1980 K10 Shake/vibration

[jbrow1]

Hi all, not sure where this specifically belongs so posting it here..

1980 K10 (3/4 leafs), 250 engine, granny tanny, brand spankin' new 31x10.50.15 tires and alignment this morning, new leaf springs, shocks, steering components this (past) summer.

Truck has been wrecked and fixed twice in the past 20 years.  First wreck was just the passenger side front fender, second wreck was T-boned in the driver side door.  All good, I survived

Anyhow, suspension is all good, steering is all good, wheel bearings all good, tires/wheels good, U-joints aren't new, but not loose and seem good.  Not many miles on em, but plenty of years. 

The vibration feels like in the past when my other truck, an '86, had bad balljoints, and would just freak out.  Although this truck, doens't freak out at all, just has a side to side jiggle that I can't figure out why?  I'm debating replacing all the u-joints and having the driveshaft balanced. 

Looking for thoughts on what else I should be looking for.  The engine runs so well and smooth, I wonder why anybody spends $$$ on new vehicles?  Probably so they don't shake.. I have a handful of old trucks from 78 to 2000 trucks, all chev/gmc, love em all.  I am thinking maybe I need to replace the frame, or at least take it for an actual frame alignment since I got T-boned?  What do ya'll think could lead to this shake?  It's more pronounced on certain roads.  Sometimes worse than others, sometimes I'm like WTH, and sometimes I think wow, this truck rides so sweet.

Thanks for any input.  Long live the old Chevy/Gmc P/U's !!

[1967KaiserM715]

Change out rims and tires, even with a worn set, I have seen new tires cause all sorts of shimmys. Rims will too.

Wheel bearings is another possibility, here you should pull the brake caliper on each side then put the tire back on for leverage(I have seen calipers provide enough force on the bearing to make it seem fine, until you remove it.)

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[Irish_Alley]

we need to know more about your issue, like at a certain speed or rpm or when you turn the wheel

[philo_beddoe]

Welcome to the club friend!!  Vibrations will bring out your worst anxiety, until you find the monster! Not knowing is the worst part.

Anyway, how is it in park or neutral reving the engine?

Your fortunate,,,my vibe taunts me!! Lol

[jbrow1]

The vibration doesn't seem to do with the engine.  It's running smooth, while parked and throttling it by hand at the carb, there's no movement other than what an engine typically does.  Before I had the tires replaced, it was around 45 mph.  I aired the tires down to 30 psi, and it then had the shake at 55, I belive it was.  Now that I have new tires, it's not as bad, but there's till a shake, sometimes at lower speeds, sometimes at higher.  Seems that when i get above 50ish though, it smooths out, and it seems to be worse on certain roads compared to others, which is weird.  Because, the road that feels the worst, is relatively new. 

I call it a shake, but if feels more like an oscillation.  Like if I had a cup of water on the dash, it would seem to want to splash in a counter-clockwise circle, like a clothes drier, revolving counterclockwise.  That's how it feels. 

I don't drive the truck a ton, nor do I drive it fast, so it's not a huge issue.  But I would like to figure it out and have the truck become my daily driver.  My '86 would run down the road full bore and never shake a bit, that's what I'm looking for, but just at the max speed limits I see at 55mph. 

Thinking of pulling the front driveshaft and seeing if that makes any difference. 

I got the wheels from a junkyard years ago, and we pun them by hand on the tire machine to verify they were not bend or out of round.  They've been gently used since then, so I don't think it's bent wheels.  Plus I'd really think that getting a balance twice in the last two months

[Nightowl]

I had a problem like that one time and it turned out to be the horizontal shock needed replacing.

[Engineer]

You have tried two sets of tires?

Sounds like it might be "beaming", only laterally. How are your cab mounts? Was the frame bent when the truck was t-boned? Do you have any broken or loose cross members or cross member rivets?

[Engineer]

I'll add the reason I think it is "beaming" is because it sounds like a resonant frequency. A bad road will have enough disruptions to cancel out the resonant frequency whereas a smooth road will allow the resonance to develop and maintain itself since there aren't any bumps to interrupt the shake.

Again, check your cab mounts first. And they aren't too expensive to replace. Loose rubber cab mounts can cause a pendulum effect between the frame and cab.

[jbrow1]

I'll add the reason I think it is "beaming" is because it sounds like a resonant frequency. A bad road will have enough disruptions to cancel out the resonant frequency whereas a smooth road will allow the resonance to develop and maintain itself since there aren't any bumps to interrupt the shake.

Again, check your cab mounts first. And they aren't too expensive to replace. Loose rubber cab mounts can cause a pendulum effect between the frame and cab.

I have never heard of beaming.  Looked at the mounts today, they are not loose.

I do think the frame is a bit bend on the drivers side, from just in front of the rear cab mount and moving up towards the front of the truck.  I think I will call a frame shop tomorrow.  Although, I can get a frame and just replace it too, I just don't want to at this point.

I jacked it up today and ran a straight edge on all four wheels, they are all straight and with no hop.  The tires as I said are brand new, and balanced.  Although one wheel, does seem to have a ton of weights on it.  I would almost think it could be the wheel with all the weights, but it had the same problem with the last tires that were on it, so I don't think it has anything to do with the tires or wheels at this point. 

Another thing, I don't have a bed on it right now.  I welded up some mounts for rear trailer light assemblies, and mounted mud flaps to it for the time being.  I'm wondering if not having the weight of the bed on the truck might make any vibrations worse.

The vibration comes on at 45mph, lasts up to 55, and is smooth at 60 and up.  That's all as per my speedo, not sure if it's right on, as I'm running 31x10.50x15 tires on it, not sure what was stock.  It should be close, but I'll have to check it with a gps. 

Wheel bearings are tight, ball joints tight, u-joints aren't sloppy or squeaking.  I did notice after going to 3/4 ton springs, the driveshaft is pulled out from the tranny about 1" farther than it used to be.  Can tell b/c of the shiny metal now exposed that used to be in past the seal.  Also the driveshaft angle is more, but it doesn't look like anything severe.  Guess I need to do some reading on that also. 

It's unusually nice for Nov. in Michigan right now, so I think I'm just going to replace the rear u-joints for the heck of it.  They are old, but not alot of miles on them. 

With a 4 wheel alignment, you think the frame being off a bit could create this shake?  I'll have to have my Dad drive it and see if it's dog-tracking.  I thought I've driven behind it before, and never noticed that. 

[jbrow1]

I looked up what "beaming" is, and it makes sense.  If I had a small vibration, now that I'm running without the bed on it, it could be very magnified greatly due to no weight being on the rear of the truck.  Maybe I'll set my snowplow on the rear frame/bumper and chain binder it down, and see if that helps.  Guess I better get on either building or finding a flat bed for it.

[philo_beddoe]

I looked up what "beaming" is, and it makes sense.  If I had a small vibration, now that I'm running without the bed on it, it could be very magnified greatly due to no weight being on the rear of the truck.  Maybe I'll set my snowplow on the rear frame/bumper and chain binder it down, and see if that helps.  Guess I better get on either building or finding a flat bed for it.

Wouldnt you have to plow in reverse? Lol...

[jbrow1]

I looked up what "beaming" is, and it makes sense.  If I had a small vibration, now that I'm running without the bed on it, it could be very magnified greatly due to no weight being on the rear of the truck.  Maybe I'll set my snowplow on the rear frame/bumper and chain binder it down, and see if that helps.  Guess I better get on either building or finding a flat bed for it.

Wouldnt you have to plow in reverse? Lol...

lol    At this point in November, it's not looking like I'll have to plow until after Christmas anyway! lol