Chevy shake?

[bigalturk1]

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I get a (Slight) Chevy Shake at 65mph, it goes away and comes back around 75mph, then it goes away over that speed. I replaced both u-joints & there is no play in the rear-end pinion bearing. The previous owner replaced the driveshaft (Still has sticker on it), I also replaced the the transmission driveshaft bushing & seal. This truck (144,00 miles) has a long yoke but it sticks out 2 inches from the transmission (1995 C1500 GMC 4.3 V6 4l60E).
PS: My 1981 & 85' Stepsides always ran smooth, I miss them!
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[Erik the Awful]

Are the engine and transmission mounts and crossmembers tight and straight? How do the tires look? Have you put it on jackstands and spun the wheels to make sure they're all true?

 

[Pinger]

Funny (for me) that this question has arisen as I've been noticing the slightest (only just perceptible) on my C2500 Suburban at 60mph. A few (less than 5) mph either side of that it vanishes. Less than 50,000 miles and there's nothing that I can think of that needs attention that could be the cause. I seem to remember a thread a little while ago that discussed GMT400s having a resonance related to chassis rigidity (or lack of!). Is that what I'm detecting?

 

[fancyTBI]

Funny (for me) that this question has arisen as I've been noticing the slightest (only just perceptible) on my C2500 Suburban at 60mph. A few (less than 5) mph either side of that it vanishes. Less than 50,000 miles and there's nothing that I can think of that needs attention that could be the cause. I seem to remember a thread a little while ago that discussed GMT400s having a resonance related to chassis rigidity (or lack of!). Is that what I'm detecting?

You are right. It’s called “Frame Beaming.” The solution is additional weight in the bed (or in your case, over the axle in your suburban) and it should go away. I can’t remember the TSB or where I read this info, which is unfortunate.

 

[Pinger]

You are right. It’s called “Frame Beaming.” The solution is additional weight in the bed (or in your case, over the axle in your suburban) and it should go away. I can’t remember the TSB or where I read this info, which is unfortunate.

Thanks. I've only recently noticed it and this thread prompted me to ask as I vaguely remember a thread that discussed it.
My LPG (propane) tank sits directly above the axle and the difference between empty(ish) and full is around 90 - 100 lbs. I'll make a point of noticing what difference re-fuelling makes.

 

[1990Z71Swede]

That was good info, we have something similar going on, at about the same speed on a 1990 K1500 RCSS.
Time to find and install that spare tire.

 

[PlayingWithTBI]

I seem to remember someone saying you can box in the frame there to eliminate the "shake".

 

[1989GMCSIERRA]

Is this a two piece driveshaft? Check the center support bearing if it has it.

Where is the shake felt. In your butt/back or steering wheel?

 

[DeCaff2007]

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I get a (Slight) Chevy Shake at 65mph, it goes away and comes back around 75mph, then it goes away over that speed. I replaced both u-joints & there is no play in the rear-end pinion bearing. The previous owner replaced the driveshaft (Still has sticker on it), I also replaced the the transmission driveshaft bushing & seal. This truck (144,00 miles) has a long yoke but it sticks out 2 inches from the transmission (1995 C1500 GMC 4.3 V6 4l60E).
PS: My 1981 & 85' Stepsides always ran smooth, I miss them!
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Had the same problem with my 02 Bonneville. Never figured out the problem but the suspension on that car was questionable at best. Biggest POS I've ever owned. Junked it soon after the first time I drove it in the snow.