strand rider

If you have a convertible , it was hot balanced.

I got that from info posted here, so don't bet large sums on the accuracy, as I kind of tuned out my memory once I found out about my situation, but have found all the assembly and balance specifics from kicking around here.

if it helps, I went with a McLoed RST with steel flywheel, looking for a light clutch pedal action. C6 master , don'y know why, followed the GM partshouse parts guy's suggestions.
It drives easily, nothing out of the ordinary, modulating the clutch is not a concern, engagement is easily controlled, you could slip it as long as you want.

I had the clutch assembly balanced, said by some sellers to be un needed with the build tolerances on this part (which seems to be true) ,but offered by the builder, so I got that, and the weights were transferred out from the old clutch. I might have overdone it with the balance, but at the labor rates involved, I wasn't wanting to under do it. Besides, with this kind of deal, the finer the balance, the better it runs. I hope.

thbwlZ

You did everything pretty close, by at least transferring the weights, but it is most likely not the same as what it was stock. FW and PP individual balance tolerances vary enough to make just transferring weights not the ideal method. As long as you are running smooth and you can't feel any new vibrations, you are good. This is only about minimizing NVH/vibrations. The engine is fine with just a closely zero balanced clutch on it.

racebum

i think this is why GM updated the book to say not to change the weights

if the OE clutch was 10g out at 3 oclock and the new clutch is 10g out at 7oclock adding the weights isn't going to have the same effect and may make it worse

lionelhutz

I've actually never read of a case where a clutch that was confirmed to be very close to zero balanced still vibrated. I actually suspect the "hot" balance was done to correct a factory clutch too far out of balance.

People who do bother to balance a replacement either install the clutch and have a vibration then do it again match balancing to the original or they just match to the original right from the start. I have read of a few cases where the person with a vibration found the replacement clutch was way out of balance.

I have yet to read of a case where the replacement clutch vibrated even though the balance of the replacement was confirmed to be very close to zero balance.

thbwlZ

I apologize if this comes across as terse or my being frustrated. After becoming so frustrated with reading all the "guesses" and "theories" about balance of clutches in corvettes, I did a lot of research and talked to the people involved doing the hot balance (those who did it currently at the time). I also talked to engineers who were involved in the past C5 segments, with the hot balance. I wanted to cut through all the BS and guessing. I did that. I got the real explanations from the real people who know.
So, I'm not trying to be a jerk, I'm only trying to correct information when I see it, and know for a fact that it is incorrect.
RANT OVER
And lionelhutz is one of the most knowledgeable and accurate contributors on this site, that I have seen, so this is not a criticism of his post.

thbwlZ

Exactly! Transferring weights was not the "be all end all", for those exact reasons. Flywheels and Pressure Plates have THEIR OWN IMBALANCES and balance tolerances. Combinations are infinite.

lionelhutz

thbwlZ - I have read a number of threads where clutches that are supposed to be zero balanced still vibrated, but in all of those cases the clutch was never put on a balancing machine before installation. Just saying what I have read mostly on this forum.

I do agree that the engine could have had some imbalance that the procedure corrected.

racebum

as we're talking about, even if the clutch is exactly zero, some engines were out more than .5oz final and used an offset balanced clutch to correct the engine. this is no different than adding weights to a wheel

thbwlZ

Believe it. With what I found out about all the individual tolerances, both the flywheel and pressure plates could be within their individual balance tolerances, as delivered, and combine to be above the 0.5oz∙in engine assy requirement. Also, the "as built" balance tolerance of the engine's internals is "well above" the 0.5 oz∙in final requirement, because the 0.5 is only for manual transmission vettes. The engine can be well outside of that 0.5 and be fine as far as reliable operation goes. So they developed the hot balance procedure to get the entire engine assy down to 0.5 oz∙in or better. The weights added in the flywheel can be dealing with imbalances from the flywheel only, the pressure plate only, the engine only, a combination of all three, or any combination of the three. In MOST cases it is a combination of all three, because all will have some variance above zero balanced, and they all contribute. There are so many combinations and possibilities as to what the FW/PP combo "needs" to be, with or without added weights, that the only way to know is to have your stock combo checked for its state of balance.

Many people can just install a zero balanced unit, or a unit right out of the box and be fine, with no vibrations. Or they might have slight vibrations, but the engine is still fine. But there are also many that will vibrate like crazy that way. It is such a PIA to pull the drivetrain, and very expensive unless you do it yourself, that changing a clutch multiple times to chase vibrations is just crazy. It so relatively cheap to have your replacement unit matched to your stock unit, zeroed, slightly out from zero, or more out from zero, whatever it happens to be, that I just think it's well worth the effort to have them matched. Anything else is a guess. If it didn't vibrate before, it won't vibrate afterwards, if you replace the clutch with something that matches it with respect to balance. I hope no one can disagree with that. But, as I'm also finding out, finding a machine shop that can actually match a balance setup instead of just zeroing everything, is more difficult than it should be. It's kind of like a cashier that relies completely on the computer screen to tell you your change, and you screw them up when giving them additional money or something to round it off. They can't do the math! If the computer can't tell them, they don't know how to do it. Zero balancing a rotating component means getting its CG to be on the axis of rotation. All the balancing equipment is setup to do that. MATCHING an imbalance situation, purposefully, means moving the CG to wherever it needs to be to create the imbalance. They would need to do that vector math separately, and it seems that is too difficult for many shops. Oh well!

In the end, I'm sure people will just continue to do things the way they have for the last 17 years with these things, and just pop in a clutch out of the box. Many will be fine, and some will drive themselves crazy trying to chase new vibrations. If its done at a dealership, they will just keep popping in new clutches until one "magically" works. That's cool.

john8642

If you're not doing the work yourself, it seems like you're at the mercy of whatever shop you use. I've been shopping around for labor estimates, and in SoCal they run between $900-$1200. Can I expect a shop to do the extra work to match the balance? I don't want to have to do this twice.

thbwlZ

Unfortunately, you probably will not find a shop that is even aware of the hot balance procedure done at the factory. They won't know what you are talking about. They will not believe that some assemblies are counterbalanced on purpose. They will most likely insist that you need to just install a zero balanced clutch. They will tell you to just install it out of the box. If you get a "good one" they may tell you to go ahead and have the new one checked, and further zero balanced, which completely misses the point.

Unfortunately, about the only way to go about it ONCE, is to do the labor of the clutch swap yourself. Take your stock FW/PP to a competent machine shop that can balance clutches, and ask them to MATCH your replacement combo to your original combo. If they say they can't do that, they can only zero them, then that's not good enough. Don't use them. If they insist that LS engines are internally balanced (which they are, by design) and therefore only require a zero balanced clutch assembly (which they often don't), then they don't understand the issue here. Good luck explaining it to them. About the only chance you have of getting them to understand is to just say you have an externally balanced engine and you would like for your entire clutch assembly (FW and PP) to match your original clutch assembly (FW and PP). Then maybe they will do that.

If you are doing it at a dealership, they will most likely NOT do any of this, and will not get it either. However, if you do it at a dealership, the work will be warrantied, and if it vibrates when done, they will have to do it again. They will keep swapping out new clutch assemblies until one doesn't vibrate. And if that doesn't happen, and you complain enough, they will maybe send out field engineers to do an in car balance. This has happened MANY MORE times than you would believe is possible. It's really such a simple matter. Make your replacement clutch the same as what you are replacing. If it didn't vibrate before because of balance, it won't vibrate afterwards because of balance. But I'm finding most people just don't get it.

Ask around some of the shops you have been asking for quotes. Ask them if they are familiar with the match balancing issue. Unfortunately, most will say "no".

john8642

Thanks for the reply. I'm not able to do the work myself, so I guess I'll check back at the shops I've talked to, and if all else fails, just have the new assembly zero balanced and hope for the best. I've bought the new parts already, so I doubt a dealer would warranty the work unless they supplied the parts. Thanks again for the information.

racebum

labor will be outrageous if you do a match balance. you will tie up one of their lifts for 2-3 days while the machine shop match balances it

john8642

That's what I figured. Most likely, I'll just have the new parts zero balanced and hope for the best.

thbwlZ

At least by having your replacement clutch checked and balancing it as close to zero as possible, you will ensure that you aren't introducing any new imbalances to the equation. You will only have the small imbalances from the engine rotating assembly, and your engine will be fine. You will either end up with operation that is as smooth as before, smoother than before, or has some vibrations you can feel. But your engine is fine in all cases. If you end up with new vibrations, and you want to get rid of them, there is a fairly easy way to do an 'in car balance" of the assembly, assuming you can easily get access to work underneath the vehicle. Again, this IS about NVH, and IS NOT about reliable engine operation.

Good luck!