The reasons behind shimming the clutch pivot ball are
often misunderstood. Ultimately what you're doing is correcting the offset
geometry of the clutch fork so that it's optimized for the clutch you are using.
When it comes to aftermarket flywheels, clutch discs and pressure plates there
tends to be some variance in the final offset distance of where the spring plate
fingers are in relation to the throw-out bearing. This distance will also
vary whenever the flywheel is resurfaced. If the machine shop had to take
.030" off your flywheel, your whole clutch assembly will now be .030" further
away from the transmission. This is when you need to shim the clutch fork
pivot ball .030" to compensate.
When to shim the pivot ball?
During the transmission install but first things
first: Inspect your clutch fork for excessive wear. Inspect the
clutch fork finger tips that push against the throw-out bearing. They should be round,
without any flat spots. The clutch fork pivot ball socket should not show signs
of wear. If it does, replace it. 1st gen owners take note: You can upgrade
to the 2nd Gen clutch fork, part# MD770506. It's much stronger than the
1st Gen fork and we have them in stock.
Why shim the pivot ball?
Because you want to keep the clutch fork at the optimum angle so that it sits in
the proper location and doesn't make contact with the transmission case when you
push the clutch pedal down. If it does make contact you will risk breaking
the transmission case where the slave cylinder bolts on. Another benefit of
shimming the pivot ball is reduced thrust load on the throw-out bearing post.
How to shim the pivot ball.
Once the transmission is initially installed into the car and just bolted down
flush to the engine, it is the time to check the position of the clutch fork.
Checking it right this moment will save hours of hassle later!!! Take notice to
where the clutch fork protrudes out through the square boot on the front side of
the bell housing. Push the clutch fork over towards the passenger side so that
the throw-out bearing is just touching the spring plate fingers of clutch. The
clutch fork should be either in the center of the square hole or preferably just towards
the slave cylinder. The photo below shows the clutch fork that needs a shim
washer installed under the pivot ball.
If
the arm is sitting off center, away from the slave cylinder you need to pull the
transmission back out and add a washer possibly two. This will get things back
in line. Do not add too many washers or the clutch fork will make contact with
the pressure plate and potentially cause other troubles, such as breaking the
throw-out bearing post off the transmission case. If you are fighting
clutch adjustment problems on an existing clutch install, get under the car and
check this out and don't be tempted into trying a lengthened clutch slave
cylinder rod. The only way to properly correct the clutch offset geometry is by
shimming the pivot ball. By properly shimming the pivot ball your clutch
will work much better and your transmission will reward you with better shifts.
Photos & revised text were borrowed
with permission from our good friends at
http://www.roadraceengineering.com
