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Old 03-01-2013, 08:57 AM   #1
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Exhaust braking stopped working

Recently on a down hill grade I noticed that my exhaust brake was selected but did not seem to be functioning. The transmission gear indicator has displayed 4 gears available (vice the normal 6) and I have heard/felt a change in engine RPM and a related decelleration in moving speed when selecting the exhaust brake in the past.

This time, no change in available gear indication on the transmission selector display. No change in engine RPM and no decelleration. Ultimately forcing me to use the brakes more than I would prefer on a steep down hill grade. The exhaust brake switch did illuminate when I selected it, but that is the only thing that seemed to function appropriately.

Any ideas before I drag it to the CAT service center?

My RV is a 2007 Fleetwood Bounder 38L with a 330 HP CAT and about 12,000 miles.
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Old 03-01-2013, 02:43 PM   #2
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The fact that the trans key pad , read out doesn't change would indicate the the trans controller is not seeing the switch activation. Even though the switch illuminates it may not be sending a signal to the controller.
I'll see if I can find any info on testing the switch, and re-post.
The key pad only indicating 4 gears instead of 6 may be an indication of bad connections or ground at the controller or key pad. Many other posts of people having to clean the connectors and re-seat them .
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Old 03-01-2013, 05:28 PM   #3
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Quote:
Originally Posted by Shallow View Post
Recently on a down hill grade I noticed that my exhaust brake was selected but did not seem to be functioning. The transmission gear indicator has displayed 4 gears available (vice the normal 6) and I have heard/felt a change in engine RPM and a related decelleration in moving speed when selecting the exhaust brake in the past.

This time, no change in available gear indication on the transmission selector display. No change in engine RPM and no decelleration. Ultimately forcing me to use the brakes more than I would prefer on a steep down hill grade. The exhaust brake switch did illuminate when I selected it, but that is the only thing that seemed to function appropriately.

Any ideas before I drag it to the CAT service center?

My RV is a 2007 Fleetwood Bounder 38L with a 330 HP CAT and about 12,000 miles.
As you slowed down with the service brake did you leave the exhaust brake switch on? If so did it ever come on as you slowed? You say that the exhaust brake switch did illuminate but did the exhaust brake indicator in the instrument panel ever come on? Could you manually downshift? Asking for 4th gear manually will do almost the same thing as the exhaust brake/Allison system asking for it. When your engine slows enough to safely shift into the next lower gear it will. This will give you some gearing deceleration but not the slight back pressure that the exhaust brake would provide in addition.
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Old 03-01-2013, 05:36 PM   #4
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My exhaust brake failed once - the air line that goes to the exhaust brake was close to the exhaust pipe and developed an air leak. Hopefully yours will be something that simple.
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Old 03-01-2013, 08:10 PM   #5
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Your default downshift is to 4th rather than the more common 2nd.

Need a couple of things to happen and having the switch in the retard position is the first. Fact that the light comes on is a good start. Then it has to sense the zero throttle position before anything else happens so the fact that the transmission indication is staying in 6th indicates that the control system isn't acting when you lift the foot off the throttle.

Is the throttle actually coming right off, or is it holding at that slightly depressed position that is actually zero throttle but not off enough to initiate the auxiliary braking.
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Old 03-02-2013, 04:36 PM   #6
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Exaust Brake

This happened to me so I did some checking and found that the butterfly in the brake was froze up. I took it apart, used a lot of Marvel Oil and now it works great. It saved me a trip to Cat. and a lot of money.
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Old 03-03-2013, 11:30 AM   #7
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The transmission allows me to shift manually and select a lower gear for downhill grades. But selecting a lower gear isn't enough to control downhill speeds on several of my frequently traveled roads. I'm hoping that with a functioning exhaust brake, I will be able to maintain safe and sub-speed limit speeds without taxing my brakes excessively.

As far as the transmission displaying 4 available gears when the exhaust brake is selected was normal operation. And it worked appropriately not so long ago.

Regarding the in dash display, I don't remember the exhaust brake indicator illuminating. So, at this point the retarder switch illuminates, but that is all.

I'm not sure how to verify that the throttle is reaching the the zero position. The peddle has no pressure on it when I've been attempting to utilize the exhaust brake. Should I attempt to pull aft on the peddle to ensure it isn't slightly depressed?
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Old 03-06-2013, 09:26 PM   #8
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Quote:
Originally Posted by Shallow View Post
Recently on a down hill grade I noticed that my exhaust brake was selected but did not seem to be functioning. The transmission gear indicator has displayed 4 gears available (vice the normal 6) and I have heard/felt a change in engine RPM and a related decelleration in moving speed when selecting the exhaust brake in the past.

This time, no change in available gear indication on the transmission selector display. No change in engine RPM and no decelleration. Ultimately forcing me to use the brakes more than I would prefer on a steep down hill grade. The exhaust brake switch did illuminate when I selected it, but that is the only thing that seemed to function appropriately.

Any ideas before I drag it to the CAT service center?

My RV is a 2007 Fleetwood Bounder 38L with a 330 HP CAT and about 12,000 miles.
IM0, because you see no change in available gear indication, your problem is electrical, (fuse?, switch?, wire?, air solenoid?, relay?).
I believe that if the butterfly is frozen... if you have another mechanical problem... or if there is a pneumatic, (air), problem, the shift indicator would still indicate the drop in selected gear, (in your case to 4), when the PacBrake is switched ON.
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Old 03-07-2013, 06:51 AM   #9
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Mine stopped working one time and after looking at everything from the engine to the front I found a connector had came off of the switch. I plugged it back in and problem was solved.
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Old 03-07-2013, 07:09 AM   #10
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As Mel stated, check for an electrical problelm. Check the switch to see if all the wires are hooked up. check for blown fuses, for bad grounds. Just because the retarder switch light is on is not an indication that the switch is fully operational. While your at it. Lubricate the pac brake also.
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Old 03-08-2013, 09:13 AM   #11
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Thanks fellas. I'll see if I can't verify that the switch is properly connected and try to trace the wires to their sources for any obvious electrical issues.

I'm unfamiliar with the PAC lubrication process. Any suggestions?
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Old 03-08-2013, 12:04 PM   #12
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I'm unfamiliar with the PAC lubrication process. Any suggestions?
Shallow
See: http://www.alpinecoachassociation.co...ps%2010.02.pdf
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