I have been chasing a drivetrain vibration on my 92 Camaro since 2003, and before that, I was chasing the exact same type of vibration on my 84 Buick Regal. I finally solved it...it was the driveshaft. However, between the two cars, I have had about SIX different shafts in there...some new, some used, some aluminum, some steel, some factory, some aftermarket.

ONLY ONE COMPANY was able to make a shaft that worked for me: Denny's Driveshaft. I can not say enough abut these guys - the owner (Denny) answered the tech line when I called and talked to me for twenty minutes - great guy!

Here was the exact symptom of the vibration, in case anyone else has the same issue:
Driveshaft speeds above 3000rpm result in major resonance through the car that is almost scary. This comes on at highway speeds, and only gets worse. Pushing in the clutch, putting it in neutral, accelerating and decelerating - makes no difference - the vibe never stops. When stopped, in park or neutral, the engine car free rev to the redline without a hint of vibration.

Between the two cars, here's the steps I took to try to remedy the situation before finally getting the Denny's Driveshaft:
Buick (carbureted ZZ4 engine, TH-700):
1. Adjustable control arms to create equal and opposite u-joint angles (both about 2.5 degrees)
2. Rebuilt tranny - TH-700R4
3. Rear - 3.73 Richmond gears w/ auburn posi
4. Used junkyard driveshaft
5. New steel driveshaft, made by a shop in Alexandria, VA (whose equipment wouldn't even go to 3000 rpm, where the trouble started!)
6. New Inland Empire aluminum driveshaft.
7. SELL THE CAR IN COMPLETE FRUSTRATION.
8. Abandon American cars for the next 3 years.

Camaro (built 350 roller w/ stealthram and Electromotive engine controller, T-5 Tranny):
1. I built the engine, and it was fully balanced with the flywheel and a new damper was used...vibes still there.
2. Rebuilt tranny
3. Aluminum driveshaft from 2002 Camaro (with factory damper). This one felt better up to 3500, then hit the death vibration just like all the others. Interestingly, this driveshaft had the worst runout of any of them, at 0.040" T.I.R.
4. Adjustable torque arm to create equal u-joint angles (2 degrees each)
5. New Denny's Shaft. Problem SOLVED!

I have read over and over about people describing the exact same problem as me, and going through a bunch of driveshafts, trannies, and rear ends (even spending $2400 on a 9" that STILL vibrates!). All I can say is that the guys at Denny's can build a driveshaft, and if you've got a fast car, there's no reason to skimp on a high quality shaft anyway. Mine was $390 after shipping. I thought it was a bit high, but once I drove it, I realized it was a bargain! I can finally take my car on the highway again!

By the way, the vibration in the Regal was so bad that it eventually loosened the pinion nut on the rear end. This make the pinion gear lock against the posi unit, which instantly locked the rear wheels. Not pretty. Luckily I was in a parking lot when it finally let go, and not on the highway. So don't drive in a car with a bad vibe for too long...I put about 10k miles on the regal's rear end before it failed.

 

By the way, I bought the 3" Heavy Duty steel shaft from Denny's, with the stock Camaro u-joint sizes. Here are some pics.

The factory shaft had huge balance weights, and the Denny's one had tiny ones. Just goes to show how crappy the stocker is.

 

looks good! what shop did you go to in Alexandria, VA? was it driveline?

 

I can't remember the name of the shop for the life of me...sorry! Bottom line though - if a shop can't spin something over 3k rpm, they probably have never balanced a shaft for high speeds.

 

I agree with the Denny's drive shaft. Put one in a different car last Summer and wow, on the highway need to keep an eye on the speedometer to keep from getting tickets. The car runs so much smoother that one can't tell the speed from any sort of vibration level. There just isn't any.

RBob.