Boredome zero

Hey everybody I'm new to the forums but have a big problem. I have 1975 mustang that I've been working on for a few years and am trying to work out all the bugs. Recently I put a tremec tr-3550 in the car and with that I got a bad high speed vibration. It starts at around 70-80 mph and gets worse with speed. I know its somthing in the drivetrain because no matter what my rpm is its there. I've tried 3 different drive shafts and none solved the problem. So I thought maybe the diff so I put a different one in and it's still there. I've heard about driveline angle and am not really sure how to check it or what the acceptable difference is. I've also changed the tranny with a standard t-5 and it didn't solve the problem. I am going crazy trying to figure this out so any input would be much appreciated thanks.

Shane R

I have same problem. I'm wondering if maybe the wrong harmonic balancer was installed for the given transmission. Mine has a c4. I need to find out which balancer is recommended. This winter I'm changing it over to a T5 manual.

roystere

What bell housings are you using for the manual? MII or late model? What year engine? Pre-82s use a 28oz balance. 82 and later use a 50oz balance. Also, if you're using a late model bell housing and flywheel on a pre-82 engine, changing the harmonic balancer to the late model balancer won't work either, you will still have the vibration. Early engines were internally balanced at 28oz so you'll still have an imbalance. I know this from experience...

Shane R

Using an '86 fox trans, bell and flywheel. The engine is an '88 5.0 HO.

roystere

Could be pinion angle or something else in the drive shaft. In the tech section of www.mustangii.net there are spec sheets for our cars by year MV something or the other.... (CRS), they may give the pinion angle I just don't remember. It also seems like Summit or Jegs carried angle shims.

Chiss

Pinion angle has to be on the same angle. If tail shaft on tranny is 3 degrees down then pinion needs to be 3 up. If you are say 3 down on the tranny and straight or zero on the pinion then you got a vibration problem. buy yourself and angle finder, find a flat spot around tail shaft and do same thing on the pinion. You will know in short order. If you happen to cut the driveshaft ensure that yokes are @same face.

racer_dave

pinion angle/trans angle. My guess is when you changed the mount for the different trans that changed the trans angle- creates the vibration. changing shafts will not fix it. either shim the trans or the rear end or both but they have to be equalized.