So, for a little backstory, I've got a 1987 Trans Am with an LG4 and 5 speed manual. I bought the car in November but only started driving it in April when the snow cleared, even with a posi rear end I noticed I was getting quite a bit of tire slip and decided my car needed stickier shoes than the burnt out 215 all seasons it came with. Today I installed a pair of Nitto NT555R drag radials sized 275/50R15 on the back end. They grip a whole lot better than the old 215 tires and have virtually the same sidewall. The issue comes from when i was driving home this night, I decided to to a little bit of a pull from 20 Kmh so i slowed to 20 and put it in first and brought my revs up to ~3500 and let out the clutch fairly quick against all better judgement. It was definitely a bad idea but what happened still surprised me, The tranny kicked p in the tunnel 4-6 inches with a loud clunk and it felt like my entire drivetrain had fallen out. I immediately thought of all the horrible things that could have happened however on the rest of my drive home I managed to get power to the ground with no strange vibrations/sounds despite having the tranny kick up an unsettling amount. I jacked the car up and took a look underneath and there isn't any visible damage to suspension and drivetrain parts aside from the usual engine oil leak and rust everywhere. Does anyone know what could have possibly caused this? My guess was that the motor mounts and possibly tranny mount on the crossmember are gone after 30 years and the motor pitched up when the tires actually hooked and brought the tranny toward the cabin with it. I've never owned a manual RWD car before but I'm guessing this kind of shifting around isn't standard on a car with just 140hp. If anyone has any advice it's greatly appreciated, I dodnt get a good look at the motor mounts because its pretty dark out and the transmission mount was pretty grimed up but it still seemed in tact. Thank you for help, I'm glad I have a reason to stop lurking these forums and finally post, however not too happy the tranny jumped up towards the cabin.

 

Yup, trans mount is trashed, same as everybody else's. They're weeeeeeeeeeek to begin with, and even moderate stress (clutch dump) is about guaranteed to break it.

Effff "get a look at". Just change it out. Takes about 2 minutes MAYBE once you get the car jacked up enough to get under it. Not worth jacking the car up and NOT changing it out, now that you KNOW FOR SURE it's broken by other means (trans flopping around without restraint).

Motor mounts are probably unaffected.

 

Thanks for the reply, good to know the trans mount is what messed up. I'll swap that out ASAP, any recommendations on aftermarket mounts?

 

Not really... the parts store variety (Anchor) seem to be fine, no weeeeeeeeeeeeeeeker than factory, but not really stronger either.

I've also used Energy Suspension, and although many people report issues with those (and I don't doubt their truth in the least), it worked fine for me.

Long term though, the only solution that will work, is to relocate the torque arm, OFF OF the transmission, so that its natural and unavoidable tendency to lift its forward end, doesn't also tend to tear the trans mount in half.

 

I agree. Sounds like the transmission mount.

I replaced mine a couple months ago with an Energy Suspension polyurethane mount and couldn't be happier. I did not use the preload plate that came with the mount. Doing so would have changed the driveline angle and I was worried about introducing vibration.

The only real issue I had was that I had to hog out some material from the slot in the crossmember. The bolt provided with the mount kit is a bit too big.

Clunk is now gone, and the car seems to drive a bit nicer overall.

 

The trans. mount on cars without the torque arm lasts a good while.
Get the torque arm mounted separately instead of on the trans.
If you get it off the trans., to keep the trans. mount from getting junked, sticking to a rubber stock mount will let the car stay quieter vs. poly.

 

Thanks for the help guys, I'm heading out of town for a week and leaving the car behind, but I ordered the energy suspension poly mount, excited to get it on the car and hopefully it lasts long enough for me to get a torque arm relocation kit. So from my understanding the torque arm relocation kit just moves the torque arm mount off of the trans and on to the tranny cross member itself so the load basically goes into the frame instead of the tranny?