Rear brake fade

[booalou]

I’m having a hard time resolving the high temp at my rear brakes on my 62 tbird. After replacing the rear brake shoes, springs and wheel cylinders my rear brakes are heating up to over 200 degrees. I have the adjusters backed up all the way. There’s no tension on the emergency brake and all my brake lines appear to be metal so no hose collapse. Any thoughts on what I’m missing

just a note that have disc on the front

[yurky58]

Are the front brakes functioning correctly? Maybe proportioning valve is bad. This can cause rear brakes to over work. There could be air in the front brakes. Try bleeding brakes and maybe fluid flush. Good luck.

[frank58]

did this begin after the rear brake service or after the front disc brake conversion?

[booalou]

I’m in my sixties now so my memory is not as good as it used to be but I’m pretty confident it started after the new shoes were installed.

[frank58]

it can only be a few things, a little more info on your setup would help. do you have a dual master cylinder, is there a proportioning valve,do your rear wheels turn freely when jacked up,
there are people here that are real experts on these things and the more info you can supply the easier it will be to offer suggestions.
I know about the memory thing.. ha ha, I'm at the point where I've forgotten more than I know

[jopizz]

It sounds like your rear brake shoes may not be releasing fast enough. You may need to adjust the push rod on your master cylinder. That's assuming that everything was plumbed correctly on your master cylinder and proportioning valve and you don't have it backwards. I would double check to make sure you have the front and rear brake lines going to the correct ports. It's also possible that your brake drums are out of round. Have you had them checked. Also you have a rubber brake hose that goes over the differential. If that is partially blocked it may not be releasing fluid fast enough.

John

[booalou]

For the first reply I do have a dual master cylinder with a proportioning valve. Both rear wheels turn pretty freely.

as for the rubber brake line going over the rear when I check all I saw was metal lines but I’ll look again to make sure I didn’t miss anything. The proportioning valve is set up correctly front ports for the disc brakes has a separate connection while the rear only have one

[jopizz]

Here's a diagram of the distribution block that's on the rear axle. There are the two metal lines that go to the wheels and the rubber line that connects to the metal line that runs to the front of the car. Because it's on the axle the hose has to be rubber as the axle moves up and down. If it hasn't been replaced recently I would change it. Also make sure it's not right up against the exhaust pipe.

John

62 rear brake.jpg

[booalou]

Thanks I’ll take another look

[simplyconnected]

Right from the git, I assume your backplates do not have deep grooves worn into the pads from the shoes. This can cause the shoes to hang up and not retract. Deep grooves can easily be restored by welding and grinding the pads flat.

I think John is on to something here. In my estimation sitting in this chair in Royal Oak, Michigan and without the benefit of pictures, HEAT is causing brake fluid to expand which further applies more brake pressure. Why? There is an adjustment between your master cylinder and your booster. If the adjustment is too tight, your master cylinder piston cannot return all the way, regardless of your pedal rod adjustment.

This is covered in the shop manual. Long story short, when the M/C is at rest (retracted), both brake lines should be hydraulically open to their reservoir. You should be able to see this happen if you look down the M/C's reservoir at the tiny little hole at the bottom. There is one on each reservoir. So, when shoe springs retract the shoes, brake fluid needs to go back into the reservoir, where it came from.

I have two important questions: Are you using a residual valve? Are you using self-adjusters?

I like self adjusters. Residual valves give a 'false sense' that the shoes are adjusted properly when in reality, the wheel cylinders keep advancing more and more until one of the pistons extends past the end causing brake fluid to spew out. Self adjusters actually move the star wheel. - Dave

[booalou]

I’m using self adjusters that were stick with the car. When we did the disc conversion for the front of the car we installed at dual MC and used a specially design tool to adjust the nut on the pin that goes inside of the MC. Could it be off a little bit causing the MC to stay loaded well it’s possible but not sure it’s the case.

Based on an earlier response I’m going to first replace the rubber brake hose that attaches the metal port at the rear end. After I bleed the brakes I’ll drive it for twenty mile or so and come back and take Infared reading on the rear hubs. Hopefully they ll be cooler then 200 degrees

Thanks ,

bob

[booalou]

Ok I replaced the rear rubber brake house and all the metal line from the passenger door back. Bread the brakes and took it for a ride for about 6-8 miles and when I returned home the rear drums were even hotter then before at close to 400 degrees with an Infared thermometer.

So now I can only think there’s something going on at the MC and/or proportional valve.

[booalou]

I will remove the MC and recheck the rod adjustment at the power booster to make sure it’s not preloading the MC.

[simplyconnected]

This is a mechanical problem that can easily be found. Instead of speculating, I would put my hands on the problem. Jack the wheel off the ground and physically turn the tire. If you can't, crack the bleeder screw. If you still can't turn the wheel, back off the self adjuster. If that doesn't help, something inside is preventing the shoes from returning. Check the backplate for grooves where the shoes ride on the pads.

It is rare that both rear shoes are dragging unless hydraulic pressure is the cause. You were wise to change the brake hose, just in case it delaminated inside. Even so, relieving fluid pressure at either rear bleeder valve will tell you volumes. Your brake system was ok with the old master cylinder. Now, it is not with the new. BTW, you don't need special tools to set the booster output rod. - Dave

[simplyconnected]

I've been thinking more about your problem and I have further questions:
Are your primary and secondary shoes installed correctly?
The only way to produce high heat is by friction. You said the wheels turn freely but that is impossible unless both axle bearings are shot. That is highly unlikely too. With the rear wheel off the ground and the drum off, check for slop.
With the drum off, take at least five good pictures at different angles. If you cannot post them, send them to me and I will for you. (simplyconnected@aol.com)

Brakes are the LEAST technical system in a car. They have few parts and brake problems are easy to troubleshoot. Use all your senses and follow generally accepted troubleshooting techniques. I am anxious to hear your response. - Dave