i repaced my rear diff a couple months ago. now the rubber bracket melted cuz of my muffler, but i have reloacted it since. no more melting. but the diff jumps when i hit the gas do i have to buy a new rubber mount or is there a different way i can fix it and have it be safe for me to be able to stomp on it

 

You probably need to replace the rubber mount. A jumping/clunking diff is usually a sign of a bad mount. And, well....yours melted

You could fab up a solid mount out of metal if you dont feel like buying a new mount.

 

i made a solid mount out of the rubber casing, its easy as pie. it really doesnt make it much louder either

 

If there was enough heat to melt the rubber isolator mount (I'm assuming you mean the front lower diff mount), then it's possible the torque arrester strap was also heated/melted/stretched and isn't hold the nose of the diff down as tight as it should. In taking the rear end apart a few weeks ago, I found my mount and strap were so old and dried out that I'm just buying new ones to be done with it. I'm sure they were no where close to strong enough to hold the diff still. Or you could go solid mount, like Shady said. Also replaced the oil seals on the diff while I had the chance.
Dave

 

now how would i go about making a solid mount? im lost a little bit. theres the bracket that is bolted to the front of the diff. and then there is the bracket that has the rubber piece on it undermeath it. the strap i think may have stretched. it has about an inch of play. soo..

 

Read this recent thread: https://www.zdriver.com/forums/300zx-z31-brakes-wheels-suspension-chassis-76/diff-mount-modification-20723/