We (@RealMcCoy and I) are having a serious head scratcher with the clutch on my VR4. The car is at Larry's shop in Oregon for a rebuild after I blew a rod bearing with a missed shift which took it to >>10,000 RPM, threw the damper off, destroyed the CAS and shook the alternator apart.
Its all built, run in and ready to go but we are having serious issues getting a clutch to work.
Larry has fitted two versions of the Clutch Masters 8.5" twin disc clutch. The original version that was fitted in 2019, saw about 5,000 miles and was replaced yesterday with a new "strapped" version - supposedly to give less chatter!! I think it was @Chris @ Rvenge Performance that posted a video showing real smooth operation of the CM 8.5" strapped twin disk.
Both have been plagued with adjustment issues. The original version would both slip and drag. The new one chatters, slips and drags even worse.
The clutch pedal assembly, master and slave cylinders have been checked, adjusted and re-checked over and over on multiple occasions and seem to be in order and adjusted correctly. I have searched every thread I can find on the subject but cant see anything we haven't checked already.
The head scratcher part is that my car has always suffered from some level of clutch adjustment issue from new back in '94. For most of the cars life, the clutch (regardless of the multiple different clutches used) would drag a little when the car was fully heat-soaked and working hard. This was particularly noticeable on race tracks. After about 5 laps gear changes would balk if rushed.
Anybody had a similar issue with dragging when hot?
Anybody else running a Clutch Master 8.5" twin disk?
Any ideas? Tolerance out of speck - bell housing, input shaft, flywheel, etc?
Sorry, I don’t have an answer. Have you reached out to CM, to see if they have any thoughts? Just to make sure, you’re using the TOB that they provided correct? I have a CM strapped installed but I’m still working my way through my build.
Is the clutch adjusted according to the mitsu manual for the car or according to clutchmasters specs? that clutch needs a lot less travel than our system has so you're either supposed to have a pedal stop or create a lot of free play in the pedal I cannot comment on how much but chris from rvenge would know roughly where. also the fork needs to be clearanced so it won't hit the pressure plate cover.
Sorry with FB being flaky lately I didn't get a chance to talk to Larry. I trust him as far as any adjustment. There's definitely not a design issue with the clutch, whether your particular unit was put together correctly I could not say, but clutch masters has always been really responsive to questions and comments. If you need the help of a "dealer" to get them to pay attention to you, let me know.
If its a physical clutch issue I'd say tear down would reveal hot spots or something obvious, indicated high spots, run out, etc.
Larry probably thought of it, but the only other idea may be the clutch boost to master adjustment on the engine side of the firewall.
Sorry with FB being flaky lately I didn't get a chance to talk to Larry. I trust him as far as any adjustment. There's definitely not a design issue with the clutch, whether your particular unit was put together correctly I could not say, but clutch masters has always been really responsive to questions and comments. If you need the help of a "dealer" to get them to pay attention to you, let me know.
If its a physical clutch issue I'd say tear down would reveal hot spots or something obvious, indicated high spots, run out, etc.
Larry probably thought of it, but the only other idea may be the clutch boost to master adjustment on the engine side of the firewall.
Thanks Chris, your input is very much appreciated. Yes, Larry checked all of those points, so the transmission is coming off again and we'll se what a visual inspection reveals.
I'm not faulting anybody, and assuming delays are coordination and covid related but yes a prod from you to CM could be very helpful. They were been a bit slow in responding, when Larry sent the broken one back to get this updated strapped replacement.
As you can imagine, with the motor finally rebuilt, broken in and ready to go, having a last minute issue with a brand new clutch is frustrating beyond belief.
I've had the same issue with a pair of RPS Carbon Twins, never figured it out... seemed to get better when driven in anger, but after it warmed up I got the same issue with it dragging and making it hard to change gear.
I think there may be two separate problems:
1) an issue with the clutch as fitted where it drags and rattles right out of the box
2) a tendency for the clutch to drag when the motor and transmission are working hard and hot - as in on road-course in track day event.
Right now, we are dealing with 1). However it seems that both myself and @MichaelMR2 have experienced clutch drag/balky shifting when hot. Looking at the clutch line routing, its very close to the rear turbo and header. So i wonder if that issue could be down to the clutch fluid getting hot or even over-heating, during prolonged running at WOT?
unfortunatly we made quite a few changes at the same time as the clutch, bluntly my car did not really get any exciting driving so I don't feel that's related, the gearbox did get rebuilt with the strengthening plates + new syncro's and it was right after this that life got harder, I found that as the car heated up the engagement point start to move slightly and eventually it would slip
when I next play with it I might try a bog stock clutch and see if everything is perfect with that... had the gearbox out so many times I'm a bit sick of doing it honestly!
unfortunatly we made quite a few changes at the same time as the clutch, bluntly my car did not really get any exciting driving so I don't feel that's related, the gearbox did get rebuilt with the strengthening plates + new syncro's and it was right after this that life got harder, I found that as the car heated up the engagement point start to move slightly and eventually it would slip
when I next play with it I might try a bog stock clutch and see if everything is perfect with that... had the gearbox out so many times I'm a bit sick of doing it honestly!
I can relate to that. I still suspect that the clutch fluid gets heated and that messes with the adjustment. For now I'll be more than happy just to have it drivable on the road. I'm getting more and more inclined to just drive and enjoy it on the street and not to take it back to a road course.
The saga with my Clutch Masters' twin disk continues. I am a pretty patient guy but I'm getting very p****d off with the lack of support from CM. CM's customer service has been horrendous. CM are adamant that there was nothing wrong with the one we have just returned but are sending a replacement anyway. But its taking weeks between communications there feels like a real lack of willingness to take us seriously.
So I have scant confidence that the replacement will be any better than the one we returned. Meanwhile the months drag on and on and on, with the car essentially built and ready to go apart form this frustrating clutch issue.
Anybody have recommendations for a alterative? It needs to hold ~550lbft now (and maybe up to 650lbft later) but also to be street-able. Any ideas?
I'd go with the Southbend clutch as well. I have the Stage 4 FE on my car and have ran half a dozen of those. I wish I had spare new ones because they discontinued them awhile ago. You'll have to talk to them about what is equivalent now because they stopped offering the high torque holding full face clutches. I've ran mine up to almost 900ft-lb without problems but it was only rated to 750 according to SB. Your power level is definitely pretty low for going dual or triple disk. I get you may be having heat related road course issues but that's going to be a trial and error type deal figuring out what disk design(puck vs full face) and material design will hold up best to the higher heat capacity. There's very little road course data on this platform.
Curious that it both drags and slips. That, to me, would point to a clutch fork travel issue.
Add to that the apparent "day one" issue "that my car has always suffered from some level of clutch adjustment issue from new back in '94. "
Have you guys examined the fire wall, or considered flexing in the pedal assembly at all?
Something about this reminds me of the problems folks have converting their autos to manual.
You wouldn't be the first one to discover shenanigans from the factory..
Curious that it both drags and slips. That, to me, would point to a clutch fork travel issue.
Add to that the apparent "day one" issue "that my car has always suffered from some level of clutch adjustment issue from new back in '94. "
Have you guys examined the fire wall, or considered flexing in the pedal assembly at all?
Something about this reminds me of the problems folks have converting their autos to manual.
You wouldn't be the first one to discover shenanigans from the factory..
I have probably added some confusion in this thread. The clutch has always been an on and off again issue with this vehicle, particularly as I have add modifications and is definitely more of an issue when the car is running hard and fully heat soaked. On the last tear down, Larry identified and fixed several issues that had contributed to this - including that the after-market bottom radiator hose was fouling the shift mechanism when hot and under full pressure. The bulkhead, pedal box, master and slave cylinders were also checked and are OK.
The issue we are chasing now is particular to the new "Strapped" CM 850 that was fitted last. This is where the sip and drag issue came together. Previously it was either one or the other. As per Larry, the CM twin disk has a very narrow window of actuation. The clutch that was supplied appeared to have manufacturing/assembly such that one of the two friction disks would always drag AND never fully clamp.
Looks like we have a solution to the issue. Larry believes that the last clutch (a Strapped CM 850) was supplied with the straps on backwards. CM replaced it and the new one seems to work. We will know for sure when the weather dries up enough to test it at >20psi of boost.
Finally got the car back on the road. The original 850 that CM supplied had the straps installed incorrectly. The replacement works and holds the stump-pulling torque this thing makes at 23llb of boost. It was still a bit of an on/off switch but @RealMcCoy figured out how to set it up for better feel with a fabricated over-travel stop and a higher volume slave. Larry also found and fixed several issues with the shifter adjustments.
The result is awesome, it's never shifted this well before, even when new and its totally drivable around town. I just drove it 360 miles back from Medford with a mix of stop and go city driving and some fast twisties - I am really pleased with the outcome. I'm not sure how long my license is going to last though, lol.
Sad to be reviving this thread.
After a few months and ~3000 miles, the clutch drag has slowly returned. Full clutch engagement is still at the top of the pedal travel and hasn't moved, the clutch doesn't slip and when moving (even running hard and hot), it shifts fast and silky smooth - easily the best than it ever has.
But getting into 1st or reverse from a stop has become a real pain, and it will creep very slightly slowly with the clutch fully depressed. It seems to be worse when the car is cold.
I seem to recall @Chris @ Rvenge Performance mentioning something about input shaft alignment and twin disc clutches?
Sad to be reviving this thread.
After a few months and ~3000 miles, the clutch drag has slowly returned. Full clutch engagement is still at the top of the pedal travel and hasn't moved, the clutch doesn't slip and when moving (even running hard and hot), it shifts fast and silky smooth - easily the best than it ever has.
But getting into 1st or reverse from a stop has become a real pain, and it will creep very slightly slowly with the clutch fully depressed. It seems to be worse when the car is cold.
I seem to recall @Chris @ Rvenge Performance mentioning something about input shaft alignment and twin disc clutches?
"Full clutch engagement is still at the top of the pedal travel and hasn't moved, the clutch doesn't slip and when moving (even running hard and hot), it shifts fast and silky smooth"
I find this pretty interesting, I'm having the same issue where my clutch doesn't do anything until the absolute end of the pedal travel, distance between fully disengaged and enagaged is less than an inch, clutch doesn't slip at all and shifts just fine, new master and slave cylinders all adjusted per the service manual
With this, my car is stock and yours is nowhere near that haha
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