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SteveNelson

40 Flathead 6 clutch release fork mystery

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I am working on a 1940 Pontiac Special deluxe coupe. The original 6 had multiple cracks in the water jacket, and ultimately I ended up with a 52 six, kindly located for me by Lowell White in Spokane, who has been a great resource. I am in the (slow) process of reassembly. I mated the 40 bell housing to the 52 engine, using the 40 flywheel, clutch assembly, throwout bearing and release fork. Lo and behold, the release fork holds the throwout bearing approximately 3/8 inch out of alignment with the mating surface on the pressure plate, 1/4 to 3/8 of an inch to the right of the centerline of the transmission input shaft, when peering into the bell housing from the rear. Huh? Since the release fork rotates on the pivot ball, I surmise the centerline of the throwout bearing rotates inward toward the input shaft centerline as the clutch is depressed, but 3/8 of an inch? Did Pontiac change the release fork geometry throughout the years, or has my garage entered a strange space-time warp? Thanks for  any help. Steve

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Hi Steve,

Not having both model throwout  forks on front of me but having the part listing shows there is a different part number for your 1940 ( 501868) vs 508923 that's listed for the  1946-53 models. Crankshaft  / gearbox Centreline is centreline however and it seems  unusual  that as  you have used the original 40 model bellhousing and associated components it should line up to the crankshaft ,/ gearbox main drive shaft centreline. 

There is a degree of axial float of the throwout bearing on the fork to allow for alignment  and movement as the fork moves though its arc when the pedal is depressed , but obviously there must be a problem to cause the mis-alignment you quote.

One thing I would suggest  you  check is the concentricity of the bellhousing counterbore , when using a mandrel fitted to the Spigot bush / bearing and a dial indicator mounted to the mandrel shaft, I have seen these bellhousings to be "eccentric" rather than concentric when checked with a dial indicator, to the extent the bellhousing had to be re-aligned and dowelled into the block to hold its position. But that amount was approx. 0.200" not 0.375 as you are seeing.   It did make for a very shuddering clutch action though.....

Can you  post a pic or 3 to make the picture clearer for us from afar ?

Thanks .

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