Team,

Looking ahead to try to fix my car's worst attribute...the clutch system.

I'm looking to go the simplest possible way...convert to single mass without the added complexity of the Ram set up.

Zip Corvettes has a conversion kit and so does Carolina Clutch; however, Carolina Clutch has a tech note about balancing the new flywheel based on the existing dual mass flywheel added weights from the factory. Zip Corvette does not mention this at all.

What's the difference here...would Zip's kit set me up for failure?

Thank you for clearing this up.
Ric

 

FYI...from CC's website: When replacing the original dual mass flywheel on the c4 corvette, you must match balance the new solid flywheel to the original dual mass flywheel removed from the car as the original is finely tuned to each individual motor beyong the factory balancing. On the engine side of the dual mass flywheel you will see approximately 30 1/8 inch holes around the outer perimeter next to the ring gear. if any of these holes are filled in the flywheel factory balancing has been altered for your specific engine. Usually if only 1-2 holes have been filled no further balancing is required but if more than 2 holes are filled it is highly recommended the new solid flywheel be matched balanced to the original dual mass to avoid any vibrations thru certain rpm ranges after the installation is complete.

 

The worst the part of the clutch system is all the aftermarket components. The master/slave are poor quality as are the TOB. And the pressure plates are usually poorly machined as well. So if you want simple and a lot headaches. That is your fix. The Ram does solve a lot of the issues, even though it takes more to set up.

 

Never a simple answer, is it?

Regardless... What's the deal with the balancing?

 

I’ve posted about the balancing many times

 

If you have what you believe would help the OP just mention(post a link) the one you believe maybe most valuable OR just post them all(links again). It's much easier for you than suggesting the OP searches for yours!

Searching 'balance' and your user ID I see you've posted in better than 30+ threads!

 

maybe if I have some time I can put in some work to help someone out… but I don’t owe you or anyone here anything.

 

Then there was no purpose for post #5!

 

All good. I'll continue researching.

 

Unfortunately, the reality of match balancing flywheels (and possibly harmonic balancers) on LT1/LT4 engines is real. I had to do this on my 93 LT1 MN6 when I replaced the clutch/flywheel. I was able to do it after the flywheel was installed by using rare earth magnets to get the proper mass and placement of the weight. Then I cut and welded a piece of steel to the flywheel. It worked perfectly but was a total pain in the ***. I believe the weight I added to the outer edge of the flywheel was around 25 grams. Not a lot of weight but enough to cause noticeable vibration.


On my SMFW there is an inner lip, like a dryer drum, where I could temporarily place rare earth magnets and move them around to find the proper mass and placement to eliminate the vibration. Centrifugal force held the magnets in place while I revved the engine.

Once I got the proper mass and location, I cut a piece of steel and welded it to the FW. I cut the steel a few grams light to compensate for the weight of the weld bead.
​
I never heard an explanation as to why GM resorted to individually weighting the FW (and possibly the HB) on the LT1/4 engines when they never resorted to something like this on the L98 engines (which also require a weighted flywheel). Even the SBC400s and the BBC454s required external weighting. But there was always an EXACT spec for the offset weight. Why did GM decide to weight the LT1 individually? It seems like a complete hack job. Like it was too much work/cost to balance the crank and rods during assembly so they just assembled the engine (without checking and adjusting the weight of the parts) and then got the motors in balance through "fine tuning" of the FW and HB.

Correct me if I'm off base. But I would really like to understand what the logic was there.
​​

 

Oh man, don't get me started. Some of quirks on the C4 are absolutely maddening. I'll leave it at that.


- Anyway, what SMFW kit did you use?
- Any issues with gear rattle?
- I assume you had access to the FW by removing the inspection plate?
- You free revved the engine until you felt the engine smooth out?

Way to think out of the box!

Ric

 

You dont owe anybody... Then why are you here? Then why would you waste your precious time with a completely worthless recommendation?

 

Match balancing to the OEM setup is probably the best since the LT4's had an additional fine tuning balance done on them.

However, I did not have that option. I bought the LT4 with a solid flywheel (SPEC). It had a bad vibration at anything over 3000 rpm. I had nothing to help me get back to the original balance.

I went with a balance based off of the L98/LT1/LT4 engines. There is a certain amount of imbalance that is the normal for them. I actually used a dual mass flywheel from an '90 L98. With the stock flywheel, pressure plate, disk, and TO bearing the car now revs to redline with no vibration.

I had Jim Jandik at Powertorque Systems check out the SPEC flywheel balance and found it was 20 gr. off . He rebalanced it to the stock amount of imbalance for an L98/LT1/LT4 for me. He was also one of the few that could rebalance a dual mass flywheel, but I think he is now out of business.

In short, match balancing is probably the best, but you can get acceptable results using the factory amount of imbalance on the flywheel. The factory used that method for all the L98's and LT1's.

Good luck with your project.

PS. If you are trying to fine tune the balance on a dual mass flywheel, see my post with the procedure.
https://www.corvetteforum.com/forums...post1597626151

 

I also have an LT-4 and it has a pretty robust amount of vibration at 3K and above. It doesn't matter whether I free rev it or rev it up in gear. At WOT and in gear, the vibrations are felt throughout the entire car.
I don't know for sure, but I'm pretty certain my clutch system is all stock. If that's the case, my DMFW must be out of balance.

Incidentally, I had my dual-mass damper rebuilt by DamperDoctor. It had one weight in one of the front facing balancing holes. It came back without it. Then again, the relationship between the pulley, the inner and outer weights was changed anyway. Somehow, the engine is actually a tiny bit smoother than it was before.

 

The flywheel is a Centerforce Billet Steel 700175. I believe the clutch and PP were also Centerforce units.

There's the typical gear rollover noise under load at low rpm. Doesn't bother me.

Yes, access through the inspection cover.

I used rare earth magnets as temporary weights inside the lip of the SMFW. Start with about 20 grams of magnet weight. You'll feel a difference right away when you start the engine and rev it up. Turn the engine off and slide that 20 grams of magnetic weight a few inches over and retest. Keep doing this until you find the location where the engine feels the smoothest. Then mark that location. And then add and subtract weight until the engine is as smooth as possible. Then you have to remove the magnets and weigh them. Then weld a permanent weight to the flywheel. Did I mention that this process was a Pain in the ***? But it did work for me.

 

Thank goodness for all the crafty people we have here in the forums. Yes, it really sounds like a royal pain, primarily due to the constant repositioning and getting under the car, etc.

As an alternative, I could glue to magnets with some industrial glue.

Thank you so much

 

OK, I just went through the document on the link you posted. I'll try to summarize it, so please correct anything that's wrong.

1- There was a DM flywheel update/change in late 1991, which appears to be the cause of engine vibrations at 3K RPMs and higher
2- Vibrations only affect L-98 and LT-1 engines (and unbeknownst to them at the time, the LT-4 engines as well). The LT-5 is not affected
3- 33-3500, 4200, and 4700 RPMs are when these vibrations are felt the most
4- The imbalance is somewhere between 90* and 195*, or put a different way, upper/right quadrant of the flywheel (when viewed front to back, cast-in counterweight straight down)

5- Four different balancing procedures were identified to correct 90% of imbalance problems

6- Begin balancing process by placing the GM specified weights as depicted in “Trial 1” or weights in the 150*, 165*, 180*, and 195* position.

7- Free-rev the engine with the clutch in between 4K and 5K RPMs. With weights in these positions, 50% of the problem vehicles would be fixed. No more vibrations above 3K RPMs.

8- If “Trial 1” does not fix the vibration, remove weights and reposition on “Trial 2” position and repeat the free-rev test. Move on to “Trial 3 and 4” if vibrations continue.

9- The amount of weight added varies from 51 grams to as much as 106 grams. This is way more than the often mentioned 20-25 grams.

10- Balancing weights

I am tempted to try this.

 

OK... sorry for the delay... haven't had a chance to get on the computer at home. The cranks for the 1RMS SBC's are balanced as an assembly from the factory. This is a zero balance on the nose, and the flywheel balance spec 23.4 oz/in. They make solid 23.4 oz/in flywheels just for this purpose, but not many options for the ZF spec flywheel (slightly shallower.)

Fidanza and Spec have aluminum flywheels with the correct depth and the dish for the spring package on the clutch plate, with bolt on kits available for 23.4 oz/in. There's probably a billet steel one for many others, but you will have to cal them up and order it properly.

For example, on a Fidanza flywheel, weight kit 337775 -- zero balance the flywheel (they seem to be slightly underweight at the weight location, usually takes a bolt or two) and then add 5.2oz @ 4.50" for the weight location to achieve 23.4 oz/in. Here's the part for that (slightly overweight BTW, I can't remember but probably 0.1-0.2oz):

https://www.summitracing.com/search?...word=337775%20

BTW here's the kit for McLoud, couldn't find the one for SPEC:

https://www.summitracing.com/parts/m...make/chevrolet

 

Thank you all for all the information. Things are way more clear now.

One more question though...please explain the oz/in measurements. What exactly does oz/in mean?

 

UNITS OF UNBALANCE:
Balance corrections are normally specified as a weight added or removed at a radius. The weight or
mass units can be any convenient units of measure. The most commonly used weight units are
ounces (oz) or occasionally pounds (lbs) and the most common mass units are grams (g) or
kilograms (kg). The capacity and accuracy of the weighing equipment available must be taken into
account to ensure that weight precision is sufficient to the task. Occasionally the weight units,
Newtons (N), are specified, but for practical use must be converted to a more common weight scale
unit. Length units usually correspond to the manufacturer’s standard drawing length units. Most
commonly these are inches (in) or millimeters (mm). The most common combinations used to specify
unbalance are ounce·inches (oz·in), gram·inches (g·in), gram·millimeters (g·mm), gram·centimeters
(g·cm), and kilogram·meters (kg·m). The order in which the units are expressed is not important, 1
in·oz = 1 oz·in.