Author Topic: Issue with front disc pistons (Read 415 times)

cmayna · « **on:** January, 14, 2009, 10:19:39 AM »

OK, I bought some new 68+ calipers, rotors and pads. I cannot retract the piston back enough to allow the pads to slide over the rotor. Though some have said that the calipers are faulty for the pistons should retract back enough for the top of the pistons to be flush with the caliper face, I have never seen this design caliper with a piston's edge being flush with the caliper face. Here's a pic of the caliper. Yes I did remove the cap and opened the bleeder before I attempted to push the piston in further.

I took it a step further and removed the piston finding that it is about .300" longer than the
depth of the cavity so no way it could be flush.

Rotors-Old ones measure .820" - .830". New ones = .950" which seems reasonable.

Pads- old ones measure .432"-.500". New ones = .545" which also seems reasonable.

I need a good /.125" worth of room to slide the calipers over the new rotors.

FYI-Yesterday I did take the new calipers back and compared them with some others but they were the same. I then went to my local NAPA and theirs were the same as well.

I'm stumped on this one.

Flysure1 · « **Reply #1 on:** January, 14, 2009, 11:31:53 AM »

I agree that is odd, I probably have put on a 100 or more sets of front pads in the 70's-80's and I don't recall any protruding out that far, you have already done what I would have first tried by comparing them with another manufacturer, are you putting quite a bit of force on the piston with a large c clamp? how close are they to fitting? there might be some difference in rotor thickness also pad variations---good luck.

Flysure1 · « **Reply #2 on:** January, 14, 2009, 11:34:34 AM »

Whoops, I see I never read far enough to see the figures you posted

Midlife · « **Reply #3 on:** January, 14, 2009, 02:57:32 PM »

Try installing the disk piston without a dust boot or o-ring (i.e. completely dry) and see if they can fit the rotor. If not, then something is definitely wrong. If they can, then you know where the problem may lay.

I had problems when I first reconditioned my KH calipers: one side simply wouldn't slide on. It turns out that the piston was a tiny bit cocked, and wouldn't retract fully due to pinching the o-ring. Once re-installed, it fit fine.

Do both sides have this problem?

Starfury · « **Reply #4 on:** January, 15, 2009, 09:44:38 AM »

My new rotors new rotors are .935"

cmayna · « **Reply #5 on:** January, 15, 2009, 03:09:20 PM »

Middy, Yeah I did a dry fit to the piston and it still stands pretty tall. I have finally given up and will be returning the calipers back to the store since they couldn't resolve the issue.
Dan at Chockostang is sending me new calipers with pads loaded which he will first do a fit test against some .950 rotors.

These calipers were not worth all the headache I've encountered. Have to move on.