Brake Troubles

[mwaldrp]

I have a 97 Jimmy SLT (4.3 L Vortec Engine) with 133,000 miles. I am having a bit of braking trouble. Whenever I brake from high speed (40 mph or greater) I feel vibration through the brake pedal. There is no loss in braking or steering performance, just the vibration. The vibration does not occur at low speed and started after I changed the following parts:

brake drums
brake shoes
return springs
hold down springs and pins
actuator lever pivots
wheel cylinders

One drum and shoe pair is a tighter fit than the other pair. In order to fit the drum over the shoes the adjusting screw must be in all the way. The other drum and shoe pair has the same fit when its adjusting screw is half way out. Could this be the cause of the vibration?

Any help is greatly appreciated.

[mwaldrp]

Any ideas?

Warped front disc rotors are an obvious place to start but the pedal pulsations didn't show up until after I replaced all the rear brake parts listed above. Is there anything besides warped rotors that could cause the vibration?

[blazes9395]

If it wasn't there before, then I would be looking at what you installed first. If everyhting looks good internally, the shoes and mounting hardware all are instlled right and move properly, take the drums and get them checked for round.

[old_master]

The adjusters is the clue, they should both be approximately the same. Check the parking brake cables, probably has one stuck, maybe more After that's fixed, adjust both sides equally until the drum very lightly drags on both sides, pump the pedal between adjustments to allow the shoes to settle in on the backing plates.

[mwaldrp]

Thank you everyone for the advice.

I seem to have two separate problems. I took the drums off, had them tested for round and found they were out (this was not a surprise). But while I was removing the drums I noticed that the new shoes on the side with tight fit are almost twice as thick as the new pads on the other side. This explains the difference in the adjusters (thanks, old master, for the tip about checking the parking brake cables but I couldn't find any fault with the cable on either side). I will remove these shoes tomorrow and get a new set along with a new set of drums then update on whether this fixed the pedal vibration.

I got both the drums and the shoes from the local parts store. They are the store brand rather than OEM or a premium brand. Is it common to have these issues with parts store brands?

[old_master]

The shoes are different, there is a primary and a secondary shoe on each side of the vehicle. Sometimes the lining is thicker on one of them. The secondary shoe has a longer lining and is installed toward the rear of the vehicle. The primary shoe has a shorter lining and is installed toward the front of the vehicle. Are you sure you installed them correctly? This is how the left rear should look, notice the different length of the lining on the shoes:

[mwaldrp]

Thanks for the info old master. I probably put both secondary shoes on one side and both primary shoes on the other. I'll correct it in the morning and update the thread with results.

Any advice on a brand of replacement drums?

[old_master]

Common mistake, even some "professionals" make it.

Drums: As long as they're round, they'll be fine. It's not necessary to get the "premium" brand. "House" brands are usually acceptable.

[mwaldrp]

Problem solved.

Thanks to all for the help.