Vibes after motor and trans swap.

[347strokin]

Hello guys/gals,

Ever since I did my LS swap on my 87' C10, I've had some rough vibe issues from idle up to about 3000 rpms (This is approximate as it's been awhile now). These vibes persist whether I'm in Park or driving under load. The reason I'm posting here is to get more exposure and the cause and effects are the same. I'll give you some background.

I installed an LS3 to a 4L80E trans with a stock converter using a new TCI flex plate specifically for this combo. The trans had 240,000kms and I was told it was working just fine. Oil was clean and no metal in the pan or drain plug etc. The LS3 runs like a top.

Once I got everything running, I always had some rough vibes right from idle up to 3000 rpm or so.

Anyways, I unbolted the torque converter and all vibes are gone and she runs silky smooth. This made me think it was a bad torque converter as it already had a ton of miles on it.

I installed a brand new higher stall TCI converter and everything seemed fine for the first hour or so of run time, but now the vibes are back almost as bad.

I contacted TCI to see if there is a way to see if my converter is bad but they want me to ship it to them in the US to cut it open and inspect it.

I've now pulled my trans out again and I'm debating getting a rebuild while it's out.

SO...MY QUESTION IS: is there anything that could be causing these vibes from the transmission even while it's in Park? Just seems really weird to have two converters doing the same thing.

Any ideas would be very much appreciated. Thank you!

Jon

 

[DoubleDingo]

I'm no LS expert. Flex plate bolts torqued to spec? Flex plate out of balance? All bolts matching and torqued to spec? If it runs smooth disconnected, the motor is balanced so that's good.

 

[347strokin]

@DoubleDingo Thanks for the reply, I did bolt the flex plate up to spec with the right hardware.

Now you guys are going to think I'm crazy but I've been researching and troubleshooting this for a year and a half now and pulled the trans twice! But I just ran across a small thread that might've just answered my question for me.

I completely forgot that my LS3 came out of a manual transmission car. I did remove the flywheel but I'm thinking the pilot bushing is still in there! I never would've thought about that. I am ecstatic and sure hoping that is the problem.

I will come back here and update this thread once I have her back together.

Once again, thanks again.

 

[Matt69olds]

If the pilot bushing isn’t your issue, maybe you can “tune out” your vibration by reclocking the converter? Granted unless you marked it and reinstalled it in the position, have the trans in and out (not to mention different converter) would almost certainly eliminate the converter being the issue.

 

[347strokin]

If the pilot bushing isn’t your issue, maybe you can “tune out” your vibration by reclocking the converter? Granted unless you marked it and reinstalled it in the position, have the trans in and out (not to mention different converter) would almost certainly eliminate the converter being the issue.

I will try that if it's not my issue.

Another thought is the crank spacer. As far as I know I don't require the crank spacer (to center the torque converter snout) for my application but I need to confirm this as well.

Thank you.

 

[yevgenievich]

4l80e either needs a spacer or correct/special flywheel