Good morning all, I have a weird vibration that has just started in my '99 suburban. 5.7, 4wd, auto, 1/2 ton 180,000-ish miles. After hard acceleration, like merging or passing, the whole truck shakes. I can feel it in the steering wheel and in the seat. Once I let the truck settle in at cruising speed the vibration goes away and I'm left with the normal vibrations and shaking you get from a 16 year old truck on M/S tires on pavement. That I can live with.

The vibration isn't so much speed related as it is hard acceleration. Last night I was merging into slower traffic when I goosed it up to 60 to merge the vibration was the same as if I had goosed it up to 75 or 80. Under mild acceleration it doesn't shake.

The engineer in me (electrical, but I can be logical) makes me wonder if one of the CV joints is binding under load and once the load is reduced it eventually loosens up. Does that make sense? Has anybody else run into this?

Thanks for any advice you all can pass my way.

Pete

 

I'd wager the u-joints on the rear drive shaft.

when you remove the drive shaft, mark which way it was on, they are supposedly balanced to be on a specific way.

When you apply force (acceleration) to the drive shaft, the worn joints are being pushed out of alignment and then vibrate.

Your CV joints are in the front between the diff and tires, but they are not under engine rotational force unless you are driving 60-80 MPH in 4WD... which may cause other issues

I haven't been under a Tahoe in a while, but the standard practice is a slip yoke on the transfer case side, and two u-joints on the rear driveshaft.

When you get fancy like the 04 Rubicon I had you get an actual fixed yoke with a CV joint. Although Chrysler (Fiat) now uses some ball joint thing that's done away with u-joints... I don't know how strong it is, but it worked fine with 35" tires on my 2012 Rubicon.



Ford, but similar.

I still don't understand why you have to mark the driveshaft, but everyone does it, so I do too.

 

I did say I'm an electrical engineer, not mechanical....and just now realized that the CV joints shouldn't be under load in 2WD. Unless I have a problem that is keeping one or both front axles engaged. I doubt that, I'm not getting any pulling or hopping when turning on dry pavement.

Time to look at the rear u joints. It does come through the steering wheel pretty strong so that's what made me think of the front end.

 

I had similar on a car once and it turned out to be a busted engine mount, on a van once and it turned out to be a bad tire and on our suburban once and it turned out to be the u-joints in the drive shaft.