I recently purchased a 96 collector edition with an LT4 6 Speed. The previous owner had replaced the factory dual-mass flywheel with a fidanza aluminum flywheel. The transmission is noisy because it no longer has the Dual Mass flywheel. I want to put a dual-mass flywheel back into the car to get rid of the transmission noise. Somebody told me that if I don't put the original Dual Mass flywheel that came with the car back into the car that it will vibrate, that the original flywheel was balanced specifically for the engine that came in the car and that a dual-mass flywheel from another car will cause the engine to vibrate. Is this true? I have a good dual Mass flywheel from another car that I want to install but I don't want to cause an engine balance issue with it. The original flywheel is long gone, the previous owner got rid of it after he installed the fidanza flywheel. It doesn't vibrate with the fidanza flywheel so I'm wondering if what I heard about installing another dual-mass flywheel into the car is true. I can't stand the transmission noise caused by the single Mass flywheel that's in the car now. I have the counter shaft shim kit that ZFdoc sells by the way, I'm going to install it while the transmission is out for the flywheel change. I just want to know for sure that I won't have any issues if I replace the fidanza flywheel with the dual-mass flywheel that I got from another car. Any help is appreciated.

 

 

Aren't all small block Chevy engines with the exception of the old school 400 small block from the early 70's internally balanced? If an engine needs a specific flywheel and balancer to balance the engine that would mean it's externally balanced like the 400 small block and 454 big block. That's why I'm questioning what the guy that told me that I need the original flywheel that came off my LT4 to maintain engine balance because as far as I know the LT1 and LT4 engines are internally balanced just like every other 350 small block which means that I should be able to use any small block flywheel on it (except for a 400 flywheel) and not have balance issues.

 

 

when chevrolet went to the i-piece rear main seal, there went the capability for an internally balanced rotating assembly. the old 2-piece flywheel flange had the capability for internal balancing.
the counter shaft shim from zfdoc reduces the rocks-in-a-can sound but it does not eliminate it. my 96 is running a solid steel flywheel, sprung disk and the zfdoc shim and still has the noise, but not as bad. don't drive in traffic and it's not bad.

 

 

The stock flywheel is not a zero balance. It is an external balance motor so one side of the flywheel is heavier.

I know the dual mass from '89 through '96 will interchange (both L98 and LT1/4, but the LT5 is different) I put a '90 flywheel on my '96 LT4 and there is no vibration. That is why I went from a SPEC flywheel back to the dual mass. Later I took the SPEC single mass flywheel that caused the vibration in to be balanced and it was about 20 grams off of what it should be, so that was my vibration problem.

For general production, the flywheels were not individually balanced to the engine, but were mass produced to the expected balance of the production engine. I have read that the '96 LT4's went through an additional check or balance and some of them may have been adjusted with fewer or more of the little plug style weights for fine tuning. I am sure balancing for each engine is the best way to go, but in practice most flywheels are balanced for the expected production engine balance.

There is a GM method for adjusting the balance shown in the pictures below. I was prepared for trying this, but I had a good result with the flywheel I installed and did not try it.

Good luck.

 

^^^^^^
Thats some good info there. But I still don't think the LT1/LT4 engines are externally balanced. The way to know for sure is to take a look at a flexplate from an LT1 automatic car, if it doesn't have a counterweight welded on it somewhere like a flexplate from an old school 400 small block or a 454 big block does then it means that the engine is internally balanced, not externally balanced. I have a feeling that the info in the post above this one is only for balancing the dual mass flywheel because it's not a single solid piece, that because it has many parts and because the surface that the clutch disk rides on moves around it will need more than just an average balancing job on it.

 

All 1986 and newer SBC are externally balanced on the flywheel side (One piece crankshaft design's). If you look at a one piece flyweel or flexplate you will see the added counterbalance.

 

 

When I ran the Alum FW on my 92-The machine shop balanced it to a LT1 Auto and it was perfect. In his opinion it was not possible to get an accurate result when comparing to the DM as it moves around to much. The LT1 is externally balanced-As others have indicated here.

Steve

 

This is how I believe most of the 'locals' around here do also and I believe one shop has 'their own' that they use and unless you've a specialty build they rather use theirs..

 

I have always heard of the one piece rear main seal engines called hybrids when it came to the balance, the front of the engine uses the same harmonic balance as a internal balance and the flywheel is external balance

 

ALL small block chevy's with a one piece rear seal made since 1986 are neutral balanced on the nose/damper end and externally balanced on the flywheel end; with two piece rear seal cranks the flywheel flange could be shaped accordingly to achieve balance; on the later one piece rear seal with a totally round crankshaft flange, the weights needed for balance were incorporated into the flywheel; GRANTED some very expensive after market cranks with one piece rear seals were neutral balanced with the addition of heavy metal and who knows whatever other magic, but I assure you that yours isn't one of them.

Flywheels were NEVER match balanced to each individual engine; "close enough was good enough"; the only problem would arise when a flywheel intended for a 305 was bolted up to a 350 or vise versa; You can put that original dual mass flywheel on your engine, assuming that the crank / rods / pistons are stock, without any issues

 

FWIW, my steel 396 crank is fully internally (neutrally) balanced on my LT4 and didn't require any heavy metal or other magic to do so. It obviously has large counterweights, and perhaps it is easier to achieve this with the longer 3.875" stroke.

 

Thanks for sharing

 

No they are not. the 92-96 LT1 engines are externally balanced on the rear of the crank and neutral balanced on the front.

 

Hey all - I hope to get your advice and points of view. Like many, I have annoying vibrations under “load” and want a “smooth as butter” experience as much as I can. Storyline: purchased a ‘94 base with worn clutch that ended life when we ramped it on a flatbed truck after we got stranded from a dead alternator. Mechanic installed Rhinopac 167426 fw with a LUK clutch kit. No balancing was performed. Upon acceleration can hear vibrations at 2,500 rpm all gears. Car likes 65 mph in 5th OR 85 mph in 6th. In between that is a noisy ride. Also have a droning sound at 75-80 in 6th. All this to say, I am thinking to revert back to a DMF to reduce vibes earlier in drive train, OR, get the Rhino balanced by a shop. Also may look into the ZF doc shim kit as described. Would love to pick up a discussion on Pros and Cons of each option. Thank you!

 

Do you feel vibrations at 2500rpm in all gears? Hearing noises is different, as is the drone, and that has nothing to do with the balance of the rotating assembly in the engine. Also, do you feel the vibrations at the same RPM in neutral as well? That is, if the car is not moving and only the engine is spinning at 2500rpm, is the vibration still present?

 

Matthew, thank you for your questions! I tested it this morning with the following results.

1. No noise at all if clutch disengaged (pedal depressed) and rev up to 4,000 rpm in neutral.
2. “Chatter” felt in gear 2-6 at 2,200-2,300 rpm and worse if speeds low in gear I.e.under load. I can somewhat mitigate by babying it through the gears if no other cars impeding my speed.
3. There is constant flywheel ticking or chirping no matter what all the time and seems worse now after my 600 mile round trip from Houston to Dallas this weekend.

Thank you!
chris