Driveshaft Vibration, The Final Solution?
It's out of balance somewhere - and about the only way to fix that on the car in the garage is with the hose-clamp method. As I said, I've tried this a couple of times. But here we go again.
There are 4 places to place a hose-clamp (obviously it could go anywhere but simplifying)
A-right behind the donut - i.e. front of the front section
B - rear of the front section
C - front of the rear section (behind splines)
D - rear of the rear section (right in front of the diff's UJ)
I've always assumed A, B or C are the likely candidates.
A because it's right near the flexible donut where any imbalance could be amplified. (although the olive and nose bushing really help here)
B is near the center flexible mount which could have the same effect, plus it's in the middle of the shaft where the "skipping rope" effect would have higher amplitude.
C is about the same as B - only worse because it's behind the center UJ and the splined joint
D, on the other hand, is right by the diff which is the most firmly located of these 4 positions, I would have thought (are you seeing where this is leading?)
My method. Attach a hose-clamp at position A. Start engine, into 5th gear, rev up to 55mph and feel the vibration. No change? switch off, shift the hose-clamp 180degrees, try again. And again at 90 degrees and 270 degrees form original. Nothing?
repeat at position B (not much)
repeat at position C (couldn't tune it out but wow it's getting sensitive to changes now. I could make it MUCH worse at C)
So try at position D, which I don't think I've ever tried because it's right by the diff (that I've changed twice) . Tried one place - and it vibrates really badly now, worst ever. So move 180 degrees and, gasp, it's smooth. Vibration is almost gone. Attach a 2nd clamp in the same location, and it's vibrating again. Remove 2nd clamp, move single clamp to 270degrees and it's better still.
Then after fiddling around for a while I found the "perfect" spot and can no longer feel it. I just went for a 30 mile test drive and I think it's gone.
I don't pretend to understand this yet - 3 driveshafts balanced perfectly on the balancing machine. 3 different UJs at this end of those shafts. 3 diffs with 3 pinion bearings etc. Various attempts to correct/alter working angles for the joints - yet one hose clamp is the trick that works!?
my conclusions after all these attempts.
- don't use poly-bushings - and softer is almost always better
- making everything super-tight so that it "can't move"...doesn't work
- get a pro to balance the driveshaft, but you don't know for sure until it's back on your car
- iPhone apps are handy, and it's physics, not magic.
Thanks to everyone who commented, suggested, recommended etc over the years. Especially Tom, Steve and Andrew for listening.