[Kingranch]

1990 gt boosted

Car pulls really hard through all gears but in 3rd I'm getting a bad vibration only under hard throttle... feels like back rear/right shakes.
No other gears vibrate even when I smash the throttle....all smooth as silk but 3rd.

Ideas? The car is relatively new I built it up w parts and the tko was supposedly newer rebuilt... I'm skeptical of that 3rd gear but I wonder why it's smooth if I baby it just not hard acceleration in 3rd only

 

[Kingranch]

Thinking either trans or maybe the Pinion angle is causing the vibration under heavy load

The car is smooth in other gears so I was thinking driveshaft is ok

 

[Dwain]

just like tires, I believe driveshaft vibrations can happen only at certain speeds. I dont know 100% if thats true, but I would think it is. Might be worth at least checking for ujoints that have play.

 

[Kingranch]

just an update.
I swapped the trans out for a tkx. 3rd gear vibration is gone now and car pulls hard and smooth.

Moral of story a vibration can be anywhere in driveline and this was caused by a failed thrust washer in trans

 

[Blown85GT]

Thanks for following up on this, I have a similar issue in my car.
I have a 3550 trans (similar to TKO) and I have a vibration under load that is most noticeable in 2nd gear and seems to be smoothest in 4th gear.
I'm planning to pull the trans and dig into it this winter or early spring.
I don't want to spend the cash on a tkx.