I bought a 00 T/A with LS6 engine:

Mods are:
Global West suspension products (track link, sub frame connectors, tubular control arm and lower front end cross member, sway bars on both ends, and a hurst short throw shifter.

Performance is very good:

While crusing at highway speed in 6th gear I get a very bad vibration ( 70mph and above)

I have changed:

-(punkin) carrage bearings
- wheel bearing
-checked the pinion gear/ bearings for resistance and excessive play
-balanced the drive shaft
-checked the axles
-changed the wheels and tires

The excelleration has no issues, only when I go into 6th gear. Has anyone seen or heard of this problem?

 

So, no one has experienced this problem?

 

So you have no vibrations on 1-5th gears? Only when you're into 6th gear? Does it vibrate when you're accelerating or on decel also? What about when you're coasting on 6th?

 

It does vibrate when accelerating and deaccelerating. As to the coasting, you still feel vibration, coasting with the engine off the same thing, just not as bad.

 

I have a similar issue. Mine vibrates in 6th during decel bewteen 65-55...

 

Coasting when the engine is off leads me to think its bad pinion angles or the DS out of balance. If you are confident it is only in 6th, the 5th/6th cluster gear might have become sloppy on the back of the main shaft in the tranny. I think I actually have this problem with different symptoms.

I get a vibe only in 5th & 6th above 80 MPH and if I clutch it, the vibe goes away. I have ruled all the driveline out.

 

I had the pinion checked, it was around +3 degrees; I have adjusted it to around -3 (based on what the fabrication guy reccommend).

Pinion Gear:
- +/- 3 degrees of play with wheel lifted(rotating the drive shaft)
-adjusted the pinion angle to what I think is -3 degrees (is this too much)

What I learned today:
-stock gearing is 3.73 to 1
-current gearing is 3.42 to 1
-while in 6th gear, during acceleration, the car pings and is very slow to increase speed, starting at 80 mph
-tq bracing, mounted to the chassis is moving when driving the car (visual evidence on the chassis), plus alot of clunck type noises
-normal driving feels better with the adjusted pinion angle, until I get into 6th at highway speed

Overall:
-car still vibrates in 5th gear (100 mph or so)
-car still vibrated in 6th gear (not as bad as before, but it's still there, but doesn't want to accelerate

Plans for tomorrow:
-tranny shop to have a new bushing installed (do you think this will help?)

Plans for Saturday:
-replace gears in rear end
-replace pinion bearing/race
-replace crush sleeve

 

I have NEVER seen a transmission causing vibration issues. Not to say it can never happen but it's most UNLIKELY. As wrd1972 has stated, the 5-6th share the driven gear and if the 6th was causing vibrations, you would also notice it in 5th. I would lean toward the driveshaft/diff.

 

guys, I had the DS straighten and balanced. I changed the pinion angle, will recheck because I was told the -3 is for drag racing; and that I should be around -1 degrees.
I have slack in the pinion gear, going to change that this weekend. Also, I was told to replace the trans bushion (tail of the tranny). Since the angle was a +3 to 4 degrees it might have damaged the bushion....

 

I've "accidently" fixed an "unknown" driveline vibration by repairing the mainshaft/5-6 driven gear. The splines were over half way worn out. Since then, I've seen several cases where a loose 5-6 gear wears a groove in the mainshaft, and it actually does cause a high speed vibration.
In the OP's car, this may still be the case, even though it only happens in 6th. If this is the cause, then it will mostly be a speed-related vibration.
One way to help eliminate this would be to go high speeds in 5th gear, and see if it vibrates.
Also, the splined part of the gear is actually on the 5th gear side, and the pressed on part is 6th. So maybe if the journal is worn more so than the splines, this could isolate the vibe to 6th.
Either way, it seems that everything else has been checked over. Might be a good idea to go into the trans. Good luck and keep us updated!

 

Fixed my vibration in 6th gear:
Things I changed:
-wheel bearings (not damaged)
-carrage bearings (damaged)
-pinion bearings (not damaged)
-pinion gears (some play 5degrees each way)
-drive shaft (straightend and balanced (damaged))
-corrected pinion gear angle( way out of spec)

No vibrations in 6th gear... car drives very good... Hopes this helps someone else

 

Good inforamtion. I'm glad it wasn't the trans.

 

Just got done installing 4.10's in my car and now I have a vibration in 6th gear only under load around 55-60 MPH I think, I havent reflashed the computer yet. I have only driven the car twice since the instal, maybe 40 miles tops. I am trying to get the rear end quiet. I am almost there but now have this to deal with. I did do a few other mods while it was apart. I did the heater hose mod, removed the rear rubber spring isolators, and coiled on some 1/2 heater hose. I also installed some prothane LCA bushings. The car sits level now, but could that little bit have caused problems with the pinion angle to make a vibration? I pulled the trans mount and it is intact, so is the TA bushing on the trans. I did put the trans in each gear then climb under the car and checked to see how much play was in the drive shaft. Sixth had more play then all the other gears. I know the shaft is spining way faster at speed with the 4.10's. Might try sticking the spring isolators back in and see if it gets better. I know its not the rear end because everything is new.