Oscillating or cycling vibration

[Kudzupatch]

Around 60-65 my suburban develops an oscillating vibration. It vibrates and then quits or almost quits about every 1 second intervals. It's just started and is very slight at this point but I can tell it is getting worse.

I am thinking u-joints, we had a Bronco once that ate them like crazy but I don't remember the oscillating though. It quits once you let up on the gas so it has be drive line. Transmission was just rebuilt 2K miles ago and that is only thing in the drive line that has changed.

Just thought I would ask before swapped them out in case there was something else I need to check.

[sntrym95]

I'd start with the u-joints. When you let off the gas you're unloading the u-joints, hence why the vibration goes away.

[OutlawDrifter]

sounds like you're on the right track. make sure and replace with a quality unit.

funny you should mention this, pretty sure the ones in my rcsb are about due. noticed on the interstate around 76mph they are getting noisy.

[JetForceF22]

Originally Posted by Kudzupatch

Around 60-65 my suburban develops an oscillating vibration. It vibrates and then quits or almost quits about every 1 second intervals. It's just started and is very slight at this point but I can tell it is getting worse.

I am thinking u-joints, we had a Bronco once that ate them like crazy but I don't remember the oscillating though. It quits once you let up on the gas so it has be drive line. Transmission was just rebuilt 2K miles ago and that is only thing in the drive line that has changed.

Just thought I would ask before swapped them out in case there was something else I need to check.

^3rd what they are saying.

I just read another thread not to long ago was experiencing, literally, the exact same problem. New U-Joints fixed the issue. Sounds everything like bad U-Joints to me.

[Kudzupatch]

That is where I am leaning. Might pull it out tomorrow.

[mountie]

After 382,000 miles, I still have a slight , similar sound. About the 75 mph speed. It never went away, and obviously, all has been changed/serviced, except for my rear end.

I just consider it a mystery.

[Keith Seymore]

Discussion regarding "oscillating" disturbances:

Originally Posted by Keith Seymore

In the biz, a "pulsating vibe" is called a "boom/beat".

It results from two disturbances, very close in frequency but slightly out of phase, such that the amplitudes gradually add and subtract over time. That's what results in the pulsating effect. The closer the two frequencies are the slower the boom/beat.

At any rate - it means you have two disturbances going on, like 4th order engine firing being very close to second order driveline, for example.

Fix either one of the disturbances (or dramatically change the frequency of one) and the pulsating effect will go away.

Originally Posted by Keith Seymore

Driveline imbalance is a "first order" of propshaft rotation disturbance (one "kick" per rev). U joints are a "second order" of shaft rotation (two "kicks" per rev).

Imbalance by itself usually results in a cabin "boom" (low frequency sound; almost more like a pressure that you sense) or a vibration that you feel, and normally is pretty steady. Large cabin volumes, like a crew or a Suburban, definitely are more sensitive to this. The boom/beat, or the phasing in-and-out, is a result of the driveline finding some other disturbance that is close to it in frequency.

[Kudzupatch]

Apparently it was the U-joint. I blew a wheel cylinder and while I had it in the shop I replaced the joints. When I took it for a drive I was so focused on making sure the brakes were OK, had a LOT of trouble bleeding them, I forgot about the u-joints but looking back I don't remember the vibration being there.

[775stepside]

I'm having a similar issue on my 89 Silverado 2wd. Just got it up and running, has new front end and new tires and alignment done. Trans fluid looks good but I haven't checked the diff. I'm getting like a humming noise at speeds around 20mph and above. Like stated above too as soon as I let off the gas it stop, and during high speed if I slightly give it gas it starts to chatter like something is loose? I'm leaning towards my u joints too

[Kudzupatch]

Never had one 'chatter', just vibrate and never at low speeds. Always around 50+.

Ujoints fixed mine and I found out part of it was the road. I still get just a little bit on two roads I travel regularly but I did have a bad u-joint.