1990_mustang_coupe

ok i just rebuilt my motor and pulled out my transmission and found a broken mount, this was causing it to shake real bad. im not sure what the problem could be and it only happens when i pucnh it and put it in fourth and fith all the other gears are fine. the guy before me did a motor swap and still has the stock 4cyl rear end could that be the problem?

dreamer1uk

So you replaced the trans mount correct?

You could pull the diff cover off that 7.5 rear end and see if you can see any internal damage. Also take alook at the driveshaft and u-joints. Most drivesahfts are balanced and if there not install the same way they came out, you will have some vibration.

How does it drive if you up shift through the gears normaly?

1990_mustang_coupe

well when im shifting like around 3 grand its fine but when i hit it up to about 5 grand thats when it shakes only in fith and fourth i didnt check and see if there was any damage o have a 8.8 rear end just to lazy right now to put it in.

Jfsram

5 grand in 5th gear. That's moving! Maybe the driveshaft needs balancing.