Dozman

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cwigg66

I'm the guy with the question, and the car they will go on is in my sig (the 85.5'). Now I know they won't fit the early NA spindles, but I intend to find a set of M030 spindles for the brakes to fit or make adapters. Is this a good route to go or not? Seems like the S4 calipers are the best bang for the buck.
Any help would be appreciated guys.

Chris

Oddjob

I only checked on the fronts, did not check for the rears - here is what I found:

'86-87 928s used 928 351 421(2) 00 front calipers, which have 42 & 36mm pistons. This part number now superceeds to 928 351 421(2) 03, which have 44 & 36mm pistons.

The Turbo S/M030 calipers were 951 351 093(4) 00, with 44 & 36mm pistons. This part number superceeded to 928 351 421(2) 02 - which now also superceeds to 928 xxxx -03.

So from what I can tell, it does look like they are interchangeable. If they are the original -00 calipers off the '86 928 (and have the 42mm larger piston instead of the 44mm), it probably is not much of a difference. The pads might wear a little less evenly.

If I were upgrading the brakes on a car, I dont think I would spend the extra time and money searching for a full set of M030 spindles and hubs - they are getting very expensive. I would go with standard Turbo/S2/968 spindles and hubs (comparitively much more common and much cheaper) - then buy caliper adapters (available from sources like Racers Edge, probably Lindsey Racing, Paragon Products, etc) to mount the Turbo S/928S4 calipers to the standard Turbo spindles.

cwigg66

Exactly what I wanted to hear about adapting the calipers ot the spindles.

Now about this caliper piston size difference, what is the deal there. Are you saying there are 2 different varieties of S4 calipers out there, each with different piston sizes? If that's the case, how easy is rebuilding them going to be (parts availablity, etc.) Thanks for the help

Chris

Oddjob

There are actually many varieties of that size caliper. The 993s use a version of it, there are at least 3 part numbers for the 944 series, and 4 part numbers for the 928 series. Most of the changes have to do with different dust seals and piston seals.

The part numbers and piston sizes came from PET, so take it for what its worth (I dont know anything about 928s, so I personally cannot guarantee the accuracy of the information).

If indeed the early 928S4 calipers have a 42mm piston instead of 44 (I do know that 944TS/M030 calipers all have 44mm pistons), and the part numbers do superceed to the 44mm piston calipers, then it may be likely that rebuild kits for the 42mm calipers will be hard/impossible to find. I dont know.

You may want to try a dealership, or a brake/brembo supplier and see if rebuild kits are available for that specific caliper. But first, check to see exactly what the actual piston sizes are in those specific calipers - it may have 44mm pistons, so it could be a non-issue.