'99 Audi A4: piston on rear brake caliper won't retract.

Have you got a decent brake piston retractor? if the adjuster's seized then it's a new caliper but normally a good retractor will solve it.

what method are you using? is it a caliper handbrake on that car? if so the piston must be pressed and turned at the same time and let the fluid out.

Yes. The foot brake and hand brake use the same caliper.

I have a piston retractor which fits into two slots on the piston and then turns while pushing. I managed to do the other side without letting any fluid out, just by taking the cap off the reservoir. I'm a little reluctant to touch the brake fluid nipple in case it shears off (as happened to me on another car once).

Got one from German/Swedish/French which worked fine on the other side.

Part of the problem is that with the brake hose and handbrake cable attached it's flapping around in mid air. I'm sure if I had a vice to hold it in I could do the job.

Ah, have you got the comedy fits al known calipers cube? When they work they're great, when they don't then Mr Draper etc's proper kit is a godsend. If you've got a compressor then the pneumatic ones are brilliant and cheaper

If not then a bit of buggering around with a g clamp & the cube might work, the audiforums.com is quite good for this sort of thimg.

Well you can try cracking the bleed nipple with a small socket, if your alternative is changing the caliper then you've nothing tolose. Chaeck the handbrake cable's slack before you try retracting the piston.

That looks just like mine except for the fact that it has only one plunger piece (the VAG one, apparently) facing the piston.

The piston has to turn clockwise as well as be pushed in, so in this case the G clamp might not work.

Except for being without a car for a day. Which would be very inconvenient this week.

It's slack enough that the wheel turns relatively freely and the cable end is up against the stop. I haven't gone as far as loosening the cable any further from underneath the car.

Oh, I see what you mean: hold the caliper with a G clamp and then use the retracting tool. Duh.

Do they turn in opposite directions? That's quite common.

The retracting tool only works in a clockwise direction, so I assume both retrtact the same way.

You can get a new piston seal & dustboot kit, pop the piston out & normally unseize it, if you look under the boot covering the end of the handbrake operating rod you can see if it's gone rusty & full of water, they do seize & become impossible to remove they're normally just sticky. If you'r carefull you'll be able to get the bleed nipple out & how else are you going to change the ancient manky brake fluid that's causing it to stick?

common on recent stuff , yes. and that fooled me for a few minutes the first time I came across it on a late mondeo, why in heavens name have it different directions each side? I can see no logistical reason for it at all. and that experience with g clamps and screwdrivers on the anticlockwise side was why I bought the pneumatic kit as it works in either direction, ebay about 55 quid

On the plunger bit there are two little ball things which should be located on the pistone so it twists it as you push it back. Not sure if you noticed that ... but worth a try.