Rear caliper inner piston help needed, I did search and found some threads, but could'nt nail it Options

[Root_Werks]

Searched and couldn't nail exactly the help I was looking for. So figured I would ask in a new thread.

My rear brakes I let the pads wear waaaay to far. Well, I've only driven the car a few hundred miles and I thought they had more meat on the pads. Nope. Long story short, both pistons on the outer sides pulled in via the adjuster just fine but both inner appear to have gone past the threads. I can't seem to get them to catch back onto the adjuster. Anyone have any tricks?

[davep]

Use a tool to push the pistons back into the bore; there are special tools to do this job; alternatively use a C-clamp. While using this tool, turn the adjuster to engage the threads.

[Root_Werks]

Thanks Dave, that's sort of what I figured. Looks like I'll be pulling the calipers off to do that correctly. Not too big of a deal. CCW to pull in right?

[Eric_Shea]

I have to ask... you are turning them in the opposite direction from the fronts right? From your note (CCW) it seems like you have it right.

If you want to leave them mounted, you can stick a fairly large screwdriver between the rotor and the piston to apply a "small" amount of force on the piston while cranking it in.

That oughta do it.

[Root_Werks]

Yes, outsides I turned CW and pistons sucked in. Both insides I did the CCW and they didn't catch. Done rear brakes dozens of times but only ever had a piston just once not be connected to an adjusting screw. So I just wanted to make sure before I started prying or "c" clamping anything.

Actually, that BMW front brake lock up thread was really good. My purple 914 is all stock brakes and this little even't has had me going through the brakes a little bit. Lots of good reading on 914 brakes lately. (IMG:style_emoticons/default/smile.gif)

[davep]

IMHO the venting clearance on the rear brakes (0.004") should be done about every 5 to 10 thousand miles. As the pads wear, the piston is hydraulically forced out, but the internal mechanism does not necessarily follow. If the pads wear 0.125", then the mechanism can be pulled out of the groove in the piston and are thus disconnected. If the clearance is never adjusted from new thickness to worn completely away then you can wind up in the situation you find yourself in. I have, many times, received calipers where the mechanism is not connected; I'd guess 60% of the calipers. In many cases I turn the adjuster CW to force the mechanism out until it snaps back into the groove; about 80% success rate. However, to retract pistons in a rusted caliper you almost always need to apply pressure on the face of the piston. My spreader tool gets an awesome amount of service in these situations. My rule of thumb is that if the adjusters do not move the pistons by themselves, then it is time to rebuild.

[Root_Werks]

That's what happened to me. This 914 sat for a number of years. Bleed the brakes, worked them, seemed okay. Did an eyeball check of the pads which looked good enough I thought for the rest of the year. Turns out the rears were farther worn that I thought. The pistons pushed past the adjusters. I haven't had a chance to mess with the inner pistons again yet. I picked all new pads this morning making sure to match front and rear.

I am sort of hoping I don't need to rebuild the rears. Well, I am sure it wounldn't hurt. I just don't have the time right now.

I'm sure it'll work, but I'll let you guys know if appling a small amount of pressure on the piston to get it back into the adjuster works or not.

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