Seized Brake Caliper

[JRC]

Hello all, I was changing out the brake pads on my 944 and as I was putting the new ones in I tried to move the caliper piston back to make room for the new pads, but I quickly found that it had seized up on both of the rear calipers.

What do you suggest I do to fix this? I have tried using a C-clamp, channel locks, and I even rented a tool specifically made for the job but even that did not work.

I am considering taking apart the caliper completely to fix it. Is there an easier way than this? If not could someone direct me to a good guide on how to disassemble the calipers.

[Gianni at Pelican Parts]

Hey JRC, welcome!

Here's a link to our Tech Article on Caliper Rebuilds and here is a link to the 924/944/968 Caliper Rebuilt Kits in our catalog.

Hope this helps you get back on the road!

[OK-944]

Not to step on any toes here, but I did this recently so its all still pretty fresh...and my apologies for not taking photos of this process. At any rate...just a few additional notes:

In my experience (others mileage may vary on this) its much easier if you remove the caliper body (containing the piston) from the “floating frame,” before proceeding with piston removal, cleanup, and resealing.

After you’ve removed the complete caliper assemblies from your car, you can pick one up and notice, that by squeezing, the “floating” frame to which the caliper is attached can be moved separately from the other, “stationary” frame (the piece which is bolted to the car so does not move).

With a bit more effort, you can slide these pieces apart. As you do this, do note the areas of sliding contact (and be sure to apply some caliper lube to these areas after cleaning them up, prior to reassembly...and don't forget those horseshoe shaped plastic pieces which go into the rear frames, as supplied in your rebuild kit, which aid in the sliding process).

Also note that there are fairly stiff springs attached to the calipers/assemblies, which aid in the proper dynamics of the working caliper - and while the springs attached to the rear calipers are pressed into curved channels and are generally easy to remove…the front springs, which are pressed into holes, can be tough to remove and you may want to leave them in place, regardless that doing so will make re-assembly of the two (floating and stationary) frames more difficult. Do be sure to note the orientation of the rear calipers’ springs, as one arm of these is more bent than the other and needs to be placed at the “trailing edge” of these calipers (as per direction of disc rotation).

At any rate…once the frames are apart, you can clamp the end of the floating frame (the one with caliper attached) into a vice…with the caliper above, “hanging” with its pressure-side facing downwards. At this point, using a hammer and brass drift (or just a rubber mallet), on either side of the rear of the caliper in turn, you can remove the caliper from the frame. Just be sure to go slowly with this, and be prepared to support the caliper so it does not drop off and hit the floor!

All else is as described in the writeup supplied earlier in this thread, reversing the procedure to reattach the calipers to their floating frames, working the springs into place as you do so (tough, but do-able)…then making sure that after all is together, the stationary and floating frames articulate smoothly (but firmly due to their springs pressure) and are able to slide past each other (slightly).

One additional note: In the case with my calipers, I’d found that while the piston surfaces were smooth, the cylinder walls, while not pitted, exhibited a bit too much staining, varnish, and corrosion (but only in places) to be cleaned up easily. So I purchased a brake cylinder hone, chucked this into a 3.5 amp, variable speed drill (amperage is important, see below), lubricated the hone surfaces and the cylinder walls with brake fluid…and, with a very gentle, light pressure adjustment, and at about 250 rpms, I honed the cylinder walls…being sure to move the hone attachment in and out at a pretty good clip, so that the cylinder walls would then exhibit a very, very slight “cross hatch” pattern. The trick here is to use the hone very briefly and check progress often…ascertaining that you’ve done just enough to clean them up without changing the cylinder diameter.

Note about drill amperage rating: The problem with a more powerful variable speed drill is that these will often be difficult to maintain at such a low (250) rpm range…the result being that instead of the desired (and very slight) cross-hatching, the cylinder walls may exhibit hone marks which are more concentric, resulting in (at least by hand-feel) a slightly compromised “slide-by” between piston and cylinder. Not sure how this would affect actual operation when installed - but hey, these are brakes…our lives depend on them!