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DansYellow66 Just wondering if using a straight versus bent finger Pressure plate makes that much difference if you obtain a good release number(.360") on the McLeod(flat finger). versus (.680") on the LUK which was a bent finger P/P. As pointed out in the other thread, I've had both flat and bent finger P/P installed with no noticeable difference in clutch engagement. Hopefully with this McLeod installed even though its flat finger, I should notice a difference. Also using the 1 1/4" T/O/B. Anyway's we'll see. Just haven't had time to finish it off as I've had stomach flu the last couple of days. Hopefully will try to finish up this weekend.
I'm not really sure - I wasn't aware that the flat finger clutch will release with half the travel of a bent finger clutch. Not sure how they would accomplish that - seems like it would reduce the mechanical leverage and increase pedal pressure. From memory (and it may be wrong) I thought the bad rap diaphragm clutches got years ago was from the flat finger ones going over center and sticking to the floor at high rpm. And the bent finger pressure plates was the answer to that. If that's in LARS thread I may need to go back and read it again.
We've been through this same type of clutch issue probably 100 times in the last 15 years, and it always boils down to the same root cause - if you use the right parts, the clutch system works - if even one part isn't correct, it won't. Yes, it's as simple as that.
It starts with the correct bent-finger diaphragm clutch pressure plate and disc, the correct "short" (1-1/4") throwout bearing, the right clutch fork, the #3729000 (1-1/2") clutch fork ball stud, the right pedal-to-Z-bar and Z-bar-to-clutch fork pushrods, and the correct Z-bar. The Corvette is extremely sensitive to having the correct parts in the clutch and linkage system; if any one of these parts is Bubba-modified, substituted, or otherwise messed with, clutch problems are guaranteed.
The only things in this assembly that are different are the flywheel, clutch disc and pressure plate. We got it out today and the problem is that the clutch is almost 1/2" taller than the old one. You can see where the fork is hitting the clutch cover. Other than putting the stock clutch back in I'm not sure what will work.
It looks like the ball is worn out too, so I'll get him to order one along with the fork.
What brand of performance clutch works in this car?
Wow - that's a mess? Do you know what brand clutch that is? I haven't seen anything like that show up here before. I would go with McLeod. Order it specific to the car and not by just picking a number out of their catalog. Let McLeod select the clutch for the car and it's purpose.
And as I'm sure you already know - everything inside there needs to be replaced. I'm amazed at the wear on the clutch fork. I hope the guy hasn't ruined his thrust bearing on the crank. If so he should sue the store that sold him that clutch.
This clutch has maybe 30 seconds on it, at least at full engagement. It went in with a new engine, flywheel, pilot bushing and throwout bearing. With the clutch engaged the fork hit the clutch cover.
It appears that the pressure plate (clutch cover) is taller than it should be. Here's a few measurements I made recently for Corvette flywheels and pressure plate:
Back of block to flywheel face:
L76 30 lb flywheel - 1 5/8 inch
L88 15 lb flywheel - 1 5/8 inch
Flywheel face to tips of clutch fingers with a clutch disk sandwiched between:
L88 clutch - 2 1/2 inches
IIRC this heavy duty clutch was used in other than L88 applications, such as L78 and LT1.
To work with stock clutch linkages, the total measurement from the back of the block to the tips of the fingers with the clutch disk installed should be 4 1/8 inches, assuming usage of the short throwout bearing (1 1/4").
Summit told me this one fits, but I’m leery of it because a 64 Impala used a flat finger clutch and this is a bent finger clutch, which is what Corvettes used. It also has no HP rating, but the guy says it’s good for 550 hp. From what I’ve read, the 92760 Muscle Car Kit is the same pressure plate as the 98760 PowerGrip Kit but with an organic disc instead of a Kevlar/metallic/organic disc. RAM’s website describes the disc as taking the clutch to 550 HP, implying that the one with the organic disc would be less, but they offer no rating for that one. Also, the 92760 is $203 while the 98760 is $337. If the only difference is the disc, the extra $135 must be for a reason. It also lists applications as GM passenger car, which originally used different clutches than Corvettes.
I would call McLeod's tech line and talk to them directly. Tell them what your friend has and let them recommend the clutch. I would not rely on a Summit tech guy.
I wonder if there is any difference in the dimensional relationships with a second generation block and flywheel that needs to be accounted for when using stock bellhousing? Is the flywheel surface to rear block machined face dimension the same as for an original 327 block?
I called and talked to McLeod's tech line. According to this guy, the problem is the flywheel. All Generation II LT blocks used a hydraulic pull-type clutch and the flywheel will not work with a push-type clutch. He said what we need is their conversion flywheel, which will bolt to the LT crank with the one piece rear main seal and work with the old style push-type clutch, along with a counterweight kit for the external balance LT crank. He said I might get lucky with finding a clutch that would work with the flywheel we have but it wouldn't be right even if it did. So, Mark's head is exploding because he has to spend another thousand bucks, but...
I called and talked to McLeod's tech line. According to this guy, the problem is the flywheel. All Generation II LT blocks uses a hydraulic pull-type clutch and the flywheel will not work with a push-type clutch. What we need is their conversion flywheel, which will bolt to the LT crank with the one piece rear main seal and work with the old style push-type clutch, along with a counterweight kit for the external balance LT crank. He said I might get lucky with finding a clutch that would work with the flywheel we have but it wouldn't be right even if it did. So, Mark's head is exploding because he has to spend another thousand bucks, but...
doesn't make sense unless the McLeod pressure plate is an odd configuration. I use a standard GM flywheel, bellhousing, and LUK clutch kit with my ZZ4 and have no problems.
Bill
I called and talked to McLeod's tech line. According to this guy, the problem is the flywheel. All Generation II LT blocks uses a hydraulic pull-type clutch and the flywheel will not work with a push-type clutch.
Hogwash. The kid at McLeod's needs to go back to the high school he just graduated from and pay attention this time. His manager has taught him to sell flywheels, not how to solve problems.
Hogwash. The kid at McLeod's needs to go back to the high school he just graduated from and pay attention this time. His manager has taught him to sell flywheels, not how to solve problems.
Doesn't matter to the flywheel whether the clutch is pull-type or push-type - it just smooths the crankshaft firing pulses, provides a friction surface for the clutch disc, and supplies gear teeth for the starter.
If the flywheel is thicker it will space the clutch further back into the bellhousing, whioch would change the geometry of the fork. That's the problem - the clutch is either too thick or too far back.
More research... I'm finally learning about new stuff instead of the usual muscle-car era stuff I'm used to. Yes, LT blocks used pull-type clutches, but the one piece rear main seal with the new flywheel started in 86 and went through 2002 on the gen 1 blocks, and from 92 to 87 on the gen 2 blocks, and there was no difference. Looks like he just needs the clutch. Now I'm back to the question - what clutch? I'm guessing the one the McLeod tech recommended will work.
I'm almost sorry I kept suggesting to talk to McLeod after that experience.
The installed pressure plate thickness is the key here. If you can get that dimension and match it closely to the OEM clutch dimension, it should be workable. I would reference everything from the engine block bellhousing mating surface. I would suggest investing in either an adjustable pivot ball (what I would do) or one of the new adjustable length TO bearings. Then do a careful set up or mock up to position the clutch fork when the clutch is let out or engaged. I would set the fork about 3/8 inch clear of the front of the bellhousing opening. That will allow a little room for clutch wear which will extend the fingers back and the outer end of the fork forward over time.
More research... I'm finally learning about new stuff instead of the usual muscle-car era stuff I'm used to. Yes, LT blocks used pull-type clutches, but the one piece rear main seal with the new flywheel started in 86 and went through 2002 on the gen 1 blocks, and from 92 to 87 on the gen 2 blocks, and there was no difference. Looks like he just needs the clutch. Now I'm back to the question - what clutch? I'm guessing the one the McLeod tech recommended will work.
Quit guessing and make the measurements in Post #27. Let us know what you have.
Quit guessing and make the measurements in Post #27. Let us know what you have.
I can't do that until Mark gets a clutch. I tried to get him to measure the block face to flywheel mating surface, but that would mean he had to get under the car and he absolutely refuses to do that. He should have the clutch by Friday, so I'll install it and check the measurements.
02-12-2016, 05:39 PM
