Rebuilding calipers, 20 degrees from what?

[na2ub]

I plan on rebuilding one of my rear calipers due to some slight dragging. The only thing that is not clear in the tech article, is what is being measured to 20 degrees. Can anyone shed some light?

Thanks,
Doug

[Walter_Middie]

[Tom '74 911]

Hopefully this helps. . . I made a little tool buy cutting up some sheet steel I had laying around.



EDIT: Walter beat me to it!!

[Winter]

You are going to want to build a stiff cardboard template as described here:

Pelican Technical Article: Rebuilding your Brake Calipers - 911 (1965-89) - 930 Turbo (1975-89)

It's really easy to get it right. I say this because I was able to do it!

I think - and others will chime in - that if you are rebuilding one, you should also rebuild the other one on the opposite side, too. Just to keep the system balanced.

I ended up doing all 4 after discovering a leak due to an aged piston seal. I figured if one was old enough to fail, the rest weren't far behind!

Let us know if you have any issues, questions. The tech article that I linked to spells it out pretty well.

Cheers1

EDIT - man, you guys are fast, thanks to walter and tom, by the time I posted they'd already chimed in! Nice work guys!

[na2ub]

I am only doing one, now, cause I have a DE soon and just need to get that drag fixed. I get the pictures, but, maybe cause I have not looked at my pistons, I still don't see what is being measured. Is the piston end "C" shaped?

[Tom '74 911]

Take a look at the pistons. It will become clearer. There are notches that you line the tool up with - you can kind of see them in Walter's posted image.

[Walter_Middie]

[vash]

just like toeing in the brake pads on your mountian bike to minimize squealling..(i think)

[Nine9six]

Originally Posted by Tom '74 911

Hopefully this helps. . . I made a little tool buy cutting up some sheet steel I had laying around.



EDIT: Walter beat me to it!!

Construction paper works just as well and is much easier to cut. 20 degrees from the wall in the caliper as seen in the diagram.
HTH

[na2ub]

Ok. I kinda figured there must be some notches or something, just have not pulled it apart yet. Secondly, I am pretty sure it is my left rear caliper that is hanging.

Can that be confirmed by rotating the wheel, or does the transaxle prevent such diagnosis? After driving, this wheel is always warmer than the other 3, but the exhaust runs close to this wheel, so I don't know how much that contributes to the extra heat. Exhaust is stock.

[Nine9six]

Originally Posted by na2ub

Ok. I kinda figured there must be some notches or something, just have not pulled it apart yet. Secondly, I am pretty sure it is my left rear caliper that is hanging.

Can that be confirmed by rotating the wheel, or does the transaxle prevent such diagnosis? After driving, this wheel is always warmer than the other 3, but the exhaust runs close to this wheel, so I don't know how much that contributes to the extra heat. Exhaust is stock.

You are correct! Raised notches, about .010 -.015"on the pistons. Its a no brainer once you get things apart. When reinstalling pistons just get them started into the seal and clock the pistions accordingly. Its nearly impossible to clock the pistons once installed, and you cant put pliars on the sealing area of the pistons (duh) ;-)
You'll be just fine once you see things apart.

[NO LIFT]

Awesome, thanks so much! I always wondered "20 degrees from what", but was too afraid of being flamed to ask.

Should I index the pistons to 20 degrees when changing between street and track pads?

If so, recommendations how to rotate without removing caliper?

[na2ub]

Thanks all. Got it all apart and I see the notches in the piston face. Putting it back together now. No Lift - You only get flamed if you do something stupid, like bolting small wheels to the front bumper to avoid curb scrapes.

Anyway, very clear now, just hadn't looked at the piston face till I had it apart. Now to make a 20 degree template ...

Also, my piston was not pitted at all, but it was kinda beat up on the outside and the dust shields were shot. Definitely doing the other 3 after my DE.

[Nine9six]

Originally Posted by NO LIFT

Awesome, thanks so much! I always wondered "20 degrees from what", but was too afraid of being flamed to ask.

Should I index the pistons to 20 degrees when changing between street and track pads?

If so, recommendations how to rotate without removing caliper?

If the pistons are clocked properly to start with, there is no reason to re-clock them when changing pads. I would check them to make sure they are correctly positioned.
If you can find a way to rotate the caliper piston without removing the caliper, we all would certainly be interested in the process

[na2ub]

Well. All back together. I ended up pushing the pistons out with the brake pedal, while the caliper was still attached. Took a little wrestling to pull them out the remainder, but not too bad considering they were sticking to begin with. After my DE I will definitely do the others. Might have to repaint the calipers while I am in there, although if I do that, do I have to buy some short shorts and move to San Fran?

[88911coupe]

Are the symptoms of a sticking pad obvious? One more thing to worry about!