The problem of bore wear on torque converter clutch pistons has been around since lockup torque converters were born. The rotational restriction on the pistons is handled by splines, pins or fingers. But centering the pistons is generally the sole responsibility of the bore. Any out-of-balance movement of the piston will cause the piston bore to scuff against the turbine hub when it moves to apply or release the clutch. Indexing the piston to the turbine and balancing this unit helps minimize bore wear. (See the Transmission Digest March 2006 article on indexing TCC piston damper assemblies to turbines.)
But having a perfectly balanced assembly and expecting it to remain that way throughout its lifespan is not realistic. Torque converter rebuilders will always have to deal with piston bore wear.
The area of the piston bore that is the sealing surface seldom shows any wear because it is not used for centering. Of course, the rest of the bore will wear faster due to the small surface area remaining.
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Article No.: TCTIP-07-06
Author: Ed Lee
Total Pages: 2
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