[d1mitch]

hey guys,

i have a vibration in my sierra that is driving me insane.

the car feels bit rough vibrating low in the rpm range (sub 3000) in any gear and then when i get up to 65km/h+ the real vibration starts (rear view mirror nearly shaking off its mount)

my old man reckoned it was missing so i have since changed the dizzy cap and rotor spark plugs and leads and lo and behold the vibration is still there.

from my research it may be the uni joints, is that the next thing i should be looking at or is there a more likely source?

would it be the driveshaft or the jackshaft? or should i just replace the unis on both?

[bumstein]

Hey Mitch..

Take my advise with a pinch of salt coz I'm really not that clued in, but from reading plenty of posts on here don't discount the kingpins in the problem solving equation..

Apparently they can cause all sorts of problems similar to this if they are worn.. But I'd make sure someone a bit more clued in than I am confirms this before tearing apart your Sierra

******Cue actual advise based on knowledgable background ********

[droverdave]

you need to determine if it is engine or driveline causing the noise.

Get it up to speed, put it in neutral, feet off all pedals. Does it stil vibrate?

[Jazzor]

Checking all 5 unis would be a great start, grab both sides of the uni and twist back and forth to see if there is any play, it will be pretty obvious if one is so far gone its making your car vibrate :S.

Other ideas... engine, gearbox, transfercase mounts?



Its not coming from your wheels?, that would be making your steering wobble too, and king pins are more a steering wobble issue .

[d1mitch]

yes to clarify there is no steering wobble and the vibration is only under load.
for example i can get up to the max vibration point (between 70-80km/h) take my foot off the accelerator but still in gear and the vibration stops as soon as i touch the accelerator again its vibrates again like switching a switch on and off turning the vibration on and off

[SierraDan]

Agree with all of the above. But also check the front hubs arent locked in. Mine were in once, with a heavily welded diff and it was shaking the car apart haha.

[losfer]

Jazzor wrote:

Checking all 5 unis would be a great start, grab both sides of the uni and twist back and forth to see if there is any play, it will be pretty obvious if one is so far gone its making your car vibrate :S.

Other ideas... engine, gearbox, transfercase mounts?



Its not coming from your wheels?, that would be making your steering wobble too, and king pins are more a steering wobble issue .

what if he doesnt check the 6th uni and thats the one thats faulty ?

[Jazzor]

For some reason I was thinking the gearbox end with the spline join didn't have a uni . 6 then.

[KEENSY85]

Could it be tires not ballanced if it only gets bad after a certain speed

[d1mitch]

yer i thought the same but tyres would normally come through the steering wheel not the chassis and wouldnt switch on and off with the accelerator. the same with any wheel balance issue really.

i checked the uni joints yesterday and they are all tight no play at all in all except for the back one with has a tiny bit (maybe 1mm) of play so im pretty sure its not them. could uni joints seize up? so they wouldnt have any play at standstill but not turn as they should when rotating?

i pulled the plugs out yesterday aswell and checked them, they are awfully black so it doesnt look like it is burning properly... i dont know what else to fix lol
could it be the coil breaking down?