I bought my RS used with supposedly 69K original miles. The T-5 in her whines a lot in 1st, 2cd, and 3rd. I will be checking the fluid to see if its low. Anyway, I have done a lot to this car and today I put on basically new stock 16x8 Factory rims wrapped with 4 new Sumitomo HTR+ 245/50/16. My problem is...the car has this kind of shake or shimmy when I'm coasting/cruising in 5th gear between 45-55 mph. The whole car seems to shimmy from the rear forward or so it seems. I thought it was an out of balance rim/tire, but it still does it after I had all the new rims/tires installed and balanced. My question is, could this be a problem in the tranny or driveshaft??? I can witness the gear shift shaking a lot, especially when it shimmys like I'm describing. 5th gear is also weird in that if I shift from 4th to 5th at anything less than 50-55 the car really seems to drag as if I shifted to early. What do you guys think is up with my car???

 

NObody has anything to say huh?

 

what are your rpms at at that speed? if they are too low that will cause that, mine does the same thing, with my cam it doesnt like to be under 2000 rmps in any gear or it does the rocking back and forth

 

The tach is broken...it reads about 1500 at idle and it even gets worse the faster I go...it reads almost 4000 when I'm cruising in 5th at 70mph.

 

How old are your u-joints?

 

I don't think they've ever been replaced...I bought the car when it had 68K on it, and it was bone stock. It now has 70K and I have done all the mods listed in my sig.

 

Does it act the same in fourth gear at that speed? If so, I would suspect something in/on the driveshaft; either U-joints or tailshaft bushing in the trans.
If it doesn't act up, I would suspect the engine tuning is off...

 

have you tried checking if your drive shaft and rear axle are prefectly straight. lined up. this happend to me with my 84 camaro. shop teacher helped me figure it out. and it was laso making a humming nosie. but i hav an auto so it was almost all the time.