if you have an adjustable torque arm... seriously just turn it down a little (make the rear point down) then drive it again. see what changes

 

That was the original configuration - I had it at -1 degrees (rearend pointing downward towards the front of the car), which was even worse than with matching (but opposite) angles, which is what I've tried most recently.

 

lees, with my only other option being to return to the factory torque arm mount, I think I want to consider doing what you've done with shimming the transmission up. In thinking about it, part of the vibration may actually be from the top rear mount of the torque arm being in constant contact with the floorpan - as the rear of the transmission was at -3, and I had to adjust the torque arm to +3 to compensate, it pushed it up very close to the floor of the tunnel.

What exactly did you use to shim the transmission, and where did you mount these shims? Pushing the rear of the transmission up should bring me closer to 0 degrees, thus allowing me to move the rearend angle back down, making it a twofold gain (lessens overall drivetrain angle differences and moves torque arm mount away from floor).

 

They are right under the bushing on either side of the bolt that holds the transmission to the cross member. I used a bottle jack on the transmission to get the angle i wanted, inserted the shims, and then tightened up the bolt, checked the angle again (insert additional as necessary).

 

Awesome, thanks. Did you have the shims made, or did you pick them up somewhere as part of a kit or something?

 

Scrap pieces of metal. I'm sure you can find real shims on jegs, or go to a hardware store and find something that works.

 

I got under my car this week, and was checking my pinion angle. My driveshaft and u-joint angles are damn near perfect neutral, but i still have a -2 pinion angle in the rear. In fact, on my old 10bolt, I had a -2, installed my Moser 9", and kept the exact same adjustment on my UMI adj torque arm, and it's still at -2. I was noticing though, the front of my driveshaft yoke has some play in the transmission. I have even replaced the tailshaft bushing in the tailhousing last year, with no luck. The play in the yoke is definitely enough to cause a high speed vibration... At this point, for me, it looks like a transmission rebuild is in store.

 

One last question - do you remember what the total thickness of your shims were? I'm currently fabbing up several using pieces of 1/8" flat steel I got at Home Depot, and was wondering how many I should be making.

 

3/8". I think the largest you might be able to get in there while still catching threads on the bolt is 7/16".

 

Well folks, major update. I finally managed to get my freeway vibrations down to a minimal, acceptable level with the torque arm relocation mount. Long story short, it was just a matter of getting the pinion angles perfect using lees02WS6's method of equal but opposite tailshaft and rearend angles. Unfortunately, his method of using shims to adjust the angle of the transmission tailshaft down didn't work for me, and only introduced a significant about of NVH.

Here are the shims I fabbed - the left shims sit on top of the transmission mount bushing (where it meets the tailshaft), and the shim on the right sits on the bottom (where it meets with crossmember).



The shims are 1/8" flat steel purchased at Home Depot. The dimensions of the upper shims are 5" x 1.25", and the lower shims are 3" x 2". I added a total of 0.5" worth of shims, but it only decreased by tailshaft angle by about 1 degree (from 3 to 2). I adjusted the rearend accordingly, and took it out for a drive - under any kind of acceleration, everything in the interior shook, making my issue even worse. Perhaps I didn't do something properly, but adding shims didn't make a noticeable change to my tailshaft angle; perhaps info on the shims I fabbed may help you.

So I went back to square one and just attempted to work the drivetrain angles. I purchased this from Amazon:



And proceeded to re-measure all angles. I measured the tailshaft at -3, and set the rearend to +2.75 (the difference left to account for rearend creep under acceleration). Taking the car out on the freeway, I noticed that the vibrations had decreases significantly, and no longer came and went. I would expect some increased harshness at all speeds given the suspension mods, so don't think it will ride like factory with the torque arm relocation mount, but as I mentioned, the ride quality is back up to what I consider to be a very acceptable level given my mods. Prior to getting the pinion angle sorted out, not only would the vibration come and go at freeway speeds, it would get sever enough to rattle my glovebox, visors, and other interior panels - you could literally feel it all the way up your body. It was not a fun place to be at 75 mph.

So that settles it, at least for my situation - properly measuring and setting your pinion angle makes all the difference. Sam was spot on with his diagnosis of my issue being pinion angle related, and lees02WS6's info and videos on proper u-joint operation were super informative. Thanks all, hopefully this thread helps others battling similar issues. I can provide more specific info to anyone who may want or need it.

 

Glad you were able to solve it. Out of curiosity I asked a driveshaft vendor, who is a sponsor here about rzeppa joints on one, or both ends, of a driveshaft (for the f-body). Their opinion was that it would not damage the tailshaft, but that it may not be ideal either depending on application.

From other research I'm understanding "depending on application" to mean not good for high torque load application.

If you can solve the problem, as a above, with correct angles you should do that, but there are options for when that's not possible.

 

question, you said it brought the tailshaft angle from 3 to 2... were you trying to point the transmission further DOWN or further UP with those shims? I was trying to shim my transmission UP like a dummy (its at -1 right now) so it is pointing down 1 degree...

I also ordered that angle finder... the UMI one i dont trust lol!

 

BUMP

Updating this. Today I got up under my car finally and messed with the pinion angle. Using a China made cheap digital angle finder, I determined my trans was 2.90 degrees downward, and my rear was 1.00 degrees upward. So I got my rear to 2.60 degrees upward and took it for a drive and the vibrations are SIGNIFICANTLY REDUCED. There is still some to a slight degree there. I did this in the driveway using a jack and jackstands to adjust, and then lower the car, so I'm sure I have some margin for error. I will be going on a drive-on lift tomorrow and getting some more precise measurements and aiming for exactly .25 degree difference to see if I can get them completely eliminated. I know I will be left with some vibes due to my mods, however.

This is what I've been looking for for so long. I'll update tomorrow!

 

I bought that angle finder csxfbird posted... I am going to remove my shims on friday, and measure out everything. ill try your difference as well and see where I am at

 

After reading most vibration related threads this may be the first that actually "solved" the issue. Congrats guys! I'm going to use CSX suggestions and see what happens. Anyone that solves their vibration issue should continue to post.

 

I'm gonna be checking mine Friday and will post up my results.

 

I will be also. Putting on LS1 front brakes, fixing the steam pipe leak behind my motor, and fine tuning my pinion angle

 

Finally figured it out. I bought this angle finder, as mentioned before in this thread:


I re-installed my poly transmission mount. Transmission was pointing down 3 degrees. I set the rear to point UP 2.65-2.75 degrees. Vibration is now GONE. I have a slight vibration at 90mph.... but that is probably from everything being solid, and it is NO WHERE NEAR as bad as it used to be. THANK GOD I can't believe it took me this long to do this research and figure out how to properly set the angle. I was just setting the rear before *sigh*.

THANKS FOR THIS THREAD. I love you all.

 

What are your measured u-joint working angles with these setups?

 

Not sure, i just measured the transmission angle and rear angle... all better!