Hey all,

So I started a thread a while ago about vibration at 3k rpm and have settled on it being an unbalanced flywheel.

It is the original or at least it is an a OE type DMF, but I do not know if previous owner messed with the weights if he swapped in a new one or, well, or if he installed it incorrectly, or maybe screwed up the throw out bearing. Geez, I have no clue what's causing my issue.

I wanted some advice on swapping to a SMF. What does it take? Is there balancing involved? Balancing that involves taking the motor out? It makes sound at idle without the clutch depressed, right?

What am I looking at? Some of the reading I've done seems to point to there being a helluva lot less headache with the SMF, but with noise. Is that about the gist of it?

I've been looking for any Vette specialists who's brains I could pick, or even hire to do the job, out here in San Antonio and have found none at all.

Any and all info would be greatly appreciated.

 

I wonder that before you start assuming, maybe there's an electronic diagnosis to remove the WAG? I've never seen an EVA(Electronic Vibration Analysis) used for engine diagnostics but certainly have seen them used for 'drive-line' vibrations and location on the car for wheel related issues. Could it be done for your issue? I'd think so.

Today everyone says 'There's an app for that' so ... yes there just might be?

https://vibratesoftware.com/

This fellow has several very interesting videos diagnostics for EVA and NVH, I've included just one I believe there are 5 or more.

The latest/newer?
A video for engine vibrations using the app?

 

Dave you've got such a wealth of information. I appreciate you. I'll check that stuff out.

What do you think about the swap though? Is it overall a less problematic system having a SMF vs. DMF?

 

Bumping this guy.

I've also read that some shops use auto transmissions to balance new flywheels for people.

I'm having trouble finding any shops that do that sort of thing or any Corvette shops here in San Antonio for that matter.

I've pm'd a few people from the forum that have claimed to have gotten this done, but haven't received a response, but I think that because those posts were kind of old, they either don't have those cars anymore or aren't active on the forum.

Hoping someone with experience with this will chime in. I'm a mechanic, but admittedly have little to know experience with manual transmissions, much less on a 29 year old Vette, haha. I'm used to just slapping a flex plate onto a crank, connecting the converter, and moving on 😁

I just want to make sure that I know what's involved so that a) I don't screw something up, b) I can identify if a shop knows what they're talking about, and c) I don't get screwed by said shop.

Dang I loathe the idea of taking it somewhere. If I could get all the pertinent info and feel confident to tackle it myself, that is definitely preferable. Except of course for the balancing of that's required.

Thanks all.

 

You might want to give Bill Boudreaux a call at 602-319-6575 (ZF Doc). He is infinitely knowledgeable on all things ZF6 transmissions and associated parts (flywheels).

 

Hey Ss,

I will try Bill again. I have sent him a few emails without response. Is his shop still pretty active then?

 

Been awhile since I talked with him. I hope he is still doing business.

 

He is, spent an hour on the phone with him yesterday. What a super cool dude!

I got some direction on what to check, but still waiting on him to send some pictures.

He's telling me my pressure plate might be unbalanced if it was changed out.

 

Does anyone have any suggestions for a full flywheel clutch pressure plate system?

What do you guys think of the RAM clutch conversion kit?

Has anyone here used this system?

 

Ok reviving again,

So I discovered that it is the flywheel. I spoke wil Bill at zfdoc and he was very helpful in getting me a little further down the right path. I found marked spots on my flywheel where the factory likely intended to put weights. There weren't any there. I put some there and the vibration improved, but it's still there damn it.

Does anyone have any experience with this or input on how to best balance this thing less taking the engine out?

I feel like I'm at the end of my rope here for lack of knowledge on how to proceed. I don't have a ton of money to drop on this vehicle for repairs since I just dropped a bunch buying it LOL.

If anyone has dealt with this, please help. I would be forever grateful! 🥲

 

I’m not sure I understand, did you replace the flywheel or trying to balance the DMF with everything installed on the car?

the balance for the single piece rear main seal Gen1 or Gen2 engines is 23.4 oz/in at the flywheel, and zero balance at the front end.

there are cast flywheels with that built in, and they sell aftermarket flywheels that have a set of weights you can bolt on for that 23.4 oz/in balance. The trick on the SMF is that it needs a fairly deep dish to make room for the sprung hub of the clutch friction disc, the DMF uses a solid hub

Edit: What should you do? You cant balance that heavy DMF once it looses balance, it's garbage. Call McLoud, call RAM, call ZFDoc, call Caroline Clutch and and order a flywheel and clutch disc, tell them what you need, I don't think we can do that for you. We've provided you with the information you've requested, perhaps re-read slowly, and let us know what part is not understood.

 

Ok, I'll explain and please excuse any ignorance lol. I purchased this car with the vibration. I didn't know it was there because I didn't push it hard when I purchased it because there were no highways near by to actually open her up. I was in town. This was my bad, I should've found a way to take it to a highway.

Getting the car on a lift, I noticed that the inspection cover was not installed. It has the stock DMF. Inspecting the flywheel, I noticed that there was only one weight on at 165 degrees, nowhere else. There were white markings along the flywheel at various holes (including 165) that Bill (ZFDOC) tells me are markings from the factory during balancing. The markings don't all look the same. Some holes had what looked like a 1 on one side of the hole and a 7 on the other side, others had what looked like a 3, others a 9 or 6. And another hole was just circled. All with the same marker. The previous owner messed with the flywheel, but I'm not sure why or what he did.

I purchased the weights for this flywheel and before I fully understood the weights thing, I used the tech data that's been floating around that gives you 4 trials for adding weights. I tried the first trial and it didn't really do anything. Then after speaking with Bill and learning a little about the marks, I realized I was starting off on the wrong foot with no weights in it to begin with (except for the one at 165). I removed the trial weights and added to the marked holes instead. Now I'm back at square one. It DID improve the vibration, but did not eliminate it. With the weights that are in there now, (I can take pictures if it would help!) the engine seems to have been smoothed out through the rpm range, except at 3k its still pretty bad. 3k is still bad, like I hate to take the car to 3k bad. Another thing Bill had me check was the pressure plate. He asked me to check for drill holes for balancing. It was drilled so it seems to have been balanced.

I'm sorry if my frustration is showing, but I don't know what to do to fix this and I've been at it for a while now lol.

I know it's bad for the mains and can cause other damage over time; it's even started leaking oil a lot more through the rear main and front. I wish I had noticed this before I purchased it, but it is what it is.

In any case, I'm at a loss about what to do and I feel bad because I otherwise really like this car. But damn it it's not really drivable this way.

What should I do? How I can achieve balance?

 

The flywheel balance is interchangeable for L98,LT1,LT4. The factory did not individually balance each flywheel (Except maybe some LT4's)

So just get the flywheel balanced (off the car) for your engine. The pressure plate and disc are neutral balanced so basically any clutch will work fine.

Take a look at AZSP33D's post. I am not aware of the balance spec, but I suspect he is more knowledgeable. Like he said if you are using a solid flywheel you must use a sprung hub disc. So make sure there is room for it in the flywheel.

I found that I had a SPEC flywheel that was off. I put in a flywheel and clutch and the vibration (similar to yours with over 3k vibrations) was gone.

Good luck.

 

Thanks for the reply. Mine is an LT4 with the stock DMF.

So what you're saying is I need to remove the flywheel and take it to get balanced somewhere? Or make sure to purchase a new one that has been pre-balanced?

I'm confused because I keep reading that it needs to be balanced to my rotating assembly. Is this not true?

Is it easier to switch to a SMF? I've been reading that the DMF can be more problematic and can't really be purchased anymore. What brand would you recommend?

I'm not certain what AZS meant by the weight he gave. I know it's achieved by putting weights in certain spots around the flywheel, but I'm not sure how to determine which spots. This is my flywheel, and there are holes for weights along the perimeter. I'd really like to achieve the factory balance on my present flywheel without having to take it off, but that's what I'm having trouble with. I was under the impression that it's possible.

 

MIne was an LT4 also. I had a SPEC flywheel and clutch. The flywheel was not balanced correctly and the clutch was damaged, so I don't recommend that brand (although a lot of people use them ok.). I put a stock OEM dual mass flywheel back on it and new clutch (Valeo) with an INA throwout bearing. My vibration and poor shifting disappeared.

A shop should be able to balance your flywheel, but most of the time if it was an original and has changed it is because the dual mass flywheel changed. The service manual calls out a test to do on the flywheel. With the base secured you try to rotate the 2nd mass. If the movement is more than a certain amount the flywheel is bad.

Balancing to the rotating assembly is the best way to do it, but in practice GM balanced them to a specification instead of to the rotating assembly for lots and lots of cars. In my case I used one from 1990 on my LT4 without any additional balance and it worked fine with no vibration.

Good luck.

 

I'm fairly certain it's stock because even the welded weight and everything is arranged in the same way it's pictured in that tech data. The holes are spaced pretty much as you described, but the picture makes it look like they're not.

Man this is terrible. So the flywheel may be bad as well?

I really want to just swap everything out and be done with it, but that's a helluva lot of money, even if I were the one to do it, which I don't want lol. I don't have a lift to use freely.

Have you heard of ram clutch? They sell an entire package for this car. A externally balanced SMF and a zero balanced pressure plate clutch assembly that also converts from a pull to a push system.

Was thinking of that, but again was hoping to just be able to balance this one because of funds. I haven't heard anyone give feed back on that system either so I don't know if anyone has been happy with it.

Maybe AZ will have more input.

 

I looked at some pictures and I agree it looks like a stock dual mass.

I have heard of RAM and several others, but I do not have any experience with them, so I can't recommend a brand for you. I had an aftermarket flywheel that was not balanced correctly, so I would still recommend getting it balanced whatever brand you get.

The single mass flywheel will add some noise to the ZF transmission. In my case it was not very much and I didn't really notice going to a different flywheel. Some people report more than what I noticed. There are also some differences in ZF's. Bill Boudreau (I am not sure I spelled that right) was very helpful when I did mine. He also sells a kit to shim the ZF a little tighter which I am told reduces the noise from a single mass.

Good luck.

 

So the question is how do I balance the heavy 30 year old stock dual mass flywheel? Once they start vibrating it's garbage. Yes, we've all heard of RAM clutch, re-read my previous post.

 

Brother, with all due respect, I have not, until now, had my questions answered definitively, but it's possible I wasn't asking properly. I am doing my best with the little understanding I have of this system and this car, since it's new to me.

This is THE first time someone has said anything definitive like "once the DMF starts vibrating, it's garbage" and "You cant balance that heavy DMF once it looses balance, it's garbage". This whole time I was searching for something solid to go off of; thinking that perhaps it was possible to fix. QC also mentioned there was a test for seeing if the flywheel was bad. I didn't know a flywheel could go bad at all lol. This is all good info that I'm building a knowledge base of.

Also, I've been in comms with Bill B. for a couple weeks and he has been encouraging me to try and balance it with the weights.

Since I have little experience in this area (that is manual transmissions), I am at the mercy of those who have it. I want to understand what you mean by the 23.4 in/oz balance you gave. How does one restore that and can it be done with it in the car? I'm guessing at this point "no". The thing with Bill is he told me those marks I mentioned above were factory made and were intended for weights, so that gave me a bit of hope lol.

One of the reasons I haven't moved forward with purchasing anything (apart from the money) is that with all the work involved, I'm afraid of reassembling only to find it out it isn't fixed. I've read posts here where people have had theirs changed with supposedly balanced ones without it fixing the problem. So, I'm trying to really understand in depth what I'm dealing with here. I've only dealt with autos and have never had this issue.

Case in point - Carolina Clutch says this "Tech Notes: 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 beyond 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. Most machine shops that do engine work will have the ability to match balance the 2 flywheels. If you have any questions pertaining to this procedure please feel free to give us a call."

I don't have the original balancing information. The previous owner sorta screwed the pooch with that one. So because of things like this, I feel like I'm flying blind.


Anyway, I really do appreciate the help, I'm just frustrated. You know, being a dude and wanting by nature to fix something, but not having the wisdom needed, yet.


So, I'm really looking at the ram clutch conversion kit that comes with everything. They says it's balanced "to LT1 specs". Based on your guys knowledge, should I still get the flywheel balanced at a machine shop after receiving it from them?

Maybe it wouldn't hurt.

 

Hey all,

Have any of you installed the RAM clutch conversion kit into your cars?

If yes, can you give me an idea of what was involved? Was it plug and play installation and your good? Or was there anything special needing done before or during the install?

Again, thanks for bearing with me while I try to figure this all out.