When I run my Z I get an annoying vibration at a certain RPM. Now I know it is not driveshaft related. I know this cause it happens in park when I rev the motor. It is amplified 100 times with a poly trans mount. It is unbearable. The vibration comes in at about 2500 RPM & goes away above 3500 - 4000 rpm. I think it might be something in the trans & I am getting an FLP Level 4 very soon so hopefully it will clear up. However any suggestions on what it might be other than a trans problem? Could my Flex plate for any reason cause this vibration? How about engine balance? I don't think engine balance is the culprit cause it only comes at a certain RPM. But then again that is why I am asking here in the advanced tech suggestion cause I really don't know.

Any ideas or suggestions would be greatly appreciated.

Thanks

 

I am having that exact same problem with my 86 Z. right around 2500rpms and it stops at about 3000rpms. I have a manual and it also happens in neutral.

 

Car is going in soon. Any last minute info you guys might have for me so I have an Idea what to have the shop look at when the trans is out?
Thanks.

 

If it’s what I think you’re describing (roughly between 2500and 3500rpm, not dependant on speed or anything besides RPM), it’s not your tranny, it’s your engine. EVERY STOCK LT1 that I’ve ever messed with has had it to some extent. Some are tame enough that you can barely notice it, some are fairly noticeable. In my ’97 WS6 while I was doing a street twin install I tried to trace it down and found that it even did it with no tranny or anything hanging off of it, just the engine and flywheel. It gets worse when you lighten the rotating mass (mine was much more noticeable with the aluminum street twin flywheel then with the stock one). I was able to get rid of a lot of it by bolting the fexplate in in a different orientation then it was balanced at (there are 3 possible orientations, 2 felt about like stock, the 3rd was a little smoother, I just bolted it up, disabled the clutch switch and started the car and revved it and decided which position felt best to me). I haven’t paid enough attention to rebuilt/aftermarket LT1’s to tell if this is something specific to an LT1 or to the factory build, but I can tell you that the ’87-92 TPI engines (essentially the same rotating assembly but with a different balancer) either don’t have it or don’t have it as bad because I haven’t noticed it.

 

ok thank you that makes me feel alot better. I was starting to worry cause I just purchased this engine from Evergreen Engine Exchange. They have never led me wrong before but I wstarting to wonder.