Rebuilding turbo front calipers
 

How critical is the piston orientation when reinstalling the pistons? I have read somewhere that 20 degrees fits it to the equation somewhere.
Thanks,
Bob

For ATE 2 piston calipers there is a tool that sets the step to 20°

But for 930 calipers the rule is to set the step parallel to the caliper guide surface at the end of the caliper box, the setback side faces down in back and up in front, ie the setback sees the rotor first.

So if I understand you correctly Bill, If the Caliper is laying flat on my bench with the trapdoor down and rotor opening up, the pistons for the front caliper should be set so the set back or lower section of the piston is facing toward the open side of the caliper? In a horizontal position in the caliper body?

Hmmmmm.....trying to follow this discussion, but, :) ......what is a trap door and set back?
Maybe a pick or two please.
Cheers,
Johan

Johan,
The "trap door" is #22 on the picture taken from PET. Porsche calls it an Expanding Spring. It holds brake pads in the caliper and provides a quick way to change pads instead of using the pins used on other models. The setback is an area on the face of the brake piston which sits lower than the rest of the face. You can just make it out in this diagram.

Sorry picture didn't post . technical difficulties . hold please

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#s 17 & 18 are at the ends of the pad box, the step is parallel to these ends, you can just see it in the diagram #12.

As the rotor rotates, it sees the lower part of the caliper piston step first

This diagram is a left front, w/ a leading caliper, the rotor will spin counterclockwise, the lower step is up, the raised step down

Thanks Bill! I get it now.

Please post pics of your progress, I will be doing this in the near future.

I was a bit surprised rebuilding my 930 calipers at the piston orientation, as I have also rebuilt several sets of SC/Carrera single piston calipers and there is an angle to the orientation on those pistons.

got a little alum plate from a PP forum member cut with the 20 degree angle to set the non-turbo pistons.

does make me wonder why the difference.

sorry I did not take any pic of my calipers showing the pistons clearly.

good luck.

The 20° angle on ATE calipers does the same thing, placing the step perpendicular to the rotor, w/ the low side meeting the rotor first. The reason is to allow outgassing w/o lifting the pad from the rotor face. w/o it the pad lifts and you get tapered wear.

http://forums.pelicanparts.com/uploa...1528739873.jpg

Ahh, Got it, thanks.
Johan

I understand. but to my eye that angle on the ATE calipers does not look exactly perpendicular to the rotor but close. maybe just an illusion to me. so on the ATE I do use the little gauge to set the angle.

Ok, I finally have finished the rebuild. I did not split the calipers, just new seals. It has taken so long because I had to wait about 10 days for the seals. Lesson 1, don't start until you have the parts. I live in FL and found the seals in GA at a company with the initials AA. They don't stock them so I had to wait for them to be shipped to GA first, Ugh! Rebuild is fairly easy, raise and securely support all 4 corners, calipers come off with 10mm allen, hard brake lines 11mm flare wrench, unplug wear sensors and remove calipers. You need about 3 cans of brake cleaner, I cleaned calipers with brake clean and an old toothbrush fairly well first. To remove Pistons i used an air compressor fitted with a rubber tipped blower. I used a piece of wood to pop first piston, then Bessey clamps on the other 3 pistons, removing and replacing in holes lightly to pop each piston one by one. I then removed the seals and scraper rings and finally cleaned thoroughly with brake cleaner. I lightly coated each seal and installed. The scraper rings are a little tougher to seat and ended up using a small Bessey clamp without the plastic protector (very carefully) so I could get the scraper rings flush into caliper body. Pistons push in fairly easily, just a little wiggle and I oriented them at 90 degrees to body as Bill recommended. Lower part of step towards the bleeder side of caliper. To mount the calipers back on car you need to install a spacer washer between the caliper body and the spindle. This is a little tricky and I found the easiest way is to use a magnetic telescopic stick tool to hold the washer in place while pushing 10mm allen bolt through. Reconnect the hard brake lines and tighten everything. Another PITA was closing the trap door, it's much easier to open than close. Brakes were bled with a Motive 109 power bleeder in order, RR, LR, FR, LF.http://forums.pelicanparts.com/uploa...1529018799.JPG
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Pictures in no particular order. I found that if I orient the scraper rings a certain way, with the edges in first on the caliper box side, they press in easiest. The 4th picture shows both sides of the scraper rings, metal side goes out. 6th picture is the Bessey clamp without the plastic guard.

Great write up. You have certainly taken the mystery out of this DIY R&R. I have found that flipping over the trap door 180 degrees sometimes results in easier closure.
Cheers,
Johan

Johan, the problem with flipping the trap door over is, is that when the trap door is closed it puts pressure on the brake pads, keeping them seated. There is a bow to the trap door which is kind of concave and I think flipping it, while yes making it easier to close would reduce the tension needed to hold pads down tight.
Just my thoughts. I know the engineers at Porsche while not always obvious to their reasoning sometimes have probably thought this out.
Bob