Low Speed Death Wobbles

[greenfourby]

Any ideas on what could cause this would be really appreciated as this is really giving me the S&*ts and I need to drive this thing every day at the moment.

At low speed i.e 10ks the steering shakes so badly that the only way to stop it is to either put the boot in or jump on the brakes.

Initial thoughts were a problem with the draglink so on went a spare one, no difference.

Checked all the ps box mounts and pitman arm, all tight.

Tiny & I did the cut and rotate until 3am this morning and if anything this has mad it worse

Caster is set at 7 degrees.

I had the wheels balanced this morning and no difference.

I have changed some although not all of the suspension bushes.

Tie rod ends have not been changed at this stage but have been ordered.

Am I missing something

Please Help

[DIRTY ROCK STAR]

my 40 was doign this at about 25km/hr

chewed my front rubber out badly.

im hoping the power steering conversion will fix it when complete???

[Mad Cruiser]

So if it wasn't the panhard bar, sometimes it can be a loose bolt/nut or the bushes are gone.

Other than that have you tried getting a wheel alignment for it ?

[greenfourby]

So if it wasn't the panhard bar, sometimes it can be a loose bolt/nut or the bushes are gone.

Other than that have you tried getting a wheel alignment for it ?

I may have to try changing all of the bushes in the springs, would this really cause that much wobble though?

When it started it was just 'instant', it did not happen gradually.

Thanks

[greenfourby]

my 40 was doign this at about 25km/hr

chewed my front rubber out badly.

im hoping the power steering conversion will fix it when complete???

I'm gonna through the cheese cutters on and take it for a wheel alingment I think..

Guy at the tyre shop took one look at the 37's and laughed.

After balancing two tyres he said no more cause it was going to burn out the motor on his balancing machine. Opps !!

[MARKx4]

my 40 was doign this at about 25km/hr

chewed my front rubber out badly.

im hoping the power steering conversion will fix it when complete???

I'm gonna through the cheese cutters on and take it for a wheel alingment I think..

Guy at the tyre shop took one look at the 37's and laughed.

After balancing two tyres he said no more cause it was going to burn out the motor on his balancing machine. Opps !!

Take your tyres to ace tyres smithfield, i know they can balance a tyre that size.

[christover1]

sounds like a problem with the steering stabilizer/or lack thereof.
larger tyres, more weight, more width and/or offset puts a lot of strain on everything.
Most trucks have a fairly skinny draglink and these can act like a spring.
At faster speeds, the heavy spinning tyres act like gyros and keep them stable.
At lower speeds the death wobbles happen.
I'd fit a steering stabilizer, or a heavy duty one if it already has one.
It doen't really "fix" the problem but does a great job of hiding it..IE the wobbles should go.
I had this proble, took a while to find out.

OF COURSE ALL STEERING PARTS SHOULD BE CHECKED TOO.

christover

[BundyRumandCoke]

Whats this on? If it has leaf springs front, check your U bolts for any that are loose. I had very similar thing, it would drive along fine, then hit a small bump and the thing would go crazy. Loose U bolts allowed the whole front axle to shake all over the place.

[markil]

When it started it was just 'instant', it did not happen gradually.

Thanks

Sounds like something may have actually broken or gave way somehow if it happened "instantly".

Mark.

[greenfourby]

sounds like a problem with the steering stabilizer/or lack thereof.
larger tyres, more weight, more width and/or offset puts a lot of strain on everything.
Most trucks have a fairly skinny draglink and these can act like a spring.
At faster speeds, the heavy spinning tyres act like gyros and keep them stable.
At lower speeds the death wobbles happen.
I'd fit a steering stabilizer, or a heavy duty one if it already has one.
It doen't really "fix" the problem but does a great job of hiding it..IE the wobbles should go.
I had this proble, took a while to find out.

OF COURSE ALL STEERING PARTS SHOULD BE CHECKED TOO.

christover

Drag link is a heavy duty one so I don't think it is flexing there, I am begining to think it may be a tyre issue.

Every nut, bolt and bearing on the front has been checked or replaced with the exception of the tie rod ends

Thanks for the advice, At least I am not alone and it can be fixed

Cheers

[greenfourby]

my 40 was doign this at about 25km/hr

chewed my front rubber out badly.

im hoping the power steering conversion will fix it when complete???

I'm gonna through the cheese cutters on and take it for a wheel alingment I think..

Guy at the tyre shop took one look at the 37's and laughed.

After balancing two tyres he said no more cause it was going to burn out the motor on his balancing machine. Opps !!

Take your tyres to ace tyres smithfield, i know they can balance a tyre that size.

Yeh forgot about them, they did the patch balancing on the pedes, I will chuck the cheese cutters on, it will look Grimace but I should be able to drive it at least.

[greenfourby]

When it started it was just 'instant', it did not happen gradually.

Thanks

Sounds like something may have actually broken or gave way somehow if it happened "instantly".

Mark.

Agreed but nothing seems broken, and correcting the caster has made it worse not better.

Heaps Frustrating.

[greenfourby]

Whats this on? If it has leaf springs front, check your U bolts for any that are loose. I had very similar thing, it would drive along fine, then hit a small bump and the thing would go crazy. Loose U bolts allowed the whole front axle to shake all over the place.

It's on a sprung over 40, 37's , 350 Chev

http://www.outerlimits4x4.com/PHP_Modul ... hp?t=44240

So Yes, Leaves in front, U bolts are all checked and A OK, made really sure that we tightened everything up last night after doing the cut and rotate, checked again this morning and all still tight.

What size tyres were you running on yours??

[Suspension Stuff]

I would be checking the steering damper as christover1 suggested.

Shane

[MARKx4]

Whats this on? If it has leaf springs front, check your U bolts for any that are loose. I had very similar thing, it would drive along fine, then hit a small bump and the thing would go crazy. Loose U bolts allowed the whole front axle to shake all over the place.

It's on a sprung over 40, 37's , 350 Chev

http://www.outerlimits4x4.com/PHP_Modul ... hp?t=44240

So Yes, Leaves in front, U bolts are all checked and A OK, made really sure that we tightened everything up last night after doing the cut and rotate, checked again this morning and all still tight.

What size tyres were you running on yours??

Have you changed your shackle bushes, or if there is any cracks in the welds on the hangers, This was my problem with my soa MK.

[Area54]

Simple. You have too much caster.

For such a large tyre you should be running around 1 degree pos caster.

You are getting too much caster correction, as the projected pivot point set by your king pins (caster) is too far forward of the tyre contact patch. The larger tyre increases the distance of the two points, increases the leverage of the tyre to influence the caster effect and contributes to the shakes. Going to a wider rim combo makes it worse, as then your projected pivot point from your kingpin angle (camber) is set well inboard of the actual pivot point of the tyre contact patch.



Reduce your caster and it WILL reduce it.

[greenfourby]

Simple. You have too much caster.

For such a large tyre you should be running around 1 degree pos caster.

You are getting too much caster correction, as the projected pivot point set by your king pins (caster) is too far forward of the tyre contact patch. The larger tyre increases the distance of the two points, increases the leverage of the tyre to influence the caster effect and contributes to the shakes. Going to a wider rim combo makes it worse, as then your projected pivot point from your kingpin angle (camber) is set well inboard of the actual pivot point of the tyre contact patch.



Reduce your caster and it WILL reduce it.

OK, Great info, Cheers

When I put the cheese cutters on I will be able to get the alignment checked and the caster measured, I'll take your advice and push the caster back to 1 degree +ve with wedges.

Thanks Heaps

[flyinwall]

has anyone thaught it might be a bubble in the tyre? its worth checking!

[greenfourby]

has anyone thaught it might be a bubble in the tyre? its worth checking!

At the risk of getting flamed for asking a dumb question.

What is a bubble in the Tyre and how do I check for it

[bazooked]

i agree to much caster.

[greenfourby]

i agree to much caster.

Thanks

Seems to be the best answer so far, looks like I'll have to get it measured and chuck in some wedges to try and bring it back.

[bazooked]

u can buy the kingpin bearings that are adjustable in 1 to 2 dergee increments, think kmac do them, that way u wont stuff up ur pinion angle with wedges.

[chevJ40]

i had the same issue on my 40 series and being a mechanic it drove me crazy trying to find out what it was becasue everything would test fine, i ended up replaceing both tie rod ens tightening my pitman arm, replacing steering dampner and then went to the u bolts all of which has made it a dream to drive on the road

[flyinwall]

has anyone thaught it might be a bubble in the tyre? its worth checking!

At the risk of getting flamed for asking a dumb question.

What is a bubble in the Tyre and how do I check for it

jack one wheel of the ground at a time and spin it while watching the tyre to soo if there is a bump in the tread and check that the tyre hasn't gone out of round ie. oval shaped instead of round

[Busiboy]

has anyone thaught it might be a bubble in the tyre? its worth checking!

At the risk of getting flamed for asking a dumb question.

What is a bubble in the Tyre and how do I check for it

jack one wheel of the ground at a time and spin it while watching the tyre to soo if there is a bump in the tread and check that the tyre hasn't gone out of round ie. oval shaped instead of round

I would check it but doubt it would be the problem due to the speed related issue. I would go with Castor, have a feeling trying to correct 7 degrees though they will spit out a bit. Good luck.

What sort of tread you running? Maybe an agressive tread on a big castor is the problem. If it is fixed by fitting chesse cutters then you may have half the problem.

[greenfourby]

has anyone thaught it might be a bubble in the tyre? its worth checking!

At the risk of getting flamed for asking a dumb question.

What is a bubble in the Tyre and how do I check for it

jack one wheel of the ground at a time and spin it while watching the tyre to soo if there is a bump in the tread and check that the tyre hasn't gone out of round ie. oval shaped instead of round

I would check it but doubt it would be the problem due to the speed related issue. I would go with Castor, have a feeling trying to correct 7 degrees though they will spit out a bit. Good luck.

What sort of tread you running? Maybe an agressive tread on a big castor is the problem. If it is fixed by fitting chesse cutters then you may have half the problem.

Just got back from the tyre shop, put the cheese cutters on and first reaction was oh, it's better. then I hit a bump and wham, back come the wobbles.

Had the alignment and everything checked and it had a lot of toe in but driving back it was no different after correcting.

Caster was about 8 degrees on both sides so consistent after the cut and rotate if a little on the high side.

I will chuck in sum wedges tonight and see how I go.

Thanks for all the ideas guys, keep em coming, it's still not fixed yet.

[Busiboy]

Damn 8 degrees is a lot !

That should nearly be running on about half the tyre?

jack up one side slowly, look at when the outer edge lifts off and when the inner lifts off. the problem might just be deforming the casing by loading up the inner sidewall too much

[beebee]

My money is on a dodgy tierod end. Have you checked for play/slop in the tie rod ends with someone else manipulating the steering wheel? Your symptoms sound EXACTLY the same as mine when I had dodgy TRE. The nuts were tight so I originally thought they were ok but the actual joint was stuffed. As soon as you hit a bump, things would get crazy.

Good luck!

[dumbdunce]

I'll put in another vote for way too much caster - it's doing shopping-trolley wheel wobbles. 6 - 7 degrees is a lot to get out of wedges - if the welding is tidy it might be worth another cut and rotate.

[Tiny]

I'll put in another vote for way too much caster - it's doing shopping-trolley wheel wobbles. 6 - 7 degrees is a lot to get out of wedges - if the welding is tidy it might be worth another cut and rotate.

dont give him ideas like that brian........seriously though we ave onother doff we can use to cut and rotaten anyway, but we need to chech \\k if it is the castor by using wedges before we chop another one up