When ever I break or speed up I here a "thunk" from the back, I don't have to hit eather one very hard to have it make the sound.
I think one of the rubber brushings are gone or smashed beyond reconition.
What do you think it might be?
It's my 85' IROC Z w/ 350 and auto.

 

From what I know, it sounds like you need a new transmission mount. you can go with rubber or polyurethane. It isnt expensive at all, i think around or less than 30 dollars
Chris

 

99% chance that it is the Transmission Mount like the guy said above. You can get aftermarket Urethane pieces for like $25-35 from Energy Suspension or Hyperflex, maybe ProThane, Moog maybe. They're a lot stronger than the rubber stock piece. Even if that doens't solve the problem, you just saved yourself a hassle in the future goodluck

 

I had a similar problem recently, and replaced the transmission mount. And if you don't care what kinda mount you get, go to autozone or advance, oem style is 7.99 if i remember correctly. However, if you have the same bad luck as i do, you won't be able to replace it on your own unless you have an air ratchet.

 

A trans mount.
It won't break any thing if I can't can't get it fix realy soon will it?
How about driving on the inter state for 1800 miles?

 

Probably not but then again...I have replaced two on two different cars and the first one took 45 minutes and the second only 1/2 hour. There was an immediatye difference felt when changing gears...i.e. P RND...it seemed overall tighter. Good luck.

 

As far as hurting anything driving with a bab trans mount. I broke a flywheel on my 78 Z28 doing the first to second shift with a bad mount. I would take it easy on it till I got the new mount in.

 

You can drive with a bad tranny mount but be REAL gentle with it....every time you nail the gas or brake the tranny is gonna flop around and thats just not good.

 

hehe i did that one time it was pretty funny....

i was in front of my buddys house, and it had just stopped raining but there was some dry spots on the road....i dropped him off and got on it, sliding nice and sideways down the street....

then i hit a dry spot and the thing hooked up and snapped the tranny mount off....AAAHHHH!!!!....theshifter came up about 6 inches higher than the top of the dash lol....all the way home when i would start to lean on the gas i could feel it sloooowly start to rise....i got a kick out of it cause its easy to change