Why Do the Squares Wiggle in the mid 60s mph?

[buffydores]

Everybody I talk to observes the same thing. Is it just frame resonance?

[Corts60]

I’ve owned 8 different squares and I’ve never experienced this. Can you explain further?

[special-K]

I've never experienced this wiggle. I've had 1/2t and 1t 2wds as well as K/5, 3/4t and 1t 4wds including Suburban. What do you and the others own that wiggles?

[kwmech]

Tighten bolts and get a good front end alignment?

[mongocanfly]

Never heard of it either

[Getter-Done]

I have owned several.
I have not experienced this.

[Warrens69GMC]

My 1978 Longbed is smooth. Never had this happen.

[Pontiac1976]

Looking at your profile pic what size tires are you running are they over sized 4x4 off road tires. If they are that may be because your running to much side wall, that may be where some of it coming from. The bigger the side wall & the faster you go the more the side wall will grow at speeds and give you some wiggle.

[buffydores]

It's nothing like death wobble. It's just certain speeds that have harmonic vibrations. Talking to quite a few folks, they experience it at between 63-67 mph. You couldn't align, balance, check or brand new anything more on this rig.

[cadillac_al]

It's almost impossible to get a perfect tire balance; even on my Cadillacs. My 76 GMC has a tire vibration between 57-60 mph. It smooths out before and after those speeds.

[Dead Parrot]

My 75 C10 does it on occasion. The vibration has survived several sets of tires, a new set of rear bearings, new u-joints, a new exhaust system, and a major fix-up of the front end.

When mine does it, it cycles between nothing and a very noticeable vibration over a couple of seconds. Tends to be at higher speeds, above 65.

Guessing it is a combo of exhaust drone interacting with tire speeds and drive line vibrations.

[Rich84]

47-52 MPH for me. More of a up and down wobble.

[buffydores]

Originally Posted by cadillac_al

It's almost impossible to get a perfect tire balance; even on my Cadillacs. My 76 GMC has a tire vibration between 57-60 mph. It smooths out before and after those speeds.

Yes. This is the experience. It's smooth at all other speeds. It's done it with multiple sets of tires. Even though I have a well balanced CV driveshaft with a properly shimmed pinion angle, I still feel like some of its there, but the rest I suspect is resonance in the frame.

[Keith Seymore]

Mine doesn't.

Rock solid as fast as you want to go.

As a former full vehicle development engineer, driveline development engineer and brake development enginer - I've never noticed it on any of the thousands (?) of squares I've driven.

K

[buffydores]

And to clarify, it feels like a driveshaft or wheel balance deal.

[Keith Seymore]

We did have a few "inherent" wobbles that got built in, but more like during the GMT400 and GMT800 days.

The longer trucks could get into a frame "beaming" mode but that was usually vertical (up/down, rather than crosscar).

I also recall a particular extended cab configuration that would wobble right off the line. Just two or three kicks, as a result of the 2 piece driveline configuration, and then clear up.

That was one you weren't going to fix without some "invention".

K

[Honest Bob]

Both my squares have a slight vibration around the 65mph mark, although I've always chalked it up to never having had an alignment or balance done on either.

[72c20customcamper]

Keith you explained what I experienced with my 77 Suburban . Truck would go up and down we used to call it porpoising. My 87 burban only did it when towing but my 77 would do it regularly.

[buffydores]

Originally Posted by Keith Seymore

Mine doesn't.

Rock solid as fast as you want to go.

As a former full vehicle development engineer, driveline development engineer and brake development enginer - I've never noticed it on any of the thousands (?) of squares I've driven.

K

Keith: You seem comfortable in this space. What would you look at? I've had the wheel tire setup balanced on a fancy machine. Driveshafts built by Tom Woods. No difference before or after.

[bigdaddy4x4]

all of the m1008 that i have owned and my 79 k30 will sway a little when acceleration you can feel it go right and let off the pedal a little and it will go back straight i think its caused by the torque from running the 4,56 gears

[Eyegore]

Originally Posted by kwmech

Tighten bolts and get a good front end alignment?

& rplace lea spring bushings and ball joints and any other warn out suspension parts

[kwmech]

One thing I forgot to mention is that these frames be it 2 or 4x had a tendency to crack around the steering box mount. Check the bolts for tight and look carefully for cracks

[Getter-Done]

Originally Posted by kwmech

One thing I forgot to mention is that these frames be it 2 or 4x had a tendency to crack around the steering box mount. Check the bolts for tight and look carefully for cracks

kwmech

I think you just Nailed this Issue.

Op needs to check the frame for cracks and add one of these.