Rear brakes still surging

[tdupont]

2003 Tahoe LT with 144k.
So I've done 2 rear brake jobs on this rig since I've bought it at 138k. First one was a frozen caliper from a clogged line, thought it was just the caliper and replaced both sides.
Now I'm on the second job, replaced all brake components, lines, and hoses. Only thing I haven't replaced is the hose that goes down to the T on the rear diff.
They still seem to wobble, I've put about 2k miles on since the latest change. Kinda lost, would appreciate some insight.

 

[OR VietVet]

Did you replace rotors? Check runout of rotor mount hub? Clean and lube caliper slide areas? Checked park brakes for binding/dragging? ETC......

 

[Fless]

Could you define "wobble?" Do you mean that the pedal pulses when you apply the brakes? Or???

 

[tomloans]

2003 Tahoe LT with 144k.
So I've done 2 rear brake jobs on this rig since I've bought it at 138k. First one was a frozen caliper from a clogged line, thought it was just the caliper and replaced both sides.
Now I'm on the second job, replaced all brake components, lines, and hoses. Only thing I haven't replaced is the hose that goes down to the T on the rear diff.
They still seem to wobble, I've put about 2k miles on since the latest change. Kinda lost, would appreciate some insight.

I assume this only happens as you are coming to a stop and you can feel the undulating? If it were your front brakes you would feel it in the steering wheels as well. But the back brakes tend to give you that undulating or surging feel. I had this as well when braking with only about 10k miles on new brakes and rotors. Obviously I did something wrong. It finally bugged me enough to get it done again. Likely the results of my sloppy job is a warped rotor and when that happens you either have to replace both rotors and brakes or grind your rotors and replace brakes as well. Also this time I ordered all ACDelco parts. You have to do both sides because who knows which one is the problem. So I replaced the rotors and brakes and also the minor components as well and it works perfect now. When you do this, be sure to take it all apart. Clean it all. Have a couple of brake cleaner cans ready to go. I clean all parts of the caliper with a wire brush ( where needed ) and brake cleaner. I very lightly wire brushed ( again very lightly not to cause harm to the walls with a soft brush as you spray cleaner in them) the guide pin cylinders then spray it with brake cleaner until brake cleaner comes out clean. When I did this, the guide pins moved in and out very smoothly. I think caked in anti seize lubricant was my problem in these cylinders. This could cause uneven pressure you would think. Anyways my problem is solved and it was because I was sloppy when cleaning the components and I believe mainly the guide pins and the two cylinder that they move in and out of. Sorry I don't know all the technical names. Also while you have it all open, adjust your parking brakes as well. I just tighten until the rotor will not go on, then back off a couple of ticks until it slides on easily.

 

[tdupont]

Did you replace rotors? Check runout of rotor mount hub? Clean and lube caliper slide areas? Checked park brakes for binding/dragging? ETC......

Replaced everything. Not sure what the runout of rotor mount hub means? New slides were lubed properly. I actually don't have parking brake shoes in it currently, went to replace and snapped the little screw in there, so no parking brake.

 

[tdupont]

Could you define "wobble?" Do you mean that the pedal pulses when you apply the brakes? Or???

Has a shake above 65mph (its 20 years old don't really care about that one). Pedal pulses when apply brake, as you mentioned. Usually only really pulses when slowing from 55 down to 20 or so. Little bit in the steering wheel everyone once in a while. I'm fairly sure that someone else had replaced the brake lines at one point so I don't think it would be those, I changed the rear hoses to the calipers and that did seem to work for a while when I redid the rest of the rear. 2k miles later and the pulsing pedal is back.

 

[SnowDrifter]

At risk of asking the obvious, have you rotated the tires?

Sometimes, out of balance tires can only show up under braking

 

[nonickatall]

At risk of asking the obvious, have you rotated the tires?

Sometimes, out of balance tires can only show up under braking

An play in axle components can make that. If you have as example wear out steering rods and you brake, then the ever-present slight unevenness of the front and rear brake discs quickly builds up and causes the steering wheel to wobble.

I would also definitely disassemble the brake calipers, take out one brake pad, reassemble the brake caliper and then push the brake pistons back as hard as possible.

Then an assistant brakes the brake pistons out completely and you push them back in again. This makes them easy to move again. This should be repeated about 5 to 10 times. At the same time you should grease the slide pins so that the calipers can move easily.

This means that the brake pads are not permanently in contact with the brake discs, which causes the brake discs to heat up. Brake discs are always slightly uneven or warped. They also have to be so that they can push back the brake pads accordingly, so that they do not permanently contact the brake disc while driving.

If the brake calipers or pistons are stiff, the pads remain pressed too ******* the disc. Unfortunately, they always heat up where they brake the most, which in turn leads to one-sided heat and this in turn can lead to distortion.

That's why imho you should always use carburized brake discs, which are heat treated again after processing, because this releases tension from the material.

 

[OR VietVet]

By the way, how do you know it is the rear brakes causing the pulsation?

 

[tdupont]

At risk of asking the obvious, have you rotated the tires?

Sometimes, out of balance tires can only show up under braking

I've rotated them once, they only have about 7k miles on them.

Doing an oil change and rotation once I get it back from the shop, new rockers going on this week.