Pete Gibbons wrote: Wasn't there an HML posting some time back about beveling the edges of new brake pads? Would that have solved the shudder-on-braking problem? If so, could the person who knows about that re-recommend and re-describe the method of beveling? Thank you. Pete Gibbons in Ithaca.

Pete, here is everything I could find relating to chamfering and vibration while braking. It's long, but I thought a repost of the info would be useful.

From: MICHAEL SELIG
Date: Fri, 12 Jul 1996 07:18:08 -0400
Subject: FW: Brake Problems

I might have some info. I had no problems with braking going forward or any strange noises. Brakes worked fine in reverse. However, if I was in neutral and rolled backwards than put on the brakes, I would get a nasty vibration. Drove me nuts trying to figure it out. Anyway to make a long story short, I started to get a leak past one of my rear diff side seals. The yoke is connected to the diff assembly via splines which transmit the torque to the wheels. However, the yoke is held in place laterally by a nut. To the yoke bolts the disc and half shaft. The nut loosened up, allowing the yoke to wiggle a little, causing the disc to vibrate, causing the nasty vibration. Also, the movement of the yoke damages the seal causing fluid loss. The fix was to replace the diff seal, make sure the nut is tight, check the fluid level, and viola, no more vibration or leakage.

Gerald
gluiz@hpl.hp.com

Many brake squealing problems can be just due to the brake pads not mating to the rotors properly. Driving slowly with the brakes on for a few minutes so called BURN IN, sometimes better seats the pads. There is also chamfering, which is grinding the edges of the pads.
MS

From: SteveBell1@aol.com
Date: Fri, 12 Jul 1996 14:15:35 -0400
Subject: Re: FW: Brake Problems
re: brakes rattle and noise

They rattle a lot when new. When I get a new one in, I have a 20 min. route I take to seat and chamfer. When you have new brakes, the edges are real square, and they rattle back and forth when applied. Do a few hard stops. Don't just hit the brakes, use progressive force untill you're standing on 'em. Then get up to freeway speeds (55-78) and do some long, slow braking, sort of a little brake throttle modulation at speed. That works for me.
sbell

From: apapalio@micron.com (Andy Papaliolios)
Date: Fri, 4 Oct 96 11:54:33 PDT
Subject: Braking chatter & shudder

The braking shudder, especially from the rear in a lightly-loaded vehicle, is due to un-chamfered brake pads. The leading and trailing edges of the brake pads need to be ground so they look like this:

\_______________________________/

A 90-degree edge will cause that high-frequency (20 or so hertz is pretty high for an entire vehicle!) vibration.

I've just replaced the rear brakes, now when I stop hard, I get a violent vibration coming from the rear. What was the problem/solution again?

Ron this is normal. The pads just have to wear in for a day or two. The way around this would be to chamfer the edge of the pads before installation (according to the AMG manual).

From: Gerald Luiz
Date: Wed, 10 Jul 1996 0:36:12 PDT
Subject: Re: Brake Problems

Does any one else have problems with the brakes sounding like a very loud growl and a shaking that make you just about come out of your seat when stopping?
I have the problem with my Hummer about 1 out of 30 times I stop, and cannot get it to do it for the dealership every time I take it in. And now the front seals on the differential are leaking gear oil all over the place. I believe that part of the leaking it do to the vibration from the braking problem.

I might have some info. I had no problems with braking going forward or any strange noises. Brakes worked fine in reverse. However, if I was in neutral and rolled backwards than put on the brakes, I would get a nasty vibration. Drove me nuts trying to figure it out. Anyway, to make a long story short, I started to get a leak past one of my rear diff side seals. The yoke is connected to the diff assembly via splines which transmit the torque to the wheels. However, the yoke is held in place laterally by a nut. To the yoke bolts the disc and half shaft. The nut loosened up, allowing the yoke to wiggle a little, causing the disc to vibrate, causing the nasty vibration. Also, the movement of the yoke damages the seal causing fluid loss. The fix was to replace the diff seal, make sure the nut is tight, check the fluid level, and viola, no more vibration or leakage.

Gerald
gluiz@hpl.hp.com

From: Christian Kuhtz
Date: Thu, 11 Jul 1996 20:58:50 -0500
Subject: RE: Brake vibs...

Warped rotors maybe? You can't fix 'em unless you replace 'em (and change your driving habits :).
Chris

At 03:32 PM 7/11/96 UT, Dave Ellis wrote:
I have the same vibration problems when braking on my 94 Hummer. It used to only happen in reverse, now it is happening more frequently and while moving forward.

From: Eddie Runner
Date: Fri, 12 Jul 1996 11:54:07 -0500
Subject: Re: FW: Brake Problems

MICHAEL SELIG wrote:
I might have some info. I had no problems with braking going forward or any strange noises. Brakes worked fine in reverse. However, if I was in neutral and rolled backwards than put on the brakes, I would get a nasty vibration. Drove me nuts trying to figure it out.

My brakes USED to make the vibration when coasting in reverse and NOT in gear and never while going forward...The service dept. could never duplicate the problem. And they could never get my brakes to squeek either but with me they squealed all the time, they always told me my pads were fine....When we were changing the fluids we took a good look at the pads and the were almost gone!! We replaced the pads ourselves cause we didn't want to be without the truck for a long time we did the rear one evening and the front the next evening (it wasn't very tough)... and now with the new pads there is almost never a squeal and I don't think I have any vibration moving backwards but I did have the vibration 1-50 times (maybe less) while braking forward when the pads were brand new.. now they are broke in a bit (2000 miles) and they never vibrate...I think its how the pads just sit loosely in thier holders, and the sharp edge gets worn off the new pads, and since braking in reverse is not as often maybe the reverse edges on the pads don't get broken in.
???
Eddie
- ----------------------------------------------------------
Eddie Runner eddie@installer.com
http://www.installer.com/hummer.html
- ----------------------------------------------------------

From: HuMN8@AOL.COM
Date: Tue, 16 Jul 1996 18:58:46 -0400
Subject: Check for loose fasteners...

To all,
From reading previous posts (Gerald) of 'Brake growls/vibrations' is crawled under my HUMMER and checked the torque #'s on the halfshalf bolts connecting to disc rotor, hence they were ALL LOOSE..even with the lock washer on...front and rear..hence 'cause for differentials seals to go bad from the vibration of the loose rotor and leaking fluids all over pads..So to all 'new' HUMMER owners who don't know this tidbit, I'd check the bolts and put lock-tite on all half-shalf bolts and re-torque. Another thing to check for is the brake fluid level, my truck still being new, was down to a quarter of fluid left in master cylinder(remember DOT 5 fluid ONLY), luckily it didn't suck down any air. I don't know where its going, but I do not have any leaks. Also do check all radiator hose clamps to ALL hoses and spigits...Some of the clamps on my vehicle were loose enough to pull off by hand with little effort and with these hoses under pressure they might pop off and leave you leaking fluid somewhere and stranded. These simple items could be overlooked at maintenance intervals..so keep on it.

One more thing, if you feel that you are losing a little horepower from the bottom end, try replacing your fuel filter, does amazing wonders for power. Mine was VERY dirty at 12K miles..I mean filthy black..I could be picking it up from the local gas station I gas up at since barely no one uses diesel, hence it sits there, God knows how long it has. If you let the dealer replace your filter, they'll charge you $150 to do so, they add its very hard to change...NOT! Very easy to do yourself..

Anyone care to add to this........any experiences.....recommendations..etc..etc..

Good Luck
Chris

From: Gerald Luiz
Date: Wed, 17 Jul 1996 16:22:17 PDT
Subject: Re: Check for loose fasteners...

From reading previous posts(Gerald) of 'Brake growls/vibrations' is crawled under my HUMMER and checked the torque #'s on the halfshalf bolts connecting to disc rotor, hence they were ALL LOOSE..even with the lock washer on...front and rear..hence 'cause for differentials seals to go bad from the vibration of the loose rotor and leaking fluids all over pads..So to all 'new' HUMMER owners who don't know this tidbit, I'd check the bolts and put lock-tite on all half-shalf bolts and re-torque.

Great advice. The problem I had was the single nut in the centerline, not the halfshaft bolts. You have to drop the halfshafts to get to them. Chris's point about the halfshaft bolts is really good. They are known to come loose. There are special locking washers you can get to better secure them. In fact, AM General is going to start using them in the from the factory after feedback from the HOA. Oh, brake fluid is Silicone DOT 5, not just DOT 5. They are not compatible.
Gerald

My dilemma a few weeks ago on with my front caliper bolt, Keri wrote:

"... How did you finally remove this bolt? Oh, and folks had talked about "9/16 wrenches" for this bolt which confused me ' cause this is a metric bolt (15mm I think). My bolt was so frozen that using anything but a properly fitting wrench would have rounded out the head..."

Keri,

Sorry I didn't get back to you sooner....After spending the weekend under the beast, I was simultaneously wresting with an exhaust system on another car and trying to finish up the multitude of other outdoor projects before the weather really got cold.

By the way, I think it was Chris that suggested the article on the Homepage, which was very helpful. After wrestling with the front caliper, with the fear that I would round the bolt off I took drastic measures. I took a Craftsman 14MM wrench, took a torch to it and bent it (I know in most states this is illegal, but hey, I was desperate, besides I was feeling like Mcgyver). Then I took a trip to the temple of Sears to confess my sins, and beg forgiveness for desecrating a tool. Salvation was found in what looks like a miniature breaker bar for a 1/4" drive socket (sorry, too many Christmas specials).

Anyway, you were right about the locktight red. I took my little Benzamatic Kit which is a propane and Oxygen combo you can get for around $45.00, and heated that little caliper bolt, and used my new mini breaker bar and 14MM socket, and it came right out. I like the Propane Oxygen combo because you can get a hot flame, and really pinpoint it instead of napalming the entire caliper. Another suggestion, in addition to a very informative article on the homepage, would be to tie the caliper up with wire which will relieve some of the stress on the brakeline and keeps it out of the way if you need to remove the rotor. Once the upper and lower caliper bolts were removed and the brake cylinder was pressed back, I greased the contact points and the rest was a cakewalk.

In addition, I had to remove a rotor which was badly scored. That was even easier. One thing you may want to remember, though, tie up the halfshaft before you remove the four bolts which go through the rotor. I took a piece of chain and put a bolt with some washers and a nut through some links so that I could lower the halfshaft slowly and far enough to slip the rotor off, and stick the bolt back through the links when it was clear. That halfshaft is heavy, especially if it's lying on your chest, and when your trying to line the holes up with the rotor to bolt it back on, it has to be perfectly aligned, so chaining it up frees up your hands to maneuver the rotor, which isn't light either.

All said and done, with the right tools, the Hummer's brake pad and rotor replacement is probably the easiest vehicle I have worked on. I think the lock tight on the caliper bolts is an excellent idea. By the way, for those on the east cost (I'm not sure how far the retail chain extends), Pep Boys Auto Parts, if they have a service facility will resurface rotors for $5.00 plus tax. You will probably have to provide the specs (by the way, does anyone know the minimum specs on rotors?), but it's quite a deal. Including my new tool the and resurface one rotor, the job cost less than $80.00.

By the way, thanks to all for the info. I hope you find some of this info helpful.

Pep Boys Auto Parts, if they have a service facility will resurface rotors for $5.00 plus tax. You will probably have to provide the specs (by the way, does anyone know the minimum specs on rotors?),

Quoting from the '93 Service manual:

Checking Lateral Runout (Fig 17-44)

1. Mount dial indicator with stylus contacting rotor surface 25 mm ( 1 in.) in from outer edge.

2. Turn rotor 360 degrees and note indicator readings.

3. If lateral runout exceeds 0.10 mm (0.004 in.) total, replace or refinish rotor.

Checking thickness Variations (Fig 17-44)

1. Measuring thickness variation of rotor with micrometer at four equally-spaced points around rotor. Measure 25 mm in from the outer edge.

NOTE: Rotor must be replaced if minimum thickness falls below 20.3 mm (0.80 in.)

-------------------------------------- End of quote

Hope that will help you.

Allan Madar