vibration at highway speeds
 

At around 70 there is a vibration and if i get off the throttle it gets worse till about 55. The problem is not there if i take out the driveshaft and put a yoke in and bring it up to 70. So far i have new motor and transmission mounts, harmonic balancer, b&m flywheel, new transmission and torque converter from monster transmission, brand new front and rear u-joints, new driveshaft, all my wheels were balanced last week, just tried putting a new 8 inch center section in the rear, and made sure my axles were straight on a lathe with a dial indicator, and new wheel bearings, and i have air shocks and tried many different heights to make up different pinion angles. Anyone have any suggestions that i have not tried yet.

Check your u joints

I bet you put in a t5 didnt you!

a lot of use on here are having the same issues. i would check the u joints and have a shop balance it for you.

bad bad bad bad idea, you are gonna ruin the floor pans in the rear of the car

You need to get your driveshaft balanced

Agree 100%

yes, driveshaft imbalance. and if its bad at 70 and getting worse when deccellerating to 50 it might be the pinion angle to low (decelleration lowers it even more)

Craig

Here is a simple solution. Start by decreasing your pinion angle and go for a drive. If the vibration gets better than you are heading in the right direction and its not the driveshaft. keep decreasing this angle until vibes go away. If it gets worse by decreasing your angle then you are going in the wrong direction. increase your pinion till it goes away. If the vibration does not change in either situation need to have driveshaft balanced. So many people will tell you that it need to be set at this degree or that degree but it seems like everyones mustangs set a lil bit different and with so many suspension variations who knows. I was told to run +3 degrees of pinion angle but with a 4 link and as low as my car sits Im running -3 degrees in order to get no vibration.

Also when I was making my adjustments a made large adjustments so i could be sure to tell the difference on the highway. In other words if i adjust it 1 or 2 degrees it may be hard to feel a difference at highway speeds. I made a change of 4 degrees and the vibration came on at 85-90 instead of 70.

I have had a vibration in my 66. It came on around 55 (this was all after I changed the rear from a 2.80 to a 3.55). I had the shaft balanced and it now comes on around 75-80. I had all the wheels balanced (old style steels), and the shop told me two were pretty out of round. I put them in the back because I had a steering wheel shake. That is now gone but I have the vibration in the back. I was assuming it was from the wheels, and was going to replace them. Could it be the pinion angle, and if so, what the hell is that? I'm assuming it is the angle of the shaft from the rear end to the tranny. How would I adjust that? (Sorry to jump in on the thread)

i tossed in a spare driveshaft i had kicking around the garage and had the same problem so. So i put my old one back in let all the air out of the shocks and temporaaily stuck 1/8 flat steel under the front of the leaf spring perches and it definetely helped the vibration is still there but its not as noticable, so i'm gonna pick up some ships and adjust my pinion angle. I just don't understand why everything was fine till i rebuilt the engine and dropped it in i started having all of these problems.