'68 Z28 - rear pass side drum brakes are sticking...don't know why

[barsteel]

Hello!

I recently went through my '68 Z28 to get it ready for driving.  The rear brakes were shot, so I installed new shoes and wheel cylinders (old ones were leaking), and had the drums turned. I took the car for a short ride, and after about 10 minutes, the car started shuddering badly. I drove it slowly back to my shop, got out of the car, and saw smoke pouring out of the pass side rear wheel. I put the car on a lift, pulled the drum, and it appeared as I may have installed the parking brake hardware incorrectly. I straightened everything out, and took it for a ride. Same deal after 5 mins. Shuddering car, smoking pass side rear brake. Pulled the drum, and all appeared well except for the spring on the bottom of the shoes, the one over the adjuster. It appeared slightly bent. So I ordered a brake hardware kit from Napa, installed it, took it for a ride, and have the SAME DAMN PROBLEM, shuddering and a smoking pass side rear brake.

At this point I'm at somewhat of a loss. I've done more than a few GM drum brake jobs, and have never had a problem.

The shoes are installed correctly.  Short shoe facing the front of the car, long shoe facing the rear.

I'm thinking that it might be the MC.  I had a '57 Chevy 1/2 ton truck a few years ago that had sticking front brakes with a disc brake/under floor dual well MC conversion. Turns out that the truck had been sitting and rust had built up in the return port in the MC, so the fluid couldn't return.

I do know that this car was not driven a lot in the past few years, so the same thing might have happened.

What stumps me is why only 1 wheel is sticking.

The parking brake works corrects, and the car seems to roll freely with the brake off.

Anyone have any idea what could cause a drum brake to continue to stick?

Thanks...

Chris
Monroe, CT

[BULLITT65]

I had a similar problem. I will tell you what it was, but I have to think this as a slim chance of what it could be:

So took my 66 impala out for a ride got a few miles down the road, and not so much of a shudder, as it seemed like a rear brake locked up.

Got it back to the hanger and one of the rear drums was smoking. After it cooled off took it all apart, and put back together with a new brake cylinder just for good measure, on both sides. At this point I knew wasn't anything to do with the brakes, everything looked fine. From experience, I figured if it was a front wheel locking up, I would have suspected the rubber brake line collapsing , so I thought how about the rubber line that sits above the rear end. I took that rubber brake hose off, and after close inspection realized the metal on one end had corroded so much that it pinched the rubber closed, and when I hit the brakes all the fluid got trapped in the rear brakes, and locked up the one. I replaced the rubber line= problem solved.

Probably not your issue, but something to look at.
 

[BULLITT65]

One other thing you can check is to make sure your adjusters move freely. With the wheel on you can hand adjust them, or just back up in reverse a few times and hit the brakes and they should self adjust. I am sure you are aware this but thought I would try to cover all the bases.

[barsteel]

Bullitt -

When I redid the rears, I thoroughly cleaned and greased the adjusting wheel, so I sincerely doubt that that's it, but I appreciate the input.

It looks like the rubber hose is original, or at least very old, so that may be the next thing I look at...it's cheaper than a MC.

Keep it coming...

Thanks...

Chris

[BillOhio]

I had a front do that and the line was collapsed. Hated to take the original off but wasnt safe. Luckliy I caught it acting up in the driveway.

[L78 steve]

Its easy to install the lower spring back to front thus interfering with adjuster operation. Drum set-ups are tricky and always use new hardware when relining.

[Kelley W King]

You might check your metal line to that wheel. if it has rust or trash in it that could be it. When you apply the brakes high pressure from the MC could get by but when you let off only the spring pressure pushes the fluid back.

[sdkar]

Maybe this is redundant, but check to make sure all the springs are functioning properly, installed correctly, and there is free movement.  Also, make sure you do NOT have the shoes adjusted too far out to begin with.  I like about 1/8 to 1/4 inch of side to side play when installing the drums over the shoes.  there are small flat surfaces on the backing plate (six maybe) where the sides of the shoes ride on the plate.  Clean and lightly grease these areas.  Finally, replace the rubber line at the junction. 

I had an instance of brakes sticking horribly, and found that the rubber hoses were the issue.  It had collapsed inside the hose, and when you push the pedal, the fluid would force its way toward the brake, but when letting off the brake pedal, the fluid was unable to drain back, thus sticking brakes.  I replaced these, and brakes were perfect again. 


 

[barsteel]

Update:

I checked the shoes and hardware, and everything was installed correctly.

I installed a new rear rubber line.  The old one appeared to be original;  If not original, then OLD.  After I got the new one installed, I tried to blow air through the old rubber line.  I blew till I was purple in the face and I barely got a hiss out of the other side, so it appears as if the hose was mostly plugged or collapsed.  I gravity bled the brakes and got a nice firm pedal.  I pumped the brake several times and checked the wheel movement, and it was fine.  No sign of a brake starting to hang.

All should have been well.

So I button everything up, hop in, and blast down the street.   After about a mile, I get that SAME telltale shimmy/shudder starting.  It's like one of the tires is badly out of round.  I start smelling the same burning smell as before.  I stop the car, and the pass side rear drum is starting to smoke.  The driver's side was getting hot, too.

One thing to note - although the pass side brake was getting hot, it did not appear to be as hot as it was previously.

So...I still have a brake problem.

My next thought is to replace the Master Cylinder.  As I'd mentioned before, I'd had the same brake problem with a hotrod '57 Chevy truck I had a few years ago.

Could the proportioning valve be bad?

Any additional thoughts?  I hate just throwing parts at a problem.

Thanks...

Chris

[68camaroz28]

Chris, just posted a picture for you showing our brackets for the brakes you requested. Since the master cylinder is wrong and you have other work to do to complete along with the rear brake issue it might be a good idea to just pull things off and have stuff re-built, checked, etc. Other words, correct and go over the entire system. 

[Z10Mike]

Any chance that the pass rear wheel cylinder has debris in it from the deteriorated flex line at the axle?  And that prevents the pressure from bleeding off back through the brake lines to the master?

[X33RS]

Probably not what you want to here, and I know you guys like to save this or save that because it's original, but when it comes to mechanicals and dependability, and you want to enjoy the car,  it's just not worth it in my opinion.

If that car has been sitting and parts are that old, I'd be revamping that entire brake system if it were mine.  Hoses are a must as you've found out, they collapse over time and is the most common brake sticking issue.  I'd replace all 3 and be done with that.
   I'd also pull all the steel lines and blow/clean them out thoroughly, if corrosion exists I'd replace.  Then replace all the disposable parts...ie: master cyl, wheel cyl, calipers, hoses, or at the very least rebuild your originals.   Brakes aren't anything to be cutting corners on. 

   I have a few cars here been sitting 30+ years and recently started reviving them all.  Went through everything thoroughly as explained above on all but one.  I only replaced what was needed to make brakes work.  Sure enough, 2 weeks in and lost a wheel cylinder.  Month later the PB booster bites the dust, likely from the master leaking fluid which I had replaced in the beginning.  I should have replaced it all front to back and been done with it.  Of course I was trying to save OEM 46 year old parts on that particular car.  Bit me in the butt.  Luckily I wasn't 100 miles from home, and even more lucky I didn't wreck it.

Anyway, hope you get it figured out.

[janobyte]

Chris, just posted a picture for you showing our brackets for the brakes you requested. Since the master cylinder is wrong and you have other work to do to complete along with the rear brake issue it might be a good idea to just pull things off and have stuff re-built, checked, etc. Other words, correct and go over the entire system. 

Ditto.   I've mentioned a few times before to those who just might of purchased, go through the car, just like any other used car. Case in point: my son's 02 Silverado I picked up for him last year. Shy of the master cylinder and ABS module, everything's replaced in the brake system. This week its up on the lift and we're replacing all the lines with a stainless/braided kit from Custom Tube.

[barsteel]

X33, and everyone else -

Thanks for the additional input.  I've come to the same conclusion and done just as you've suggested.  I have an original, correct, dated coded booster, a correct MC, and all new hard and soft lines on order.

The calipers had been replaced a few years before I got the car, and they work perfectly, so I'm not that worried about them.  I've already replaced the rear wheel cylinders, shoes, and hardware, so I'm good on that front.

I just want to get the damn brakes working so I can enjoy the car for the fall.

Chris