Right rear brake locking up early

[jfw432]

I've got a 79 C-10 longbed. I've replaced the brake booster and master cylinder as well as both rear wheel cylinders and the front left caliper.

Went to drive it the other day and everything felt fine. No pulling under brakes or anything. However, when I push on the brakes any harder than casual stopping, the right rear tire locks up.

My first thought was air was in the left rear but then I thought that the rear brakes come from a single line so if air was in the system, it would affect both brakes right? Any ideas?

[D13]

Pull off the drum and see if you've lost the axle seal or the wheel cylinder seal is leaking. Leaking axle seal caused my right rear to lock up way before the rest. Got progressively worse until it started locking up at low speed. Particularly suspect if, like me, you had to beat the drums off.

[homemade87]

I had the same thing. Most likely the drums are out of round. When it rolls around it will catch the high spot. You will most likely see it happen at slower speeds.

As D13 said, If there is any fluid present it will do the same thing. If not I would turn the drums or get new ones. Last ones I got were not that expensive for new.

(note) If you ever apply the park brake when the drums are hot it will warp them .


This is correct .
My first thought was air was in the left rear but then I thought that the rear brakes come from a single line so if air was in the system, it would affect both brakes right? Any ideas?
jfw432 is offline Report Post Reply With Quote

[jfw432]

Interesting idea on the warped drums. There is no fluid leaking down on the tires. There was before I replaced the wheel cylinders but I sprayed everything down pretty well with brake cleaner.

I'll try to pull the drum tonight and look closer. I'll swap the drums and see if the problem switches sides as well.

[Adams74Chevy]

Originally Posted by jfw432

Interesting idea on the warped drums. There is no fluid leaking down on the tires. There was before I replaced the wheel cylinders but I sprayed everything down pretty well with brake cleaner.

I'll try to pull the drum tonight and look closer. I'll swap the drums and see if the problem switches sides as well.

So the wheel cylinder was leaking and you replaced it and sprayed down the shoes with brake cleaner or did you replace the brake shoes? I would put new shoes on it if you only hosed them down with brake cleaner.

[jfw432]

Yeah I just hosed down the shoes and did not replace them. Only replaced the wheel cylinders as the shoes has substantial material left. Never really had a problem just hosing down the shoes before but in fairness all other vehicles have been shorter wheelbase cars or SUV's so there is a little more weight on those tires so any problems may not have been noticeable as easily as a long bed pickup.

[franken]

If one side was leaking, I'd guess there's less friction on that side, so the other locks up.
Check the self adjusters are there, free and the star wheels can turn and adjust. Then go to a big parking lot and back up and stop. Repeat several times to let the brakes self-adjust.
Retest.
You could still have air is the side that doesn't lock up as well.
Start w/ the inexpensive tests/fixes.

[jfw432]

Both sides were leaking really bad when I bought it. This isn't my daily driver and I felt lazy today but I'll try to rebleed the lines, swap drums, check the adjusters, and spray everything down again.

[D13]

I have never been succesful reusing shoes or pads after fluid contamination. Drums, yes. Not the shoes. They seem to be porous enough that the fluid seeps into them and then bleeds back over time. I have seem people heat them up with a torch but there's a fine line between boilng out the contaminates and cooking the lining. Personally the $40 is good peace of mind.

[jfw432]

Well the right brake shoes and drum were a little gooey so I cleaned it back up (Really really hate replacing anything on drum brakes). Anyway, that was semi-successful. Now both rear tires lock up under slightly harder braking...lol

Guess I need to double check the front calipers and make sure they are bled properly. If that doesn't do anything, I'll chalk it up to being a big heavy truck with no weight on the rear tires.

[motornut]

so brake fluid got on the shoes or grease?
either one I'd replace the shoes with new ones.
they could be swollen and appear to have lots of material left,rip right off when needed
locking up the rear will make the truck slide,worse if the pavement gets wet.

[homemade87]

I agree , If they got soaked they will never work right. Replace, They are not that expensive.

[86c20]

now i dont know why poeple like to fight this one. shoes will hold brake fluid. so sprying them down dont really work.....ish. have i done it? yes but was vary light cought the leak fast. in a pinc i have soaked the shoes in gas or degreaser as parts here are slow and need the truck. but they where replace the following week.

most of the time if one locks over the other its out of adjustment. and one turn will make a lot of diff in the power of the brakes.

[chengny]

Are your leading and lagging/trailing shoes installed in the correct positions?



Incorrect positioning of the lead/trail shoes was identified - in a GM memo to their dealer service techs - as the number one cause of a rear (drum) brake grabbing condition.

Since the steel shoes are identical (only the length of the lining material differs) a full axle set - consisting of 2 leading shoes & 2 trailing shoes - can be wrongly installed in three different ways:

1. Lead and lag reversed on one wheel - but correctly installed on the other wheel.

2. Lead and lag reversed on both wheels.

3. Both leads installed on one wheel and both lags on the other.

Only in the first combination will the issue manifest itself in just one brake set. In either of the other two scenarios, both brake sets will be prone to grabbing.

The relevant parts of the GM service bulletin:

Shoes/Linings incorrectly installed.

Each side should have a leading and trailing shoe. The lining surface on the trailing shoe will be slightly larger than the lining surface on the leading shoe. The trailing shoes should be installed in the rear position on each side, while the leading shoes are installed in the front position on each side. If the shoe positions are reversed, the braking performance will be very grabby and prone to wheel lockup.

The rest of the causes in order by percentage of total:

Brake linings contaminated with brake fluid or gear oil.
Incorrect shoe size or type.
Loose or broken brake lining.
Brake shoe adjustment too tight or too loose.
Weak or broken return springs.


What to Check For


Look for the following common mistakes:

Leading and trailing shoes are reversed.
Both leading shoes are installed on one side while both trailing shoes are installed on the other side.
Inspect the wheel cylinders for signs of leakage or sticking, replace or rebuild as necessary.
Inspect the axle seals for signs of leakage. Gear oil leaking from the axle seal will usually be indicated by a spray pattern starting at the center of the drum and spreading outwards. If any signs of gear oil leakage are found, the shoes and seal should be replaced.
NOTE: Leakage at the axle seals is often caused by worn wheel bearings. If the vehicle has high mileage, it is recommended to replace the wheel bearing along with the axle seal.

Inspect all brake springs and replace if any appear worn or distorted.
Inspect shoes for correct fit with drum and backing-plate.
Inspect brake lining for cracks, missing pieces or poor bonding to shoes.
Check for proper adjustment, readjust as necessary.



Note:

The image above has a couple of flaws:

1. It shows a greatly exaggerated difference in set back at the top of the linings

2. It also shows the same big difference at the bottom - in reality there is no difference in set-back at the bottom. Lead and trail look the same at the bottoms of the shoes.

Below are some images of an NOS brake assembly that show the actual configurations.

Top:



Bottom:




I apologize if you were already aware of the lead/trail difference and have already checked and eliminated that as a possible cause. This info may be helpful to someone else in the future.