brake piston won't compress all the way

[eoverly]

I'm replacing the rear brake pads on my 05 X5 3.0 and I can't get the piston to compress enough to get the new pads on. Does the piston compress all the way into the caliper? Even using a C clamp my piston is sticking out at least 3mm. Thanks.

Ed Overly
05 X5 3.0

[hlgilbert]

Yes, they go in all the way. I use an expansion tool, but have friends that use C-clamps. They've always used them and always will, but I found the tool is easier, because of this problem. Even with the tool, I first leave the old pad on so I don't take a chance screwing up the piston, and screw it until the piston is sticking out a millimeter or two and run out of screw, then back off, put the second pad in also, with the tool between them, and screw it until the piston fully compresses. I did mine today. I suspect yours is just cantankerous, having not been that far in for a year or so.

[eoverly]

Lin, are you saying that the piston screws in at the end of its travel into the cylinder instead of pushing in straight? Thanks.

[beecee]

when you push the piston in so that the fluid in the caliper gets pushed out rather than back up into the line. This will also release the pressure and should make pushing the piston in a little easier.

I always open the bleed screw when piston back in. Give it a try.

[eoverly]

I knew to try that- opening the bleed valve to relieve the hydraulic pressure. It didn't help. Thanks for the tip though! I'm getting convinced that the piston is as far in as it going to go and I might have to file down the pads a little.

[beecee]

which means it might not work properly for braking purposes. May need to rebuild the calipers. Or see if a local shop can get it free.

[hlgilbert]

No, sorry for not being clear. Its my compression tool that I runs out of travel and I have to back it up and put in a shim to get it back all the way. It should just squeeze back. Maybe try WD40? Maybe pump the brake, or have someone do it while you watch, and get the caliper out again, then compress it again. By the way, I just take the cap off the brake fluid reservoir, and it pushes the fluid back up into it. After I do one, I pump the brakes to get the fluid back into the lines and caliper, then do the next. If I do two without doing that it will overflow.

I recall a set of pads that were very difficult to get on, but I put a block in, a shim, and compressed again and then struggled and finally got them on. I don't know why yours won't go back unless it has some corrosion?