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Old 02-19-2013, 12:22 AM   #15
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I suspect you have the same Freightliner XC setup the rest of us do in this class. And that's an exhaust brake on the engine and a force downshift command to the Allison. In the stock config, you take your foot off the fuel, the exhaust brake closes, and the transmission starts downshifting to it's preset gear as RPM allows.


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'06 Itasca Meridian 34H, CAT C7/350
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Old 02-19-2013, 12:39 AM   #16
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Originally Posted by csrrsr View Post
We have every receipt of every nut, bolt, oil change etc. that was ever put into this coach since new. There's nothing for the transmission. The switches are definitely factory installed, however, they do not coincide with the switches shown in our Discovery Owners manual. Maybe it was a special order?
I believe that the switch was put there by the coach maker, the transmission was put there by the chassis maker. One does not demand the other.

I run a CAT in a Freightliner chasis, with a allison 6 speed. I have yet to see a allison retarder in a MH. That does not mean that it has never been done. The basic retarder installed in a MH would tend to relocate lose objects to the front of the coach when engaged. Of course on the way they would tend to fall to the floor. The allison retarder is for those heavy loads where slowing down is right up there with very good brakes all of the time. It has no wear and tear on the transmission except by running the oil temp upscale and it can raise the oil temp in the transmission to the breakdown point of the oil if over used. Unless you want to buy a new or rebuilt transmission there are missing parts in the regular allison transmission. If memory serves correctly the rotor is not installed and the other components required to support the retarder will also be missing. It may be the stator that is missing but that is part of the rear housing of the transmission. You can of course do anyhing as a retrofit. But if it is installed as a afterthought then you will have to find a rebel to program the transmission ECM to operate the retarder. Allison service will not do it without the chassis maker sayng it is OK to do this to their chassis, and that authorization will have to be in writing. How do I know this? I asked for the authorization, the answer was that Freightliner had never run my chassis through the testing needed to authorize the retrofit. They claim that the retarder can be so agressive as to damage the chassis components. Could I find a rebel to program the allison? Yep, I have the program and the interface to do it myself. Do not have the deep pockets to retrofit the transmission.

There are two other common brake assist systems, one is a jake brake, it upsets the exhaust valves just enough that the compression is not high enough to fire the cylinders. This turns the engine into a big compressor that is now belching unburnt fuel. Some of the new ECM's see this and shut down the injector system when this happens. Now you have a clean running compressor powered by the weight of the MH rolling down hill. Tends to slow you down. The second is an exhaust brake, very simple it is a damper vane in the exhaust pipe that closes off the exhaust pipe. Even though the engine fires at idle it is running with a potato shoved up the exhaust pipe. In fact it quits running and turns into a big compressor that has no way to get rid of the compressed gases. Very effective in slowing things down. These last two are not as agressive as the allison retarder. Oh, and BTW you will need a huge transmission oil cooler if you retrofit it with a allison retarder, this keeps the oil cool so it does not brake down from the heat.

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Old 02-19-2013, 12:13 PM   #17
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Still haven't received a call back from Fleetwood? If I have what Jeff described, the sound of the exhaust brake is sure different than the whop..whop sound in my truck. The MH sound is more like the whining down of the transmission, but then again the exhaust brake in the truck is up front where I'm driving and all the sounds of the exhaust and engine are in the back of the MH. All the info on the retarder in the Allison owners manual must be a generic version given out to every Allison owner? I did a short look of the exhaust coming from the engine and never saw an exhaust brake, but I guess that's not to say it isn't there somewhere. Sure wish Fleetwood would call me, if I have what Jeff described I already have the exhaust break making this thread pointless.http://www.irv2.com/forums/images/smilies/sad.gif
02 Fleetwood Discovery 37U, 330 Cat pulling a 2006 diesel Liberty..or..2011 4dr Wrangler..or..20' Lund Salmon/Halibut Hunter
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Old 02-19-2013, 01:12 PM   #18
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Finally.....Jeff, you were correct. Allison called me after investigating the model and serial number of the transmission. It does not have a full retarder in the true definition of a "brake retarder". But, it does have a retarder that is used in conjunction with the pac brake! Yup...it's got an exhaust brake. The retarder is used to bring the gearing down when the RPM's are optimum to go to the next lower gear as a result of the exhaust brake bringing the RPM's down. He said without the retarder, the transmission would never gear down making the exhaust brake very ineffective in stopping the coach all on it's own. I guess I won't be installing an exhaust brake after all. Learn something every day. Thanks every one.

02 Fleetwood Discovery 37U, 330 Cat pulling a 2006 diesel Liberty..or..2011 4dr Wrangler..or..20' Lund Salmon/Halibut Hunter
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brake, transmission

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