So this weekend I changed out third members in my 9inch with new gears, locker and all.

Well before I changed out to this new third member I had allot of vibration issues as it was but could never pinpoint it down with the number of em that I had (because old third member was TOAST). Well now I changed out this third member and I am getting a vibration that seems to get higher with speed. At first it seemed like it was only in 4-6th gear but the more I drive it I'm pretty sure its from about 35mph+.

I wasn't sure if it was my driveshaft being too short so I took it back out today to check. Here's what I got.
My old driveshaft is this PST 3.5in aluminum driveshaft. It was too long so I had to use an old steel 3rd gen driveshaft I had,
had the unjoints changed out to convert it to a 1350 yoke. If you can't tell the spray painted orange one is the steel one.



Here is how much engagement I have. About 2.75inches



Here is the difference in fronts



Here is a possible culprit perhaps?
Looks like that weight may have come up a little at one side.



Well I put it back in there and still vibration. I checked pinion angle and set it accordingly and still vibration.

I'm starting to think it's actually my transmission that could be messed up. When I stuck the driveshaft
on the output shaft and started turning I could hear a bunch of clicking inside the trans. I tried shaking back and forth
but couldn't tell if it was play in the output shaft or if the driveshaft was just turning.

I'm kind of stumped, I'm going to try throwing in a different trans when dmy buddy is done with my spare.
I'm thinking maybe whoever it was that painted this driveshaft may have thrown off the balancing or it's the trans.
When I dump the clutch into 6th or 5th gear on the hwy (While not accelerating or high rpms) It feels like that trans kind of moves back and forth. Also when car starts to surge with the locker engaging on a turn or in first gear that it feels and sounds like that trans moves back and forth.

I can get the car up to 70 mph or so, take it out of gear and notice vibration all the way down coasting to 35mph or even lower.

I have poly motor and trans mounts. Transmission is mounted solid, don't see where any movement could come from with that. The transmission however has been whining ever since I got it from 1-3rd gear and makes allot of noise when in neutral with the car running, but it has done this for about two years now.

What makes me think it could be something in the transmission is when I go in reverse and it lunges I can hear movement in the drivetrain which sound or feels like the trans is sliding forward and back. I checked all the mounts on trans though and I know it's in there solid.

Should the driveshaft have been balanced when throwing on conversion U-joints?

Anybody have any input on this? Perhaps another view on what I'm thinking or something I have not thought about?

Thank's allot guys....sorry about the novel.

 

Same problem here..subscribed!! Good luck..

 

Blahhhh.....Put the car on jackstands, found one side wheel wobble.....Took the wheel off.....looks like I got a bent axle