GM Service Manual - Driveline Vib Diagnosis

[Keith Seymore]

Posting here, for future reference -

[Desert1957]

Good Info, Thanks Keith

Desert

[Allenohana]

Keith:
Thanks for posting this. It really helped me a lot!! You da man!!

[hatzie]

Thanks.
GM Service training manual?

[Keith Seymore]

You are welcome.

Originally Posted by hatzie

Thanks.
GM Service training manual?

No - I think I grabbed that one out of an S truck regular service manual.

K

[hatzie]

The detailed information on working angle calculation is much better than the 1989 1990 or 1991 RV service manuals.

[Ski-me]

Thanks Keith on this....can't read it at work but will look through it on my home computer tonight, but skimmed through it on my phone. Perfect timing......I am currently trying to figure out a driveline vibration and no one can shed anymore light on it.

New CV Driveshaft with a 2.5" lift and a SYE kit at t-case. I know yours looks to be more stock, slip yoke type, shafts but maybe there's something in there that will help.

Appreciate it!

[LostMy65]

Thanks
I was just searching for info on this.
Here is one I found:
http://www.hurst-drivelines.com/file...ration-FAQ.pdf

[LostMy65]

Another:
http://www.drivetrain.com/parts_cata..._problems.html

[LostMy65]

And another:http://driveshaftvibration.com/drive...brationcauses/

[WB72]

Great info here thanks Fellas.

[Keith Seymore]

Adding the images as attachments so they don't get lost -

[Keith Seymore]

...

[Keith Seymore]

If you can follow this thought process you can fix any vibration problem.

It's all a matter of "divide and conquer".

K

[Man With A Gun]

Good stuff, Keith. I've got a mild pulsing vibration around 60-70 mph.

I'll see if I can go thru the flowcharts and find the problem.

[Richard2112]

Yes this is very useful. Thanks

[Keith Seymore]

Originally Posted by Man With A Gun

Good stuff, Keith. I've got a mild pulsing vibration around 60-70 mph.

I'll see if I can go thru the flowcharts and find the problem.

Thank you;

A "pulsing" vibration is what is known in the biz as a "boom/beat".

It is caused by not one but two vibrations that are close enough in frequency so that they sympathize. The "fade in-fade out" aspect is a result of the amplitudes adding and subtracting as they pass by each other. We used to experience this regularly when I was in band class in high school and actually used this characteristic to help tune our instruments (slower boom/beat frequency means the two vibrations are getting closer together; faster means farther apart).

If you can find and fix one or the other of the two offending components then you fix the boom/beat aspect.

Engine firing frequency (4th order of engine rpm) and driveline u joints (2nd order of driveline) are a couple usual suspects. Hopefully this gives you some ideas.

K

[wilkin250r]

I definitely have a "boom/beat" problem in a 72 I'm fixing up. The vibration is fairly high frequency, so I'm assuming it's a driveline issue and not a tire issue, but the vibration also fades in and out with a regular rhythm.

Am I correct in assuming the transmission HAS to be part of the problem? Exactly like you said, Keith, amplitudes adding (in phase) or canceling (out of phase). With a driveline imbalance or u-joint, it would be a constant vibration. It wouldn't fade in and out because there is nothing to change. The planetary gears in the transmission are the only thing I can think that would allow two similar vibrations to fade in and out of phase with each other, so one of the vibrations HAS to be in the transmission. Yes?

(Actually, as I type this, I suppose the ring/pinion gears could also allow two vibrations to add/cancel each other)