Death wobble!!!!!

tomsoffroad · Post by **tomsoffroad** » Mon Oct 31, 2011 6:38 pm

Got an issue with Sams KZN130. As the heading says it has death wobble. The castor is set at 2deg. We have changed this from 3deg and tested it reasonably well this arvo. All good................. Not so :oops:

Didnt do it while testing but did on Sams drive home.
Is 2deg too much? I've searched ore and the general opinion is caster.
Any other ideas??
Ive decide that from now on any link set up I do in the front of any truck the top link will be adjustable.
Another note is the Rob-mu's prado was set at 3deg when I linked it's front and has no issues :oops:

It doing my head in and we need help

Lynx · Post by **Lynx** » Mon Oct 31, 2011 6:40 pm

Youve done all the usual checks, wheel bearings etc? how did you set the castor?

Cheers Daniel

Sadam_Husain · Post by **Sadam_Husain** » Mon Oct 31, 2011 6:43 pm

did you throw a skinny little set of wheels on it and take it for a blast to see if that makes any difference?

QUADRACER · Post by **QUADRACER** » Mon Oct 31, 2011 6:48 pm

is the damper too soft,also check if the problem gets better if you let the tyres
down.

Lynx · Post by **Lynx** » Mon Oct 31, 2011 6:51 pm

Hey tom, what steering setup and stuff did you use?

Cheers Daniel

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 6:58 pm

at present it has no steering dampener as i need to get the brackets to put it on the draglink. The wobble is so intense i think a steering dampener would only mask some of it. The wheel bearings are fine as well. It only happens upon braking around the 70-60km/h bracket. Engine braking doesn't set it off. The tyres (33' maxxis buckshots) are pumped up to about 34psi. I will try deflating them a bit to see if it helps. We adjusted the castor by lengthening the upper link by about 2mm putting the castor at around 2 degrees. I need to give the tierod and draglink ends a good going over as you can rotate them side to side along the length of them but its hard to get any play out of them along the length of the bars.

Daniel. Tom used the stock ifs box with the 70 series pitman arm. the box is still in its factory position and the rest is the same.

Sam

Lynx · Post by **Lynx** » Mon Oct 31, 2011 7:00 pm

so its only under braking?

tomsoffroad · Post by **tomsoffroad** » Mon Oct 31, 2011 7:04 pm

Youve done all the usual checks, wheel bearings etc? how did you set the castor?

Yes

Set the castor off the top mating face on the passenger side king pin on the knuckle.

did you throw a skinny little set of wheels on it and take it for a blast to see if that makes any difference

No but it is only on 33/12.5/15's. Its getting 35's in the near future.

QUADRACER
Post subject: Re: Death wobble!!!!!

is the damper too soft,also check if the problem gets better if you let the tyres
down.

Hasn't got a dampner at the moment. As for tyre pressure...... Id say Sam is taking note of this thread.

Hey tom, what steering setup and stuff did you use?

Cheers Daniel
Hey tom, what steering setup and stuff did you use?

Cheers Daniel

Its all standard Play-doo steering. I put the Prado pitman arm on the Surf box.

So am I correct in thinking that that castor is right???
Thanks for your ideas fellas, can't beat having talented people to bounce ideas off :mrgreen:

Lynx · Post by **Lynx** » Mon Oct 31, 2011 7:08 pm

castor seems allgood, 2deg should be fine, but if its wobbling under brakeing then id be looking at disks, calipers and the hub swap.

Cheers Daniel

ClassicCruiserSpares · Mon Oct 31, 2011 7:09 pm

Lynx wrote:castor seems allgood, 2deg should be fine, but if its wobbling under brakeing then id be looking at disks, calipers and the hub swap.

Cheers Daniel

Id agree if its only doing it under braking.

hosehustler · Post by **hosehustler** » Mon Oct 31, 2011 7:15 pm

I know its a good 3 link setup but could the diff rotataing a little when you brake, essentially altering the castor :?:

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:20 pm

the hub swap we did is the one what rokhound (forgive me if i am wrong) with the calliper mounted on the other side of the knuckle posts. The discs are new so they shouldn't be warped The calliper isn't touching either on the discs.

Sam

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:25 pm

oh also the brakes are fine at any other speed. it doesn't do it when i am decelerating between 100 and 80 or 100 and 70 but just between the 70 to 60 mark it happens.

Sam

Lynx · Post by **Lynx** » Mon Oct 31, 2011 7:31 pm

id be looking at wheel balance then, and just because they are new parts doesnt mean there arent flaws in them.

Is it pulsing the brake pedal?
Are the bearings new or old ones?
Have you tried bleeding the brakes?

Cheers Daniel

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:35 pm

nope just the steering is shaking. Yeah this is true about the new parts. The bearings are the old ones off the ifs but they are only a year old and have been re-greased about 4 times on each side. everytime i stripped the front they got cleaned and re-greased. The brakes were bled after we did the swap and they were only pumping out clean fluid. I will look at putting the rear wheels on the front tomorrow and dropping the pressure to see if that helps.

Sam

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:41 pm

hosehustler. Yeah that would cause a problem but although the johnny joints allow for a hell of a lot of movement they are very stiff joints and i don't think there is enough slack in them to cause too much of a problem. It brakes quite flat as well so its not like it dives and changes the castor. this is all new to me so forgive me if i say something stupid.

Sam

Sadam_Husain · Post by **Sadam_Husain** » Mon Oct 31, 2011 7:43 pm

jammysammy wrote: I will look at putting the rear wheels on the front tomorrow and dropping the pressure to see if that helps.

Try higher pressure as well I pump all my tyres (beadlocked simex and creepies) up to 40psi to get the death shakes out of them on the road

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:44 pm

i will give that a go too. i am getting kind of desperate as i want to get it cert'd but i won't get one as it is

Sam

Lynx · Post by **Lynx** » Mon Oct 31, 2011 7:45 pm

id also check the races for the bearings and completly in, but its not pulsing the pedal, so its not pushing the calipers back in. Yeah, try swaping the wheels around. Are the wheels balanced? hows the power steering? all bleed up? and new fluid?

and you could proberly move the castor back to 3deg, its a pretty good number.

Cheers Daniel

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:51 pm

i will strip the fronts tomorrow and have another good look. Yeah no pulsing through the pedal. The callipers aren't binding on the rotor from what we have seen looking at it. The power steering i haven't checked yet it will have a look tomorrow in more light. Um the wheels have some weights on them. Not sure if they are still balanced. I will go see a mate tomorrow if i can get some time off work to get him to check the balance. What do you think about the tierod and draglink ends. I need to give the tierod and draglink ends a good going over as you can rotate them side to side along the length of them but its hard to get any play out of them along the length of the bars.

The castor will be staying as is at the moment as tom had to cut and re-weld the upper link today to adjust it.

Sam

Lynx · Post by **Lynx** » Mon Oct 31, 2011 7:54 pm

Yeah you should be able to turn the like that, to a degree, ie, not very sloppy.

Other than that and without actually being there, im out of ideas at the moment, report back with your findings

Cheers Daniel

Sawdoc · Post by **Sawdoc** » Mon Oct 31, 2011 7:56 pm

Had a similar issue years ago with a small Diahatsu F10 i owned. Started to develop a death wobble, after checking every thing out i pulled the damper off to test it and the wobble became way worse. I bought a replacement and fitted it and the wobble dissapeared. It supprised me the difference with the new damper.

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 7:58 pm

yeah i will have to give it a good looking over tomorrow. its not very safe. Even though i don't currently have a steering dampener it shouldn't be do this.t

Yeah i am hopefully getting one this week and i will see if it helps.

Sam

niblik · Post by **niblik** » Mon Oct 31, 2011 8:09 pm

i dont run a damper on the fawdy or vomitron.. granted they are both trailer queens, but have driven them both at road going speeds under braking too and they've both been fine.. the dampeners just mask the issue rather than fixing the problem..

play with tyre combo's on the front then castor..

SMOKEY · Post by **SMOKEY** » Mon Oct 31, 2011 8:21 pm

I would have said wheel balance, but it should still wobble at the given speed and not just after braking. Try another set of wheels ?...?. FITZY

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 8:27 pm

yeah that is what is puzzling both Tom and I. It is only doing it while using the brake and only around the 60-70km/h mark. i have another set of tyres i can borrow. they are a/t tyres.

Sam

rokhound · Post by **rokhound** » Mon Oct 31, 2011 8:49 pm

10-1 says it will be the panhard. Either the bushes or the mounting. What speed have you had it up too?
The other thing to make sure is that the knuckle bearings are all new and not mixed and matched.
When going up to 35" tyres you can run 6 deg or so of castor quite comfortably, and the main thing castor effects is the self centering of the steering. You could also try having a fiddle with the toe and see if that helps.
I had real major issues with the original truck with DW (couldn't get it over 60 kph). It was all related to the panhard, but but running toe out I could control it a bit (not ideal, but it worked).

SamLogan · Post by **SamLogan** » Mon Oct 31, 2011 9:05 pm

there are brand new bushes top and bottom of the panhard. i have had it up to 120 and it shook a wee bit but i put that down to having 33's on uneven Canterbury roads with no steering dampener. We did a knuckle rebuild kit when we put it back together so they should be fine. Tom checked the pre load on the knuckle and he said that it was fine. Yeah it is in need of a wheel alignment but i need to sort the rear panhard out first apparently as the guy who i saw about the wheel alignment said they use the rear axle as a reference point. I have lengthened it but the angle its on causes the rear to float a bit around corners but thats another problem in itself.

Sam

rokhound · Post by **rokhound** » Mon Oct 31, 2011 9:14 pm

The other thing that may be happening is that you are getting deformation (read twisting) on the axle housing. I was speaking to Croz last week and that is the reason he gave for doing 4 link setups as opposed to 3 link.

mud_slinger · Post by **mud_slinger** » Mon Oct 31, 2011 9:23 pm

2 degree castor is wat ifs trucks run, i wouldve thought about 4 degrees would be for beam axle or round abouts?