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Wes V |
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#1
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Member ![]() ![]() Group: Members Posts: 482 Joined: 11-October 07 From: Los angeles Member No.: 8,211 ![]() |
I'm rebuilding a set of rear "M" calipers for my 914 and have a bunch of questions.
1. Inside the bore of the caliper there is a pin that goes into a mechanism within the piston. What the heck is it for? How do I remove it? Is it screwed into the caliper body or just press fitted into place. It needs to be removed in order to hone the bore. 2. If I can get rid of the "pin" within the bore of the caliper, what pistons can I use. I know it's easy to remove the mechanism within the piston (simple snap ring), but I have to get new pistons anyway. An actual porsche part number would be nice!! (Stoddard lists some aftermarket 38mm stainless steel pistons, but I'm not sure if they are applicable or have the stepped to surface talked about in the next point) 3. The pistons have to be installed (rotated) as shown in the following diagram. (IMG:http://www.performanceforum.com/wesvann/914a/piston-angle.jpg) This places the lower "stepped" surface of the piston in the upper position. It's not due to the pad having an "index'd" matching surface (the pad just has a flat surface), and as such I've got to ask why it matters? (I have to assume it's so that the initial "bite" of the pad is lessened on the leading edge) 4. Are any of the "rebuild" kits better than others. (the kit normally is just the piston o-ring, dust seal, and retainer clip) Are there any to avoid? 5. The four bolts that hold the calipers together are 7mm (from the factory) and when loose, the parts of the caliper sure sure do flop around a lot!! Has anybody used 8mm bolts to help alignment and also be stronger. Where would you get 8mm bolts in the correct grade (12.9?). If you just use the factory 7mm bolts, are there any secrets to keeping everything aligned while tightening. (since I'm talking about the bolts, what should they be torqued too?) Other than the factory, is there a good source for the bolts? 6. Any idea on cost of zinc plating? (the parts have been blasted and clean) Wes Vann |
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davep |
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914 Historian ![]() ![]() ![]() ![]() ![]() Group: Benefactors Posts: 5,154 Joined: 13-October 03 From: Burford, ON, N0E 1A0 Member No.: 1,244 Region Association: Canada ![]() ![]() |
Just like Eric, I've been rebuilding calipers for about 25 years. You do need to have the proper tools, like the Ribe bits (and thankfully I have a great source for them as the bits do break occasionally). If you use the wrong bit, the likelihood of damaging the unobtainable bolts is quite high. I have searched the world looking for the M7 hardware, and even the OEM supplier does not offer the bolts on the market. I can get the bolts custom made, but The cost per bolt is VERY high, as is the minimum order. I make many of the custom tools, for the various procedures, myself. Sure I can slap together a pair of calipers in a couple of hours, but not if I want to do it correctly. The liability if something was to go wrong is just too high.
The knock-back pins and the orientation of the pistons was developed with a lot of engineering effort over many years. I believe that if the parts are there, then keep them, and use them correctly. Trying to second guess years of research by experts when you are an amateur is not a good thing. |
Wes V |
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#3
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Member ![]() ![]() Group: Members Posts: 482 Joined: 11-October 07 From: Los angeles Member No.: 8,211 ![]() |
OK, bolts are an issue.
901.352.978.12 is NLA. So, here is what I did; I went by ARP and picked up 1/4"x28 bolts and nuts. 1/4" is slightly larger than the original 7mm. (IMG:http://www.performanceforum.com/wesvann/914a/bolt1.jpg) (IMG:http://www.performanceforum.com/wesvann/914a/bolt2.jpg) They are installed with the head of the bolt on the opposite side from the original configuration due to the the shoulder on the bolt head being larger than the shoulder on the nut. The shoulder on the nut just barely fits within the cavity on the caliper body. The shoulder on the bolt head doesn't fit. No special tools. Just a 5/16" 12 point deep socket. Total cost for both calipers was $22.35 Now I expect to hear about them not being strong enough! Wes |
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