Okay, so I've combed through lots of messages on the topic, but still don't have a solution. More recently, I found a message that described the noise like a 'box of rocks' following the swap from a DMF to a SMF that's the most accurate description of the noise/vibrations I get. Well to recap my story (from other forums). I just went to switch out the clutch on my '92 LT1. After discovering the bit about my flywheel not being resurfaceable, I went with a SMF knowing that it might well make some additional noise when idling with the clutch out (in neutral). So I had to return the RAM clutch kit that I'd purchased since it didn't have a sprung disc. I got a complete kit (including SMF) with sprung disc at Spec Clutches. They installed it and I turned right around and brought it back to the mechanic. 3 techs and one trans specialty shop employee have now driven in and while I haven't had the opporutnity to speak with them personally, I'm told they agree that the noise is an internal problem with the transmission. (and here I thought the flywheel was expensive :( ) Anyway, it DOES sound like a box of rocks now that I've read it described that way- but the LOUD noise is present throughout every gear shift and basically any time the engine is under load. This is uncharacteristic to descriptions I've read so far. I can stop it only be letting off the gas or pushing in the clutch. But yes, it's very loud. And the vibrations can be felt throughout the car. I don't want to vibro-sand my cylinder walls using my pistons.

I spoke at length with the VP of fidanza flywheels at midamerica corvette's funfest today. He seemed to be about the most knowledgeable person I've yet spoken with in regards to this issue. What he told me (and I've read posts here that support this) is that GM used the DMF to basically 'cover up' issues with a naturally unbalanced engine. The DMF that I have (had) was custom balanced and matched for my particular engine. Now that I have a SMF- it doesn't compensate. I can still get the DMF back from the shop- they still have it. Seems that the proper repair would have adapted the new flywheel with the same balancing of the DMF. This is where I start to get confused. So the DMF- if I were to mount it on a pipe and spin it- SHOULD be wobbly and spin untrue because it is weighted to counter my engine's 'unbalancedness'.? Now correct my physics if I'm wrong, but that seems to imply that the same amount of weight needs to be mounted in the same position on the SMF in order to even things out. Even though its a lighter overall flywheel (and, BTW- despite the problems, the performance improvement is impressive!) the necessary counterweights and orientation should not change. Also, it will be important to mount the flywheel at exactly the same rotation as the previous one. Can this be done? How?

Can this be balanced dynamically? Thinking it through it seems like you would have to take it on faith that the counterweights position is correct and just drill as the DMF with no dynamic balancing. If you were dynamically balancing (like a tire) you'd want the end result not to be true, but to be unbalanced in the same way. Can a machine do this?

Sorry so confused- maybe it IS a transmission problem, but even after all this info and research I don't feel like I'm much closer to an answer or solution. Please help if you can! Thanks!
-Kevin
*Also- one final thing I've been pondering today: The theory I've described above is the #1 suspected explanation for this problem, BUT if I push the clutch in and rev the engine- it revs pretty smoothly and yet the flywheel is still spinning. Maybe the vibrations are just most evident in the components past the flywheel?


**Oh, and also, I think I can smell burning clutch or something when I stop.


[Modified by kevin-design, 5:16 AM 9/21/2003]

 

IF the SMF is that far off, the engine will not be balanced.

A step back. The dude with Fidanza is kinda right....

the flywheel was balanced with the rotating mass of the engine. This made the motor a hybred internally/externally balanced engine. I do not agree with his comment that they "did this to cover up a poorly balanced engine". This is not an uncommon practice.

If this was true, why does the LT1 equipped Camaro, with a 6spd manual, NOT require a DMF???

It's the tranny!!! The ZF is a unique design. That design makes it very noisy. A poorly balanced flywheel will exagerate that problem. I don't remember the exact terminology for the mechanics, check http://www.zfdoc.com for more detail. Bill is da man, yo, when it comes to the ZF 6spds found in the Vette.

I would NOT drive the car until this problem has been fixed. The problem is with the flywheel. it will require removal. For giggles, remove the unit and have the new SMF removed and have it neutral (sometimes called zero) balanced. I would be curious to see if the SMF is properly balanced.

Good luck, welcome aboard, and keep us posted!

 

What SMF flywheel did you go with. Did you have the balance checked before you installed it?

 

Thanks for the quick responses! You meant, 'I would NOT drive this car..' after driving it for 90 minutes each way to effingham today, right? :) Ouch! I guess I was hoping that it was all part of the break in process. They tell you that you shouldn't drive hard for the first 400-450 miles while the clutch settles in. I haven't had the opportunity to drive a new clutch before, so I didn't know what to expect. And there is a peculiar smell when I stop- maybe what burning clutch smells like- but not being familiar I couldn't say for sure. I'm still going with the unbalanced flywheel as my #1 theory for now- optimistically hoping that it won't require a transmission repair/replacement. Good question regarding the SMF for the camaros- I will ask him directly as he gave me a card. I have thought up some other questions too (it's Bob Scheid- VP of operations). I guess fidanza fabricates the flywheels for a LOT of other major manufacturers.

Regarding the neutral balancing of the flywheel- I would expect this to be done at the factory- I doubt if my mechanic did that. Still, what I really need in this case (still sticking with my theory) is a correctly counterbalanced flywheel- not neutral, right?
Anyway, thanks for the help! keep it coming, this ain't over yet!

Also, thanks for the welcome! I'm pretty into forums and have been reading for a while now- just hadn't posted till now. I'm now a member here, at CAC, at thirdgen.org and at delphi's Battlebots forum. What a great community! Is there a chatroom somewhere here? (or anywhere online for that matter?)
Thanks!
-Kevin

 

as far as the SMF is concerned, get it neutrally balanced first.

I had a serious run-around with SPEC 18 months ago. I would never buy from them, or recommend their products. the one they sent me did not fit worth a damn.

And when things switched from phone to email, they forgot who the hell I was... and started flaming me... all to save a few cents on the phone bill.... :mad

basically, they sent me the wrong pressure plate. miss-packaged... and they would not refund my $$.

azzholes.

as for the flywheel... I donno they can balance it to the DMF. I have heard people use that term, but the only way I know to do it is through an engine rebuild.

also, the Fidenza, being aluminum, is TONS lighter, and will be noiser than the iron Camaro SMF.

 

Re: Flywheel balance

It is my understanding that the LT1/4 engine is externally balanced. That is, the harmonic damper and flywheel both are unbalanced by themselves, but together with the crankshaft form a balanced unit. This was standard practice on the 400 CID small block, but was not used on the 350 until the one piece rear seal design required a smaller crankshaft flange for the flywheel. This is a rather un-elegant design. An internally balanced crankshaft, with neutrally balanced damper and flywheel would be ideal. For cost reasons GM chose not to do this.

The Double Mass Flywheel on the LT1/4 is unbalanced by itself. Therefore, any Single Mass Flywheel replacing it must be unbalanced to the same degree in order for the crank/damper/flywheel assembly to be in balance.
The GM 4+3 flywheel which TPIS uses as a single mass replacement is unbalanced, for example.

If the flywheel that you are using is balanced by itself, a severe engine unbalance will occur in the LT1/4. This will cause lots of vibration, shaking, and general mischief.

3 Solutions:
1) Use the Stock DM Flywheel and live with the extra mass.
2) Use someone's unbalanced SM flywheel and tolerate a little extra noise from the trans. No vibration however.
3) When you redo your engine, have the crank guy internally balance the crank, so you can use neutrally balanced dampers and flywheels. This removes even more flywheel mass. Still have some trans noise, but less since the flywheel is now balanced.
A clutch disc with damper springs helps too.

 

Your engine is externally balanced and it's done at the flywheel. You need to have the new flywheel dynamically balanced exactly the same as the original dual-mass. Take both flywheels to the machine shop and have them do it.

 

Okay- so from the sound of it we're about 90% certain that the whole problem here is the fact that the flywheel is not properly counterbalanced? That explains the 'box of rocks' noise and vibrations from the drivetrain? I would hear it most when the drivetrain is engaged because when its not, there's really no gears or components to make the vibrations more noticable.

Is the DMF indexed in a way that would allow me to position my SMF in the same orientation? Is there a pin or just the bolts (how many?- 6 bolts=6 possible orientations) Will I need a new flywheel or can you add counterweights to your typical SMF flywheel?

I don't think this explains the burning clutch smell though, does it?
I'm planning to go and have a nice chat with the owner of the shop tomorrow. I was originally planning to do this repair myself, but having never changed a clutch, I thought it would be best to pay an experienced mechanic so that it doesn't get messed up. Is it reasonable for me to expect them to re-do this job at their expense? The only reason I think I may be held partly responsible is due to the fact that I selected, purchased, and provided the clutch/flywheel kit for them to install. But shouldn't they have known? Thanks for any opinions or additional info!
-Kevin

 

I believe that the SMF included with the kit was steel- The Fidanza guy spoke very highly of Spec. He even suggested that if they did give me a steel flywheel with the kit, he may be able to arrange a free exchange to aluminum. From what I've seen so far, it might be worthwhile. The performance gain is more than I'd expected. More importantly I may need a different flywheel in order to counterbalance it correctly from the sound of things. We'll see how it unfolds.
To anyone reading this:
I'm inexperienced with the clutch/flywheel issues that I've learned so much about this week. I'm going to discuss this situation with the shop owner tomorrow- I think I understand the problem and solution pretty well at this point, but if I'm missing any important information, please advise now. Thanks!
-Kevin

 

Went back and double checked the shop manual on my 95 LT1.

Both the harmonic damper and flywheel originate neutral balanced, but have weights inserted in both of them to counterbalance the crank. The shop manual specifically instructs that if either is replaced, then the weights need to be removed from the old part and inserted appropriately into the new damper/flywheel in the same location to keep the engine balanced. Both parts are indexed to a specific position relative to the crank.

Because the weights are removable, both damper and flywheel can be used on an internally balanced crank engine by simply removing all the weights. You then have neutral balanced parts.

Hope this clears up some of the confusion.

BTW, the manual lists the DM flywheel weight at 36.5#. So a good aluminum SM flywheel of 15# or so will remove a lot of rotating mass.

 

Here is the response from spec:

Kevin,

The SC05S flywheel you received form us is balanced exacting to your DMF.
Maybe you need to describe your trouble to me, as it is unlikely your
trouble is balance related, unless you have built your motor with
aftermarket parts that require a balance alteration to your factory DMF.
The flywheel will only bolt up one way. All L98, LT1 and LT4 flywheels,
single mass and aluminum, are balanced the same from the factory. That
flywheel we sold you is a factory GM balance steel flywheel already balanced
for your '92 Vette. The only way the flywheel could be wrong is if your
stock DM was balanced to an aftermarket motor. That can be fixed by just
match balancing the steel SMF to the dual mass. Takes about 20 minutes.

Thanks,

David
SPEC
800-828-4379


Speaking with David today, he said that all GM flywheels are balanced the same from the factory, not individually per engine as I was led to believe. He continued to describe the ZF as a great transmission but much louder than the Z56. The DMF in his opinion was installed to hide the noisyness of the transmission. The Flywheel is not neutrally balanced but they are consistantly the same factory spec. Please let me know if you have any more information. Thanks!
-Kevin

 

Kevin - the note from Spec is dead on. And you're talking about two different things all at once.

First, when going to a SM versus a DM, you must use a flywheel that is balanced to the "factory standard external balance" to keep from building bad vibrations in your engine. Note that you need to be sure the DM you removed was only balanced to the factory external balance spec and not modified by someone. If you were to use a zero balance flywheel on an external balance motor, you'd be in trouble very soon. You can only use a zero balance flywheel if you get your rotating assembly internally balanced - good machine shop, mallory metal, $$.

Second, the noise. There are two different noises with the SM. One is the rattling "like a metal box full of rocks" at idle. That's not from the engine, it is the transmission/clutch as others said. Again, the reference to ZFDoc is a great one. The other noise is a shaft vibration during light-to-moderate acceleration that you will hear up to 3.5-4K RPMs or so. This is from the length of the shafts in the ZF. It's the price we pay for better performance.

The end result is some noise, but if you want optimum performance during acceleration and deceleration, the SM is the way to go.

If you want street quiet, stay with the DM. Good luck, Paul :flag

 

I’m reading this thread with much interest and learning quite a bit about the SMF and the DMF. NavyVet made an interesting comment about a noise from the drivetrain. I have a 94 LT1, 6 speed, 85Kmiles and under acceleration everything sounds normal. By acceleration I mean everything from light to hard. My issue is at cruise speed of 60 to 80 when I’m in 6th I get a noise that comes from the drivetrain that is like a hard knocking. It’s something like if a tire were out of balance and it was hitting the heavy spot. If I push the clutch in and coast at 75 it is smooth and quiet. If I am holding a steady speed and slightly increase the throttle to hold the speed I get the vibration and noise. It’s like a bad bearing some where in the drivetrain. Does anyone have this same problem?

 

For anyone interested- here's the current status:

Took my car to the transmission shop that they'd already taken it to and talked to the same guy they did. Went for a little ride, and he couldn't give me a conclusive answer to what was wrong.

Went to another place, a mechanic took it around the block, returned looking like this: :confused: Said he didn't think it was the transmission, but maybe the shift forks weren't seated correctly. Said it wasn't vibration but it was noise. (doesn't physics require vibration to create noise?!) Took it to yet another transmission place. Made an appointment, and they put it up on a lift and used a stethescope and everything. This guy said that there was a)trouble with the bearings on the input shaft of the ZF transmission. b) something wrong with the clutch as you can smell it burning all the time.

Somewhere in the middle of driving it around to these places I stopped at the original garage and took them for a drive so they could smell the odor- not having changed a clutch I couldn't confirm what that smell was. They agreed that it was burning clutch smell. They told me that the clutch specified a 400-450 mile break in, and I left thinking that clutch skipping/slipping was the cause of both problems as in my mind a slipping clutch would create both noise and excess friction explaining both symptoms.

After all this info, I'm almost back where I started since nobody has made a confident conclusion. The one fact I know for sure is that it wasn't doing this before the clutch/flywheel replacement. Can a clutch replacement trigger a bearing failure in a transmission? Seems unlikely two major problems would pop up at once. Maybe the dropped the trans while operating on the clutch?!? Any ideas?
Thanks!
-Kevin