Brake caliper rebuild on an SC.

[Jdub]

Well I spent some of my vacation replacing the old stainless brake lines with DOT-approved stainless lines and rebuilding all of the calipers. I knew I needed to go through my calipers due to squealing (despite new 'pads and silencing paste) and the fact that at least one seal was torn.

All of this has been covered by the Pelican tech articles, this 'board, and others, so I will not bore you with the details. However a few tips for those about to undertake this project.

= A bicycle floor pump can push out the caliper pistons. Use 1/4" OD hose into Schraeder pump end, locking with lever, then push 3/8" OD hose whose ID is <1/4" over the top of the other hose. Twist open end of hose into hard brake line opening of caliper. Close bleed nipple. Observe advice on not letting one piston pop out, and note that the pistons move very slowly, so let the pressure do the work before you go ahead and pump harder (i.e. give it a bit of time to work). For difficult pistons, clean the front edge of the piston with WD-40 and wipe thoroughly, then push piston in a *bit* to cause movment. Apply pressure and watch piston move out smartly.

= When you put the circular bore seal in, very lightly cover it with silicone grease and put it into a clean, ungreased bore. The excess that pushes up from tight fit of the seal will be enough to coat the remainder of the bore for the piston.

= DO NOT push pistons all the way into the bore, or even close to that when rebuilding. Instead, put them in far enough so that when the brake pads go in you will have to push the piston in to make room (I happened to do this "dry" with next to no fluid in the lines so I did not have to monitor backflush at the master cylinder resevoir). Failure to do this on the workbench means doing this later on the car via the brake pedal (that is, pushing the piston out). When pushing the piston in with caliper remounted on the car, the closed end of a 19mm or equiv. wrench will fit nicely on the piston metal only, avoiding tearing the seal. My point here is that you must have next to zero room between pad and rotor to avoid the soft pedal feel post-bleed. An alternative to this is to simply use old brake pads during the bleed process, thus "artificially" forcing the pistons out. When you go to your new pads, pull some fluid from the master cylinder reservoir and gently push the pistons in for your new pads.

= Did you know that the cross-shaped return spring held in by the caliper pins helps the pads go back into the bores (along with the vacuum on pedal return)? To clean these up, I gently sanded the "feet" of the return spring where they meet the pads with 1200 grit to get the crud off and hopefully provide a smooth surface for the pad to mate to. This may be overkill...

= Bleed the brakes with only the 'pins in, sans return spring. This will help push the pistons out should you still have wiggle room between pad face and rotor. May not always work, but every bit helps...

= Put silicone grease around the end of the bleed nipple (but not in the bleed holes!) to prevent ingress of air during bleeding, esp. w/ the vacuum bleeder. Manual bleeding should be performed as the final step.

The whole operation, with new lines, was pretty straightforward. Now, no squealing and a better brake pedal feel than before, and it was VERY good before! Also, no more squealing!!

John

[Roland Kunz]

Hello

= Did you know that the cross-shaped return spring held in by the caliper pins helps the pads go back into the bores (along with the vacuum on pedal return)? To clean these up, I gently sanded the "feet" of the return spring where they meet the pads with 1200 grit to get the crud off and hopefully provide a smooth surface for the pad to mate to. This may be overkill...

Yes they help a bit but they are mostly for antinoisepurposes.

Grüsse