typical problem. Car vibrates like crazy once it hit about 75. What I have done so far to find the problem with no success is:

Ive tried setting pinion angle to 0 degrees, +2, -2, +4, -4

Ive tried flipping driveshaft 180 degrees. even though i knew this wouldnt work

I set the car up on jack and ran it up to 75 with both the wheels on and off. vibration does not change either way.

It is a four link set up in the rear so the pinion should be ~ -1. Next I will pull the drive shaft off and run it up to 75 with no drive shaft, see if maybe the tranny is creating the vibration although I can tell it is coming from the rear. Should the universal joint have any play at all? when i tried shaking the shaft I can feel just a hair of movement and I mean a *&nt hair.

 

when did this start? was it fine...something was changed then the problem started or it just showed up one day?

At high RPM in low gear is it smooth as silk?

-Gun

 

Yes at high rpm low gear it is smooth as silk. Its always done this since I finished the build. Just thought I would of figured it out by now

 

Hope it's not what happened to me which which ended up being the main bearings. However, If it was a main bearing, it would do it in all gears. Can you pull the drive shaft off and run it without the oil spewing all over the place?

 

did you mess with the rear i had similar problems with one of mine. Couldnt figure it out. Took it to a shop after trying everything they removed the rear cover and it was a mess. pinion bearing went bad and took out everything in the rear. got that fixed and it took care of most of the problem but still had a minor vib at highways speeds. Got the drive shaft rebalanced and it got better but still had the problem. Never did figure out the problem fully but rear and possible drive shaft being out of balance or bent. And check the rear.

 

Okay

Has the trans and drive shaft been used together before without issue or are they new friends?

Has the driveshaft been balanced?

is the vibration a high frequency (turns objects in the mirror to fog and makes buzz in the shifter and or pedals)

OR

Is the vibration a heavy low frequency (jiggles the fat in your face and makes the side windows bang around?)

AND FINALLY

is the vibration amplitude (strength or severity) linear or exponential with speed in 5 mph increments after you notice it...
For example if its linear 70 mph: just noticeable 75 is twice as bad 80 is twice as bad as 75 and 85 is twice as bad as 80. (gradually gets worse)

If its exponential 70 is just noticeable 75 is twice as bad 80 is 4x as bad as 75 and 85 is 16x as bad as 80 (rapidly gets worse and you are certain that by 90mph something would explode

-Gun

 

Gun_

Trans and drive shaft are brand new. The drive shaft was purchased from JE REEL. And was balanced. Have not had it re-checked though

The vibration I would call a heavy low frequency. It starts to come on at about 2700 rpms when in OD. From there it gets worse the faster you go. By 3200 its rediculous

 

Is there a way to take the drums off and running it on jack stands without having the rear brakes applied. Maybe its one of the drums

 

Have you checked the front end? Tie-rods, tires off balance? Bent rims? Its worth a shot, I have serious vibrations and couldn't figure it out for hours, it ended up being a bent rim.

 

If the trans tail shaft busing is new, the yoke is new, the DS is new and balanced and the vibration is a low frequency. I think you have issues with a low speed item.

I think you could have a bent axle.
maybe an out of balance drum as you suggested
maybe a failing axle bearing (oil any where?)
I think its something along these lines.

BUT

just for fun check for any play between the slip yoke and the tail shaft bushing push up down left right on the slip yoke and see if you notice any play between the bushing and the yoke.

And yes Removing the wheels and drums with the car on jack stands and accelerating to speed should be safe I dont see any problems..yet with doing that.