Another Driveline Shimmy

[73novaguy]

So here it goes! I have just recently installed a Hotchkis TVS Kit. And today I went and got the front end aligned. Now they set everything up just fine and the TVS kit went in just fine! But now all of the sudden I have excesive vibration under load in all gears! As long as you are "coasting" or not under any heavy load there is no vibration, but say you come to almost 15MPH in second and slowly roll on the throttle then it feels as if a helicopter is gonna land on the roof! The vibration seems like it is more towards the center/rear of the car/ Crawled under there and the u-joints appear to be fine (should be they have less than 2000 miles on them and they were fine before I did the lowering). So the tranny (TH350) and rear end (Mosier 12 bolt) are both new items with les than 2000 miles on them and the driveshaft has been balanced. So what do I look for now? I thought that it might be the exhuast run to close to the bottom of the cross member so I lowered the exhaust and gave myself 1/8 to 1/4 of room and the vibration still exists! Any Help please! I was gonna drive it to Milwaukee this weekend for the Milwaukee Mile races, so any advice! If you need any pics, let me know! Thanks guys!

[dhardison]

Justin have you checked the pinion angle since installing the Hotchkis kit? Maybe you have too much positive pinion angle (pinion pointing up at the floorboard). I had to install a 2degree shim to get mine right and actually I could use 4degrees to get it perfect.

Only other thing I can think of is... How much yoke do you have in the trans at ride height? Too little will cause a bad vib (especially under load), but too much is just as bad as it will beat against the tail shaft.

Both of these issues would be felt under load.

Dan

[73novaguy]

I didn't install any shims in the rear since the TVS kit! It looks like the rear end yoke points towards the ground! And no I didn't check to see how much engagement I have, but it was fine before and lowering it should cause it to gain some engagement! Because when i lifted my 1/2 ton I lost a bunch of engaga,ment

[sinned]

I didn't install any shims in the rear since the TVS kit! It looks like the rear end yoke points towards the ground!

Most powertrain combos have negative angle (point down at transmission) which means the pinion needs to be positive (opposite the transmission). How much is it pointing down? A lot or just a little? Any idea what the trans angle is or the driveline itself? An angle finder would really help you right now.

[dhardison]

Did you have the 'shimmy' before the front end was aligned?

Is it possible that you don't have the rear u-joint completely seated in the pinion yoke? If your pinion yoke has the side locating tabs it's very easy (at least for me) to get the u-joint stuck on top of one of the tabs instead of beside it.

If it were me I'd put the rear end up on jack stands. Have someone look under the car (from a safe distance) while you lightly run it through the gears. If no shimmy, then it's in the front end, otherwise you'll hopefully be able to see what's out of whack.

Dan

[73novaguy]

I don't have a angle finder, but will try to find one and give you guys some measurments. And I'll get her up in the air and see what else I can see! But it had the shimmy before the front end alignment, so I know it is a drivetrain shimmy!

[68BNUT]

I had a jeep cj5 and after I put a lift kit on it, it had the same problem. The lift kit didnt take in for pinion angle. If thats the road your looking down then your on the right track. Ahhhh the good ol days wondering what was going to shake off first!!

[CAMAROBOY69]

My first question would be-- How much did you lower the car? When you lowerd the car did you get the driveshaft shortened??? If not it could possibly be further into the rear of the transmission than necessary and when you give the car gas it is causing the rear dif to lift just enough to bottom it out into the tranny yolk. Look at the rear seal on your transmission. If it is getting tore up or starting to have excessive wear, then get the driveshaft shortened. And while you are under there check your pinion angle like they mentioned in the above posts.

[73novaguy]

Well I put in the 4 degree shims and the shimmy has pulled a great Hudini vanishing act. I just dropped the leafs down enough to get them in snugged er back up and took the car for a cruise and tadda, bad vibrations are gone! So thanks guys! I am about two seconds away from posting a pic in the Project Update section, hope you all like it!