sierra death w0bbles

[dad]

hey all.
have searched bible, but no luck, so here goes
scored 2 sets of f100 rims on monday, put 4 on, and went for a drive.

as soon as i hit over 30 kays i got massive death wobbles, on the front wheels and steering.

had a look underneath and all seems tight
figured it must be an egged tyre so put my stockers back on
but the death wobbles are still there.

is it possible that the extra load (on the bearings) due to the larger offset of the rims caused a frail wheel bearing to let go? also is this what would happen if your wheel bearings shat themselves?

or am i way off track? any help would be greatly appreciated guys

nic

[ScrawnC]

Ahhhh...... the death wobbles.....

This topic seems to pop up every now and then but I haven't heard of a solid answer to the problem yet. I guess just start with the basics and work from there, check all steering joints and bearings for play, get tyres balanced and rims/tyres checked for out-of-round/buckles. Don't worry about the steering damper as this will only 'mask' the problem, not fix it. You should be able to drive without the damper and not have any problems.

[alien]

have you had the rims with the tyres you plan to run balanced??? the rims are probably warped.

[Gwagensteve]

Check EVERYTHING in the front end.

It seems that it's rarely one thing, but a range of small factors multiplying.

Wheel bearing tension
Knuckle seals (felt and rubber)
Caster
Bushing condition
Kingpin bearing condition
Worn shackles
Ball joint wear
Steering box wear

Often any one of these (or a small amount of wear/out of spec in all of them) may result in the wobbles.

The steering damper won't really help. Rim offset and balance will make it worse, but a clubmember who normally runs unbalanced beadlocked Q78 swampers with 2.5" backspacing, no steering damper and longish shackles had unbrearable death wobbles when he went back to stock tyres (he's never had it with the swampers on it.... go figure)

Apparently worn knuckle seals are a major cause.

Steve.

[alien]

he probably doesnt feel it on the larger tyres because theyre running at a comparitively lower pressure than the stock ones and the extra sidewall height is cushioning the wobbles.

my mazda 323 got a big dent in one of the rims, and during the impact the tyre lost half its pressure and was running at around 15psi - there was zero effect on my steering or anything, even though the rim was visibly deformed... so i experimented and inflated the tyre back to 32psi and it was wobbling all over the road. Needless to say once the rim was replaced and the wheels re-aligned the wobble was gone.

[Gwagensteve]

There's no obvious explanation alien - the swampers weigh at least twice as much as the stockies, have never seen a balance weight and have far more offset -

I have had massive death wobbles with all sorts of small tyres, and some big ones. IMHO the tyres don't make that much difference on their own.

Steve,

[joeblow]

now take everything above into account. your front end must be mechanically sound and i asume your running standard steering components?
1- when you increase your tire diameter, you increase your toe in [31's or above, severly.]
2- caster should be the same with bigger rubber.
3- adjust toe until the reading is 0mm overall.
4- take it for a drive and see what happens, if it gets better keep going out in small increments.
unfortunaley with big rubber the bearings on the front end aren't designed to take the load of say a 33, so some compromise will have to be reached. let me know how you go, i'll bet money toe fixes it!

[ScrawnC]

Apparently worn knuckle seals are a major cause.

Steve.

I'm guessing you mean the swivel wiper seals? How would these contribute to wobbles? I'm not trying to be smart, just interested.

[dad]

thanks for all the input guys

i didnt put my original wheels back on the same corners when i put em back on. putting them in their proper places helped alot.

have discovered a dodgy ball joint also

will fix the bj, and leave as is till i get decent rubber for the new f100 chrome sunnys, and getem all balanced and aligned

should do the trick

thanks again

[Gwagensteve]

Apparently worn knuckle seals are a major cause.

Steve.

I'm guessing you mean the swivel wiper seals? How would these contribute to wobbles? I'm not trying to be smart, just interested.

No no , I didn't believe it either, but they have a significant dampening effect on the knuckles and apparently it is a fix.

Joe, how does tyre diameter effect toe?

Steve.

[joeblow]

will show you soon....

[Gwagensteve]

You are "correct" if you measure toe in millimetres. Which it isnt.... It's measured in degrees for exactly the reason you have drawn - toe must be measured independent of tyre diameter because the effect of toe is at the road surface not at the leading and trailing edge of the tyre.

Most tyres have a contact patch which is wider than it is long at highway pressure (or they're pretty close) so toe will be only minutely effected by diameter.

I generally rough align cars parallel, but have not ever seen a connection between death wobble and toe or tyre diameter and death wobble. are you advocating toe out?

I any case, caster has a large effect on death wobble. It can often be cleared by increasing caster.

in any case, how does a 31" to 32" change toe more severely than from 30 to 31? The relationship will be linear, no? i.e if you added another 30mm to your 80mm, you'd gain another 4.19mm of toe.

[joeblow]

try it people...proof is in the pudding

[christover1]

After ruling out all possible steering parts wear or failure.
I upgraded my steering stabilizer and never had a problem again.
The stock zook ones don't like larger tires etc.
Mine was completely stuffed, and another stocker may have been fine.

It is clear to me that a heavier, larger tire would not be a cause of the problem, but would certainly exagerrate a problem that already existed.
It can be worsened by dried mud on wheels etc.

Never had death wobbles with power steer, and now don't use a steering stabilizer.

christover

[SiKiD_01]

get a new steering damper.

i have had 4 mates with sierras, and at some stage, they have experienced the wobbles.

my friends car has only stock wheels and tyres, but she get the wobbles bad after any tiny bump in the road.

on all 4, OME dampers have been fitted. part number: OMESD30

you can get RTC dampers, but i don't rate them.

[dad]

ive actually been planning to get a decent damper for some time...

i wouldnt mind rtc just for the wank factor, but now im wondering if its not gonna be as good as a 'normal' one after last comment

[Gwagensteve]

RTC - don't bother.

Remember, steering dampers don't fix anything - they only mask a problem so you don't notice it until it's really big.

Steve.

[dad]

ok thanks for the tip..

[bigzuk]

my drover had huge death wobbles when i brought it.

I put new tyres on it and the wobbles were gone. i may have been bad tread wear causing it also?? just a thought?

[dad]

turned out to be my front r caliper died, was causing a bit of drag on the wheel

and yeah bad tyre wear wasnt helping

[GRPABT1]

Ok guys, after putting my new 15X8 -24 offset rims on the sierra I have noticed a bit of the old death wobble at around 60km/hr which is annoying. I've had a look and the only thing that pokes it's head up is a the steering box is leaking (has been for a while probably due to me flogging the piss out of it when trying to get the pitman arm off). Now considering the wobbles aren't that bad could this be the ONLY problem perhaps? Cause I wanna tackle the front wheel bearings, seals etc eventually but they seam to be pretty good atm. Also should I be looking at fixing the steering box or just replacing it?