I don't have an answer, but I share your frustration. My car has had some level of clutch drag almost from new (I'm the original owner). This has persisted through two different transmissions and motors, two clutch slave cylinders, two master cylinders and countless clutch pack variations.I have been fighting disengagement issues with my 91 VR4, when I first got the car I noticed that sometimes it made a little clunk when preloading the drivetrain (switching to/from reverse), pedal was all the way in, first thing I did was to flush and adjust the pedal, it had some threads left before blocking the master but nothing really improved.
Next thing on the list, the car had the master cylinder replaced, so I went and adjusted the clutch booster rod as per FSM, I don't recall the extra adjustment but it was out of spec.
Not really a change, I was having that little clunk and I guess it was also making the synchros work harder.
I had an issue with the input spool and had to drop the transaxle to change the shaft and before doing that I remember a post from Rvenge that we need at least 3/4" of displacement for proper clutch disengagement.
I performed a measurement, put a dial indicator at the end of the clutch fork, magnetic base on the firewall, I got like 0.526", almost 1/4" missing!
I replaced the hydraulics (both exedy units), clutch hose and adjusted the rod again, going just a bit on the tight side, also did a clutch job (new flywheel and pressure place) while I was doing the spool/shaft replacement, I did replace the fork and also shimmed the pivot ball using an exhaust washer, just to account some wear of the fork (pivot ball looked fine), fork stays just a bit to the right side (engine/flywheel).
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Repeated the process and got like ~0.580" after bleeding and adjusting the pedal again. I'm still suffering from that slight clunk that tells me that there is a disengagement problem.
Can this be an issue with aftermarket cylinders? I read about that in the DSM world, but what got me concerned is that 1/4" that seems to be missing, what do you guys run now that the OEM master cylinder is discontinued?
I'm being too concerned or looking at something unrelated? but for me seems clear, drivetrain should not be preloaded if the car is not moving and transaxle is totally disengaged from the engine.
By any change have you measured fork travel in a good card or is there any spec for that?
By the way I'm running a stock exedy replacement clutch, heard that some aftermarket pressure plates have different geometry and you need to shim the pivot ball accordingly.
Yes, for sure after-market clutches require variations in set-up. You need accurate measurements of the clutch throw (the distance between where the release bearing just touches the clutch and the depression required to fully release the clutch plate) and the total thickness between the flywheel and the clutch release fingers. Then you can calculate if the fork pivot needs spacing and lever ratio to determine if the slave cylinder is giving sufficient travel. This is most accurately measured with the clutch out of the vehicle in a press.
However, one useful indication comes from where the clutch engages as you release the pedal. If full engagement is towards the top, then it's likely that you do have enough travel and it could be that the friction plate is sticking or binding on something.
I'm having this exact issue with a Clutch Masters twin disk set up. One of the friction disks is hanging up on something and causing excessive drag. This has been an on and off issue for about 1000 miles, following a total rebuild 3000 miles ago. It worked great for about 2000 miles then started to occasionally drag to the point that it will sometimes refuse to engage 1st or reverse.
I tried to identify any specific conditions that made it better or worse but is just seems totally random. I'm getting ready to pull the transmission to see what's going on - ughhh.