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Old 07-08-2012, 07:53 PM   #1
Join Date: May 2011
Posts: 34
pacbrake question

Hello! I purchased my 96 American Eagle DP with the 8.3L Cummins a year and a half ago and never had an RV with a pacbrake. When I flipped the switch the transmission shifted down and my air gauge would climb from the normal 125 psi to 140 but I never really felt like it was actually slowing me down and worse noticed my engine RPM would climb at the danger point listed in the manual so I flipped it off and never used it. Now going to the hills of Tennessee I would like to use it if possible so I read up on it.

I lubed it correctly but made the following observations: My pac brake piston slides and I assume there is a spring that retracts it because I can only manually pull it out about half way before it gets tough to keep pulling...I assume this is normal and there are no problems there. I took off the air supply line that connects into a T valve. On one side of the T is the air supply connection. On the other side of the T it is completely open but has threads. The bottom of the T goes into the piston. With the motor running and switch flipped, the piston does not activate. So, here are my three questions.

1. Does the coach have to be in gear or running at highway speeds to allow the piston to close? If so I guess I can't see if it closes unless somebody is driving down the freeway and my head is under the rear bed over the motor. Seems like a bad idea.

2. I know it should have a fuse....anybody know where it might be? I couldn't find it with the fuses by the batteries on the right rear compartment.

3. Is this T valve that the air inlet hose goes into supposed to have a cap on the other end of the T to keep the air from blowing all the way through it or is it supposed to be open for some reason? I can literally look in one side where the air supply line goes in and see through the valve on the other side of the T. Thanks for any ideas!

I posted a picture of it. You can see the air supply line go into the top of the piston and its open on the other side. Air can blow right through it instead of down into the piston.
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Old 07-09-2012, 07:15 AM   #2
Join Date: May 2011
Posts: 34
Ok I called Pacbrake and they told me there should be a one way check valve on the other end of that T fitting. Said sometimes they wear out and blow out. I ordered it so I should be good with that part of the question. Will see when it comes. I was referred to another company to order it and it comes as an adapter/check valve combo. Seems odd that an adapter and check valve would just blow right out the back off that.

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Old 07-09-2012, 07:31 AM   #3
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Tim- here is a link to the PacBrake exploded parts diagram that should help w/your questions on its make up.
Baja-tested '08 2-slide 36'
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Old 07-09-2012, 07:44 AM   #4
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Thanks Mike! Looks like #2 on the parts list below is what I have coming. Hoping Spartan or Fleetwood can help me with my fuse location.
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Old 07-09-2012, 08:04 AM   #5
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I didn't see anything in your first paragraph that suggested anything is necessarily wrong with the exhaust brake. The transmission should downshift until max safe RPMs are reached - that gives you the most braking. The ECM & transmission electronics are supposed to prevent over-revving. You won't feel much slowing in 6th and 5th gear, but as the transmission continues to gear down you get more and more effect.

Does your transmission target 4th gear or 2nd gear when the exhaust brake comes on? That is settable in the control logic. If its 4th, you may want to get it changed to 2nd - much more braking available that way.
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Old 07-09-2012, 12:32 PM   #6
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Mine targets 4th gear. The only thing that happens is the transmission shifts down and my air gauge climbs from the normal 125 psi to 145 psi. I feel no slowing down and actually can speed up so im in 4th gear but can hop up in speed from 60 mph to 75 mph making the coach be at that crazy high speed in 4th gear too high in rpms. At minimum without anything on the other side of fitting where the air inlet hose goes if it was actually putting air into it, im sure it just blows right through it as I can see all the way through it. Not really sure how I can test it without going down the road at freeway speeds and pushing the button all while sticking my head in the motor below the bed.
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Old 07-09-2012, 12:49 PM   #7
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I called American Coach. They told me 1992-1996 coaches do not have a fuse for the pacbrake. They use automotive breakers in the front panel under the box that has warning labels all over it probably labeled "exhaust brake". I doubt a breaker is flipped. So, guess question #2 is solved. My only question that remains is can I test this system any other way than driving down the road at highway speeds and sticking my under the bed to watch this thing?

The only reason I'd like to test this prior to when my check valve comes Wednesday is because we leave on our trip then. If that valve comes and turns out even though I need this valve that's not the only problem with it then I am stuck. If I know that no air is even being supplied to the brake now then I can still figure it out today and tomorrow. I will know that if I feel the air being blown right through the T fitting when activated. I just don't really have somebody to drive this thing down the freeway and activate the button while I put my head in the motor and feel for the air. Obviously without the check valve I won't feel the thing slowing down as the air just blows right through the T fitting so I have to feel for the air.
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Old 07-27-2012, 04:25 PM   #8
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Not an expert here, but I cycled my PB by applying 12V to the operating solenoid. This does not test your entire system (activation switch, etc) but it will tell you if the PB cylinder is operating.
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Old 07-27-2012, 05:03 PM   #9
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My '99 American Dream will drop to 4th and the motor revs up higher but gradually drops and slows the coach. However it's definitely not like a "Jake Brake" that's for sure. When I was first running this Pac Brake i was shocked at how it worked. I then read the manual and it said something about not revving over 2700 rpm. Also not supposed to have the cruise activated while using the exhaust brake. I had the coach make some bad/harsh clunks when I first got driving it. I was using it on flat ground for slowing down but I guess it's more intended for steep grades. I still don't like the way it works but if don't have a jake I guess it's better than nothing.
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Old 07-27-2012, 06:11 PM   #10
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When I hit my brakes, it shifts from 6th to 4th and I can feel a bit of a braking sensation when the pac brake is energized. I pretty much never turn mine off. If I am going down a steep hill, I will shift into 3rd or 2nd if needed. I try to adjust my speed so that I do not have to use the coach brakes very much and keep the RPMs around 2400. There have been a few steep hills that I have used 1st. If my RPMs go high (probably over 2700) the trans will override and upshift. That will get your attention when that happens!

I bought some of the pac brake lube and the local Cummins dealer told me to forget it, it just burns off fairly rapidly, so in 86,000 miles, mine has not been lubed.
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Old 07-27-2012, 07:07 PM   #11
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You should feel a difference when the pac brake activates although it may be hard to tell if the transmission shifts down. Any engine braking is best at higher engine rpm so you may not feel the effects of the engine brake if your engine is not near its max allowable rpm.

On a previous coach I suspected the exhaust brake had quit working and on a down grade, shifted the coach to 4th gear manually and and at higher engine rpm, 2100 in my case, turned on the exhaust brake. Nothing changed so I figured the exhaust brake wasn't working. I took it in for service and the tech discovered the wire had come loose from the exhaust brake switch. After the repair I tried the same experiment and I could definitely feel the exhaust brake kick in.
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Old 07-29-2012, 12:50 PM   #12
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Possibly I can provide a little additional information about determining if the PacBrake system is functioning.
I have had two Monaco Dynasty's (1995 & my current 2001) that used the standard Pacbrake activated by a simple foot switch.

First, the Pacbrake will only function when the RV is being driven and is above about 13-15 mph. Below this speed the ECM will disable the Pacbrake function. In addition, the engine ECM must see a 0-throttle position before the Pacbrake will energize, and to be on the safe side I would make sure the cruise control is 'OFF' for at least testing purposes.

Secondly, since you are able to see down-shifting, this is not likely the problem, but for information make sure that the Pacbrake relay is working, of which mine was located under drivers seat in an outside compartment. This is typically a standard Bosch block style, 5-pin relay. I have had one of these fail and nothing would function in terms of the Pacbrake functionality.

What I have done to determine if the Pacbrake air control solenoid is working, is to connect a 12 vdc test light into the wiring that powers the Pacbrake solenoid. This can be done by simply connecting one leg of the test light into the 12 feed wire to the solenoid and connect the other leg to a good ground. Then make the test leads long enough so that you can have it near you in the drivers compartment. In this way, you can observe the test light when activating the Pacbrake. If the light lights up when you apply the Pacbrake, you know that the control system is working, by at least providing power to the solenoid. If the light illuminates, you don't feel any braking action, then I would suspicion that the solenoid is not working or the air cylinder is stuck.

If the light illuminates when activating the Pacbrake, then I would test the solenoid my providing 12vdc power to the solenoid coil itself and see if it activates. If it does activate, then it is a problem with the air cylinder or the line going to it. In your case, if you can see through the 'T' then the air would blow directly to the atmosphere and not try to power the air cylinder. I have attached a photo of my Pacbrake cylinder and you can see that I do not have the one-way check or quick-release valve that appears to be on your air cylinder.

My air solenoid valve is located under the front wall of the bed that is directly over the engine, slightly towards the drivers side and above the rear of the engine as shown in the photo. As information, to constantly monitor the operation of my Pacbrake system, I have ran a wire and indicator lamp into my drivers area and mounted it on the left side console. This way, whenever I activate the pacbrake, the light should illuminate and I know that i am at least getting power to the solenoid valve assembly. If I don't feel a significant amont of braking, but get down shifting then it quickly points me to the area of concern with my Pacbrake system to aid in troubleshooting diagnostics.

Hope this helps and you get your system back in full operation ASAP

Yukon Jack
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Old 07-30-2012, 09:52 PM   #13
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Wow....thanks to all for your responses! I learned a lot about the system and am happy to report that all is well now with my brake. I basically ran out of time to run over the system throughly so got lucky with the one part I ordered being the problem. After talking to Pacbrake directly, I learned two things.

1. They will tell you what part you need but refer you to the nearest dealer by you. Only problem here is if that dealer doesn't have the part in stock, you have to wait longer for the part to be shipped from Pacbrake to the dealer, then to you. Having little time I had to talk to two guys from Pacbrake insisting on them selling it to me direct due to my time constraint. It is more expensive if you buy direct from them but quicker so before any trips, be sure to check your brake and give plenty of time to get a part for it to keep price down through their distributors/dealers.

2. In my year coach (1996) and earlier there is no fuse for the Pacbrake. It only has breaker usually located on the firewall. Knowing my electronics worked ok as the transmission shifted to the targeted "2" gear I focused on the brake itself. I took the thing apart and realized I could blow straight through the valve. Seemed odd that it was possible as if I could blow through it, how can the air go into the piston? I learned in my year and earlier, that valve inside has a "quick release" one way check valve. It has a diaphram. This diaphram allows the air to go into the piston and not all the way through the T fitting, but then allows the air to escape/release when not in use. This was the part I had to order. The whole "T" fitting shown in the picture as the quick release valve is located inside it. It comes in two parts (valve and adaptor). I had it installed in no time and paid $35 plus shipping.

With this new part I lubed the brake with Trilube (found at my local True Value hardware store) and headed down the open road and hoping that this was my only problem with the brake. If not I was just going to take it really slow and easy. Lucky for me it all worked great and I was very happy to have it on several steep hills!

Thanks to all for your replies. We are happily camping now.
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Old 07-30-2012, 09:53 PM   #14
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On a side note and something I'd like to share in case any of you come up on this situation.....I had zero problems while on vacation with one exception. My own stupidity led me to drop a complete set of keys at the bottom of the lake 35' down. Having no luck with a large magnet recovering them, I went back to my spare set. I have never used the spare set but they appeared to have had duplicates of every key including the square GM ignition key. Upon trying them, all worked except the ignition key. I had no way of starting it up. After going through many hoops the process to get me started again was NOT as simple as having a locksmith come out and cut a key. I learned that even with the key code, you have to be lucky that your tumbler in the ignition hasn't been changed before getting another code that your manufacturer on the chassis doesn't have and that your key groove for that code is correct. Although our ignition was your basic one designed in 1979 and still used in our 1996, it was fairly complicated.

The BEST and cheapest solution here for any of you that may get in this pickle is this: 1. Call your chassis builder and have them ship you a new key tumbler. This will eliminate the locksmith having to take out the tumbler and several days return with a correct one himself.
2. Call a locksmith and have him professionally drill out the side of your ignition allowing the tumbler to be manually turned so it can pop out as the tumbler won't come out if not in the "accessory position" which is obviously not possible without an ignition key to turn it to that position.

Total cost was $23 for a new shipped tumbler and $69.50 for the locksmith to drill out the old tumbler then install your new one.

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