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Old 01-22-2007, 02:46 PM   #1
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We have a 1999 Dutch Star D/P with a 300 CAT. This past summer we travelled to Alaska with friends also with a Discovery D/P. Comparing the exhaust brakes his worked much better holding him back on most hills, mine on the other hand had smoking brakes a number of times. I guess my question is, can they stop working or only partially work and if so what is the cure.

Thank You in advance.

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Old 01-22-2007, 02:46 PM   #2
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We have a 1999 Dutch Star D/P with a 300 CAT. This past summer we travelled to Alaska with friends also with a Discovery D/P. Comparing the exhaust brakes his worked much better holding him back on most hills, mine on the other hand had smoking brakes a number of times. I guess my question is, can they stop working or only partially work and if so what is the cure.

Thank You in advance.

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Old 01-22-2007, 03:19 PM   #3
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They can definitly stop working. The electric/air solinoid can fail, the brake butterfly valve can stick open or it cannot close completely due to carbon buildup. I would suggest you get a qualified repair shop check it out. They may have to remove the brake assembly for cleaning.
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Old 01-23-2007, 04:11 AM   #4
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Welcome to iRV2.

Yes, like most mechanical things, exhaust brakes can fail or require service. It's a good idea to have it checked out. Also, be aware that everything is relative when it comes to hills and braking. You undoubtedly hit some pretty good grades on your Alaska trip. If your friend's coach had a larger Cummins with a true compression brake it will outperform a smaller engine with an exhaust brake. Also, exhaust brakes work best at high RPM. If your brake was kicking in at a lower RPM it won't be as effective as if you were to manual kick it down a gear when beginning your descent. If all of those things were equal though, you'll be needing some service work.
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Old 01-23-2007, 08:01 AM   #5
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I too recently questioned the proper operation of my PacBrake Exhaust brake. I found that I get about the same deceleration with the exhaust brake engaged and letting it downshift itself as I do when I select a lower gear and manually 'force' it to downshift without the brake on. In other words, I don't see (or hear) any difference with or without the exhaust brake 'helping'.

Looking at the operator manual for the coach, one section references periodically lubricating the exhaust mechanism and exercising it by grabbing/turning it with a pair of pliers. I evidently don't' have a big enough pair of pliers because I could budge it at all. I suspect the big spring and the solenoid are holding it open, maybe. Is that common or is it stuck?

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Old 01-24-2007, 07:01 PM   #6
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Have same problem with my pacbrake. Anyone know how to check or test these. thanks Jack
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Old 01-24-2007, 07:57 PM   #7
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There is a hill on I-20 West coming out of Dallas where I can verify proper exhaust brake operation. It is about a 4% grade at the top and I generally start it with the flow of traffic about 65mph. At that speed, my transmission isn't going to kick down so, when I throw the switch, the only thing that is going to happen is the e-brake deploys - or not. I can definitely feel the difference in resistance with the exhaust brake on and off. About half way down the hill, I turn the switch off and can feel the RV start to "free wheel" again.

I'd suggest trying the e-brake at a higher speed where the current engine rpms are not going to allow a downshift. I put an engineering change on my exhaust brake solenoid wiring so I know exactly where it is and won't hesitate to jumper 12v directly off the battery (after disconnecting the harness connection to the solenoid) to see if the cylinder moves. Mine needs air pressure so I'd need to be sure that the air tanks were charged before trying that test.
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Old 01-25-2007, 12:47 PM   #8
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when climbing steep hills the rubber boot on the tps can inflate and prevent the throttle from closing the sensor. use a sharp nail or ice pick and poke several holes in the bottom of the rubber boot. then when you start down the hill the sensor will activate the pack brake. you will notice rpm increase when the pack brake is activated. if it is working properly you will not have to manually select a lower gear. 1996 kountrystar spartan mountainmaster chassis.
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Old 01-25-2007, 02:19 PM   #9
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Regular lubrication of the Pac Brake is important. As part of the lube process you must remove the air line at the end of the ram which forces the brake closed and put in a drop of Pac lube. While that line is off, connect a blow gun fitting to the end of an air hose fed either from your onboard air supply, usually at the front of the coach, or from a stand alone compressor. Push the end of the blow gun gently into the opening vacated by the air hose going to the air ram on the Pac Brake and pull the trigger of on the blow gun once or twice. You'll immediately see if the Pac Brake is seized or not. This process also helps to distribute the lube in the air ram. Note: You don't need much more than 30 lbs. of air pressure to activate the Pac Brake using the blow gun.
Good luck.
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Old 01-25-2007, 04:13 PM   #10
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I suspect the difference between your rig and your friend's Discovery is the transmission programming for the e-brake. Most likely his is seeking a lower gear sooner than yours is, resulting in more effective e-brake operation. Have yours checked out, or simply note which gear the transmission targets when the e-brake is engaged. It it is only 4th gear, go to an Allison shop and get it re-programmed to target 2nd gear, so that you get more braking sooner.

If it is already targeting 2nd gear, you have a problem with the brake and should have it checked out.
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Old 02-02-2007, 06:31 AM   #11
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I found the exhaust brake on the CAT C7 in my previous Journey 39W worked more effectively than the exhaust brake in my current ISC. The difference seems to be in the upper rev limit. The CAT would go up to 2900 while the Cummins ISC seems to cut off about 300 or 400 revs less.

Anyone with an ISC find the same low cut-off on theirs?

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Old 02-03-2007, 01:31 PM   #12
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Lots of variables here, 2 coaches with the same engines can have different braking action from the EB due to one being heavier, different ratio rear ends etc. As someone else stated get your allison shop to program the tranny to go to 2nd rather than 4th. It's not gonna go directly to 2nd but will do it faster thru the gears.
Once yearly I take mine apart by disconnecting the air line to the cylinder. Pull the top C-spring clamp off of the pin, pull the pin then work the arm of the valve. If it's free it should be able to move with just finger pressure. Use the PacBrake lube or Super Lube which you can get at Lowes/Home Depot, etc. A little test to see whether the EB is working. The brake is set to disengage at 15mph. As you're nearing a stop with the EB on watch your tach, it should lose several hundred RPM when the speedo reaches 15, I can actually feel it.
To me the biggest thing when descending hills is to start out in the same gear you went up in. Keep the RPMs up in the 2200/2500 range, you're not gonna hurt the engine, it's governed to X RPM under load but has no load on it with the EB engaged. If it's real steep grade and your coach is heavy like mine you may have to use your service brake to bring the speed and RPMs back to your preset point but do it in short hard applications.
Canuck had a good point about using the soft tipped blow gun to test the brake also. Hadn't thought of that one. Always used a jumper across the solenoid.
Also, use the EB everytime you stop, saves on your brakes and keeps it loose.

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Old 02-04-2007, 06:51 AM   #13
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Ron, I was able to turn my pac brake and get the shaft lubed. It took quite a bit of pressure, but I was able to get it to extend. On my coach, I was told that if I had a 12V power source I could get the solenoid to activate without the engine running. I didn't do that and use a screw driver and pliers to turn it. I used anti-seize compound on mine because I can't seem to find a local source for the Pac lube.
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Old 02-04-2007, 07:29 AM   #14
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Camping world carries it, or at least it is available online. There is one in woodstock only 13 miles away.
I'd call before I actually drove over there though.

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Woodstock, GA 30188

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