Clutch Fork; Solid Mass Flywheel Conversion Issue
Thread Starter
Instructor
Joined: Jul 2019
Posts: 111
Likes: 8
From: Long Beach, California
Clutch Fork; Solid Mass Flywheel Conversion Issue
So I did the solid mass flywheel conversion on my 95. Everything went well as I purchased a nice already surfaced flywheel and pressure plate from a user and got the clutch disk I wanted. I fitted it all and the clutch fork hit. So I cut down the ribbing on the fork to clearance for the pressure plate and everything was working fine. I have out a few thousand miles both street and canyon driving on this now and have not had an issue till today. I noticed a sound at a stop light and realized that it sounded like my clutch fork was hitting the pressure plate AGAIN. I really do not want to take the trans and all that out again without finding out if anyone else has had this problem converting their cars. I read up and down forum posts before I did this swap and never read anything like this happening to anyone else. Nor did I read anyone using a special fork.
Any help or ideas?
Thank You
Any help or ideas?
Thank You
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
Yeah, you should not have had to clearance anything to make this all work. That should have made you stop and reassess everything before putting it back together. Before you tear it all down again, you might try pulling the locking screw from the bellhousing and making sure the fork pivot stud is fully tightened into the bellhousing. If it's backing out (toward the inside) then maybe that can be fixed without pulling the transmission and bellhousing.
Thread Starter
Instructor
Joined: Jul 2019
Posts: 111
Likes: 8
From: Long Beach, California
Yeah, you should not have had to clearance anything to make this all work. That should have made you stop and reassess everything before putting it back together. Before you tear it all down again, you might try pulling the locking screw from the bellhousing and making sure the fork pivot stud is fully tightened into the bellhousing. If it's backing out (toward the inside) then maybe that can be fixed without pulling the transmission and bellhousing.
Plus that locking cover for the fork is covered by the trans when bolted in. I would have to remove the trans to access that cover. Though I had it very tight and the cover on so I do not think it is that backing out, but definitely something to look into.
Drifting
Joined: Jul 2004
Posts: 1,353
Likes: 291
From: MA
I mean it is a clutch that doesn't fit in the car technically etc. so I did not think twice about having to clearance
Plus that locking cover for the fork is covered by the trans when bolted in. I would have to remove the trans to access that cover. Though I had it very tight and the cover on so I do not think it is that backing out, but definitely something to look into.
Plus that locking cover for the fork is covered by the trans when bolted in. I would have to remove the trans to access that cover. Though I had it very tight and the cover on so I do not think it is that backing out, but definitely something to look into.
The design really sucks!!
Pro
Joined: Apr 2018
Posts: 557
Likes: 105
Yes bad design. When I did mine on the my 96 there were wear marks on my pressure plate showing it was rubbing. Bill told me it was a bent fork at the end where the SC puts pressure on it. It looked fine to me no marks or anything. But on his recommendation I went ahead and ordered a new fork and ball stud from Melrose Corvette. This is a new unit. I checked them when I got the new one and sure enough the original was bent just a tiny bit. Install the new fork and new stud and it has plenty of clearance. If you have to grind on it some for clearance you may have weakened it enough to bend over time. If you end up getting another one, which would be a good idea so you know the end is correct geometry. Once you clearance it for the pressure plate take it somewhere have a backbone welded it so you are certain it cant flex.
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
Plus that locking cover for the fork is covered by the trans when bolted in. I would have to remove the trans to access that cover. Though I had it very tight and the cover on so I do not think it is that backing out, but definitely something to look into.
Last edited by MatthewMiller; Dec 21, 2020 at 03:29 PM.
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Thread Starter
Instructor
Joined: Jul 2019
Posts: 111
Likes: 8
From: Long Beach, California
Well seeing as all ZF6 Corvettes came with dual mass flywheels, any non dual mass flywheel set up will not be for the car by definition. Yes I know there are full conversion kits for the cars, but even those while designed for the car are still an aftermarket modification.
I bought mine from a forum member who went another route, so it is the cut down Camaro flywheel, sprung disk, and a vette pressure plate.
I bought mine from a forum member who went another route, so it is the cut down Camaro flywheel, sprung disk, and a vette pressure plate.
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
Well seeing as all ZF6 Corvettes came with dual mass flywheels, any non dual mass flywheel set up will not be for the car by definition. Yes I know there are full conversion kits for the cars, but even those while designed for the car are still an aftermarket modification.
I bought mine from a forum member who went another route, so it is the cut down Camaro flywheel, sprung disk, and a vette pressure plate.
I bought mine from a forum member who went another route, so it is the cut down Camaro flywheel, sprung disk, and a vette pressure plate.
What's the reason for using a flywheel from another application? I'm actually asking - not being rhetorical. There may be a good reason I'm not aware of, but there are lots of options for buying solid flywheels specifically for ZF-equipped C4s, at a variety of weights.
Thread Starter
Instructor
Joined: Jul 2019
Posts: 111
Likes: 8
From: Long Beach, California
Yeah I suppose you have a point there on the term conversion, but i digress not really important.
As for the reason? Well they were done earlier in the car's history due to no one making single mass flywheels so the Camaro one was the only option especially after GM discontinued the dual mass and stock ran out. As for why I did was cost. I could get the whole set for less than half what the cheapest aftermarket option was and those I didn't like. This way I could get a disk I liked.
Since you brought it up i went back and read through the conversation with the seller and actually it was not a Camaro flywheel. It is a Spec flywheel (so made for the C4), and a Valeo replacement pressure plate (OE style). So my guess reading through other's posts is that my disk is thicker than OE (likely is as I put in a dual friction) and that extra spacing is causing over extension of the arm and creating contact with the pressure plate. Since I went and cut the fork to clearance instead of finding out this info my first go around I think the fork has bent. Thank fully I have another and I think will just need to have the pressure plate surface machined down to compensate for the thicker clutch disk.
As for the reason? Well they were done earlier in the car's history due to no one making single mass flywheels so the Camaro one was the only option especially after GM discontinued the dual mass and stock ran out. As for why I did was cost. I could get the whole set for less than half what the cheapest aftermarket option was and those I didn't like. This way I could get a disk I liked.
Since you brought it up i went back and read through the conversation with the seller and actually it was not a Camaro flywheel. It is a Spec flywheel (so made for the C4), and a Valeo replacement pressure plate (OE style). So my guess reading through other's posts is that my disk is thicker than OE (likely is as I put in a dual friction) and that extra spacing is causing over extension of the arm and creating contact with the pressure plate. Since I went and cut the fork to clearance instead of finding out this info my first go around I think the fork has bent. Thank fully I have another and I think will just need to have the pressure plate surface machined down to compensate for the thicker clutch disk.
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
Since you brought it up i went back and read through the conversation with the seller and actually it was not a Camaro flywheel. It is a Spec flywheel (so made for the C4), and a Valeo replacement pressure plate (OE style). So my guess reading through other's posts is that my disk is thicker than OE (likely is as I put in a dual friction) and that extra spacing is causing over extension of the arm and creating contact with the pressure plate. Since I went and cut the fork to clearance instead of finding out this info my first go around I think the fork has bent. Thank fully I have another and I think will just need to have the pressure plate surface machined down to compensate for the thicker clutch disk.
- If the disk is the Centerforce Dual Friction unit, I ran the exact same one in mine with no problems at all (Fidanza aluminum flywheel). I don't think it's different enough in thickness to cause a problem.
- I might be thinking about this backwards, but I think that on a pull-type clutch like in the C4 ZF6, a thicker disk would actually push the TOB further toward the transmission (away from the flywheel), and therefore raise the fork off the pressure plate casting more. IOW, I don't think that could be the cause of your rubbing even if it were the case. That would not have been the case if the flywheel were too thick: in that case the whole clutch assembly would be pushed toward the transmission and possibly cause interference with the fork.
I agree that you most likely have a bent fork, based on the info you've posted. Double check the pivot, of course. If the new fork fits with no rubbing, then you can leave the clutch bolted up. If it still hits the pressure plate, then you should double-check the "height" of the legs on the pressure plate where it bolts to the flywheel. They should be between 0.195"-0.205" from the friction surface. Just make sure. They don't make these new replacement clutches with the same quality as the old US-made Valeos. All of these are made in one foundry in China, regardless of the name on the box. I doubt it's standing too far off the flywheel or else you'd have a problem with pedal engagement height, but just make sure.
Thread Starter
Instructor
Joined: Jul 2019
Posts: 111
Likes: 8
From: Long Beach, California
On the thickness part. If something like the plate was too thick then it would push the on the pressure plate surface. In return this would push the release bearing and the fork towards the rear of the vehicle as the pivot point is to the left of center. This would place the arm in a position that stock would be partially depressed. Assuming the slave cylinder could push the arm more, full engagement would make the arm contact the pressure plate to the left of the pivot point. Of course that is the theoretical version, but that is what was happening on mine.
See this post for similar contact issue. Link should take you to comment #26. Now I do have the short ball which means that it isn't ball length that is the issue.
So my options are 1: ball backed out 2: arm bent or 3: a little of both. My main worry with any of these or course is that it was rubbing there in the first place under first install, which I guess could be the flywheel standoffs. I have some investigating to do.
See this post for similar contact issue. Link should take you to comment #26. Now I do have the short ball which means that it isn't ball length that is the issue.
So my options are 1: ball backed out 2: arm bent or 3: a little of both. My main worry with any of these or course is that it was rubbing there in the first place under first install, which I guess could be the flywheel standoffs. I have some investigating to do.
Le Mans Master
Joined: May 2005
Posts: 7,342
Likes: 2,272
From: Central Maryland
FWIW, I installed a Spec extra-weight, billet SMF in my '94 about eight years ago. I went with a Spec Stage 2 disk, and the Spec PP. I did not replace the fork or pivot ball stud, and have had zero problems with it. No clearance issues when first installed, or at any time since.
Live well,
SJW
Live well,
SJW
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
So my options are 1: ball backed out 2: arm bent or 3: a little of both. My main worry with any of these or course is that it was rubbing there in the first place under first install, which I guess could be the flywheel standoffs. I have some investigating to do.
Pro
Joined: Apr 2018
Posts: 557
Likes: 105
If it didnt rub before and now it does something has changed/bent. There are a few items that can change in the system. The most likely are the fork is bent, the stud is bent or moved, or maybe the TB has a problem of some sort. The pressure plate stand offs would have been a problem at the start.
What stinks is you will have to take it apart to find out. Having done it 3 times myself coming out is pretty quick, going back in the alignment can be a battle.
What stinks is you will have to take it apart to find out. Having done it 3 times myself coming out is pretty quick, going back in the alignment can be a battle.
Safety Car
Joined: Jun 2010
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Drifting
Joined: Apr 2014
Posts: 1,699
Likes: 231
From: Hawthorne CA
When you do get everything figured out and put back together, I had the same issue and figured out it was the wrong (stock) pressure plate. After the pressure plate swap I didn't have interference issue any more but I used the same fork that had been rubbed and then after about 200 miles this happened:
Attachment 48339829 Attachment 48339830 Attachment 48339831[/color]
Attachment 48339829 Attachment 48339830 Attachment 48339831[/color]
Last edited by AgentEran; Dec 26, 2020 at 12:41 PM.