Passenger rear drum locking

[Frankenchevy]

A weird problem started with my Suburban. The last couple times I’ve driven it. It will lock the passenger rear tire a couple times in the driveway on gravel, but then won’t do it for the rest of the trip. There’s no pulling or otherwise while driving on pavement and when I return home, it does not lock in the gravel—only the first few depressions of the brake pedal when I initially set off on a drive.

I pulled the drums to check the adjustment and found that my driver side parking brake cable was sticking, which I thought may have affected my initial drag adjustment. I disconnected the parking brake cable at the equalizer, made sure there was a gap between the front shoe and the parking brake lever, then I readjusted the drag. It still did the same thing when I left for my drive yesterday.

All of the springs and other hardware inside the drums do not appear to be worn. The shoes are still the old style with the riveted friction material, but otherwise appear to be in good shape, and neither they nor the drums appear to be contaminated. The thickness from side to side looks consistent, and the shoes are installed in the correct positions(shorter material in the forward position).

My thought is to replace the parking brake cables(due to sticking), springs, hardware and put a new adjuster in. I have new AC Delco wheel cylinders, but I am apprehensive to replace them as the current ones are not leaking.

If this doesn’t work, I may see if the drivers side brake line needs to be blown out. At that point, I’ll likely throw the new wheel cylinders on. If the line is the culprit, I’ll be perplexed as to the reason why this problem only occurs for the first few brake applications…

Separate question: what is the preferred methodology for setting drag on the drums? I have been doing this by having one tire on the ground to eliminate feedback from that side changing the way the drag test feels on the side that I am currently adjusting. On the first adjustment I went by feel. I think the issue with this is that rotation of the differential and driveline makes it a little bit more difficult for me to ascertain how much drag is attributable to the brake adjustment versus the drivetrain rotation. On the second adjustment, I kept rotating the tire and going one click at a time on the adjuster until I heard the brake shoes dragging on the drum. This resulted in very little extra drag above and beyond what the drive line was already imposing, but wasn’t so loose that it affected pedal feel. Does this sound like a bad approach?

 

[Ricko1966]

I adjust them too tight to move,to center the shoes on the drum,the I back them off until I can just hear them scraping.

 

[Frankenchevy]

I adjust them too tight to move,to center the shoes on the drum,the I back them off until I can just hear them scraping.

To back them off, do you press the “ratchet lever” out of the way so the adjuster will spin decently well in the other direction? It’s a pain in the rear to get it to spin backwards otherwise…

 

[Grit dog]

The fact of the matter is if they’re operating properly they will self adjust quickly so unless you’re trying to stop a trailer going downhill 1 mile after installing them it doesn’t matter.
I get them close. If there’s a lip on the drum adjust so the drum barely fits over and then adjust up with the start wheel until hear a bit of scraping.
Regarding your one wheel locking up, it sounds very very minor and you have old brake pads.
Have you really driven and worked the brakes? I’d take er for a spin on a back road and do a little impromptu brake bedding, and see if it helps. Or swap drums side to side and see if it follows the pads or drum or goes away completely.

 

[Finkaire]

Check the hoses

 

[Frankenchevy]

Check the hoses

I suggested I’d try this above, but the fact that it will happen twice at first, or not at all, then never happen for the rest of the day is confusing if it turns out to be the hose…

 

[Grit dog]

I don’t think hoses, just old brake pads and a little sticky.
I’d also consider doing a redneck rehab. Scuff up the shoes a bit and scuff the drums up real well.
But first swap drums assume it’s a sf rear so that’s easy.

 

[JBswth]

A weird problem started with my Suburban. The last couple times I’ve driven it. It will lock the passenger rear tire a couple times in the driveway on gravel, but then won’t do it for the rest of the trip. There’s no pulling or otherwise while driving on pavement and when I return home, it does not lock in the gravel—only the first few depressions of the brake pedal when I initially set off on a drive.

I pulled the drums to check the adjustment and found that my driver side parking brake cable was sticking, which I thought may have affected my initial drag adjustment. I disconnected the parking brake cable at the equalizer, made sure there was a gap between the front shoe and the parking brake lever, then I readjusted the drag. It still did the same thing when I left for my drive yesterday.

All of the springs and other hardware inside the drums do not appear to be worn. The shoes are still the old style with the riveted friction material, but otherwise appear to be in good shape, and neither they nor the drums appear to be contaminated. The thickness from side to side looks consistent, and the shoes are installed in the correct positions(shorter material in the forward position).

My thought is to replace the parking brake cables(due to sticking), springs, hardware and put a new adjuster in. I have new AC Delco wheel cylinders, but I am apprehensive to replace them as the current ones are not leaking.

If this doesn’t work, I may see if the drivers side brake line needs to be blown out. At that point, I’ll likely throw the new wheel cylinders on. If the line is the culprit, I’ll be perplexed as to the reason why this problem only occurs for the first few brake applications…

Separate question: what is the preferred methodology for setting drag on the drums? I have been doing this by having one tire on the ground to eliminate feedback from that side changing the way the drag test feels on the side that I am currently adjusting. On the first adjustment I went by feel. I think the issue with this is that rotation of the differential and driveline makes it a little bit more difficult for me to ascertain how much drag is attributable to the brake adjustment versus the drivetrain rotation. On the second adjustment, I kept rotating the tire and going one click at a time on the adjuster until I heard the brake shoes dragging on the drum. This resulted in very little extra drag above and beyond what the drive line was already imposing, but wasn’t so loose that it affected pedal feel. Does this sound like a bad approach?

This sounds like you have a lightly leaking wheel cylinder. Chemicals on the linings will cause them to lock like that. Check by pulling the rubber boots back. If any brake fluid drips out, you have found the problem. If that is not the problem, it could be a leaking rear wheel oil seal - gear oil on the linings will do the same thing - make them grab and lock.

J. B.

 

[Frankenchevy]

This sounds like you have a lightly leaking wheel cylinder. Chemicals on the linings will cause them to lock like that. Check by pulling the rubber boots back. If any brake fluid drips out, you have found the problem. If that is not the problem, it could be a leaking rear wheel oil seal - gear oil on the linings will do the same thing - make them grab and lock.

J. B.

Good point, and I’d thought about this, but didn’t pull the boots back on the wheel cylinders; I only inspected externally. I’ll check again.

 

[elbpony]

I'd still not forget the hoses. I had a similar though more severe lock at my front discs but, after all was checked and replaced but the hose, it was it - the hose. At first the rubber was selective on when to block the cylinder or not. It got worse until to a final full stop. We even switched hoses left to right and they worked fine then on both sides, so I ruled that out. In the end though, it was the rubber hose. Miraculous thing