Rear brakes sticking sometimes??

[turtle5353]

Hey guys, I had a quick question concerning my rear brakes. What in the brake system would cause my rear brakes to hang up sometimes?? Is there a check valve in the distribution block that could stick? Or would it be in the master cylinder itself?  My car was originally equipped with non-power drum brakes. I have since converted to 4 wheels disc brakes, but retain the stock non power master cylinder and distribution block.  I did this 8-10 years ago with no issues so far till now. When driving normally everything works as it should. But if I have to stop the car faster than normal or harder than normal the rear brakes will drag for a time then slowly release. On the way home the other day my one rear rotor was almost glowing red by the time I got her pulled over. Let it set for a minute and it released and was good to go again. I was driving the other day and felt it start to drag then felt it release and roll as normal. Any thoughts?? Other than distribution block is there anything else in the brake system??  If I need to replace that, I am thinking of just swapping everything out and putting the power brake setup I have out of the old 72 vert that I have been stashing for years. I have the brake booster, master cylinder, and underdash bracket for power brakes. Then pull the distribution block and swap for adjustable valve. whats your thoughts ???

 

[Bru]

My first thought is you have a sticking brake caliper.

Why not just jack it up and do a rebuild on both rears? The rebuild kits are farley inexpensive .

 

[c9zx]

Kevin,

   Did you remove the residual check valve from the master cylinder? Chuck

 

[turtle5353]

Bru, I don't believe that its the calipers. Both sides are doing it and I have never seen 2 calipers fail at the same time. But I may be mistaken. I think something is keeping the pressure to the calipers and not letting fluid return to the master.

Chuck, I have not touched the master cylinder. The master was new about 10 years ago and I installed it the way it came from the box. It is a non-power drum brake master. Where is the residual check valve?? inside? on the side where the lines go in?

 

[c9zx]

The valve is a very small, spring loaded device. It is located behind the brass seat in the outlet port for the rear brakes. The seat usually can be removed with a sheet metal screw and a pair of pliers. Remove the valve and reinstall the brass seat. This may or may not be the cause of the problem but, the residual valve should not be used with a high mount MC and disc brakes. I hope you get it sorted out. Chuck

 

[TheRktmn]

Just tossing it out there, but what about the rubber line between the rear brake line from MC and the rearend?

These tend to swell internally over time and some of the new brake fluids can accelerate this. Normally the first sign of this is not being able to bleed the rear brakes, but could it be that the hose has swelled to the point where pressure can go to the calipers, but not release as quickly?

 

[turtle5353]

The valve is a very small, spring loaded device. It is located behind the brass seat in the outlet port for the rear brakes. The seat usually can be removed with a sheet metal screw and a pair of pliers. Remove the valve and reinstall the brass seat. This may or may not be the cause of the problem but, the residual valve should not be used with a high mount MC and disc brakes. I hope you get it sorted out. Chuck

Chuck were these installed in all master cylinders? What is high mount mc? Is that the non power mc? 

If I swap to the factory power brake set up will I need to remove that valve from the new mc?

 

[turtle5353]

Just tossing it out there, but what about the rubber line between the rear brake line from MC and the rearend?

These tend to swell internally over time and some of the new brake fluids can accelerate this. Normally the first sign of this is not being able to bleed the rear brakes, but could it be that the hose has swelled to the point where pressure can go to the calipers, but not release as quickly?

Bob, I will check that hose too! It’s old as hell!

 

[c9zx]

It was installed in all MCs on the drum brake side. High mount means above the wheel cylinder/caliper as opposed to low mount on a frame rail like a drag car or street rod. Chuck

 

[72HCODE]

based on the information the first thing i would do is replace the soft rubber line, flush the system and rebleed with new fluid. then go test.

if the front lines are just as old as the rear i would replace them as well.

 

[turtle5353]

Thanks guys! Lines in front and back were replaced about 8-10 years ago. But the one on the axle to frame is probably older.

 

[Don C]

+1 on Chuck's recommendation.

This might help

https://www.freeasestudyguides.com/residual-check-valve.html

 

[turtle5353]

+1 on Chuck's recommendation.

This might help

https://www.freeasestudyguides.com/residual-check-valve.html

Nice! Thanks don. I never knew that! Its just weird that it has worked for years and now just started acting up. I am leaning toward tearing everything apart and finally upgrading to the power brake system. Since I have the parts laying in the garage.