It has taken over a year and countless hours, but I finally got rid of a bad driveline vibration coming through the T5 shifter handle at highway speeds- 70-85 and higher. The amplitude peaked at 80-85 and got a little better if taken to higher speeds. The vibration increased significantly (scary) if shifted into neutral or the clutch was pushed in when coasting at speed. No other noises, just bad vibration /sound through the shifter. Vibration still there if engine is shut down and coasting at 75+, or with the clutch in and engine idling, so it was a driveline issue, not engine or clutch issue.

This first occurred after a somewhat large repair project where the car was apart and off the road for 4+ months. During that time I changed the pinion seal and the output shaft seal on the T5, among other things like drivers side floor pan. I was not sure what had changed to cause the vibration.

1st step was replacing the stock steel driveshaft with an aluminum 2001 LS1 shaft. Vibration got worse!. I had the LS1 aluminum shaft taken to be balanced at a local Fleet Pride, and the tech said the balance was great- “better than most shafts when brand new”, but he put a small weight on it to make it “perfect”. Still had the vibration. I then bought a brand new custom aluminum shaft from an eBay deal, and the problem got only slightly better, but was very much there. To summarize what had been done, without success, to try to fix the vibration:

1) LS1 driveshaft
2) Balanced LS1 driveshaft
3) New Custom Aluminum Driveshaft -ebay deal
4) New transmission output bushing
5) New OEM style rubber trans mount
6) 1 New OEM engine mount
6) T5 Rebuilt, main (output) shaft checked and less than .002” runout.
7) New clutch, pilot bearing, throwout bearing
8) 9 bolt rear torn down and new bearings installed, bearing preloads set to spec
9) Removed tires and rotors and rev car on jackstands- vib still there at 75+
10) Hose clamps positioned on driveshaft to try to “field balance” - moderate improvement, but not good enough
11) Adjusted pinion angle by placing shims under trans mount, which brought the pinion angle from -2.4 degrees to -1.8 degrees. I wanted -1 degree, but could not get there with trans mount shims
12) Axles checked to be straight and within spec runout at wheel flange
13) New brake rotors
14) New ring and pinion and new (used) pinion yoke- problem slightly worse and now vib felt like also coming from back. Turns out the the replacement yoke had more runout than my old yoke

15) 2 weeks after the ring and pinion job, one of the bearing rollers between the input and main shaft on the T5 stopped “rolling” and destroyed the bearing surfaces on main and input shafts in the process. I think the driveshaft vibration may have killed the bearing, which then killed the main shaft and input shafts.

Here are the steps that actually fixed it. These 4 things were done at once so it is hard to nail down which actually fixed it:

1) T5 rebuilt with new main shaft and new input shaft
2) New Denny’s Driveshafts 3” steel driveshaft, claimed good to 10,000 rpm
3) Pinion angle set to -0.5 degrees relative to crank/trans centerline
4) Ujoint clips modified at rear yoke to reduce driveshaft runout at rear yoke to 0.002”

I just took the car for a ride last night and it was smooooth at 80mph, which had previously been the worst speed for the vib. I am a happy man.


All I can say is if you work at any problem long enough, it can be solved.

 

wow man, good on ya! looks like lots of hard work!

 

I had that problem when my car was NEW, back in 89. It turned out to be the driveshaft, which eventually destroyed 5th gear. new tranny and new 1LE ds fixed the problem.

 

I had horrendous driveline vibration problems (at similar highway speeds) in my 84 Buick Regal after installing a 4L60. I went through (almost) the same hell as you as well, but in a different order. I think from comparing the two cars, we can narrow it down to the tranny shafts or the u-joint clips. Here's why:

1. I started with driveshafts. Steel, aluminum, new, used, balanced, different diameters, you name it! None of them fixed it. Sounds like you had the same experience, so throw out driveshaft as the problem.

2. Rear end ratios - I tried changing between 2.56 and 3.73 ratios (both completely different axle assemblies). The commonality was that they both vibrated at the (roughly) the same driveshaft speed, which points to the tranny or engine.

3. Rear end pinion angle. I had adjustable control arms and a very good angle finder. I even tried misaligning them intentionally. Nothing made the problem better or worse, actually.

4. I never seemed to have any vibration problems with the TH-350 I had in there originally, and I used both the 2.56 and the 3.73 with that setup. Obviously, in my case, this pretty much points to the tranny as the culprit.

Can you explain how you modified the rear u joint clips to reduce the driveshaft runout? I am not sure how that would be done unless the 9-bolt has a completely different u joint yoke than a 10 bolt (i've never looked at a 9 bolt).

 

To explain the u-joint clip mod:
I had runout evident in the driveshaft, but it was actually due to runout in the differential yoke. The runout was aligned almost perfectly with the axis of the u-joint where it seats into the yoke. All 3rd and 4th gens use inside style u-joint clips. To make a compensating adjustment, I had one of the clips machined 0.010" thinner, and used a clip shaped piece of 0.010" shim stock on the opposite side to take up difference. I installed driveshaft with the thin clip on the "low" side of the yoke, and this effectivly moved the driveshaft centerline within the yoke and reduced the runout to 0.002" , where it had been 0.019" before. This should only be done to address yoke runout, not runout that is built into the shaft.

The way to tell if runout measured in the driveshaft is due to the rear yoke or the shaft itself is to mark where the high and low spots are on the shaft, then unbolt the driveshaft and index it 180 degree in the rear yoke . Recheck the runout. If the high and lows spots on the shaft have swapped, for example, the spot that was previously "low" is now high, then the runout is in the yoke. If the high and low spots stay in the same locations on the shaft, then the runout is in the shaft. Most shafts have a little runout, and it is balanced out with weights by the manufacturer.