I just picked up a 1989 Camaro RS 305 v8 with 79k miles with a 700r4 trans and its making a popping sound under the car around the mid section where the trans is and the rear, more by the mid though. It only happens under hard acceleration in 1st and 2nd gear. It is not only a loud popping sound but also you can feel it. It sounds and feels almost like a big rock is hitting the floorboard really hard.

Any suggestions?

 

Welcome aboard thirdgen.org.

Your transmission mount is broken. The rear end is held from rotating by a "torque arm" that goes up to the rear of the transmission. This puts a load on the transmission mount, and when it breaks, the rear of the transmission is jerked upward under hard acceleration. There isn't much room between the top of the tranny and the driveshaft tunnel, so what you're hearing is the transmission thumping up against the bottom of the car.

Not too hard to replace. You need to get the car up on jacks stands or ramps, put a piece of board under the transmission pan and jack the transmission up off of the crossmember, and replace the mount. The part is about $20-$30, polyurethane is more durable than stock-like rubber.

 

On a somewhat related note, what if one has somehow lost the bolt that holds the torque arm to the tailshaft. Perhaps by way of careless storage. What is the length and size of that bolt so I can replace it. (not the two that bolt the main part of the mount to the tailshaft.)

 

Ok, cool. I was hoping that's all it was. Thanks a lot five7kid.