Highway vibration 55-65mph

Hi folks,

Looking for some hints/pointers.

86 C20 454.

Drives great, many parts recently renewed... but ive got a highway speed vibration.

55-65mph got a decent vibration through the whole body of the car. Its not through the wheel or pedals, but through the body. Whole centre console is shaking (sometimes quite violently) and the chairs are bouncing left to right etc. Not the nicest thing to have and takes away from what is otherwsie a really sweet truck to drive.

Can anyone help with pointers?

Thanks

Typically through the body like you're saying means it's coming from the rear of the truck. Front end vibration you usually feel through the column/wheel and pedals.

First thing is to check wheels and tires closely. Make sure the wheels haven't slung a weight off or the tire is misshapen like a belt slipped/broke. While the back of the truck is on jack stands, put a couple lug nuts back on to keep the drums on, start it and put it in gear and go look at the axle shafts. Make sure they're not wobbling/have runout showing a bent axle.

Was the driveshaft ever out? If so, you might pull it back out, rotate it 180* and re-install.

What about motor mounts/transmission mount? Are they in good shape? If they're sagging really bad it can cause a vibration and should be replaced.

If none of those free things solve it, I'd try taking it to a tire shop that has a road-force balancer to check the wheels and tires.

When vibrating at speed put tranny in neutral. If vibration continues would eliminate engine related issue.

Thanks.

Im pretty sure its not the wheels and tyres, as they are almost new. However, I will get them rebalanced, just because its the easiest place to start.

Will update.

I am a field engineer for a major car company. I deal with vibrations all the time. Just because tires are new does not mean they are good.

Road Force is a trade name used by Hunter for radial runout of a tire. Hunter usually measures it in Pounds. The Hunter machines can be set for hundredths of an inch. Other tire equipment manufacturers measure it in inches. Think of a tire sidewall as a series of springs. The ideal tire has the same force all the way around. In reality there is a variation. If this difference is high enough you will feel it.

First thing you want to check is if you have a bent wheel. The Hunter tire equipment can measure wheel runout as well as tire runout (road force). If your wheel has a little bit of runout the machine can try and minimize the Road Force by machine the high spots and low spots. If you wheels are perfect it is a waste of time trying this.

I have gone through 10-12 tires to find 4 that have low Road Force. You can feel 15 lbs or higher. This happens with all name brand tires not just the cheap ones.

kapitein said:

Hi folks,

Looking for some hints/pointers.

86 C20 454.

Drives great, many parts recently renewed... but ive got a highway speed vibration.

55-65mph got a decent vibration through the whole body of the car. Its not through the wheel or pedals, but through the body. Whole centre console is shaking (sometimes quite violently) and the chairs are bouncing left to right etc. Not the nicest thing to have and takes away from what is otherwsie a really sweet truck to drive.

Can anyone help with pointers?

Thanks

Click to expand...

I used this method to smooth out my suspension. I did this procedure before and after changing out my rear springs. Added a 4 degree shim to get a better drive shaft angle. Cup of water was smooth at speed.

This will also help you understand the importance of pinion angle.

edgephoto said:

I am a field engineer for a major car company. I deal with vibrations all the time. Just because tires are new does not mean they are good.

Road Force is a trade name used by Hunter for radial runout of a tire. Hunter usually measures it in Pounds. The Hunter machines can be set for hundredths of an inch. Other tire equipment manufacturers measure it in inches. Think of a tire sidewall as a series of springs. The ideal tire has the same force all the way around. In reality there is a variation. If this difference is high enough you will feel it.

First thing you want to check is if you have a bent wheel. The Hunter tire equipment can measure wheel runout as well as tire runout (road force). If your wheel has a little bit of runout the machine can try and minimize the Road Force by machine the high spots and low spots. If you wheels are perfect it is a waste of time trying this.

I have gone through 10-12 tires to find 4 that have low Road Force. You can feel 15 lbs or higher. This happens with all name brand tires not just the cheap ones.

Click to expand...

you can find wheel high points and low points and tire high and low with a dial indicator
But it does also kinda require having a perfect bearing to check them like a tire balancer hub (to be as minimal as possible, so the dial indicator is only reading those things)

kapitein said:

Thanks.

Im pretty sure its not the wheels and tyres, as they are almost new. However, I will get them rebalanced, just because its the easiest place to start.

Will update.

Click to expand...

And look at each tire, find out how much weight is put in each spot, tell or show us whats the most amoutn of weight in a spot

Been going through this same problem everything double checked..Found my driveshaft to be .030 out of true. Having it straightened as we speak...hopefully that fixes the vibration...if not ???????

Well, I never expected it, but it was the wheels/tyres.

I managed to get a Hunter alignment done this morning.

Rear wheels both 3.5oz out of balance and needed rotating on the rim.
Front wheels both 2oz out of balance.

Its now near perfect, what a difference!

Last question - I have a C20 with the 8 lug axles. The wheels are lug-centric.

Is it possible to get hub-centric rings for these cars, as that would probably remove last tiny amount of vibration.


ps. Pretty pissed at the first shop to do such a poor job of balancing the wheels.

Usually it's the first thing to check, alongside with the easiest. Then move to drivetrain and rotating assemblies (bearings/axles).

Glad it was something as simple as that and guess that shop won't be getting any repeat business from you in the future.

Most tire shops don't want to go through the hassle and time of getting the tire perfect on the wheel. At one shop, I specifically asked for my rear tires to be dismounted and spun either 90* or 180* or whatever the machine thought it needed to try to minimize the weight and vibration I was having. Said I'd gladly pay extra. They charged me extra. I went "out for a smoke" around the side of the building and watched the kid on the tire machine pull the old weights off, spin the wheel up and put the exact same amount of weights back in the exact same spot on both wheels.

Kid then left my ticket sitting there and did 3 more sets of wheels before bringing it back in to the counter to make it seem like he'd taken the time. I grabbed the wheels to inspect and then politely asked to speak to the manager. Show him where there was no glue residue from weights being removed so the new ones were in exactly the same spot, showed him the picture I took of the weights before I brought the wheels to them and how the new weights matched exactly. I'd also made a small mark on the wheel as another reference because I know how tire shops are. Then told him what I'd done on my "smoke break". He was so embarrassed and pissed. I told him I either A) wanted a full refund and I'd go elsewhere, B) wanted a full refund and they allow me to use the machine to do it myself and explained I've done tire mounting and balancing before or C) wanted someone to go back and do what I asked for and let me watch. The manager gave me a refund, made the kid redo them the proper way while the manager and I both watched and he was super apologetic. I think the kid probably got fired soon after cuz he's not been there the last few times I've been back for other tires.

kapitein said:

Well, I never expected it, but it was the wheels/tyres.

I managed to get a Hunter alignment done this morning.

Rear wheels both 3.5oz out of balance and needed rotating on the rim.
Front wheels both 2oz out of balance.

Its now near perfect, what a difference!

Last question - I have a C20 with the 8 lug axles. The wheels are lug-centric.

Is it possible to get hub-centric rings for these cars, as that would probably remove last tiny amount of vibration.


ps. Pretty pissed at the first shop to do such a poor job of balancing the wheels.

Click to expand...

Do your wheels have enough area in the hub for a ring to sit? I've never done it but I would think if there's room, you could just measure the hub and order some generic rings and try them