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Old 09-23-2012, 12:58 PM   #1
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Exhaust Brake Adjustment

It seems that the Exhaust Brake on my diesel pusher is not working properly in that it does not slow my coach as much as it did when new. The brake is definately working because the action has been tested. I am wondering if it is possible that an accumulation of carbon is keeping it from closing, if so , how could it be cleaned? Also could it be adjusted, and what would be the proceedure?
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Old 09-23-2012, 02:29 PM   #2
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Originally Posted by BillyDS View Post
It seems that the Exhaust Brake on my diesel pusher is not working properly in that it does not slow my coach as much as it did when new. The brake is definately working because the action has been tested. I am wondering if it is possible that an accumulation of carbon is keeping it from closing, if so , how could it be cleaned? Also could it be adjusted, and what would be the proceedure?
I have no idea on yours, but most big trucks have a 3 position switch to select 2/4/ or 6 cylinders to work on. Should be real close to the on/off switch. You might look and see if yours has that. Makes a BIG difference...
Monkey
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Old 09-23-2012, 09:38 PM   #3
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I have no idea on yours, but most big trucks have a 3 position switch to select 2/4/ or 6 cylinders to work on. Should be real close to the on/off switch. You might look and see if yours has that. Makes a BIG difference...
Monkey
Monkey,
You are referring to an engine that has a real "Jake" brake built into the head of the motor. Exhaust brakes are an add on which closes a flap across the exhaust thus building up back pressure within the motor.
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Old 09-23-2012, 09:57 PM   #4
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I would suggest that you find out what type of unit you have (Pac Brake, Variable Geometry Turbo, etc.) then use Google to look for real answers to your exact problem.
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Old 09-24-2012, 07:39 AM   #5
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Monkey,
You are referring to an engine that has a real "Jake" brake built into the head of the motor. Exhaust brakes are an add on which closes a flap across the exhaust thus building up back pressure within the motor.
You are correct sir. Very sorry for popping off before engaging brain.... Helped my dad install an exhaust brake on his pickup many moons ago.
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Old 09-24-2012, 07:54 AM   #6
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It seems that the Exhaust Brake on my diesel pusher is not working properly in that it does not slow my coach as much as it did when new. The brake is definitely working because the action has been tested. I am wondering if it is possible that an accumulation of carbon is keeping it from closing, if so , how could it be cleaned? Also could it be adjusted, and what would be the procedure?
Exhaust brakes, such as a PacBrake, need to be lubricated a few times throughout the year depending on the use. I would recommend using Tri-Flow and then using the lubrication procedure from PacBrake, make sure ALL points are lubricated well. See chart below.

Then retry the coach and exhaust brake on a downhill grade to see if it has restored your exhaust brake back to normal.

If you have a PacBrake, I would also suggest switching out the normal PacBrake for the upgrade unit called PRXB. I did and it has helped with all of the weight i am carrying.

Dr4Film ----- Richard
Attached Files
File Type: pdf PacBrake Lubrication Chart.pdf (79.0 KB, 83 views)
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Old 09-24-2012, 02:55 PM   #7
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The PRXB Pac brake is designed to have a greater braking force at lower RM than the older style Pac brake. If you compare the braking power charts for both you will see the braking force is virtually the same for both until your RPM gets down to about 1700 RPM. Below 1700 RPM the PXRB has quite a bit more braking force than the older version. I considered upgrading to the PRXB until I realized my Allison 3000 transmission automatically downshifts at 1900 RM with the exhaust brake on so I would get no gain of braking force with the PRXB.

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Old 09-25-2012, 08:56 PM   #8
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On my cummins ISB 5.9 had the same problem, after going over the exhaust brake I found the problem was leaking exhaust manifold. Replacing gasket restored braking.
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Old 09-29-2012, 08:34 AM   #9
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The PRXB Pac brake is designed to have a greater braking force at lower RM than the older style Pac brake. If you compare the braking power charts for both you will see the braking force is virtually the same for both until your RPM gets down to about 1700 RPM. Below 1700 RPM the PXRB has quite a bit more braking force than the older version. I considered upgrading to the PRXB until I realized my Allison 3000 transmission automatically downshifts at 1900 RM with the exhaust brake on so I would get no gain of braking force with the PRXB.

Jim
Jim,

With all due respect, I challenge your statement and evaluation of the upgraded PacBrake PRXB based on a chart versus practical application. That data may be true for your coach and Allison transmission but it is not for mine.

I have made two trips to Alaska using the same roads both times. The first trip was made with the standard PacBrake. The second trip was made with the upgraded PRXB. I can definitely tell a big difference in performance and it was well worth the cost. My coach is 36,000 lbs and my trailer is 11,000 lbs.

First off, what's important is not when your transmission down-shifts, it is the up-shift points that are important. The speed which you are traveling is the criteria, not what the rpm's your engine is at.

My Allison is programmed so that if your speed is 54 mph or higher and the PacBrake switch is ON, when you remove your foot completely from the accelerator pedal, the PRXB engages and the Allison transmission immediately downshifts into fourth gear with a aim point of 2nd gear as displayed by the SilverLeaf VMSpc that I am using. The rpm’s will jump up over 2000 – 2200 rpm’s. The coach will begin to slow depending on the steepness of the grade. It works the best once the coach reaches 53 mph or lower as the Allison will be in 3rd gear and will continue to slow until it reaches 2nd gear and about 15 mph. If the speed is 54 mph or higher, the Allison transmission will be in 4th gear and will continue to pick up speed until you tromp on the brakes to get the mph 53 or below.

On steep grades, I will keep the coach lower than 54 mph. Once it reaches 53, I do NOT allow the Allison to up-shift into 4th gear. I tromp on the service brakes and drop the speed down to 45 mph. it will then creep back up and I tromp on the brakes again. On VERY steep grades, you want to start at the top of the grade going slower, say around 35-40 mph, then use the service brakes occasionally to bring the speed back down to 35-40 mph.

This technique and method has worked great when using either the standard or upgraded PacBrake however, now that I have the PRXB, I find that I do NOT need to tromp on the service brakes as often as I did when I had the standard PacBrake.

Information based on practical use and not from a data sheet. Just my opinion.

Dr4Film ----- Richard
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Old 09-29-2012, 08:49 AM   #10
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Personally I would not drop my speed to 35 or 40 intentionally. That's a good way to make some truckers mad especially if your in the truckers lane. And if your in another lane then the auto's will try to run over you.
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Old 09-29-2012, 09:21 AM   #11
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Truckers will get over thier mad.The safest way to drive is to do the hills and grades at the speed you figure is safe for your unit..I have sometimes asked a trucker if they wanted arond me before a steep area and most have declined.I used to drive a big rig and all people should be taught to drive thier vehicle and let the other person drive thiers,its called sharing the road.Forgive the rant it is not meant to be but I would sooner have someone slow down than be pulling my sheets off the bed to bandage them up.Been there Don,t need to do it again.Keep safe.jeffp an old trucker with millions of miles.
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Old 09-29-2012, 10:05 AM   #12
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Rich,

We may both be saying the same thing just a different way.

When the exhaust brake is on the Allison 3000 transmission computer controls the downshift RPM. The default setting for a C-7 Cat engine is 1900 rpm. The default downshift controlled gear is 2. That means the transmission computer will downshift the transmission at 1900 rpm with the exhaust brake on until it reaches second gear then it will disengage. You will see a 2 in the shift selection window telling you that is the target gear that is selected for exhaust brake application in the computer. That can be changed to any gear you want with a reprogramming of the Allison computer. Several here have had theirs changed to 5 so they can keep the rpm lower before it downshifts. They use the throttle to control the on/off when it is set that way.

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Old 09-30-2012, 08:59 AM   #13
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Personally I would not drop my speed to 35 or 40 intentionally. That's a good way to make some truckers mad especially if your in the truckers lane. And if your in another lane then the auto's will try to run over you.
it obvious that you haven't driven the same 9-10% grades that I have through the Yukon and British Columbia. As for the truckers, if they are fully loaded, I am usually either following them up at the same speed or following them down at the same speed. They are driving just a safely as I am making sure we get over the mountain in one piece. As for the autos, in most cases there will be an extra lane, if not then they either have to wait or attempt to commit suicide by passing which some have done recklessly.

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Rich,

We may both be saying the same thing just a different way.

When the exhaust brake is on the Allison 3000 transmission computer controls the downshift RPM. The default setting for a C-7 Cat engine is 1900 rpm. The default downshift controlled gear is 2. That means the transmission computer will downshift the transmission at 1900 rpm with the exhaust brake on until it reaches second gear then it will disengage. You will see a 2 in the shift selection window telling you that is the target gear that is selected for exhaust brake application in the computer. That can be changed to any gear you want with a reprogramming of the Allison computer. Several here have had theirs changed to 5 so they can keep the rpm lower before it downshifts. They use the throttle to control the on/off when it is set that way.

Jim
Jim,

On my trip back from Alaska, I have pulled many grades and done many hills up to 10%. With the most recent ones on the I-5 in Oregon and California through the Siskiyous, on the way up my rpm's are at least 2000 or more with the boost WAO. Once the top has been crested, the rpm's start to drop and the mph goes up until we head down. If I am doing 55 mph, the tranny will be in 5th gear and the rpm's will be about 1500. Once we start down, the PacBrake engages and the rpm's immediately go up to over 2000 rpm's, the transmission drops to 4th gear. The Allison will show 2nd gear but the important gear to watch is what gear it is actually in. You will get far better performance in either 3rd or 4th gears with the rpm's between 2000 and 2500 than you will when the Allison reaches 54 mph where it will up-shift to 5th. That's why I always tromp heavily on the service brakes just before it reaches 5th gear to lower the mph down to 45 or so. I will so as low as 35 depending on the steepness of the grade. With 9-10% grades, I will keep the mph between 35-45 mph and I will also have my hazard lights flashing.

Dr4Film ----- Richard
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Old 09-30-2012, 09:47 AM   #14
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10%???
Some of the steepest grades on the Interstate Highway System are located on Interstate 5 in southern Oregon. Although most freeway climbs are built on grades of 5.0 percent or less, northbound I-5 traffic must climb a 6.13 percent grade to reach Sexton Mountain pass.
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