Vibration at higher RPM after Transmission mount change

[Nitro Nick]

Hey guys,

I saw that my tranny mounts were shot and I had them left over from the poly mount kit when I did my Engine mounts from Garagistic. Since I was down there I wanted to do a transmission fluid change as well. After the transmission change which previous owner told me they had redline in it, I swapped to a 75w90 Royal purple gear lube. I replaced the transmission mounts and did the fluid change and upon the first test ride I am getting a pretty serious vibration above 2.5k RPM. It happens more related to the engine speed than anything else. Clutch in, out, in gear with clutch in all smooth. but when you rev the engine at any speed or standing still the vibration will occur. It did, without a doubt not do this before the maintenance items as described above. Really at a loss at the moment and could use some help. when i drove it if I keep it under 2500 RPM it stays fairly unnoticeable. I just don't know what could have caused this. I did raise the transmission to remove the old mounts and laid it down on the new mounts without issue. Not sure if that could have bent something or if its related to the fluid change. I did fill it up until it ran out of the fill hole. At a loss at the moment.

[dude8383]

Throw some rubber mounts in. The polyurethane mounts are the issue. They transmit all of the driveline vibration into the chassis.

[Nitro Nick]

Well the culprit was the mounts. I threw in some new stock rubber mounts and now it is as smooth as butter. It seems the stock mounts that were on there, which potentially were the originals were taking the brunt of all of the vibrations especially with the poly motor mounts. When I changed over to the poly tranny mounts there was nowhere for the vibration to go which is why I was getting so much feedback in the cabin. And when I mean feedback, it was really bad. I've worked on cars most of my life and it felt like something was wrong with the engine or driveline. Very surprised, so think twice about doing both of the mounts and be prepared for the feedback you are going to feel. It did dampen a little bit when the car was warmed up but for a street car I don't think its worth it to do both. I kept the poly motor mounts in and went back to stock tranny mounts and will continue to monitor how they hold up. Thanks for the response dude8383