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gregh

Driveshaft/Differential Noise & Woes (Long&Probably

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1970 ‘02 with Ireland Engineering 5-speed kit – with rebuilt drive shaft – 3-bolt flange – new guibo – new center bearing. I’ve probably got less than 1500 miles on 5-speed setup.

Ever since I’ve installed the 5-speed I’ve had problems with a noise that sounds like it’s coming from guibo/center bearing area. For lack of a better description the noise sounds like muffled popcorn popping (or marbles in a rotating rubber drum) – related to the speed – when I put my hand on the DS tunnel while driving I can feel vibration. The noise is much worse under acceleration and at slow speeds. In fact the noise/vibration appears to disappear altogether at higher speeds – say above 40 mph.

I replaced the center bearing and that helped for a little while – maybe a couple of hundred miles. But the noise came back. I have not changed the guibo but when I changed the center bearing the guibo looked in good shape – no cracks – mushiness etc.

When reinstalling the driveshaft after replacing the center bearing it took quite a lot of effort to get the driveshaft in place – it seemed like the DS was a bit on the long side. This may be because I didn’t loosen up the differential mounts.

I’m pretty sure the drive shaft is straight in the up and down direction. I can’t say whether it’s straight in the left/right direction – I’ve never checked and I don’t know if that can be an issue. If the seam running the length of the bottom of transmission is the centerline of the transmission then it is within an eighth of an-inch of the being centered (based on the distance from the original transmission mounting tabs).

When turning the driveshaft by hand there doesn’t appear to be any interference.

The last piece of the puzzle is that when I put the car back up on jackstands this evening I noticed that the rear subframe mounts were completely shot. The rubber bushing and the tabs on both sides were hanging a good inch below the bottom mounts! I guess this explains the thud noise I hear under hard acceleration and when the rear wheels spin on sand when started from a standstill. There’s also a lot of leaking oil in and around the differential area.

So after all that background what am I doing wrong? Are my bad subframe mounts causing a wobble in my driveshaft, which in turn causes the center bearing to fail? Or do I need to try work harder on centering the DS?

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I am a rank amateur with some of this stuff, and I have not done a 5-speed conversion, but I would think of these three things:

1. If the driveshaft is aligned but as you said, a bit too long, then the diff may be moved forward and backward a bit to acommodate.

2. Replace the rear subframe mounts, if they are as beat as you say then it may help.

3. Dumb question, but do you have the "isolating donut" in place? The rubber donut that fits between the shift platform and the transmission tunnel? I didn't buy one and after replacing all those pieces, my car was really loud until I ordered one from my dealer, slit it to slip into place, and secured it with a zip-tie.

Good Luck!

Andrew

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This post is like the guy who can't start his engine after a 'tune up' and in the last paragraph mentions he didn't bother fitting spark plugs.

Sorry to sound sarcastic, but everything in the driveline is connected so anything loose or worn will affect it.

Renew the broken/worn bushes, loosen the diff. mounting bolts and let it 'settle' re-tighten, fill it with oil and test drive again.

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Worn subframe mounts can transmit more driveline vibration to the rest of the car. I had this wobble (for a lack of a better term) that would manifest itself after about 30 min of highway driving on my '76. I replaced the very worn out subframe bushings a few weeks ago and the wobble has gone away. Also the car stopped tramlining and wandering all over the place around town and on the highway. Under hard acceleration with worn mounts the rear subframe will move, which could also throw off the drivetrain alignment.

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Who balanced the tail shaft after shortening it?? If they didnt balance it thats your noise. I have the same noise after replacing the centre bearing, I got the 2 halves together wrong, one spline out and the noise and vibration is worse than when I started. Beaner7102

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