justoyz2

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?

99FormulaM6r

iTrader: (2)

Sounds like tire balance or possibly a bad alignment (but more so balance). Does it have this same vibration if you cruise at 70mph in 5th?

justoyz2

Nope, no issues with 5th gear; I have been driving the car in 5th.
It has no issues with anyother gear except for 6th gear.

99FormulaM6r

iTrader: (2)

You could probably post this in the manual transmission section as opposed to suspension then. I guess that's my only suggestion, lol, don't know how else to help!

1 FMF

iTrader: (1)

i would need to look at the t56 service manual, I don't remember what shaft the 6th gear sits on in the transmission. if it's on a separate shaft than 5th gear then that could explain the reason 5th gear has no vibration, so it could be a shaft/bearing issue in the trans. 6th is also an overdrive gear, just like in an auto trans if you were to heavily load an overdrive gear such as towing you can wreck it, Or I should say because it is a small gear they can chew up easier so you might just need a new 6th gear.
What you can try to do is when you have the vibration at speed is
(a) hold clutch in while still in 6th, still have the vibe?
(b) with clutch in, shift out of 6th into a netraul position, have vibe?
(c) release clutch with shifter in neutral position at speed, have vibe?

if you have vibe in all 3 cases then it's a wheel, drivetrain, or transmission output shaft problem. if it goes away for one of the cases then thats pointing to a transmission problem.

and you can drive on level road at 50mph in 6th at 1200 rpm, still have vibration then?

justoyz2

I think I have narrowed it down to one of four things or a combination of the
four: (6th gear is not the problem, if it were bad, I would hear grinding or noise)
-pinion angle
-transmission shim(surrounds the yoke)
-engine/tranny mounts
-too low gear ratio

Tomorrow:
-check pinion angle to tranny


Saturday:
-install 3.73 gears
-install engine/tranny mounts


Monday
-recheck pinion angle to tranny if any problem exist