Hummer Brake Servicing

Servicing the Brakes

One of my rear calipers locked up on me, I was lucky I caught it just a short time after it happened. I knew before too long I would have to change out the brake pads. This just made it sooner then I wished.

Replacing the pads for the front and back are almost the same, but let me tell you, the rear is a lot more work. The rear caliper has a emergency brake cable and help when it's dis-connected. Dis-Connecting it is easily done by removing a cotter pin and a "C" clip on the cable. And the rear piston must be turned while being compressed the same time, a bear while under the truck with out the Kent Moore Tool.

The photos below are of the rear caliper, the front caliper is smaller and does not have the emergency brake linkage.

Click on photos for larger image.

To remove the caliper, you need to remove the two capscrews that secure the yoke and caliper to the adapter. It is tight getting to the top capscrew. The service manual recommend using a crowfoot, but I recommend a 14mm ratchet/wrench.Make sure the caliper is supported to prevent damage to the brake line. If you are going to remove the brake line, use a 3/8 flare nut wrench, if not, you can damage the flare nut fitting and you will have to replace it.

To bottom out the front caliper, place a caliper compression tool within the caliper and turn the handle until piston is like the picture below.
For the rear calipers, you will need to turn the piston clockwise(as you are looking at the top of the piston), about one or two turns and then compress the piston as far as it will go, the turn the piston again and then compress again, repeat until you are all the way to the bottom. I highly recommend the Kent Moore brake compression tool.

You may wish to removed the caliper in order to get better access to it so that you can turn the piston, but that also required disconnect the brake line. (not a good idea if you can help it)
Your calipers (front & rear) should look like this when fully compressed and ready for mounting.

The local auto part place, NAPA, has pads from $20 a set to about $50, a set is 4 pads, 2 for each side.
Always replace pads in sets.

Pads:

NAPA # MES-7122A-M.
NAPA AE-7122-A

Rotors:

AC-Delco 18037672
GM 12338387
Napa 86591
Raybestos 56591

Once you have the caliper compressed, connect the brake line. Place the brake pads on the adapter. Apply lock tight to the the tapped holes of the adapter, and secure yoke and caliper to adapter. Tighten capscrews to 30-40 lb-ft. If the rear, re-connect the parking brake cable.

Next you may need to bleed the brake lines to make sure no air is in the line (if you have dis-connected any of the brake line, you will need to bleed the lines). Make sure you use only DOT 5 brake fluid on the Hummers. Most cars and truck use DOT 3, and DOT 3 & 5 do not mix. When bleeding the brake line attach a hose line to the bleed vent and make sure all the air is out of the system. You can get a "One Man Brake Bleed Line Kit" to help prevent from air getting back in the system, they are good, but not perfect, a two man operation works best.

Some where along the lines, some one put DOT 3 in my brake system on top of DOT 5, I had to drain all the lines the best I could in order to get the DOT 3 fluid out. While doing the brakes on a friends Hummer, I found that he too had two types of brake fluid in his system. Click here and see what I found & what was done. - Chad's Brake Job - 11, April of 1999.

Easy, right!? The first one took time to figure out how to compress the caliper, what the service manual does not tell you much about, is that must screw the caliper piston down once you have compressed it.

Just my luck, my left rear caliper was locked up, the piston would not move at all. A new replacement caliper had to be ordered from AM General, this item you cannot get at the local auto part place that I know of.

New caliper assemblies come complete with a set of brake pads.
Unless you already have a matching set of pads for both sides, I would not use the ones that came with the new calipers. Pad are not all made the same, some are harder, while others are softer and wear quicker but take less pressure for braking.

If your rotors have to be turned, the shaft, or halfshaft as it is called, has to be dis-connected. There are 6 bolts that dis-connect the shaft and brake rotor from the output flange of the differential. When re-installing the rotors, use NEW lockwasher to secure the halfshaft and rotor back to the output flange.

Re-Surfacing the rotors maybe required if your rotors are warped, or have grooves cause by the old pads. If they are just glazed, I would just re-surface them using a sanding pad, or Brake Rotor Surfacing Discs.

Note: Before I had change my brake pads with the pads from NAPA, I something would get this awful vibration due to the brakes. The dealership replaced them because of this before, but with the stock pads. Since changing to the Raylog pads, this has never happened again. How nice it is, not only cheaper then stock pads, but got rid of the awful shakes that I would get.

Just got the tool made by Kent Moore Tools for doing the brakes that the dealers are using. Here are some pictures of it.

Brake Job, using the Kent Moore Tool

11-Fab-99: Forgot the socket, found out that you can buy the socket that I was making from Kent Moore Tools for about $60.00. But if you get the whole brake tool, you will find it's a lot easier to do a brake job.

Other options: Pusher tool - You can order the the pusher tool (Assembly only, Lisle Part #25470) for under $30 and and you maybe able to get a socket made by Dave Breggin. for under $50.

Cut up Rear Brake Caliper! Yeah, I cut up my old one to see what made it tick. Click here to take a look for yourself.

	To remove the caliper, you need to remove the two capscrews that secure the yoke and caliper to the adapter. It is tight getting to the top capscrew. The service manual recommend using a crowfoot, but I recommend a 14mm ratchet/wrench.Make sure the caliper is supported to prevent damage to the brake line. If you are going to remove the brake line, use a 3/8 flare nut wrench, if not, you can damage the flare nut fitting and you will have to replace it.
	To bottom out the front caliper, place a caliper compression tool within the caliper and turn the handle until piston is like the picture below. For the rear calipers, you will need to turn the piston clockwise(as you are looking at the top of the piston), about one or two turns and then compress the piston as far as it will go, the turn the piston again and then compress again, repeat until you are all the way to the bottom. I highly recommend the Kent Moore brake compression tool.
	You may wish to removed the caliper in order to get better access to it so that you can turn the piston, but that also required disconnect the brake line. (not a good idea if you can help it) Your calipers (front & rear) should look like this when fully compressed and ready for mounting.