MonsterBilly

So I installed a new tail shaft bushing and yolk! everything has been replaced and re-balanceed and I am still vibrating at about 65mph.

I am so frigging frustrated.

So i bought 4* shims and shimmed the rear end in each direction and neither did the trick. It did make it a little better but not much.

I did talk to a guy at an 4x4 shop here and he said that it was most likely do to the fact that the drive shaft angel is causing the problem. He said that because the car is lowered there is not enough angle on the shaft to properly spin the bearings in the U-Joints.

I will post the angles again for the engine, driveshaft, and the pinion to see if anyone here has a solution.

B

Coupe

I cant remember, is this the car with the 8.8 rear end in it?

eZ

tail shaft of tranny should be opposite of rearend. if the tranny points down 2*, the rearend should point up 2*. have the wheels been balanced? sometimes the balance weights will come off.

JMD

I don't think the 4X4 guy is right...He might have a partially valid point if the u-joint were worn in, but your u-joints are new right?

MonsterBilly

Everything is new. The tires, wheels, shaft and joints, yolk and bushing, and the rear end. I even swapped out an additional T5 that I had and it was still there.
Yes the rear end is a 8.8. However, it was vibrating also with the previous factory installed 8"

When i set it up, The trans was pointed down at 3* I installed the rear end with the pinion pointed up 2* . I have the 5 leaf mideye springs so the rear sits low.

I do have a poly trans mount. Could this be causing a increased transfer of the vibration as compared to a rubber?

TexasAxMan

If the trans is pointing down 3*, then the diff should point up 3*. Why did you set it for 2*, or am I missing something?

Coupe

And (Forgive me if this has been addressed already) you have had that drive shaft balanced locally?

JMD

The up 2 degrees up on the rear (vs. 3 on the trans) actually makes sense on a leaf spring car, the axle will probably wrap up about 2 degrees (depending on how stiff the springs are and how much power is being laid down) on acceleration, either way it is close enough not to be a problem..

Have you checked the trans output bushing that has proved troublesome for so many posters on here?

Gun Jam

Modern drive line advised me against the polly mount...he said if you really want to be sad install one.

Maybe you should switch to the rubber one.

Could I trouble you to describe the vibration again?

1) what is the frequency of the vibration is it more like thump,thump,thump or zzzzzzzzzzzz

2) where do you feel it most?

3) how does the vibration amplitude (strength or severity) increase with speed. If it starts at 65 is it twice as bad at 75 and twice as bad at 85 or is it 10x worse at 75 and 100x worse at 85?

-Gun

MonsterBilly

I set the pinion one degree off to allow for axle wrap as stated above. Also, I was told and read that there must be a working angle move properly.rking angle for the U Joints to.so the vibration starts about 60 mph with a fast high frequency. Then as I accelerate it become worse and the frequency increases. It does have a pulse to it. The pulse becomes more rapid as the speed incrases as well. At 80mph it feels like the underside of the car is going to explode!
I feel the vibration in the entire car. Floor boards, dash, and the steering wheel.
from about 60 mph, if i let off the pedal and coast, the vibration starts to increase without the pulsing. it will get really bad down to about 30mph then i goes away.

While driving It is far less under load then when cruising.


if i take he car to about 70 and the vibration is horrible, I can take the car out of gear and chut the engine off and I am reall able to focus on the vibe. The trans tunnel feels like a cheap 80s hotel bed that was filled with a roll of quarters.

Coupe, the shaft was balanced up to 10k rpms and it is nuts on.

The yolk and tailshaft bushing are brand new.