Basic Brake Repair :

Replacing Front Brake Pads and Rotors
On A 1999 GMC Jimmy Or Chevy Blazer

May Also Apply To Full-Size Chevy/GMC Pickups, Yukon, Chevy Tahoe, Suburban, Etc.

 

In This Article:

Front brake calipers are removed by removing slide pins. Brake bracket is removed so rotor can be slipped off hub. New rotor is installed, bracket is replaced, pads are set in place, slide pins are lubricated and caliper is re-installed.

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Skill Level: 3 (Intermediate) Time Taken: About One Hour

By Bruce W. Maki, Editor

Introduction:

This 1999 GMC Jimmy didn't have any brake problems. It didn't need to have the brakes replaced, but I replaced them because I had the car in my garage for some other repairs.

My reasoning was: "While I have the wheels off I might as well rotate the tires... and I'll replace the brake pads while I'm at it." This may sound stupid or wasteful to you, but it works for me. I don't know when I'll be able to work on this car again, so I decided to fix everything that I could.

After I had safely raised the car and placed it securely on jack stands, I removed the wheels.

 

Thoughts On Rotating Tires:

When I'm removing all the wheels from a car, I will rotate the tires if it's been 5,000 or more miles since the last tire rotation.

When I remove a wheel, I park it near it's new location. I don't just drop the wheels anywhere... I'll get them mixed up. Since I can't remember schnitt anymore, I get into the habit of doing things the same way, and my habit is to do the little things when I think of them, because later I won't be sure if the wheels are sitting at their new locations or old locations.

 

To remove the bolts, I needed to turn the steering wheel to expose the back side of the disc brake unit.

Of course, for the right-hand side (passenger side) I had to turn the steering wheel the other way.

 

GM Front Brake Anatomy:

This is a rear view of the the left front brake assembly.

A: Caliper Slide Pins (2 places) These need to be removed so the brake caliper can be removed and the brake pads replaced.

B: Brake Bracket Bolts (2 places) These need to be removed IF the rotor needs to be replaced.

C: Brake Line Connection Bolt. There is no need to touch this for a simple pad/rotor replacement. This fastener only needs to be removed if the brake caliper needs to be replaced. Removing this connector will allow air into the brake hydraulic system, and then the air will need to be purged by bleeding the brakes.

 

Removing the caliper pins:

These fasteners can be tight. I used my impact wrench on the bottom pin, but there wasn't enough room to use the impact wrench on the top bolt...

... So I used my "poor man's impact wrench"... a box-end wrench and a dead-blow hammer.

I think this bolt head required a 16mm wrench.

 

I unscrewed the caliper pins. Note the black grease on the smooth part of the pin. This is normal.

 

The pins after I wiped off the brake grease.

The pins need to be wiped off and examined. If there are any major rust spots, the pins should be replaced.

Brake pin lubrication is a maintenance requirement that is commonly overlooked. In my experience the grease doesn't last nearly as long as the brake pads, so by the time the pads are worn down the pins are often badly rusted and difficult to remove.

I have seen caliper slide pins that had no traces of brake grease and were so badly corroded that they could barely be removed... even after they were unscrewed fully.

 

Pushing Back The Brake Pads:

To simply remove the caliper, the pads need to be pushed back at least a fraction of an inch. This can often be achieved by simply rocking the caliper back and forth, or by usng a small pry bar.

If the brake pads are being replaced, the caliper pistons need to be fully pushed back into the caliper cylinder bore. I use one or two large C-clamps to squeeze between the outboard pad and the back of the caliper housing.

Since this is a 2-piston caliper (a premium design!) I needed two C-clamps... otherwise the pistons get torqued kinda sideways and don't retract nicely.

 

Once the pistons were pushed back, I was able to simply slide the caliper rearward (away from the axle).

It's surprising how easy this comes out, once the pistons are pushed back. It just about falls out.

 

It makes you realize that those two little slide pins have to withstand all the forces of braking... and that can be a LOT. Two pins per side, a total of four, withstand all of the braking forces on the front axle. And they say that the front brakes do 70% of the braking on a typical rear-wheel drive car. (For a front wheel drive car the figure is 85%.)

Needless to say... those caliper slide pins are important.

 

Important!

DO NOT let the caliper dangle by the brake hose... the hose can be damaged which can result in loss of brakes if the line ruptures.

I used a bungee cord to support the caliper. I threaded the bungee cord around the shock absorber tower. Other vehicles may have different (and easier) methods of attaching some sort of support.

The caliper can also be supported by mechanic's wire, string, or rope.

 

The brake assembly with the caliper removed.

 

 

I slid the outboard brake pad out of the bracket.

On this vehicle the pads simply sit in slots in the bracket... there are no fasteners.

 

To remove the bracket, I used an 18mm box-end wrench to loosen the bolts.

(I used my impact wrench on the lower bolt, but there wasn't enough room to reach the top bolt, so I had to use a wrench.)

 

Then I removed the bolts.

Just in front of the bolt, and to the left, you can see the rubber boot for the slide pin.

 

 

Then I removed the brake bracket.

 

The inboard brake pad was still sitting in the bracket... it wasn't necessary to remove the pads to remove the bracket.

 

At this point, the brake rotor was just sitting on the hub. I simply pulled it off.

This design is similar to most front-wheel-drive cars... the rotor is not attached to the hub. When the wheel is installed the rotor gets pinched between the rim and the hub.

However... the front rotors on a 2-wheel-drive truck or rear-wheel-drive car are much different. On those vehicles the rotor is part of the front hub, and the outer bearing must be removed to remove the rotor.

 

Saving The Brake Rotors... Or Not:

While the outboard surface of the rotors looked fine, the inboard surface was not good.

 

Close-up view.

There was a wide strip of loose rust on the inboard surface of both front brake rotors. If the rotors are going to be re-used, this rust will be removed by the machining process.

I would not recommed re-using rotors like this without getting them turned at an auto parts store or garage.

I scraped off some rust so I could measure the thickness of the rotors.

 

Using a precision caliper, I measured the thickness of the rotors. This rotor measured about 28.5 millimeters.

The minimum thickness was stamped on the back of the rotor: 27.6 millimeters. I had less than one millimeter of metal that could be machined off. That's not enough!

So I decided to buy new rotors. They cost $29 at my local NAPA store. I thought that was a pretty good price.

 

About Those Brake Pads...

The pads were not badly worn... but they were not wearing evenly.

The red line is parallel to the surface of the brake lining. Note the gap between the red arrows. This area was rubbing against that strip of rust that I mentioned earlier.

 

Comparing the thickness of the new pad (on the left) to the old pad (on the right).

The old pads have lots of material remaining. IF the rotors weren't so messed up, I would have just re-assembled everything and checked the brakes in another 10,000 miles or so.

 

Preparing To Reassemble The Brakes:

The old pad (right) had metal spring clips that needed to be transferred to the new pads...

 

...Like this.

I just used a small screwdriver to pry the spring clips off. I think these clips primarily keep the pads from rattling.

 

I used a file to clean up the sliding "ways" on the brake bracket.

This is important. On older vehicles the pads often don't slide very well because these grooves become rusted. Then the pads rub against the rotors all the time, which accelerates the wear.

 

Before using the rotors, I removed the surface oil with brake parts cleaner.

 

Reassembly:

This is the front left wheel hub area before the brakes were put back together.

 

At this point the front bearing could be replaced (by removing that large nut on the spindle) and the constant-velocity joints could be serviced.

 

Before re-installing the brake bracket I applied a small dab of copper-based anti-seize compound to threads.

 

Then I set the brake bracket in position and inserted the mounting bolts, and tightened them firmly.

 

I also applied a small dab of copper-based anti-seize compound to the ends of the brake pads, to help them slide better and to slow down the corrosion process.

Important: DO NOT use too much lubricant. Excess lube could get onto the rotor or the face of the pads and reduce the braking ability.

 

To install the pads, I had to insert the top end into the upper groove on the bracket, and then slip the bottom end into the lower groove.

 

The brake assembly after both pads had been installed in the bracket.

 

Optional:

I applied some disc brake anti-squeal compound to the outer surfaces of the brake pads. This material is supposed to help absorb vibrations and reduce brake noise. I really don't know how well it works... but I had a tube of the stuff so I used it.

This goop needed to dry for at least ten minutes before installing the caliper.

 

Not Optional:

I applied a liberal amount of silicone-based brake lubricant to the slide pins.

 

I slipped the caliper over the brake pads...

 

... and installed the slide pins.

 

Then I tightened the pins with a ratchet and socket.

These need to be quite tight.

 

The completed front brake job.

Now the wheels can be replaced and the car lowered to the ground.

When I took mechanic's training, the instructors insisted that we should always complete one side before starting the other side... so we would have a proper assembly to serve as a reminder of how all the various parts go together. This is especially true when there are complicated anti-rattle clips and springs that are not obvious in their assembly methods.

This GMC Jimmy did not have anything complicated.

However, the one-side-at-a-time approach is kinda difficult when you want to take both rotors to a shop for machining. I would suggest taking pictures with a digital camera so you have a record of where each part belongs.

More Info:

Tools Used:

  • Jack Stands
  • Floor Jack
  • Impact Wrench, Air Compressor (Optional)
  • Basic Mechanic's Tools
  • Sockets: 16mm, 18mm
  • Wrenches: 16mm, 18mm
  • Dead-Blow Hammer
  • 6" C-Clamps (2)
  • Bungee Cord

Materials Used:

  • Brake Pads, Set Of 4
  • Brake Rotors, Pair
  • Brake Parts Cleaner
  • Silicone-Based Brake Lubricant
  • Copper-Based Anti-Seize Compound
  • Disc Brake Anti-Squeal Compound

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© Copyright 2007 Maki Media Group LLC

Written July 13, 2007