M1010 suddenly vibrates at low RPM

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My M1010 suddenly developed a powerful vibration at low RPM, whether parked or moving. I had things running smoothly and quietly, until a few days ago. Now it's smooth and quiet above about 820 RPM, and it vibrates violently below that.
https://youtu.be/DAg0p8qhiOM

I did a search, and read a bunch of threads about this. I still could use some guidance from those with more experience.

At first I thought it was a loose belt, but the tensions are correct. The upper alternator belt does vibrate, as usual, but it was pretty quiet until a couple of days ago. Here is a shot of the alternator belts:
https://youtu.be/wSw4cfK8Da0

I've read about the harmonic balancer causing vibration problems. John at Hillbilly Wizards checked mine out at 2,500 miles and said it didn't need to be replaced. The truck has 6,000 miles now, but I see nothing moving in the balancer:
https://youtu.be/2ruydbnJzSM

And here's a shot looking down the P/S and A/C belts.
https://youtu.be/cu6lSzGQMCk

The belt tensions are correct. The air filter bolts are tight.

Unless someone has a better idea, my next step will be to remove all the belts and see if it still vibrates. If not, I'll add them back one at a time until the problem returns. I hate to do this, though, since I just got the new belts all broken in and set to proper tension...

I'm hoping someone who knows these trucks will see or hear something in these videos that will give me a direction to pursue.

Thanks,
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[cucvrus]

I am guessing at best. I say the power steering bracket is cracked or broken. Since they are hard to come by I would suggest removing it and getting it repaired. Do you have ALL the power steering brackets and bolts tight on that steering bracket? That is a common issue. I am going to be removing a power steering pump today on my Terminus M1009 for replacement of a power steering pump pulley. I hope that helps. I have fixed a few of the power steering pump brackets myself. A welder and a few scrap brackets make a good heavy duty bracket. I will see if I can get some pictures. Good Luck.

 

[gavland]

just guessing but if its automatic check the flywheel and torque converter to see if a weight fell off that helps balance it. if a flat little peace of metal falls out when you take bottom cover off that's it.
happened to me on my gas Chevy truck before.

 

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I am guessing at best. I say the power steering bracket is cracked or broken... Do you have ALL the power steering brackets and bolts tight on that steering bracket?

I checked the bolts on the PS bracket. They're all tight. I see no evidence of breakage, and when I put my hand on the bracket, I feel no pronounced vibration.
https://youtu.be/mc4kRKqwsQI

just guessing but if its automatic check the flywheel and torque converter to see if a weight fell off that helps balance it. if a flat little peace of metal falls out when you take bottom cover off that's it.
happened to me on my gas Chevy truck before.

I put my hand on the valve cover, and felt no unusual vibration there. An unbalanced flywheel would vibrate the entire engine, right?

I put my hand on the alternators, and felt the usual level of vibration there.

Then I tried the A/C compressor. That seems to be the problem. I pushed in the cold advanced screw to increase the RPM while I had my hand on the A/C compressor, and the increased RPM made the vibration stop.

I thought perhaps it was low on gas & lubricant. It took 4 cans of gas on recovery, ~3500 miles ago, and I've not had occasion to use the A/C since testing it then. I went to check the pressure, and perhaps put in another can of gas, and it turns out my fitting is too small. I've used it on a number of cars, but I guess I need a bigger fitting for the truck.



I know A/C compressors are not an issue for most CUCVs, but I'm sure the SS community has far more A/C expertise than I do. I've changed belts and added gas, and that's about it. So I have a 30-year-old AC compressor with 6,000 miles on it, and very little time with the A/C turned on. It suddenly developed a serious low-RPM vibration with the A/C turned off. Is there anything I can do, or do I just take it to a shop that does A/C?

 

[cucvrus]

Cut/remove the belt. It is winter time and you don't need it now. That is just an idea. And you ask for ideas. When you do get it fixed. Spend the money and get it converted to 134A get rid of the R13 if you haven't already.

 

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Cut/remove the belt. It is winter time and you don't need it now. That is just an idea. And you ask for ideas. When you do get it fixed. Spend the money and get it converted to 134A get rid of the R13 if you haven't already.

When I first bought it, I had a local mechanic check it out, change fluids, etc. before driving it 1,000 miles home. He converted it to 134A. At least I paid for him to do that. Is there a way I can tell if it was done properly?

Thanks,
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Edit: Found this. Tomorrow I go looking for the smaller, low-side fitting. We'll see if it just needs oil.

 

[KansasBobcat]

Cut/remove the belt. It is winter time and you don't need it now. That is just an idea. And you ask for ideas. When you do get it fixed. Spend the money and get it converted to 134A get rid of the R13 if you haven't already.

Same symptom on another vehicle and cutting the belt worked great!

 

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Well, I feel really stupid.

I added a couple of cans of refrigerant to the compressor. It made no difference. So I gave up for now, and removed the belt. And even that made no difference! So I stood there poking around, feeling the vibrations, and they were definitely coming from the compressor, but it had no belt?!?! Then, out of the corner of my eye, I caught a glimpse of a washer under the compressor that was dancing to the vibrations. Washers aren't supposed to dance. I'd overlooked the rear pivot bolt on the A/C compressor, and it was loose. I tightened it down, and the vibration stopped immediately.

So those who said it was a loose bolt were right. I thought I'd tightened everything, but I missed one. Not my finest moment. Thanks for all the advice.

 

[m1010plowboy]

Loose nuts

I like it when a plan comes together! Nice easy fix and it's good to have some bunny remind us to check all our nuts once in a while.

 

[Chaski]

Nothing like a good DOH! yelled aloud followed by a facepalm. At least it was only you, that NEVER happens when you have an audience.