Rear Disk Brake Question

[pontiacgp]

I am planning to finally put the rear disk brakes on my GP. I did the mock set up a few years ago so this winter it'll be one of my projects. In my research I have read that the end play on the axles can cause some problems with the axle forcing the pads to back off which causes a low pedal. I have also read that the axle movement can cause a pulsating pedal. Apparently GM used different C clips in the F bodies when they went to rear disk to control the side play.

I know a few of you have converted the rear brakes so have any of you experienced the problems I have read about?....Thanks for reading

 

[455'ed80Regal]

I put LS1 brakes on mine this past spring with new rotors and have not experienced anything like what you are describing. Don't have a lot of miles on it since, so only time will tell if I experience anything like this.

When I pulled the brakes off the car at the salvage yard, the C clips looked like regular ones to me. Regardless of what C clips you use, one should aim for .005 min clearance. I have about .007 clearance between the axle and retaining pin so not very much movement in mine.

Don't have what I think is a low pedal using a stock disk/drum master. Took forever to get the air out of the lines, but once I did the pedal is great.

Just my experience. Everyone's car is different and will vary from others though.

 

[ssn696]

I had to shim the backing plates to center the calipers on the rotors. I hope that helps with the issue you describe. Have not driven on them, yet.

 

[pontiacgp]

I had to shim the backing plates to center the calipers on the rotors. I hope that helps with the issue you describe. Have not driven on them, yet.

I shimmed mine as well when I did the mock up, I moved the caliper bracket 1/8" to center it. It the movement of the axle that I read about being a problem. I came across a couple of forums where the guys were talking about it but I have never heard of the problem discussed before. I know there is a number of members here who have done the conversion and I have not read any complaints so I'm just checking with the guys in here to make sure.

 

[axisg]

Its got to be 4 or 5 years now since the swap for me ( got to be at least 10000 kms maybe closer to 20000 ). I have not experienced anything like mentioned. The 7.5 with c-clips is a pretty sloppy setup so I do expect some "tolerance" to the noises it makes. When mocking up my car we bolted the brakes on the car with the pads / rotor / caliper intact. I recall there was still some back and forth of the axle within the tube but it was nothing more than the caliper pin sliders can take up. I cannot see how the piston could be pushed back into the bore ( causing low brake pedal ) before the caliper pins would centre the caliper on the rotor. I am still running the drum disk proportioning valve as well ( as the internet says that matters ). I was always taught not to do any hard braking whilst cornering, if it were a track / rally car I could see where there is a possibility that it may come into play but in my driving experience its been nothing but an excellent upgrade.

 

[LedSled]

Adding a shim to backing plate may not be enough alone unless the shim is able to split the difference and the pads do not hit on either side. You can get different thickness C clips to get your axle play down to .003-.005 which should eliminate your issues. Use a regular feeler gauge to check this tolerance. You may still need the backing plate shim to get the caliper centered on the rotor. Getting the axle play between .003-.005 is something that should be done anyway, disc or no disc.

 

[ssn696]

Where did you find those C-clips?

 

[LedSled]

I have not bought them but you can buy them online from usual sources. Look for sizes of .150 and up. You may get into a situation where you need to sand one down for the best fit. Also, check with a local rear guy or transmission shop. They will have them too.

 

[pontiacgp]

Thanks for the idea and I'll check out for the C clips but I the 67 Chevelle rear which has 28 spline axles

 

[455'ed80Regal]

Where did you find those C-clips?

I got mine at O"reillys. Bought 2 packs as they come with one of each thickness clip. I needed both the thinner ones for my axles.