I bought my 99 last week knowing there were a few problems we could fix. There was some mean howling coming from the rear end around 40mph so we had to replace the rear dif. The howling stopped, after we replaced it, but we found out some new stuff in the process. We think either the drive shaft is out of round, and I also need to replace the filter in the transmission, or something is loose in the rear house of the transmission were the drive shaft goes in. You can feel rumbling in the seat at certain points while raising speed. When it goes to shift into another gear (automatic btw) it is very smooth. It also takes a few seconds to shift into drive / reverse. If anyone can give some ideas as to what it might be I would appreciate it greatly.

 

make sure the bolts that hold the driveshaft to the pinion on the rear end are tight, sometimes they come loose after reinstallation if not tight enough, that could be the rumbling.

 

yeah once i got under there again and checked after i put my driveshaft back in and found they were loose enough to spin by finger... LOKTITE!!

 

Could always do a 5spd swap, that way you know exactly how everything went back together and arent worried about someone elses handy hack jobs.

Congrats on the new car too, its kinda like a mino resto but without rust to deal with like classics.

 

Thanks for the suggestions. Bolts and all are still tight.. Still making a rumbling. Maybe I need to get the Drive shaft rebalanced?

 

it may have been put back on wrong, your supposed to mark where it was lined up to the pinion, and reinstall to the mark, but i totally forgot to do that when i had mine off a few times and i never got a rumbling. not sure if that would be your problem. i dont see how the driveshaft could have came unbalanced itself tho

 

Could always grab an aluminum DS and see if that helps, if it doesnt at least its an upgrade and you can move on to the next part that might be doing it.

 

Well I got some advice from a mechanic. He said most likely the person who owned it before me rode it hard and stomped on it from a dig and that could have thrown the DS out of balance. Now I need to find a shop that can test the theory...

 

a stock v6 mustang doesnt have enough power to mess with the driveshaft when "stomping on it from a dig", plus the wheel would have just lost traction

 

Changed the filter and replaced a bad bushing in the tranny and now shes running nice and shifting into gear smoothly. Yay