Brakes on a Hummer

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Brake Pads


The only way to get these pads is from AMG part number 5745162C. I've been told that the Hawk brakes are supplied by Porterfield and that Porterfield makes some very good Carbon Kevlar pads.

I'm writing this to show how to do a simple pad replacement on the rear of a Hummer without using the expensive ($350) Kent Moore tool. The fronts use the same pads as the rears. The only difference is that the rears have the parking brake hardware and require you to turn the piston in order to retract it. On the fronts all you have to do too retract the piston is to squeeze it with a channel lock pliers or use a retracting tool. You don't even have to remove the front undercarriage protection.

The front calipers are from a jeep. The rear are unique to Hummer because of the parking brake mechanism.

Brake Lines

Brake lines are a very important part of a car's braking system. This steel tube holds the brake fluid that is responsible for making the brakes work. Through the movement of the fluid, braking force is transferred from the master cylinder to each of the wheels. Exposure to the elements, handling a great amount of pressure and moisture in the brake fluid cause these tubes to deteriorate and eventually fail.

The brake lines on the Hummer / H1 are standard 3/16" lines with standard double flare fittings. A 3/8" flare nut wrench is used for most of the fittings, with a 1/2" wrench (flare) also required for the outer fitting on the brake calipers.

One of my readers sent me an email in December of 2014 about a new type of copper-nickel brake line that is much easier to work with than the standard hard steel lines and is inherently corrosion resistant. Hard steel lines are like working with steel conduit. You can't just feed them around obstacles. You have to pre bend them with a tubing bender or they'll kink. The steel is hard and takes a lot more effort to form flares on the ends.

I found that the rear driver side brake line was badly corroded and leaking. After removing all the lines, drivers and passenger I went to the local auto store and found out they have a new material for break lines made out of a copper Nickel alloy in 50ft rolls. To say that this was an easy install is an under statement. With a friend feeding it, I guided it towards the rear unions. It was very easy to flange,and bending is a dream. I did need some plastic tube to act as spacers at the clamp. But all said and done it took about 45 minutes to get everything installed and tightened down,  The other advantage is not having to ever worry about corroded brake lines.

It turns out that copper-nickel brake lines are not new. They were used in cars prior to 1930. With the advent of mass production steel was cheaper to use.

Repairing Brakes

For most of us our rotors are fine, and the braking system is in good shape. I'm hitting on other subjects because you should be cognizant of other problems for safety reasons. I am including the pages from the AMG manual on rebuilding calipers for reference at the end of this page. Remember, these are your brakes, so there is no room for compromise when repairing them. If you get over your head or find other problems that cause you to get over your head find someone qualified to fix it right, even if it means towing your truck in.

If any pad on your truck is thinner then 1/8" all 4 of the pads on the front or rear should be replaced as a set. What about the rotors? I only turn the rotors if they are badly scored or warped. If you run your finger nail over the rotor and can feel deep scratches have them turned. I've found that it's usually not necessary to turn the rotors. The new pads will wear in and conform to a little bit of a rough surface. Turning the rotor removes material making the rotor thinner and eventually weak enough to require replacement. Warped rotors are caused by overheating and will wobble when rotated. You might also feel a pulsing in the brake pedal. Sometimes turning can fix a warped rotor but it may need to be replaced. If they need replacement I use Aimco rotors that I get at Autozone. Their number is 186251 5701. They cost about 50 bucks each.

New pads will chatter and cause vibration and sometimes violent shaking. This is the sharp edge of the new pads hanging up on the rotor. Take the new pads and chamfer the edges off as shown in the photo. The hummer pads float in the calipers so you do not need any clips or adhesive to hold the pad in place.

From the AMG service manual:
If you have measuring tools the rotor thickness should not vary more the .005" measured 1" in from the outside at 4 equally spaced points around the rotor. Too check for warp setup a dial indicator with the stylus contacting the rotor 1" from the outer edge and rotate the rotor. There should not be more the .004" variation. Brake rotors have a minimum thickness value cast into them (.815"). If you end up turning them don't use a rotor that ends up too thin.

If you do have to turn the rotors you will have to remove the half-shaft bolts. The lock washers are one use type called Nord washers. Make sure you have a set of lock washers (get them from AMG) in hand when you reassemble. You don't want the half-shaft bolts coming out.

You should also check for any brake system leaks. If you've been experiencing drips under the truck's brakes and or a declining level in the master cylinder inspect the brake lines, fittings and pistons. The biggest cause of leaks are piston seal leaks. If you see brake fluid on the pads and on the caliper and it's not dripping down from the brake line fitting it's probably the piston seal. In rare cases the caliper could be defective with scratched or out of round cylinders.

When I check brakes on a Hummer I always check the right rear first. The three Hummers I've owned a 95 gas, 96 turbo diesel and a 98 turbo diesel have all mysteriously gone through rear brakes as much as fronts. In fact, most cars go through twice as many front pads as rear pads because most braking action is in the front because when a car stops the weight shifts foreword putting a greater load on the front brakes. Another problem is that all the brake pads on the Hummer seem to wear unevenly. The pad on the piston side of the caliper tends to wear twice as fast. The other strange thing is the right rear on all three trucks has usually worn very unevenly. The piston side pad has worn twice as much as the other. On the 95 and 96 the piston pad also wore unevenly being much thinner towards the front then the rear. I've found that uneven wear problems are greatly reduced with the Hawk pads.

I have finally found the answers to the uneven break wear. I spoke to a chassis engineer at AMG. He said that the uneven wear is a function of single piston calipers. He said that the short brake life is from off road when using BTM (brake throttle modulation). The brakes have to hold the torque of the engine in order to lock the spinning wheels. This causes major brake wear. Just as an aside he said that the brake proportioner valve (only on non-abs trucks) is a 200 psi unit.Another reason the Hummer uses up brakes is that the rotor is spinning twice as fast as the wheel because the geared hub has almost a 2:1 ratio. But why the right side wear? One plausible theory is the following: I was talking to the mechanic at the Hummer dealer. He said that the right side of all cars wear more then the left because when you drive on the right side of the road (as we all do in the USA) the right side of the car is always exposed to more dirt since it's closer to the curb gutters and shoulder. This makes a lot of sense especially when the roads are wet. The dirt washes off the center crowned portion of the road and collects as mud puddles on the right just waiting to be splashed up mostly under the right side of the car. Over time the right side gets dirtier and wears more.

Another reason the pads will wear unevenly is because the caliper is supposed to float on the mounting adapter. What happens is the caliper guide pins will bind up occasionally and cause the uneven wear. Go under the truck every couple of months with a big screw driver and make sure the pads are free. You can also clean up and put a little grease on the guide pins. The NAPA pads help compensate for this uneven wear by making one pad longer then the other. This pad goes on the piston side. I still recommend the factory pads.

Trucks with ABS, 1999 and newer use DOT3. All trucks 1998 and earlier use DOT 5. You should also check the brake fluid to make sure that DOT 3 was not mixed in with the required DOT 5. The DOT 5 is silicon and does not mix with the DOT 3. If you see two colors in the master cylinder you may have a problem. Draw out some fluid and put it in a clear bottle. If you have two different kinds you will see a stratification showing one fluid floating on top of the other. If you find this problem you will have to bleed out the whole brake system with fresh DOT 5. DOT 5 comes yellow and dyed purple. Depends on the supplier. Have both here. And also old purple DOT 5 can lose its color over the years and turn yellow. Here's a very good explanation of the different kinds of brake fluids.

Note: 99's and newertrucks with ABS and TT4 use DOT 3.

What You Need

Before you start make sure you have the following on hand:

Latest part numbers can be found in the Parts Cross Reference

These maybe good numbers for Rotors. NAPA rotor 86591. I used Aimco rotors that I get at Autozone. Their number is 186251 5701. They cost about 50 bucks each

Suggested Tools:

Note the brake caliper tool is now available for around 89.00 from MAC tools

The original tool from Kent Moore 800-328-6657 (2 - 3/8" socket)
Caliper Compression Tool. PN J-42553 sells for 350.00.

Note: as of 2000 AMG has come out with a new improved hawk brake pad that in my opinion is the best one to use. According to the AMG engineers this pad tested to wear 4 times longer. I have been using them in my truck for over 3 years and noticed that they stop better, wear better and seem to fit looser in the caliper. This may help in keeping them from binding up (common problem on Hummers) and wearing unevenly. These also came with the Permatex Ultra Disc Brake Caliper Lube. If you are in the need of "Hawk" brake pads, try any Hummer Dealer or; 1-800-981-3783. The pads for the H1 are the "Hawk HP SuperDuty" series. I have also used NAPA semi-metallic riveted brake pads #AE-7122-AM but these are not as good.

If you need caliper rebuild kits with piston seals etc the Kelsey Hayes part numbers are XX703342307 or Raybestos WK1473.

(The Dust Boot that is supplied with the Raybestos WK1473 kit isn't worth a darn! The lip that slips into the seat around the Piston does exactly that, It slips in! I later got an AMG boot and found the Lip to be a little taller so that you could "Press fit" the boot in.)

2003 Prices
- AMG 05579865 Front Caliper Rebuild Kit (2-calipers, no bleeder) $16.82
- AMG 05744403 Rear Caliper Rebuild Kit (1-caliper no bleeder) $15.62
- AMG 05578802 Caliper Bleeder Valve $0.65
- AMG 05597172 Caliper Bleeder Valve Cap $0.48
- AMG 05744405 Rear Caliper Rebuild Kit $37.80

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