front discs are blazing hot!! (rubbing)???

[chev-obsession]

I recently swaped front disc's on my 69 and we took the truck around the block no more than 2 1/2 miles, when we got back home we could smell something.... turns out it was the front brakes, they got so hot the the lug nuts burnt my fingers, so something is wrong and we can not seem to figure it out.

I was wondering if any of you guys ran into this problem when you swapped to front discs??? any help is greatly apperciated!!

[vasquezmrysvll]

check for restrictions in your lines and hoses, your piston may also be partially stuck causing it to not retract into the bore after brake appliction.

[cdowns]

did you swap the master cyl and propertiong valve too?

[jim zag]

Drum brake master cylinders have residual valves in them to keep wheel cylinder rubber cups from leaking. They will keep your caliper pistons from returning. If you have a disc brake master check to see if your brake rod adjustment is too long and not allowing the piston to return all the way back.

[lolife99]

I agree with jim zag.
What parts did you change when you did your disc brake swap?

[ERASER5]

What parts are new and what parts are used?

Like jim zag said, you must use a disc/drum master cylinder. A drum/drum MC will not work. (disc/disc MC are another story, so if you have one, say so)

Calipers - old calipers can stick. Especially if they have been sitting.

Rubber brake lines-- old one can collapse inside causing the brakes to bind.

Did you add power brakes (vacuum booster setup)? If you added the power setup, is it the type for our trucks with relay bars or a later model with a straight rod to booster setup?

The setup for the pedal/booster/MC can be tricky. You need just a wee bit of booster movement before the pin hits the MC piston. The vacuum booster should be all the way released when the brake pedal is released.

The more info you give us, the better we can respond.

[my67chevytruck]

all good advice. you didnt overtighten the castle nut when you installed the rotor did you.. IIRC you torque to 17 lbs to seat the bearing then back off 1/2 turn then torque to 12 lbs.... someone will correct me....

[beautimus]

something else comes to mind to add to the other suggestions mentioned above. the caliper could be sticking. not the piston, but on the mounts.
to explain, when you apply the brakes the piston forces the brake pad against the rotor, then as you continue to apply the brakes the caliper is forced over on the mounts so that the opposite pad comes into contact with the rotor. its easy to check, just disasemble enough to compress the piston.
then reassemble everything. grab the caliper and see if it is free to move in and out. if its binding , theres your problem. to fix it just clean and lightly lube up the 2 caliper bolts. and work the caliper in and out on the mounting bolts untill it feels free. there should be a little drag but no binding. this is what makes the brakes release, and wear evenly. after the truck is driven you should get a little heat, but not a lot.

[chev-obsession]

ok thanks for all of the input!!!

when i converted all of the parts i swaped the old master cylinder and proportioning valve (disc brake proporting valve and mc) i got new brake lines it is a power booster . i got new calipers so i dont think that is the fact they are old and stick...
i will check the castle nut when i get home tonight, i didnt torque them down we just kind of got them tight to where we thought that they were good enough. the drivers side is the one that was doing it the worse. the passenger side was way way cooler.

i think it might be the pedal rod... it looked like it was touching the firewall.

move advice is greatly apperciated!!!

[72truckster]

I had the problem of the brakes gradually applying as the truck heated up. Within about 5 min. to the point where they became smoking hot almost locking up. Yet when cool no problems. So I re-blead them and that fixed the problem. I guess as the air in the lines heated up, it must have displaced some of the fluid increasing the pressure.
Good luck and just a suggestion.

[chev-obsession]

ok i thought i might try that

[beautimus]

just another thought, i think i remember a post a month or so back when someone was asking what lenght the rod was supposed to be, between the pedal and the booster. i wonder if the drum brake pushrod is longer and may be keeping the brakes slightly engaged. If nothing else works out, it might be worth investigating.

[ERASER5]

If he went from manual brakes to power brakes, it is not even the same rod regardless of length. The ends are different.

[chev-obsession]

we worked on it tonight...
we re-bled the brakes, checked the spindle nut, and they didnt seem to help any.

Any ways we narrowed it down to the rod between the pedal and the booster. its so clsoe to the right length but it hits the fire wall!!!

if i adjust it out (towards the grille) then it would engage the brakes even more, but i cant go in (towards the seat) because it will hang up on the firewall.... (well i could adjust it in but it's still going to hang up??) am i right? or is it different?

I really dont want to cut the fire wall since it didnt come that way and thats simply not the right way to do it. but thats what it seems like what you would have to do. ugh!!! one thing after another!!! i really apperciate the help guys!

[chev-obsession]

Originally Posted by beautimus

just another thought, i think i remember a post a month or so back when someone was asking what lenght the rod was supposed to be, between the pedal and the booster. i wonder if the drum brake pushrod is longer and may be keeping the brakes slightly engaged. If nothing else works out, it might be worth investigating.

dude, you read my mind

[lolife99]

Do you have any pics you can post?

[chev-obsession]

yeah but not until around 6 pacific time..

[chev-obsession]

this afternoon my dads mechanic buddy came over and we look through it and we found out that the lower caliper bolt was somehow touching the right side of the rotor. also he said that i shouldnt of painted the calipers.... that it could be holding it back too.

well i took some pics to see what you guys thought. the pics are not that great, sorry!

[chev-obsession]

oh btw, he also said that my pedal rod was ok.