My car makes a thunk noise when shifting from 1st to 2nd under heavy accelaration and heavy braking. Anyone have any ideas?

 

Mileage?

Might want to check motor/tranny mounts.

 

Ive got 77K miles on it. I took a look at the 2 front motor mounts and they seem to be ok. Is the 3rd one located above the front diff.

 

Automatic?

 

5 spd

 

This sounds familiar to me in the automatic, but I cannot think of what it is....

Some use I am huh?

Driveshafts maybe (like U joints or play in the axles/ bad CV joints)

Dang my old mustang used to make this noise... What was it? Probably will end up being an internal transmission problem, but you should check to see if there is play in your driveshafts or axles.

 

Come to think of it I think it was a bad U joint. But that is in an auto... I guess it would apply the same in a 5 speed.

 

it didnt start doing it until i hit a big dip and kinda came down on the front pretty hard.

 

check your snub mount and tranny mounts

 

where is the snub mount located?