to fill the retarder cavity. You should also notice the transmission temperature gauge rising. When going high speed or on a mountain you need to watch that temperature gauge like a hawk. With light application of the pedal the retarder is actually working much harder than the brakes are, so it's kind-of a "retarder only" application.

Here's how I use mine:
City: switch ON, apply brakes normally. At those speeds the slow down doesn't last long enough to worry about the trans temp too much. But scan that gauge just like all the others while driving.
Downhill interstate mountains (typically 6%): I keep it in 3rd gear. When the RPMs get up to 2100 (55 mph or so) I slow down with the brakes to 45-50 mph. I have the retarder switch ON unless the trans temp gets too high - ideally I want to keep the speed down such that I never have to turn it off. I like to see the temp rise to no more than 230-250 F, as read on the dash gauge. It falls fairly quickly once your off the brakes. If I feel like I'm having to apply the brakes too often, I slow down even more to get it under control. For me, I want to feel like there is still plenty of brake capacity to slow down to a complete stop if necessary. Be conservative and go slower than you need to until you gain a feel for it. If you feel uncomfortable then you are probably going too fast. Steeper grades on roads will require 2nd gear speeds.

So, in general, I have the retarder switch on all the time unless:
1. Transmission temperature gets too high
2. Icy or otherwise slick condition exist (I always avoid driving in those conditions but sometime weather can surprise you); the reason for this is to avoid unexpected rear axle lockup and loss of control.
3. I want to exercise the brakes to avoid glazing the pads due to too much light applications.

Re: Detroit/Allison Confusion

Reply #7 – July 06, 2018, 07:55:41 pm

John,

EXCELLENT DESCRIPTION.

Absolutely keep engine RPM near the high end of the RPM range, as the water pump (and therefore transmission cooling) is maximized.

And, if you have to apply the brakes (we are talking about the service brakes/brake pedal) do so strongly enough and long enough to slow you down-- depending on grade/gain in speed, enough to drop to the next lower gear or slowly work from mid to high RPM in the gear you are in .

QUESTION: With the configuration you have, do you need to stay (lightly) on the service brake for the retarder to stay on or ....... This is a CRITICAL question for those new to your generation coach.

Re: Detroit/Allison Confusion

Reply #8 – July 06, 2018, 08:16:40 pm

Quote from: wolfe10 – July 06, 2018, 07:55:41 pm

QUESTION: With the configuration you have, do you need to stay (lightly) on the service brake for the retarder to stay on or ....... This is a CRITICAL question for those new to your generation coach.

Answer: Yes. No brake application means no transmission retarding.
According to the service manual I have for the transmission, 100% retarder application occurs at 85 psi. So, it's full on when the brakes are still around 75% of full pressure (assuming the air tanks are around 115 psi). It also "feels" that way when you compare brake pedal effort with and without the retarder.

Re: Detroit/Allison Confusion

Reply #9 – July 09, 2018, 09:55:41 pm

Hi, I have both systems on my Grand Villa. One is labelled retarder the other engine brake. Both are activated with electric switches on the dashboard. I've been using the retarder all the time and never had a problem with the trans oil temp. I use the engine braking or jake brake on long and steep downhill.

Re: Detroit/Allison Confusion

Reply #10 – July 09, 2018, 11:35:19 pm

Help us out. What exact coach do you have?

Re: Detroit/Allison Confusion

Reply #11 – July 10, 2018, 05:50:03 am

his other post..........
6V92 silver ?

Didn't know FOT put retarders on in '88

Re: Detroit/Allison Confusion

Reply #12 – July 14, 2018, 05:07:42 pm

Brett,

Will further investigate and report back next week. I just ran over some of the road I contemplate driving in Aug, and definitely want to know all about this system prior to embarking!

Thanks again.

Re: Detroit/Allison Confusion

Reply #13 – July 14, 2018, 05:08:29 pm

Thanks very much for this information and material. I will compare the photos with my retarder installation.

Re: Detroit/Allison Confusion

Reply #14 – July 14, 2018, 06:36:48 pm

Randal,

The "B" in the trans plate indicates it has a retarder. The transmission is also longer as I remember.

Pierce

Re: Detroit/Allison Confusion

Reply #15 – July 14, 2018, 06:55:30 pm

Here is some retarder info for your transmission:

Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 11, 2025 ...

Detroit/Allison Confusion

July 06, 2018, 01:14:00 pm

Re: Detroit/Allison Confusion

Reply #1 – July 06, 2018, 01:58:07 pm

Re: Detroit/Allison Confusion

Reply #2 – July 06, 2018, 02:02:24 pm

Re: Detroit/Allison Confusion

Reply #3 – July 06, 2018, 02:54:27 pm

Re: Detroit/Allison Confusion

Reply #4 – July 06, 2018, 06:07:21 pm

Re: Detroit/Allison Confusion

Reply #5 – July 06, 2018, 06:42:52 pm

Re: Detroit/Allison Confusion

Reply #6 – July 06, 2018, 07:44:22 pm

Re: Detroit/Allison Confusion

Reply #7 – July 06, 2018, 07:55:41 pm

Re: Detroit/Allison Confusion

Reply #8 – July 06, 2018, 08:16:40 pm

Re: Detroit/Allison Confusion

Reply #9 – July 09, 2018, 09:55:41 pm

Re: Detroit/Allison Confusion

Reply #10 – July 09, 2018, 11:35:19 pm

Re: Detroit/Allison Confusion

Reply #11 – July 10, 2018, 05:50:03 am

Re: Detroit/Allison Confusion

Reply #12 – July 14, 2018, 05:07:42 pm

Re: Detroit/Allison Confusion

Reply #13 – July 14, 2018, 05:08:29 pm

Re: Detroit/Allison Confusion

Reply #14 – July 14, 2018, 06:36:48 pm

Re: Detroit/Allison Confusion

Reply #15 – July 14, 2018, 06:55:30 pm

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