Author Topic: Strange power-on wobble. Suspect ujoint  (Read 463 times)

Offline Geom

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Strange power-on wobble. Suspect ujoint
« on: October 21, 2019, 10:20:03 PM »
Hey guys, hope you are all doing well. It has been a while since I’ve posted on here, which I suppose is kind of a good thing, lol.

Anyway, my 4107 has developed this strange wobble from the back-end. It happens, usually under power, when reaching 60-62mph. It usually stops at higher speeds, but sometimes not. It also does it in second when climbing a hill at ~45mph.

It’s done this before and the problem “went away” for a while, so I just ignored it.
Well it is back again. It seems to have developed after removing the rear tires to replace the rear-wheel bearing seals.
I believe the seals are good and everything there seems to rotate as expected.
I’ve had the tires checked and balanced, and they were out of balance. But they’ve been rebalanced and I have centramatix wheel balancers installed on the rear wheels. 

Anyway, since after all of that, I’m still getting this power-on wobble, I suspect that the ujoints are the problem.
I got under the bus the other day and tried to rotate the joints and I’d say I have and inch or two of deflection/play in either direction.

I’m currently north of Albuquerque and guess I need to find someone to do the work.
We’re heading toward the Phoenix area.

What are your guys’ thoughts?
What can I do?
Should/can I keep driving it? (I’m limiting myself to under 60 mph).

Anything else I should check?
Can any shop do this job or does it need to be an “old bus aware” shop?
Where can I source the ujoints from? Luke? The book states they’re 1701 and 1708 ujoints. No joy just searching for that online.

As always, thanks for any help or advice you can offer,
George
1966 GM 4107
6v92 Turbo
V730

Offline Jriddle

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Re: Strange power-on wobble. Suspect ujoint
« Reply #1 on: October 22, 2019, 04:06:03 AM »


I got under the bus the other day and tried to rotate the joints and I’d say I have and inch or two of deflection/play in either direction.

George

You shouldn't  have any deflection in your U-joints. (I assume you mean up and down side to side play) If you have an inch or two you need to fix this right away. You don't want to loose that drive shaft causing other problems.

John
John Riddle
Wells NV
1984 MC9

Offline chessie4905

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Re: Strange power-on wobble. Suspect ujoint
« Reply #2 on: October 22, 2019, 04:12:44 AM »
It is a common 1710 series u-joint, should be easily obtainable at any truck parts dealer. They aren't  that expensive either. If you do it yourself,  make sure to keep shaft pieces in phase. Grease after installation, they put almost no grease in them for shipping. GM #695232. Number probably has been superseded by now.

Even Amazon has them, although a little more costly than some.
I would pull the shaft and have a driveshaft shop replace them if the caps are rusted tight. They make a tool to remove them or you can whack the yokes back and forth to start the caps off. A good shop will inspect bearing boxes in yokes for wear and balance shaft if necessary. Btw, that is a very short driveshaft.

GMC h8h 649#028 (4905)
Pennsylvania-central

Offline chessie4905

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Re: Strange power-on wobble. Suspect ujoint
« Reply #3 on: October 22, 2019, 04:31:55 AM »
You are probably referring to rotational play. Either way if they are good or shot, I'd  just replace them and not having them on your bucket list anymore. While you are down there, make sure rear engine mounts are good. Broken mount/s have been known to cause vibration also.
GMC h8h 649#028 (4905)
Pennsylvania-central

Offline Bill Gerrie

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Re: Strange power-on wobble. Suspect ujoint
« Reply #4 on: October 22, 2019, 08:13:08 AM »
You might want to check the radius rod bushings. Be very careful under the bus. Block it so it won't come down on you if anything went wrong. Better safe then sorry. DO NOT use concrete blocks to block the body. Solid wood only.

Offline Geom

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Re: Strange power-on wobble. Suspect ujoint
« Reply #5 on: October 22, 2019, 09:20:07 PM »
Thank you all for the replies. Very useful!

To clarify the deflection I was referring to was indeed rotational. I can turn the shaft/knuckle about an inch or two in either direction.
I did not notice any lateral or vertical deflection -at least none I could easily perceive.

Thank you chessie for that part number. That helped a lot.
When I search for that number though (1710 series) there are several,  but they have additional numbers. I presume those are significant?
I was able to find that GM part number (at a higher cost) but those numbers don’t match the ones I find elsewhere.

I’ve also found that GM part number posted with half-round vs full-round. So I assume full-round.

Also, I assume it’s the same part number for the transmission and differential sides?

I’ll check the engine mounts, but I really hope it’s not that! This was a rebuilt engine install about 18 months ago. So fingers crossed it isn’t that.

 Visibly, the radius rod bushings look good -at least for what I presume their likely age is :)

I could not find a driveshaft shop here in Santa Fe, only a truck shop. I’ve called them and hopefully they can work on it :/
There appears to be a decent driveshaft shop in Albuquerque, but it’s an hour away. I have been driving it a while like this but I’m not sure how far I’ve been pushing my luck :)

How many hours do you think should be appropriate for this job?

Thanks again all!
George

1966 GM 4107
6v92 Turbo
V730

Offline chessie4905

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Re: Strange power-on wobble. Suspect ujoint
« Reply #6 on: October 23, 2019, 04:37:33 AM »
If you remove it, probably one hour, assuming everything is ok and the slip joint splines aren't shot, and bearing cap holes in yoke aren't  egg shaped from extreme wear.
The 1700 series joints come in various configurations. That is bearing cap styles. Your style has caps with 2 short bolts to attach them, there are caps without bolts that press into yokes with snap rings to retain them, etc. Quality also varies. Best u- joints have smaller diameter needles in greater quantity. Also some cheap imported joints may not have proper hardened or not hardened bearing journals, resulting in shorter life. In that application, I would only use a name brand, USA made ones, but they may only have non name ones. Whatever. If you do this job yourself, be extremely  careful not to lose or get a needle out of place.
GMC h8h 649#028 (4905)
Pennsylvania-central

Offline Dave5Cs

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Re: Strange power-on wobble. Suspect ujoint
« Reply #7 on: October 23, 2019, 07:16:18 PM »
George sent you a PM
Dave
"Perfect Frequency"1979 MCI MC5Cs 6V-71,644MT Allison.
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Online luvrbus

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Re: Strange power-on wobble. Suspect ujoint
« Reply #8 on: November 01, 2019, 05:34:30 AM »
I think you have a bigger problem than just U joints call me today 
Life is short drink the good wine first