Early GTV to late GTV driveshaft switch? - Page 4 - Alfa Romeo Bulletin Board & Forums
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post #46 of 48 (permalink) Old 04-05-2015, 11:10 AM Thread Starter
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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.

-Richard
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post #47 of 48 (permalink) Old 04-05-2015, 02:30 PM
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Hi Richard. I chased a rod bearing knock all over the car for a year because I didn't want to admit the engine needed to come out. I feel your pain.

Gary Williams
Many Alfas. All gone, but none forgotten
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post #48 of 48 (permalink) Old 01-28-2017, 07:00 PM
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More than once I have found the transmission output flange nut loose when doing driveshaft work. I remove the flange now and check the mating surfaces, as the wobbling flange and shaft can create grooves that prevent the flange from running true even when tight. Same goes for the input flange on the differential. More than once I have had to flatten the surface that mates to the bearing inside to get the flange to run true. Seems the flanges are fairly soft metal.

Glad you figured it out!
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