Author Topic: Rear disc brake wear 99 marquis  (Read 8324 times)

Bruce Sevier

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Rear disc brake wear 99 marquis
« on: November 20, 2014, 09:41:55 PM »
The rear brakes on our 99 Marquis wore out in 20,000 miles.  This is the second time this has occurred.  In the last repair, the slide pins were replaced, new rotors, new pads and a spring kit to force the pads away from the rotor. Yet the front brakes have not been replaced in the 50,000 miles we have driven the coach. These are Meritor brakes.  Have a SMI air brake system for our towed car.
The work was done at a reputable shop, and they have worked closely with a local brake parts supply house.
Any suggestions would be greatly appreciated.
Thanks
Bruce Sevier
Bruce Sevier
99 Marquis

Gerald Farris

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Re: Rear disc brake wear 99 marquis
« Reply #1 on: November 20, 2014, 11:03:49 PM »
Bruce,
Improper lubrication practices will cause accelerated wear on your brakes. Are you sure that the brake calipers have not been improperly lubricated? The specific lubrication procedure for your calipers can be found in the Meritor service manual. Never let the lube guy grease your brakes when he is lubing the chassis. This is a common mistake since the calipers have grease fittings.

The other common issue on that model coach is undersized front air chambers. Some of the early models came with T20 air chambers on the front brakes. These small air chambers caused poor front braking and accelerated rear brake wear since the rear brakes (with T30 chambers) had to do most of the stopping. After this issue became apparent, the factory started using T24 chambers on the front. However, on my 2000 Marquis, I was not pleased with the braking performance and uneven front to rear brake wear with T20 front chambers and T30 rear chambers, so I installed T30chambers on the front also. This gives me almost even wear between the front and rear.

Gerald   

Bruce Sevier

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Re: Rear disc brake wear 99 marquis
« Reply #2 on: November 21, 2014, 02:05:24 AM »
Thanks Gerald
I would hope at the last service they used the proper grease on the calipers.  I looked at the brakes today in the shop and the left side pads were worn the same, and the inner pad on the right side was metal to metal.  Both rotors had many surface cracks and the pads looked like they were over heated.  It seems the rear brakes do most of the braking as I have never replaced the front pads in the 50,000 miles I have owned the coach.

I am curious about your having changed the air chambers.  By installing the T30 air chambers on the front brakes increases the application pressure on the front brakes, which reduces the braking load on the rear brakes?  Next question is how difficult is it to install the larger front chambers on the front brakes?  Is this something I can do or would it be better to have a shop install them?  This sounds like the solution to this problem. 

Thanks so much for your reply.

Bruce
Bruce Sevier
99 Marquis

Gerald Farris

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Re: Rear disc brake wear 99 marquis
« Reply #3 on: November 21, 2014, 03:03:51 AM »
Bruce,
For obvious liability reasons, I can not tell you to modify your brakes to alter their original configuration. However, if you decided to do this on your own, the only thing that is the least bid technical, is cutting the shaft to the right length. Everything else is just unbolting the old unit and installing the new ones.

I removed the front wheels to make the job easier, and it took about an hour from start to finish. However, I think that you could do the job without wheel removal, but it would be more difficult. I do not see any reason that the average mechanic would have difficulty with changing your front air chambers.

From your last description, you may have over-lubricated brake calipers. This happens if someone greases the calipers without purging the excess grease. That is why I referred you to the Meritor manual for the right procedure. A clay based grease is mandatory, but you also have to use the proper procedure.

Gerald 

Jerry Pattison

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Re: Rear disc brake wear 99 marquis
« Reply #4 on: December 18, 2014, 05:08:37 AM »
Bruce, I have a 98 Marquis.  Beaver started using the Safari (Magnum) chassis that year, replacing the Gillig.  In that chassis, they used front brake chambers that were too small, and did not actuate the front calipers enough to engage the rotors, so all stopping was done by the rear brakes.  I had the same problem and Beaver agreed to replace the actuator chambers for me, even though I lived in Las Vegas.   A good friend of mine with the same coach rear-ended his friend because he could not stop, and that event led to the Beaver factory analysis of the faulty (small) chambers.  If your coach has not had the chambers replaced, and you have a Magnum chassis,  then it needs to be done, else you will not ever use your front brakes.  Hope this helps.

Adam Hicklin

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Re: Rear disc brake wear 99 marquis
« Reply #5 on: December 18, 2014, 06:15:35 AM »
How are the air chambers identified?

George H. Wall

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Re: Rear disc brake wear 99 marquis
« Reply #6 on: December 18, 2014, 11:57:28 AM »
Gerald,  I have full air DRUM brakes, on a Magnum chassis. Does this problem affect mine also???   Henry

Gerald Farris

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Re: Rear disc brake wear 99 marquis
« Reply #7 on: December 18, 2014, 07:45:36 PM »
Adam,
The brake air chambers (cans) can be identified by their size. The chart below is an easy reference as to chamber size. When you refer to an air brake as a T 20 or a T 30, the type or T number is referring to the square inches of the diaphragm. Therefore at 100 PSI a T 20 chamber will generate 2,000 pounds of pressure, but a T 30 will generate 3,000 pounds of pressure at 100 PSI.

Gerald


Gerald Farris

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Re: Rear disc brake wear 99 marquis
« Reply #8 on: December 18, 2014, 07:48:07 PM »
Henry,
If you have drum brakes on a 2002 Patriot, it is a Monaco design change (the same reason that you have a Cummins instead of a Caterpillar) and this issue does not effect your coach.

Gerald