Driveshaft or U Joints?

[87GrandMarq]

I took a video but you can’t hear the noise so I’ll try to describe it. On my 87 mgm there’s a vibration through the body pretty much at anything above 30 or so. Now when I get to about 60 it starts to vibrate worse and there’s a hum. It’s sort of like a week bearing hum but it comes on within 5 mph and increases with speed and instead of a steady hum it’s like it oscillates. I know I’m not the best at describing noises but that’s the best I can do. I have u joints on standby as I’m sure the ones on it are original but could it be the driveshaft itself?


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[DerekTheGreat]

Oscillates. That sounds like a bad u-joint to me. They kind of pulse. If it was the driveshaft, the whole dash would shake and all that.

[87GrandMarq]

I’ll do the u joints maybe this weekend when I have more time off. Yeah it’s like a pulse and it comes on quickly instead of a wheel bearing sound that starts off at low speeds and gradually gets louder. And I couldn’t change the sound when I would steer the wheel either way so I’m sure you’re right.


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[WagonMan]

A good indication of bad U-joints is a major "clunk" when shifting from drive to reverse. Any noises then? WagonMan

[kishy]

A good indication of bad U-joints is a major "clunk" when shifting from drive to reverse. Any noises then? WagonMan

I will +1 this but I will also note that U-joints can be bad, and still tight.
I would also guess that most of these cars by this point have a little bit more lash in the diff than they originally did, which can contribute a clunk, so a clunk also does not guarantee the u-joints are bad.

Specifically, when the bearings in the U-joint dry out and start to seize up, the joint can be tight, but it does not move smoothly on the bearings, so it vibrates as it fights changing angles through the dry bearings.
If it gets like this, it can be totally silent from inside the car, but might make a slight squeak-squeak-squeak noise when just idling forward in gear as it rotates.

U-joints kind of suck to change but they aren't super expensive, and if their history is unknown, I'd just change them if it were me.

I still have a wicked vibration in the wagon, at much higher speed than you, which I believe is coming from somewhere in the rear end. Keep in mind there are several bearings back there which can and do wear and fail, so your problem could be back there.

If you can safely support the car in the air and let the engine idle in 1, with wheels turning freely, you might be able to get a better feel for where the noise is coming from which will help tell you where the problem is. This is extremely dangerous though, the risk of the car dropping off whatever you put it on is higher with the wheels spinning, and the risk of damage or injury if it does fall is also higher with the wheels spinning.

[gadget73]

Pulling the driveshaft and running the joints through their full range of motion will tell you right quick. If its notchy or stiff at all, its done. It should move smoothly through the full arc of motion with no sign of hangup.

[87GrandMarq]

Driveshaft or U Joints?

I don’t have anywhere to safely put the car up on stands but that would be a great idea. And good call on the rear suspension. I’m sure it’s all original, is there anywhere that sells rear control arm bushings for these cars?

Wagonman, no there’s no thud going into gear.

Gadget, it’s easy enough to pull the drive shaft and change the u joints so yeah I think I’ll do that and check for stiff bearings. That was my thought as you and Kishy pointed out. The car has unknown mileage and I know has a few periods of sitting so I’m sure there’s bound to be something stuck.


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[jaywish]

while it is out make sure the shaft is true.

[gadget73]

and do not put the slip yoke in a vise. Someone did that on my car when the U joints were changed before I got it. Couldn't ever get the damn thing to not leak at the tailshaft until I actually inspected the yoke and found the vise teeth marks on it.

[massacre]

and do not put the slip yoke in a vise. Someone did that on my car when the U joints were changed before I got it. Couldn't ever get the damn thing to not leak at the tailshaft until I actually inspected the yoke and found the vise teeth marks on it.

Wow

[87GrandMarq]

Some people just shouldn’t work on cars…

And yes I’ll definitely check to see if it’s straight and the weight is still there.


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[DerekTheGreat]

Ashley's '89 did not clunk when put in gear. However, it had a pulsing vibration that started around 65mph and got pretty noticeable at 80. Front U-joint was bad.

[87GrandMarq]

That’s pretty much how I’d describe it. And has a humming sound too like those trucks with the big tires.


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[gadget73]

joints have to be really bad to have enough slop to bang. usually means the needle bearings have completely disintegrated. They get dry and start binding long before they turn completely to powder. Its one of those deals where if you ignore it long enough eventually it will start to bang but very unlikely it went from perfectly fine to making nasty noises with nothing in between.

[DerekTheGreat]

U-joints have to be really bad to have enough slop to bang...

This.