brake caliper piston PLEASE HELPPP!!!

The rear drivers side brake caliper piston isn't compressing and I have the special tool to do it. Any ideas?

Are you saying that when you turn it, it won't "screw in" or compress ?

Good morning,
 
I'm doing the rear brakes as we speak.  I have an 2003 A4 and I tried to force them back also.... as I've done with American systems, but with no luck.  The instructions that came with the rotors and pads say that we should loosen up the bleeder screw and then back the piston up.  I'll be trying that route.
 
Good luck,
 
Erwin

Thank you erwin Good luck on your install. However my story is a little worse. unfortunatly i did not have heavy duty jack available so i decided to use my tire changing jack and low and behold the jack bends and the car falls on my spare tire. Had to call a friend ( on christmas eve mind you) to come with his jack so I could put the tire on. The piston wasnt compressing because i just flat out wasn't putting enough force into it.

PS Erwin do you have to use the special tool for yur car?

quote:

ORIGINAL: Haban

Good morning,

I'm doing the rear brakes as we speak.  I have an 2003 A4 and I tried to force them back also.... as I've done with American systems, but with no luck.  The instructions that came with the rotors and pads say that we should loosen up the bleeder screw and then back the piston up.  I'll be trying that route.

Good luck,

Erwin

You probably wont be able to compress the piston with a "C clamp" like american cars. I think its based on the way the parking brake works but anyway, you'll need the tool to allow you to rotate the piston. I think it's rotated counter clockwise to compress it in. Hope this helps.

It is rotated clockwise.

The procedure I used on my 2.7:
1.Disconnect the battery.
2. Pump the brake pedal 30-40 times to release brake pressure.
(Common procedure on all cars but this one)
3. Pressing-rotating the pistons - in vain!!! - The system is pressurized.
4. Reconnect the battery- the ABS engages, the valve opens to allow flow to the brake reservoir.
5. The piston easily gets to the bottom.

Quite an exercise, it seems to me the rear calipers are unchanged since mid-80.

Has anyone tried this battery disconnect and re-connect? I have the same problem... been trying to rotate (clockwise) the driver side caliper piston back and it won't budge. I got the passenger side to move with what I think would be too-much effort. I will try the battery now...

What I have tried so far...
-The rubber boot on the cylinder is missing so I have cleaned that surface (tooth brush and brake cleaner only), drenched it with liquid wrench.
-opened the bleeder value (a little fluid came out but not very much compared the effort and pressure that was placed on the special tool).
-Leveraged the tool with a extender bar and it still won't budge (I reconnect the caliper to the hub after removing the rotor so that I could place all my weight onto the bar without damaging the rubber lines).

The cap on the matercylinder has been removed thoughout these attempts.

Any additional advice would be greatly appreciated/ Thanks.




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This is the driver side.... it won't move!!!


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Close up 1 of cylinder...


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Close up 2 of cylinder...


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Passenger side completed...with much effort!

I will post my results with the battery disconnect and reconnect...

UPDATE:
I tried the battery disconnect and re-connect to release the ABS... No luck. The driver side rear caliper piston will not move.
I WAS able to get it to rotate in the caliper using a channel-lock plier on the leading edge (being careful not to mar the piston wall) and it would rotate with a bit of effort but it doesn't seem to be retracting...only rotating.
When I then try the special tool, it won't move again...? I am putting all of my weight onto the tool (200ibs), the mater cylinder is open and the bleeder valve is wide open. About 2 table spoons of brake fluid has coem out of the caliper...nothing more.

I have contacted the dealer about a new caliper...it will be a couple of days to arrive...not a stock item. I am off work today and would love to try anything you can sugfgest before I spend the $265 for the new part. Please let me know. Thanks.
Patrick

im pretty new at auto mechanics and im going to school for it. but you might want to consider looking at the master and its components to it. ive heard of a metering valve that wont allow you to bleed your brakes unless it is eather pulled out or pushed in. it might be in your module i dont know but i would check for it. i did mine and i had no problems compressing them but i did not clap of the lines and ended up sending the contaminated fluid through my hcu and now i have an abs light that wont go away and im not paying for another module. abs is a crutch anyway. im going down in a blaze of glory good luck with your brake job

oh i just thought of something. if its not too much then just disconnect the caliper compleatly and try using compressed air on the part where the brake line comes in and blow the piston out make sure to put padding on the other side of caliper for when it comes out. i also remebered that the reason you turn them in is because the piston uses helical cut gears that can be easialy striped and if they are you do need a new caliper. come to think of it i bet that is the problem. i just can seem to remeber what it is that people do to strip them. i just remember that its easy to do if you dont know about it. well i hope that ive help as best i could.

Thanks. I'll start looking for a metering valve to see if this helps.

undo the bleed nipple and rotate and push the piston back ( sounds filthy ) some of the later cars need diagnostic tool to retract the break piston because its electronic

OK. I got to retract. It took an unexpected amount of effort but I removed the rotor, re-assembled the caliper mounting bracket and the caliper so I could hold the caliper still while using two hands on the retraction tool. What I ended up using was the channel-lock pliers on the end of the tool so that I could be maximum leverage...anyway, it took a while but it eventually went back.

Either I am a 200lb weakling or this thing was stuck. Anyway, I just test drove the car and all seems to work fine. Thank you for your help and advice. I rely on these forums and am glad that I have them in my "tool box"

Patrick