U-Joint Going Out? - Major Noise...Please Help

[76sierraclassic]

Hey guys....been a while since I've been out here...haven't had much time or money to spend on the old '76....

Need some help/advice please....

Driving down the road the other day, stopped at red light, and when I started accellerating away from the light, there was the most awful noise coming from my truck. I don't know why, but the first thing I thought of was a big piece of rusty barbed-wire had gotten wrapped around my driveshaft or in the fan or something and was beating the crap out of a fender well or the bottom of my truck. I pulled over into the nearest parking lot to look around and didn't see anything out of whack. I got back in made it maybe 20 yards down the road and it did it again. Pulled over again, looked around again, still nothing looked wrong. I got back in and drove probably for 4 miles with no noise at all, everything running great, and then I turned into a parking place, and there was the noise again but it only lasted a couple of seconds this time.

I sat with it idling and revving it slightly to see if I could find what it was, but everything sounded fine, so I headed on. I could go for several miles, and then hit a bump in the road or turn or something and it might or might not make the noise again - there appears to be no consistency with it.

I was talking to a buddy of mine and he suggested it might be the u-joints going bad. Others have told me that it wouldn't be quite as loud as this if it was a u-joint, but I just have no idea.

I crawled up under the truck this evening and there is some kind of bracket at the back of the transmission sandwiched between the tranny and the tranny mount. Not sure what it's for, but it sticks out about 18 inches towards the drivers side, and it's a little bit loose. I could grab it and wiggle it, and when I did it would hit and make noise. I'm guessing that maybe this shouldn't be moving whether it's the source of my noise or not.

Not sure if it matters or not for purposes of this thread, but I have a 350 engine with the Turbo 350 auto transmission, long-wheel base with a one piece driveshaft.

Any ideas or suggestions will be greatly appreicated!!!!!

Thanks,
Mike W.

[89 crew]

Carrier berring is another possibility. I would take the truck for a drive (not far from home) till it made noise. when it did I would pull over and check the U-joints and carrier for heat. If they were all about the same temp and a reasonable temp look elsewhere. If you find something hot replace it if it can't be lubed. If your bracket is what I'm thinking of, it is a support brace for the speedo cable.

[magnethead]

Originally Posted by 89 crew

Carrier berring is another possibility. I would take the truck for a drive (not far from home) till it made noise. when it did I would pull over and check the U-joints and carrier for heat. If they were all about the same temp and a reasonable temp look elsewhere. If you find something hot replace it if it can't be lubed. If your bracket is what I'm thinking of, it is a support brace for the speedo cable.

no carrier- 1 piece shaft

[blaserman]

If you have any play in the shaft it is the joints,as far as the item you were talking about my son had one on his truck that went bad and made a lot of noise, was a bit_h to change.

[76sierraclassic]

Well, I think I may have found out what the problem is....not 100% sure yet, but should know in a little bit. I think a nut has backed out and is being knocked around by the flywheel. I drove it a little while this evening, and when it finally started doing it, it won't stop. I crawled under and saw all kinds of little dents in the inspection cover, so I gotta believe that's what it is.

Thanks to those who replied to my post!!

Mike W.

[76sierraclassic]

Well, in case anyone cares to know, that was the problem...a bolt had come loose, hung on the inspection cover by the starter, and on it's way out it bent the shield enough that it was bouncing off the other bolts that were still in the flywheel.

Thanks,
Mike W.