Why do I keep shredding my new rear disks?

Got a new rear end with disc brakes (Eldorado type) from a board member. Went from 2.78 to 3.42. I should also mention I got my carb and dist rebuilt by John Osborne. I mention this because it was running so much better that I was driving it, well..spiritedly. But certainly not beating on it. Anyhow get back to the garage after a quick 10 minute ride and my rotors (zinc coated) are scored, pads are shredded and the caliper is leaking. Manufacturer of the kit says I beat on them to much and sends me a new (not rebuilt) caliper no charge. I cut the rotors, install new pads and caliper and take it for a nice slow ride. Drove about 20-30 minutes and all is well. Brakes feel great and no mess. So I take it out today for a spin and Hear a noise under the car. E-brake cable was hitting the exhaust so I tightened it up and made sure the car still rolls with the brake off. All is good for 15 minutes till some you know what pulls in front of me and I have to stop short. Next thing I know I smell brakes and take it back to the garage. This time the drivers side has pad/rotor debris all over the rim and the inside of the tire is streaked with brake fluid, but only 25% of the tire is streaked, like as it was spinning there was a short burst of brake fluid and it stopped. The rotor looks good but Im not sure what to do at this point. Hard to believe that one panic stop could shred the pads like that. Any suggestions? This is getting old. I want to enjoy the car before its snows.

 

sounds like you left the residual pressure valve in the master cylinder or combination valve (not sure where it is in your car). If you didn't take it out when doing your swap, then it's there....

 

Master is SSBC and is supposed to be for 4-wheel disc. I called them first and they said it would be fine. The proportioning valve is however a disc/drum (aftermarket from inline-tube). You think thats the issue?

 

???

I'll be starting my rear Disc conversion this week. Hope I dont have any problems. I've seen Bonded brake linings shear off their backing plates before. I am going to use a set of GM factory rivited pads. As for the Calipers blowing their seals I could see a defective one or {set ?} Just because one blew before the other ?? As for fluid pressure being the cause just can't see a duel system that is designed for safety and correct brake application creating a massive pressure that would blow the caliper seals ? And depending on what type of Valve you have to controll front to rear brake application. Although while studying for an ASE Brake test there is a formula chart that shows master cylinder bore size to wheel cyl / caliper bore and the force that is created. I'm curious to see what problem you have. Sent a message to George Nenadovich. He is real sharp on rear disc brake conversions and Buick Performance Founder
www.buickperformance.com

 

Some combination valves have a residual valve in them. One easy way is to jack up the rear end, and then pump up your brakes. If they are dragging, then you have a good idea that is what's happening.

 

Heat ?

So, do you think that his rear Brakes are overheating and burning the pads till they fail, Also damaging the Calipar Internal seals ?

 

I'll give that a try
Thanks

 

Did you change the rear brake hose (goes from frame x-mbr to the top of the pumpkin)?

Once you get the rear tires off the ground...have an assistant pump/work the brakes in the same manner as you drove and encountered the problem while you check for free rotation. I don't think in-line tube would have sold you the incorrect combo valve. You should have no problem with the master cylinder since it is new.

The rear hose may be the problem not letting the pressure release from the calipers.

 

George,
All new hoses came with the kit. Wwen I bought the proportioning valve it was when I had drums in the back. I see they make one for disc/disc but I thought the only difference was the amount of pressure that was distributed. I'll call them in the morning and ask about the residual pressure valve.
Thanks