Hey there, I'm just doing my rear breaks. I bought a set I used rear calipers that are in great condition. However the cylinders don't seem to decompress 100% in.. I'm using my rear caliper tool to turn them in and they only go so far. Should the cylinders reset all the way back into the caliper on the rears? I've already ordered some new calipers but if there is something I'm missing here then I'll just send them back and use the used set... Thanks -Myles
Which rear caliper tool do you have? The worthless "cube", or a tool set similar to the Harbor Freight that screws down to put pressure on the piston, while you turn the piston in?
It's pretty hard to get enough force onto the "Cube" to retract the caliper pistons. Especially when the brake pads were very worn before replacement. In those cases, it seems like the pistons jam, and it can take quite a bit of force to get them to begin retracting.
If you are rotating the tool, and the caliper piston is not retracting, you probably need to increase the amount of force pressing on the piston (don't Yogi Bear it, just give the pressure adjustment a 1/2 or a 1/2 turn at a time).
I use a extension to the short handle provided on the Harbor Freight tool to get the leverage needed to start the pistons retracting when they're really stuck. I have the older tool set (came in the red plastic case), and I've turned the pressure screw with the extension I have (I use half of the handle from an old compact floorjack) hard enough to snap the rollpin in the pressure screw assembly of the brake tool (connects the pressure screw to the tool end at the caliper).
The newer Harbor Freight brake tool set (comes in a blue or black case with more pieces and a lifetime warranty now) has a stronger modified one-piece pressure screw assembly that eliminates the rollpin.
If the caliper boots are brittle or cracked and dry, or torn, it would be a good idea to replace them before retracting the pistons. The MKIV rear calipers use the same seal kit as the MKIII rear calipers. Buy the TRW caliper seal kit. The quality of the rubber is much higher that the auto parts store junk, and the TRW kit only costs between $6-$8 (does two calipers).
Last edited by germancarnut51; 10-15-2012 at 01:27 PM.
some brakes are just difficult, you will have easier time if you loose the bleeder screw and cover with rag then force piston back in. you will have to clean up some spills, and bleed the brakes and add some fluid but heck beats getting frustrated not able to compress the piston back. I think the rare bleeder screw is a 8mm or 7mm.