Vibration and ride quality

[69SCSS]

hey guys, now that I've driven my truck about 500 miles I am slowly working out the kinks and wondering something. While I don't expect my '68 to be as smooth and quiet as my '02 Silverado or my '11 xB, I'm not sure what's "normal" for the truck. I know it's short wheelbase so it's going to be bumpy. What I have are some vibrations that only happen occasionally, and only at highway speeds. Above 55 I get what feels like a front end vibration that goes in waves. Beyond that I get a little bit of lateral shake, but that's a lower magnitude. I am suspecting that my front alignment is not quite right. I had it done when I had the 402 in the truck and never got it above 40mph while it was running, so I don't know if it had the same issue then.

I plan on taking it to the alignment shop again and have them check it, but what is normal? I would think the truck would at least roll smoothly up to 70-80mph?

Helpful specs: All new front and rear bushings, bearings, etc. 3.5 / 4 drop with 2.5" spindles. Manual steering.

[brad_man_72]

Alignment, have tires ballanced (make sure they are round and the wheels aren't bent), have the driveshaft ballanced if it has been worked on since it was ballanced last.

[Lee H]

Did you checked the trans and pinion angles after the drop?

[Mr Handy]

I would start at the road and check the wheel balance, then alignment.
I had mine out on the toll road a few weeks ago and was rolling 65/70 and she ran nice and smooth. I have rebuilt the suspension, new springs, shock, ball joints, wheel bearings, idler bearing, U-joints, trailing arm bushings. I am running 2.5/4 drop spindles/ springs, and front and rear sway bars.
I do get a little bit of a harmonic hum right at 60 but I think that is aerodynamics or the motor and my wife has no idea what I'm talking about when I say "Do you hear that?"

One thing that also comes to mind is the steering box, how much play do you have? if it is real tight it could cause binding, but I don't think that would cause your problem.

[Hart_Rod]

I had a similar issue a there is a lot of good advice here, check: tires, wheel balance, drive shaft balance and pinion angle, quality shocks and correct shock angles for lowered trucks. Do you have polyurethane body bushings? They will make for a "choppier" ride. I chased a vibration for a couple of years and addressed or checked all of these components. Come to find it out it was a new set of Moser axles that were machined incorrectly. Go figure? Oh well, at least I have it figured out now.

[brown7373]

What kind of tires and how old are they (by the DOT code)? Old tires can begin to separate internally and cause vibrations before they have a (possible) catastrophic failure. Most sources say 7 years is about the limit, but 10 or more is a ticking time bomb. Ask me how I know.

As to not like your 2002 Silverado, my 72 has all good stock suspension parts and a proper alignment, with original stock heavy duty rear springs and runs modern regular size radials. People usually comment on how nice and smooth my truck is. Your 68 should have the same potential with the right combination of parts and alignment. Some modifications may trade smoothness for more performance.

[Lattimer]

All good advice. I agree with starting at the road and working up.

On my truck I replaced all of the wear components (ball joints, tie rod ends, sway bar bushings, trailing arm bushing, shocks, etc.). Tires are new and rims are 80's rallyes. Steering box, column, etc. are all new.

Truck is perfectly smooth up to 90 mph. Between lowering springs and being swb, it is stiff over bumps. But I have no vibration and it tracks nice and straight.

I did "customize" the alignment by following one of the alignment threads on here, and it now handles much better.

[69SCSS]

Thanks for all the input. The wheels / tires are new, so I'm going to start at the alignment. The driveshaft angle is something I have thought about, I could get some shims and adjust it.

It's not rattling itself apart or anything, though, it's just some mild vibrations, but if it's supposed to roll smooth then I"ll be tracking them down and fixing the issue.

[michael bustamante]

Also check the lca and upper control arm bushings. As well as the u bolts holding the lca's