ZF Transmission info

[Craig Burnett <zatarian@xxxxxxxxx>]

Hello!

This is Craig the transmission rebuilder.  I'm new to the group and
relatively new to the net.  

I saw a post relating to forward clutch failure in ZF automatic
transmissions.  Let me share some professional info with the group.  

The ZF automatic is engineered to run some ridiculously high line
pressure in Park, Reverse, and Neutral, (P.R. & N.) around 190 psi.,
(anything over 70 is a waste in P. & N.).  The input shaft has a hole
in it that feeds the forward clutch.  This hole is sealed (isolated,
if you will) off by a rotating metal sealing ring on either side of
it.  The rings seat inside the stator shaft of the pump.  The stator
shaft splines into the torque converter.  

A little ring, bore, and bushing wear; I mean just a tiny bit, and
you have torque converter pressure (190psi in P, R, & N) leaking past
the front ring, into the forward clutch circuit.  The clutches then
drag (you usually can't feel it) and burn up very quickly.  Limiting
operation in Park, Reverse, and Neutral to an absolute minimum will
extend the transmission life considerably.  

When I rebuild a ZF, I use some "tricky" reengineering.  First, I
provide a "line to lube" pathway, increasing lube oil available to
the geartrain under high throttle conditions.  Second, I machine a
pocket in the valve body casting to accept a .250" checkball.  Then I
fabricate a hole and seat for it in the separator plate in the
forward clutch exhaust circuit bypassing the insufficient orifice
type forward clutch exhaust system.  Third, I shim the accumulator
springs to firm the shifts somewhat without raising line pressure
past dangerous limits like cheap shift kits do, which aggravates the
ring leak conditions in the forward circuit as well as all other
circuits.   

This tech is available in the Trans industry, but is seldom used, as
the time necessary to create one of these units is considerable. I am
lucky enough to be sort of semi-retired and can take whatever time I
need.   

Bye for now. 

Craig  


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