After rebuild, converter comes back with uneven wear on the friction surface, and may have complaints of chatter on lock up application. Problem : If rebuilder is using a brand new, "replacement" lock up piston, some of the pistons do not sit perpendicular on the turbine hub splines, causing the piston to be *bleep*ed to one side.
Solution : During rebuild, check the piston on the turbine. With the converter inverted, spin the turbine on the stator. Visually check to see if the turbine has any "up and down wobble". If it does, check the stator assembly to make sure that the caps are flat and completely in place. With the turbine now flat on the stator, place the piston assembly onto the turbine. Spin the turbine again to see if the piston assembly has any "up and down wobble" (See FIG 1).
If the turbine is spinning flast, but the piston does not, then you need to slightly modify the piston so that it can sit flat on the turbine. Place the piston into your lathe and SLIGHTLY cut the ridge that contacts the turbine hub. Only cut the piston so that you can get a 100% cut around the bore, DO NOT cut more than necessary. See FIG 2.
Spin the turbine and lock up piston on an inverted converter. If the turbine spins "flat" on the stator, but the piston has an "up and down wobble", then the piston needs to be slightly modified so that the lock up clutch surface becomes parallel with the front cover mating surface.
To cut the piston so that it will sit parallel to the turbine and front cover, place the piston as shown into your lathe. With a small boring bar or similar tool, go in and LIGHTLY cut the back ridge of the surface that the o ring rides on. DO NOT cut anywhere on the o ring surface, and make sure that you do not cut the splined area either. Only cut enough material so that you get a 100% cut on that ridge.