Community Forums

jwalt · 02-08-2013, 03:00 PM

What exactly is a retarder on a 2000 DP with a 4 speed Allison transmission? Could it be an engine brake or an exhaust brake or a hydraulic retarder on the trans? Also since there is only 4 speeds is 4th an overdrive? Thanks for your help.

Smitty77 · 02-08-2013, 05:32 PM

I've seen Fleetwood call some of their DP's Exhaust Brake a 'Retarder'.

4Spd in a 2000 DP I would think is unusual? Most had the 6 spd Allison in that era.

What is the coach you are looking at? If it is a Foretravel, then good chance it is a trans retarder - but a 4 spd in 2000 model year would surprise me?

More info would allow those with more knowledge in this area to help.

Best to all,
Smitty

Hooligan · 02-08-2013, 06:26 PM

The Allison AT500 series transmissions are 4 speed. They have a hydraulic retarder. The AT 542 was used in some motorhomes.
The hydraulic retarder is located at the output of the transmission. A vaned rotor is driven by the output shaft in a cavity that fills with transmission fluid when the retarder is activated. The rotating vanes and stationary vanes in that cavity reduce the speed of the output shaft. The fluid was contained in an accumulator and pushed by air pressure into the output cavity. (See page 19 in the manual)

http://www.allisontransmission.com/s...t=OM1334EN.pdf

jwalt · 02-09-2013, 08:53 AM

The unit I'm referring to is a 2000 Rexhall Anthem. 33' with 275 hp Cummins and I'm told a 4 speed Allison. Could the seller be wrong about the trans? If it really is the 4 speed is 4th an overdrive? Is the "retarder" really an engine or exhaust brake? I'm getting nervous about seller's lack of knowledge of drivetrain specifics..................Thanks for the help

Smitty77 · 02-09-2013, 09:23 AM

I was aware of the AT500 series, just not sure if it came in the Rexhall 2000 year coaches.

OP - I see to easy ways to get answers:

1) Call Rexhall - they built it, they would know
2) Or, check in with the Yahoo User Group

I know many of the Rexhalls (a coach I like) from that era came with Spartan Mountain Master chassis, which is a good chassis.

Your comment about the owner, makes me wonder about history of maintenance? If they are not sure of what is in the rig, opens the question on what they know about it's maintenance too??

rexhall_motorhomes : Rexhall_Motorhomes

Best of luck on what you find,
Smitty

spike45 · 02-17-2013, 09:08 PM

Quote:

Originally Posted by jwalt

What exactly is a retarder on a 2000 DP with a 4 speed Allison transmission? Could it be an engine brake or an exhaust brake or a hydraulic retarder on the trans? Also since there is only 4 speeds is 4th an overdrive? Thanks for your help.

A quick check with Google on Allison trans with retarders will show they do offer some models with a true retarder. The classification of retarders is NOT engine brakes such as Jake Brake or exhaust brake. Retarders operate on the principle of a rotating wheel in a housing (part of the transmission) that has oil introduced to provide drag on the rotating member. Retarders have the ability to have the amount of retardation to be dialed in as you descend grades. They are a lot easier on the engine. Hydraulic retarders are used on large mechanical drive mining trucks very effectively. Some retarders such as on Caterpillar engines used a second "flywheel" in a housing that used engine oil flooding to produce drag. Very effective.

phinneyj · 02-18-2013, 01:45 AM

Spike45, Seems to be a lot of discusions going on about exhaust brakes, jake brakes, retarders, etc. My rig is the Cummins 8.3 CM850/Allison 3000. I have an exhaust brake. What I was wondering is if the MH can be retrofitted with the retarder? ..if so would it be worth it. Appreciate your explanation above.

MartinP · 02-18-2013, 07:49 AM

If the egine is rated @ 275hp then the trans is likely to be a 1000 series or a 642. The retarder was used on the 542 which is limited to 235 hp unless some one has upped the origonal hp rating.

Martin

Genset · 02-18-2013, 04:18 PM

Allison has many models with the Retarder as an options, The retarder is an expensive option, very effective. My Foretravel has the ISM500 with the MH4000R with the retarder. Would not feel nearly as safe with a Jake Brake which I have too much experience with

Dave M

EZDZIT · 02-18-2013, 11:00 PM

As you dial in more retard effort you will notice the trans fluid temperature more or less in proportion. As you step on the go pedal again the trans fluid temp will drop quickly.

However on a long downhill grade when significant retard effort is necessary you may find the high trans temperature worrisome.

Mr_D · 02-18-2013, 11:05 PM

Quote:

Originally Posted by EZDZIT

As you dial in more retard effort you will notice the trans fluid temperature more or less in proportion. As you step on the go pedal again the trans fluid temp will drop quickly.

However on a long downhill grade when significant retard effort is necessary you may find the high trans temperature worrisome.

The temp rise is enough to cause Allison to consider it's use to be extreme duty and require more frequent fluid changes too even with TranSynd.

95foretravel · 02-19-2013, 07:44 AM

The Allison Transmission designation for a hydraulic retarder will have an "R" in it. For instance mine is a 3060R. Retarders and exhaust brakes are not the same and are frequently confused.
Gary B

Genset · 02-19-2013, 08:02 AM

Max hemp of retarder oil is 250f at sump sensor, my experience with using it on steep 6 mile down grades is to slow to 50 mph select 4th keep rpm under 1800 use foot brake lightly keeping oil temp under 220f, very easy and simple without panic, also have disc brakes that are used very little.
Dave M