Hey everyone,

I put a 96 LT1 into my 3rd gen earlier this month. I have noticed a vibration that gets progressively worse the faster you go. You start to notice it around 70mph & it just gets worse & worse from there. I know how a out-of-balance tire feels & this is not it. I think its drivetrain related. I also have a squeel coming from my clutch while it slips when I start off. I am wondering if the two are connected. Lastly, I tried to top it out on the highway & the car wouldnt pull past 110mph.


During the swap I...
Resurfaced the flywheel
Installed a new pilot bushing
Installed a new clutch kit
New wheels & tires


Thanks in advance,
Mark B

 

sound like a motor/flywheel balance issue the motor is internally balanced and the flywheel is external. See if there's a weight on the flywheel. Just my thoughts

 

The flywheel is a stock 3rd gen T5 flywheel

 

Does it vibrate only when the car is moving, or will it vibrate at the same engine speed sitting in the driveway in neutral?

 

Car moving only.

 

Then it's not related to the flywheel or clutch.

 

What else could it be other than the wheels being out of balance?

 

driveshaft, pinion angle (due to motor mount and/or trans mount height), or perhaps a bad u-joint among other things.

 

get your alighnment checked toe and sometimes camber will cause vibration at high speeds especially toe

 

Sounds like a driveshaft or u-joint to me, possibly a weak tranny mount.

 

Yea, start with the pinion angle, it's easy to check. An unbalanced driveshaft will give that type of vibration as well.

 

I agree with jim but want to throw in pinion bearing, i've had em go out and i first noticed a prob at high speeds then a month or two comes that dreaded "wroar" and it's the easiest of em all to check grab that drive shaft and try to shake it if your head's the only thing moving it's good LoL (if you dont get the lame joke try it and u'll get it)

 

Probably driveshaft. Try spinning the shaft 180 degrees and see if that helps.

FWIW, 4th gen LT1 6spd cars vibrated like crazy. The fix was the 1LE aluminum driveshaft from the 3rd gen. That got rid of most mine but not all of it. I then went to a ACPT carbon fiber shaft and was completely smooth.

 

Were thirdgens balanced at the flywheel like the LTXs? That could be the problem there.. If they are not and you used a thirdgen flywheel theres the trouble, I had a flywheel with just a slight mismatch once and it was terrible.

 

LTx engines are actually a 0 balance engine, mine doesn't have weights on the flywheel.

 

Sorry LTX engines are not zero balanced unless you do so on a rebuild when you spin balance your rotating assy.. From the factory they are zero balanced in front (with a neutral balancer) but on the flexplate or flywheel they have a weight... they are balanced on the rear.. Unless somehow you have some sort of oddball, which I guess is possible.

I have never seen one without a weight molded into the flywheel or flexplate and it is common LTx knowledge that they are rear balanced from the factory, CZ28.com is a good source of info on LTx balancing, my rebuild book also mentions it, as does my own observations... though like I said oddballs are possible..

with a stock 3rd gen flywheel/flexplate on an LTx if not match balanced to the one that used to be on the engine his engine is out of balance. I had this trouble with a spec flywheel that was supposed to be match balanced to the LT1 factory weight, shook like crazy.. Check this out folks, if you think they are neutral, look again..

 

I was thinking about the zero balance on the front, but it is wierd mine doesn't have any weights on the flywheel..guess it is an oddball.

 

Damn. How do I rectifiy this problem without the stock T56 Flywheel? Would a machine shop be able to look up the balance I need, or is each engine different?

 

its just internal or externally balanced you can buy a flywheel with a removable weight and ethier put the weight on or not

 

There is a standard weight on the LT1 flywheel that should be pretty close if not dead on regardless of the engine.. your best bet would be to look for a used stock flywheel in the f/s section of cz28.com or find a buddy/junkyard that has one lying around, then have a machine shop match them... I wish I would of known this would come up.. I just threw my old one away and my new one is useless since it is an slp version spun balanced to my new assy.

 

I have the exact same problem. Did you try and re-balance the flywheel? or did it end up being the driveshaft. i thought i was the only one with this problem. Any information would be greatly appreciated.

 

Its got to be in the flywheel. I have looked into everything else. I picked up a T56 last week to replace the T5, but I havent had a chance to put it in. Hopefully this weekend it will happen. I will let you know if it solves the problem.

 

I was interested to see how long the T5 would last behind a LT1.

 

mine lasted a couple of years and was still fine when I pulled it out and swapped in a T-56. just had to replace the synchros once