Brake/Retarder SetUp.

[Oonrahnjay]

    OK, guys.  I've got a little bit of a "hive mind" question here.  I'm in the middle of putting a US drivetrain (Cummins 8.3 ISC engine with Allison B-500) in my bus.  To make the rear end ratios work out and also convert to an air suspension, rear axle from the donor bus (a 2003 Gillig low floor) will be going into the bus too.  Since the rear axle will bring disc brakes, we're looking at using the front axle from the Gillig too (no final decision on that one).
    The Gillig rear axle has a Gross Axle Weight Rating 10,000 pounds heavier than the one that it's replacing.  We're talking about a *serious* upgrade in weight capacity, braking, etc. 
    A big issue in this swap is that the original engine transmission was perpendicular to the centerline of the vehicle.  The new in-line layout of the Cummins/Allison means that there will be an significant increase to the length of the bus so I'm doing everything I can to shorten the length of the power unit.*
    The Gillig came with a retarder on the transmission and the big transmission cooling unit outside the radiator.  After we got all the components out of the Gillig, it was apparent that the retarder valving and piping added significant width to the transmission (could live with it but it wasn't optimum).  But the big thing was removing the retarder valving and controls allowed the use of the shorter rear bearing housing.  The mechanic who works with me has a day-job at the Charlotte/Mech County bus garage -- his opinion was that the retarder is a good thing to have (essential for in-town transit work where the drivers have either the accelerator pedal slammed to the floor or brakes stomped on to get stopped at the next stop to stay on schedule).  There's also the issue of every bit of heat that the retarder generates is put into the transmission and its fluid and the radiator/cooler package.  So our dilemma became -- how important was the retarder to my application?
    Our decision was that since I'm going to larger-capacity, modern disc brakes -- and I don't have to run to any schedule and I can take my time in traffic or down big hills -- that the reduction in length of the B500 of about half a foot was worth deleting it.  It's sort of late to be asking advice since we already did it (I had a transmission shop change and flush fluid and change filters and inspect bands, bearings etc. even though the transmission only had about 15 months of service on it), but do you think that we made the right decision, based on all the variables that I'm looking at here?   I know that there are advantages to retarder but it this seemed right.
    Any thoughts or info?   Thanks,   BH

(* The driveshaft from the Gillig is about 13" between U-joint centers at the slip-joint's most pushed in position and it seems to be about optimum for length, considering angles of the U-joints, suspension movement etc. so there little opportunity to shorten that.)

[solodon]

In an RV application I don't see the need for a retarder.  Especially since the brakes are such a large upgrade in capability.  If RVs of the same weight don't come with a retarder seems your decision was a good one. 

[TomC]

If you convert all brakes to disc brakes, the retarder is not necessary. The hydraulic retarder creates a lot of heat. Without, you'll have a much simpler setup. You don't have to worry about hills with disc brakes. Good luck, TomC

[chessie4905]

Do they have Jakes or similar for that engine that could be installed down the road?

[Oonrahnjay]

Do they have Jakes or similar for that engine that could be installed down the road? 

     I have thought about asking that question.  I have service and electrical manuals and there's no mention of any compression brake in either one but there's lots on the retarder controls, etc.  I suspect that they planned to depend on the retarder.  Jakes (or similar) would be great.

[Lostranger]

I wish you wisdom on this one, Bruce. I'm so in love with my retarder that I cannot offer an unbiased opinion. I've never driven anything that stops like my Gillig. I have the impression that I could dislodge the entire conversion if I wanted. I can't imagine life without it.

Jim H.

P.S. I hear about the "heat" issue regularly. I'm forced to conclude that either the engineers who designed the retarder or the ones who specified it on my bus (and many other late model busses) are stupid.

[luvrbus]

The engineers were not stupid they were designed for stop and go in transit buses to save brakes, they are not that great in hiway coaches and will generate a lot of heat when operated at 80% I have one on my B500 Allison I never use

[TomC]

Both the Cummins ISC (8.3 liter) and the ISL (8.9 liter)-both the same basic block are available with real Jake brakes. They work reasonably well-I would much rather have a Jake brake then a transmission retarder. As Clifford said, transmission retarders were designed for stop and go. Jakes are best suited for over the road type driving since the activation of the Jake brake keeps the engine warm while going down a long hill. They are so popular now, the new Detroit DD13, 15 & 16 all have them built into the engine. The Cummins ISX15 also has it built into the engine. The Cummins ISX12-you have to order the engine with it that they add to it. I don't know about the Navistar or Paccar engines. Good Luck, TomC

[chessie4905]

http://www.dieselpowerproducts.com/p-6727-pacbrake-prxb-exhaust-brake-peterbilt-330335-cummins-isc.aspx


yours at lower part of page?
Didn't see any compression brakes listed for yours.

[Oonrahnjay]

... As Clifford said, transmission retarders were designed for stop and go. ... 

    My mechanic usually uses the words "transmission retarder" and "brain dead drivers" in the same sentence.  IYKWIM ...

[luvrbus]

Yep Don Laughlin's shop foreman says the same,one fried a B500 in a VanHool Tue coming down from Union Pass into Laughlin on AZ 68 it is 11 miles of 6 to 8% grade it never fails they lose one every year because of drivers error