Measuring a clutch

Hi, I have an AFT clutch in our alcohol altered. I bought this as a 10.5" clutch. Can somebody tell me which is the measurement that defines the size please as I do not seem to be able to find a measurement on the clutch that equals 10.5". I have just purchased a second clutch which I bought as 10.7", when I compare the floaters and discs they appear to be identical. Hope someday can help.

 

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O.D. of the friction surface is what dictates the clutch size. Problem there is if you try to get a dead nuts diameter measurement on the O.D. of the pressure plate steel, there is usually a little fudge room and it's hard to measure the OD accurately unless you've got a huge set of calipers with really long flat edges, or a CMM.

As for the 10.7 stuff appearing identical, it depends on the bolt circle of the studs and the diameter of the stands you have. It is pretty common practice to run a 10.5" disc in a 10.7" clutch just because the 10.5" is a more common size and the bulk of the wear on the clutch happens well inside the OD. If you check the OD of the discs, they should be almost dead nuts 10.500-10.490" Big thing that can bite you on the discs is actually the ID of the friction material. If the ID's aren't consistent, like some have been cut back further, that can change your tune in a hurry.

I don't know off the top of my head that the AFT will have the same bolt circle for the stands as the 10.7", so if you interchange them, the pedal may not work on the AFT at the end of a run because the floater stuck into the stands from heat growth. And if the AFT floaters are too small on the bolt circle for the 10.7", you'll have rear main problems for sure.

 

is it the 12 stand pedal clutch or a older fuel style think most AFT are 10'' 6 stand or 11'' 12 stand pedal clutch's then the 10.5 and 10.7 crower glide style fuel ones

 

See if the 10.7 discs will fit within the stands on the 10.5 flywheel with some clearance. I have found they will not.

Dale