lateral runout

What would cause lateral run-out on both of my rear tires?

I had a vibration a while ago and thought that I had "thrown a weight". got them balanced and then noticed lateral run-out. Fronts were fine, so I rotated the tires front to back (directional tires). Now the rears are vibrating again. Lifted the rear and noticed lateral run-out again.

The frame where the rear lower control arm mounts looks to be bent due to poor lift placement. Could this cause this? if so, how do i fix it? Would bad bushings do this also??

I was looking to replace the rear arms with aftermarket that will allow for the addition of a sway bar and they will come with new bushings.



If the axle is not "true" how do I measure?

Way back when I was a paid mechanic,the first thing I did was get someone to drive your wagon and I would follow
and watch for any signs of "Crabbing"as in walking sideways.Watch closely how the rear end follows the front.If you
have a vibration it should be easy to spot.
You can then do some precise measurements using the chassis points that the body shops use to see if the frame
or axle is bent.I think the measure points are in your chassis service manual.I am looking in my manual shortly.
Take Care
Jim Gordon

My FSM won't be here until the 6th, so any help would be appreciated.

Crabbing cause lateral run-out? I thought it just caused wear on the leading edge of the front tires. ( the car is sideways, but the rear tires are still straight)

tires old?? radial bands broke,. hard hit to a pot hole loaded heavy will damage the radial beads, bands,. whatever they are called,.they shift and seperate under the rubber cap,.running the tires too soft too,. mark the high spot,.then mark where the valve stem is,. deflate and move the tire on the rim half turn,. air it up properly,. check it again,. if it still has runout in the same spot then its tire,. if the high spot is still in the same spot relative to the valve stem,. then its the rim,..
jm2c
nick

Nick, I would agree with you, but the ones that were slightly "wobbly" and moved to the front have almost fixed themselves. Not perfect, but close, which leads me to believe that there is something wrong with the rear geometry.

At first I thought it was a bent rim, but it doesn't matter what tire (had 3 sets) are on the rear, it ALWAYS happens....... even before I started pulling the trailer.

Rotating the tires every 3K miles prevents it from happening, but I got tired of doing that so often and it's treating the symptoms, not fixing the underlying problem.

Treadwear is even across the tire so tire pressure is good (keep at 38-40psi) no cupping, so bearings are good, no feathering , so alignment is good.

I have just over 35K on this set and are due for some new tires and I don't want this to happen to them.


And Nick, your 2c is worth 4 to me as I know you know.

If the rear end isnt square with the frame the car will "Crab" down the road.Sorry thats the word I have always used
to describe the axle not being true with frame.Sounds like the improper hoist/lift has damaged the suspension and/or
the suspension mounts.You still have to find those chassis holes to measure the distance between the axle/frame.
Sorry but I dont have a chassis manual so I think the measuring holes are located on each frame rail below where
the back and front door meet.These holes are exactly opposite each other and appear to have no purpose.Its just
a chamfered hole in each frame rail parallel to the opposing frame rail.
Are you confused yet because I am?
Jim Gordon
OK this sounds as strange as it probably looked but I fingered both my wagons and neither of them have chamfered
holes,just plain holes about 1/2"diameter!!!!
I am done

easy quick measures,.
bottom centre of each balljoint (grease fitting) cross ways to lowest point of the inner lip of the brake drum should be at centre of the axle tube,.a big "X". measure front to back each side for comparison,. that'll tell you your track,.( front end could be skewed due to poor bushings etc,.)
two plumb lines off the front bumper shock plates two off the rear, cross measure again,. that'll tell you if your frame is straight or parallelagrammed slightly,
front plumb lines to lowest point of rear brake drum will tell you if the rear end is straight in the frame,.(assuming the frame is true),... car needs to be on dead flat surface,. and rolled back and forth 10 feet by hand before measuring,.so the drive train and suspension is in a relaxed position.,,.
don't be surprised to find things off somewhat,. especially a 14-15 yr old car,.i,d be concerned if more than an inch or so,. the tire track front to rear can work out, and it'll carry a slightly skewed body down the road with no tire wear,.especially if its had a 4 wheel alignment using the rear axle as the mean.
This is only a quick hillbilly way of determining how far out things are,. frame holes have been known to be not always in the right spot,. (the sedan front axle misplacement etc,.)
I,m sure some egghead will be along shortly with the proprer way of doing things,. :lol

rear tires are handling torque, so they will become more pronounced than steer tires,.IF as you say the fronts have "fixed themselves,. well,. its not magic,. tires are either "F'd" and the belts are moving around,. or they're not "F'd" and the belts are fine,. but from 1 condition to the other reinforces my point,.

Fingering the holes in your wagons rear end or its frame rails, or your own rear end hole,. is not very scientific and will only work if you,ve recently had 1/2 of your penis removed,.

Nick

piece of thread with a 3/8ths nut works as a plumb line,.

With your way, I would assume that putting it on a lift would defeat the purpose as frame/body flex would change geometry?

Such a way with words.Still better to be half a penis than a TOTAL DICK and thats on a good day
Take Care
Jim Gordon

I was being sarcastic.........

I was referring to the wonderful and always friendly NICK.
Sorry I wasnt more help but at least I tried
Take Care
Jim Gordon

Krzdimond wrote:

I was being sarcastic.........

Me too ( see over size font)

aw fer chrissake you guys just add a half page of smilies to any of my posts and you'll all be fine,.

See, I missed that. I thought you were being helpful as it is late and I cannot see well anymore.

you know us rednecks cain't read that fast, please type slower next time........