Tuesday, January 7, 2014


 Saab V4 flywheels are, at the youngest, 40 years old and virtually ALL of them must have their pressure surface [see drawing, above] lightly machined to remove damage from clutch slippage or chatter.  A critical dimension of 0.660" from the pressure surface to the pressure plate mounting surface must be maintained. If this distance is NOT maintained, the aft surface of the release plate [the hexagonal flat plate in the center of the pressure plate [see photo, below] will not be in the correct fore/aft position. That surface must be 0.125" to 0.140" aft of the three flat pressure plate surfaces [the ones with two big holes, each--see photo below].  If not, the clutch will NOT release, and the release bearing arms will strike the surface of those same three flat pressure plate surfaces.  NOT good. 
This customer's machinist had machined the pressure surface and the pressure plate mount surface allright, but the measured distance was 0.670", not 0.660", which allowed the hexagonal release arm plate to sit forward too far, down in between the 3 flat plates [the ones with two big holes, each]. Although the clutch disc and the pressure plate were both new, the clutch would NOT release and the release bearing arms hit the pressure plate. The customer sent the whole schmere to me for correction.  
There are two solutions:  1] Machine the flywheel to get the critical dimension to 0.660", or 2] Shim the flywheel.    This is a shimmed flywheel/clutch/pressure plate assembly. 
I used a special tool in my shop press, disassembled the new pressure plate and added 0.030" valve spring shims under each of the six coil springs in the pressure plate. This was to compensate for the shim 0.024" plates [in red, in the photo] that I fitted under the pressure plate mount bolts.   The 0.024" shim plates moved the pressure plate so the release bearing plate was in the correct position--0.125" aft of the three flat plates.  HOWEVER, adding the 0.024" shim plates takes too much mechanical clamping action off the clutch disc and the clutch will slip.  The 0.030" valve spring shims restore the mechanical clamping action [and adds just a touch more than stock], so the clutch works just fine and the releases properly.

Interesting "fix" for improper machining.

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