With all of the master cylinder, slave cylinder, clutch replacement musings of late, I thought I might post my most recent project.

I just finished converting my '86 4+3 Z51 from an automatic to a ZF 6 speed. This car started life with a 4+3, was converted to a 700R4 in '95, to a 4L80E in '97 and back to a 700R4 in '01. The transformation back to a manual began in the later part of '06 and is now complete. I started with a CenterForce, dual mass replacement flywheel (700175) and ARP bolts, added a McLeod Street Strip disc (261871) and a stock Valeo pressure plate with new GM bolts. I am also using the BMW/Castrol fluid in the transmission.

I have the usual clutch disengagement story, with an unusual twist:

Like almost everyone else who either has a ZF or has converted to one, I had an inordinate amount of trouble with the hydraulic system, or so I thought. The clutch would not fully disengage and the car would start moving as soon as the pedal left the carpet. I replaced the stock D.O.M. slave cylinder with an aftermarket cast model, no better. I replaced the stock DOM master cylinder with an aftermarket cast model, no better. We bled and bled and vacuum bled and reverse bled and bench bled and bled some more, no improvement.

It was time to turn our attention elsewhere (the unusual twist begins).

I started considering the geometry of the entire system the only thing I had not replaced was the clutch pedal. If you smashed the pedal to the floor, to the point you were smashing the carpet, the clutch would almost disengage. I conducted several searches for a bent clutch pedal here on the forum, only found two instances even hinting at such a problem and neither on came to any closure. At this point the clutch pedal was about an inch and a half to two inches below the brake pedal, which did not seem correct, so out came the pedal. I stuck a long bolt through the top of that pedal and through the top of a new pedal, lined up the M.C. push rod anchor pins, low and behold the pedal pads were almost three inches apart, WOW. Now the clutch pedal ia about an inch higher that the brake pedal.

The new pedal is in and the ZF shifts "like butter!"

I could not be happier with the combination; the clutch grabs good but is a bit jittery. Three of the six springs in the McLeod hubs are over molded the polyurethane making it stiffer than conventional hubs. The single mass flywheel causes the transmission to make noise, as expected, but I never experienced the level of noise canceled by the dual mass flywheel. None the less it makes no more noise than I would expect from a transmission with straight cut gears. It makes some unusual noises in neutral with the clutch disengaged similar to an occasional “chunking” sound.

I think I can live with it!

 

nice to see it worked out for you. i am planning on swapping the 700 r 4 out for a zf6 in my 84. if i am recalling the posts ive read correctly if u have a one piece rear seal ya need to use the dual mass flywheel and if u use the 2 piece rear seal ya need to use a single mass flywheel. however if im not mistaken the single mass flywheel has to be properly ballanced for it to work. i beleive i also read something about the bellhousing being diff with certain aplications might have been with the lt4 im not sure. do a search for zf6 swap and ya should find the same posts ive read regarding these things. again im just giving this info based off my memory of what ive read not actual experience im sure someone with more experience will chime in.

 

I wish I had seen this sooner. The ZR1NetRegistry site has that in the common issues section....actually if I remember right GM had a TSB out on bent clutch pedals. I don't recall if it was a ZR-1 issue only or common to all zf6 cars.

Glad to see that you solved it!


Tom

 

Now that I have a new pedal, it is easy to see how this happens. My pedal does not reach the floor now. The only lower stop is the master cylinder bottoming out. If a person were constantly speed shifting and not acutely aware of pedal travel the pedal stalk could easily be bent by over travel.

 

Both myself and my buddy that have zf6 cars have replaced the pedal due to it being bent.. I swapped from a auto to ZF in 1996 in my 89. I replaced the pedal this last year..

my buddy has an 84 that had the 4+3, now a ZF6, same thing pedal was bent..

 

What he said. BUTTER!