tech ?

[Lee Thompson]

There are 2 types of forward drum pistons--stamped steel and aluminum). The steel ones have a check ball assembly in the drum, the aluminum does not--correct? The aluminum piston has 2 small holes in it and when air checking they leak. Why are they there? Do they replace the check valve used in the older steel pistons drums? I am contemplating plugging the holes when used with a billet drum which has the check ball assembly. As alway, open to any and all replys. Thanks.

 

[chris718]

the aluminum piston with the bleed holes and checkball omitted in the drum combination is used to reduce harsh engagements from park reverse or neutral to drive.kind of strange because they removed return springs from the retainer in this combo.the holes in the piston are covered up by the wave plate when/as it is compressed during clutch apply.this is called the feed /bleed type.some say that if you use the steel piston with the drum with no checkball itll not release the clutch during shifts from drive to reverse neutral or park.if this was the case the feed bleed combination would never release.oil is exhausted at the manual valve.no ball causes a slight delay in exhaust rate.however use the feed bleed aluminum piston with either type drum and the steel piston with the drum with ballcheck.the aluminum piston is more desirable imo,even though they ocassionally crack