Martin, in the thread you link to there is some confusion about the correct terminology. All clutches for the C3 Corvette have the "bent finger design". A flat finger clutch (which was used in the older C2 cars) have the clutch fingers parallel to the flywheel and uses a longer throw out bearing.

Faster Rat uses the term "curved fingers" for clutches where the part of the clutch fingers, that touch the throw out bearing, are bent backwards. I think this is a much better design than the Sachs design which is also a bent finger design, but has straight "finger ends".
Go with either a Luk or Centerforce clutch, they both work and fit.

 

I also have this problem on my 69 427/390. I believe that if you reface the fly wheel you need to go to a longer ball stud in order to keep the release lever at the correct angle. The best answer seems to be to use a adjustable ball stud. Unfortunately, these install from inside the bell housing, but then they are adjustable from the outside so that you can fine tune the linkage.
I also remember reading that there are long and short throwout bearings. Might be something to look in to.

 

LUK Repset 04-049 ordered. Should be here in a few days. Will be interesting to see if it makes a difference.

Sweden is showing its best sides now. It very nice weather, late spring/early summer. If anyone ever considering a visit to Sweden, this is the time of the year.

Major car shows coming up very soon, the most important one is Power Big Meet in Vasteras early July. bigmeet.com Over 20000 american cars. I think its the biggest car show in the world these days. Absolutely worth a visit.

/Martin

 

Today I pulled the transmission out and the Sachs clutch also, the LUK kit is ready for installation. Here's what I have:

Sachs kit: K5552-03
LUK: 04-049
Old (that was in the car): Unknown

Here are some pictures:

Ball studs. To the left is a new one from Corvette Central, in the middle the one that was in the car, and to the right the CA stud. I will use the new short one from Corvette Central.



Release bearings. To the left is the LUK bearing, in the middle the old one, and to the right the Sachs bearing. I see no reason for not using the LUK one. One major difference I can see is that it's partly made of some sort of composite plastic material.



LUK pressure plate:



Old pressure plate:



Sachs pressure plate:



I'm going to bolt everything back up very soon - if anyone has any suggestions, or if I should do any more measurements please step in.

Will be very interesting to see if the LUK kit gives a better pedal feel and not requires pedal in the floor mat for a release.

Martin

 

Finally found time to reassemble everything back with the new LUK Repset clutch. Now the clutch fully releases without any problems at all. Perhaps still a bit far down on the pedal travel, but absolutely not a problem.

Unfortunately, when I crawled udner the car when idling to check how the TO bearing contacted the pressure plate fingers, I noticed that the fork wobbled quite significantly when TO bearing just starting to touch the fingers. This pulsation could also be felt in the pedal when just touching the TO bearing to the fingers. At higher rpm's it can easily be felt and it does not give the quality feel of a newly installed clutch.

So after a sleepless night, I teared down the clutch again. For the third time. Took less than one hour. A close examination of the fingers shows that they were quite unparallell and flimsy located:



I did compare with pictures I took before installation, and the same problem can be seen there. This leads to an uneven TO bearing contact with the fingers just when it touches. When pedal was pressed further down there were absolutely no pulsation felt. Just when riding the TO bearing on the fingers.

Not easy to replace this clutch. Tired...as for now I probably reuse the old clutch and use the new Sachs TO bearing. Since it was only the TO bearing that was bad from the very start...

 

Does the clutch engage smooth or does the car chatter? I was able to feel my clutch rumble a little but not pulsate. You might want to return that pressure plate or entire clutch for another brand? I used Hayes clutch kit listed as the stock replacement.

Also make sure your z bar and fork are straight if they are original. Its not uncommon to have an egged out hole or a bent fork

 

Yes, with the LUK clutch it enages smoth and nice, no chatter. Only disturbing thing is the clutch pedal pulsation.

I have installed the old clutch disc and old pressure plate with the new Sachs throw out bearing. No pulsation and a decent release Point. Just got back from a 650mile drive to Power Big Meet this weekend, and all worked quite good. The only annoying thing with the old clutch is that it has a tendency when hot to require more pedal travel before a full release. Don't know what can cause that though.

I have contacted the seller of the LUK kit and see if they are willing to send over a new kit, since my current one is obviously damaged one way or other.

I replaced the clutch fork and ball stud when I first started this little exercise, since it's so easy to do when everything is apart.

We'll see what happens. I keep posting the progress here....

Martin

 

One year later:

The unknown brand stock clutch have been working the last year without any incidents. ONLY thing is that the release point on the clutch moves down towards the floor when car gets really warm, i.e. cruising at car shows etc.

Something bad happened this weekend though at Power Big Meet Saturday night cruise. I could feel a clutch slippage at low speed, and the release point was much lower than usual. After some initial checks at the roadside I could readjust the linkage to have a full release and get home in one pice. When releasing the clutch, a very significant vibration could be felt when clutch started to engage.

Teared down yesterday. This is what I discovered:



This is the throw out bearing from the new Sachs kit, i.e. this bearing is not more than 1 year old. HOW could a failure like this happen?? Can I have done something wrong in the installation of the tko? The clutch fork is brand new...and seem to have survived.

One pice of the TKO wrecked havoc on the pressure plate springs, so now I'm changing everything. Again.

Now I have ordered in:

- Centerforce Dual Friction clutch kit P/N DF735552
- Centerforce tko bearing P/N N1716
- Adjustable ball pivot stud (didnät check the brand)

Anyone running this setup with known good results? Or am I wasting more money here.

The shop did also have McLeod 75124...

Its hard to get a "true" feel of what works. After reading some people really hate the CF clutch, and claims they destroy flywheels, does not work with Corvette linkage etc. etc. etc.

I guess we'll see...

Martin

 

Finally found some time to install:

- New Centerforce dual friction clutch kit
- New Centerforce throw out bearing
- Clutch fork is only 1 year old, reused that
- New ball pivot stud, the longer version to have the correct distance as per CF instructions (4.75").
- Original bellhousing
- Did not change pilot busihing, as this is only 1 year old also, with very low milage, non magnetic bronze type
- New Z-bar and clutch rods

Pedal feeling is great. Very, very happy with that. Very easy to shift through gears and reverse also. Couldn't be better.

BUT.

The car has a shudder precisely when the clutch starts to engage. It's not extremely violent, but bad enough for me not being satisfied with this yet. The shudder goes away *completely* when pedal is released ever so slightly. Shudder is worst on 1st gear and reverse. I can also feel the shudder when shifting down through gears when coming to a stop.

Now, the speed shop that sold the clutch did not recommend me to resurface the flywheel since it was not burnt, cracked and apparently looked straight (checked that with a straight edge). I can't rule out the flywheel completely of course. I was also in a bit of a hurry to get the car back on the road for some major car shows over here, and all the machine shops are closed for summer vacation (1 month with entire country shut down). Start to regret this decision now though....would have been better to use a new flywheel I think.

I have driven the car for say 150 miles this weekend. Only relaxed around town driving, no abuse what so ever. Should I hope that this shudder goes away when the disc is "worn in"? Or could it be something else that shows up with the new clutch kit? Transmission mount is new, drive shaft U-joints are new (from trans to diff).

I can change the engine mounts and half shaft U-joints first, since that's nothing compared to pulling the trans out again. But I suspect the transmission jack will be rolled out very soon again...

But is was a nice car show this weekend though.

Martin

 

When I installed the Centerforce clutch on my '68 I did use a Centerforce flywheel. I found that the clutch need actually needs some 'abuse' before it bedded-in. My new engine was rated at 528 bhp and demolished one new engine mount within a hundred yards. Poly mounts are a good investment.

 

Update:

New engine mounts, but with no difference. No real surprise, the old ones was in quite OK condition.

So today I teared down everything again, to have the stock 68 flywheel resurfaced. It have some obvious "hard" spots, that might be causing the chatter. I regret I did not resurface when I first installed the new Centerforce DF clutch kit. I have only driven the car 200-300miles, so I hope I have not caused damage to the clutch disc and pressure plate surface...

I will install a new pilot bearing also, even if the old one was also quite new.

We'll see what happens.

It took only 1 hour and 5 minutes from start to transmission on the floor this time.

Martin

 

Did you have some chatter also when the clutch just started to pull in?

Martin