death wobble on the semi...

[sceep]

anyone have any ideas where to start on diagnosing a death wobble on this thing?

seems to only happen with a significant load 13k+#'s and only when you hit a bump just right.

have alot of hauling to do this year and i'd like to get this under control before something lets go.

only has 184k on the odometer.

http://www.dana60.com/sceep/a4f/gunnison/rig.jpg

[MMiller]

When you mean DW, is it pulling the steering wheel out of your hands, or are you getting a vibe like a tire out of balance? I'd check the basic stuff, TRE's, kingpins, wheel bearings loose, steering gear box worn, alignment.......Did it just start?

How are the front tires wearing? Are they balanced? I have Badyears like that on the front of my service truck. They are cupping badly, and I get bad vibs out of them. Next week a new pair of Michelins are going on with Equal in them for Balance. My dad's T600 kenworth had a vibration in the front end, that would not go away. When it needed tires, he got new Michelins, new Aluminium rims, and equal in to balance them. Now it drives better then any pickup, and the truck as probably 600,000 miles on it.

Michael

[sceep]

When you mean DW, is it pulling the steering wheel out of your hands, or are you getting a vibe like a tire out of balance?

Michael

feels just like normal death wobble on the trail rig.

wheel jerking back and forth, and the cab wagging back and forth on top of the axle.

not fun with #20k on the trailer doing 63. :eek:

[MMiller]

Wow, that is not good. Have you done anything yet? I don't really have anymore ideas. Usually trucks like this don't experance this phenomenon. Second and third gen dodges do, first gens usually don't. I just figured it was a coil spring/track bar thing, and leafs didn't show this problem much.

Michael

[speedo]

Since you probably don't have air ride suspension and it only happens when you have a significant load I would guess that your caster is changing enough with the rear dropping that it puts you into the DW zone. I have seen this happen on buses with air ride when the leveling valves are out of adjustment enough to change the caster just slightly. Either low in the rear or high in the front.

Gus

[sceep]

Wow, that is not good. Have you done anything yet?
Michael


havent even climbed under it to look at anything yet.. just noticed it yesterday morning when i had a good load on it.

Nate

[littlejer]

Just a suggestion, but check out your rear suspension for wear too, we have had a couple T800 kennys at my work start to get funky because of wore out control arms in the rear, it was more going around corners and unloading 1 side of the suspension though. I know its different trucks, but it might help out a little

[85 Chevota]

I'd bet that it's a bad tire...

[Robert]

Obviously, check your drag link and TREs, K-pins, wheel bearings. Also check the shackle pins. I have seen MANY times when worn shackle pins have caused a shimmy.

To check the steering parts:
Have a helper work the steering wheel back and worth with the engine off. Use your hand to feel the ball joints to detect any freeplay.
To check the K-pins and Wheel Bearings:
Jack up the fron axle so the wheels are off the ground. Use a long pry bar, inserted into the holes in the wheels to pry upwards. Look for any movement or looseness. You may need a helper to look at the knuckle to determine if the movement is in the wheel bearings or king pins. If the king pins are worn, I would suggest Kaiser No Ream King Pins. Easy to install, no special reamers required, and they last forever.
To check the shackle pins:
Insert a LONG pry bar between the spring and the shackle mount. Use the pry bar to try to seperate the shackle apart vertically. Any movement indicates worn shackle pins and bushings. If the shackle pins are worn, do the front spring pins as well. Worn shakle pins will alter your cast angle, giving you all kinds of shimmy.
If you have cupping in the front tires, get new shocks. Cupping indicates the tire is hopping, meaning the shocks are not doing their job of keeping the tire on the ground.

[redcheetah]

I have hardcore DW on my TJ with a leaf spring conversion in the back. I don't mean to thread jack. I just wanted to say that I appreciate all the above info even though they are two totally different rigs. Just checked the caster and toe last week and it has yet to solve the problems. I will check the above advice and hopefully that will help.

PS - I love that Ford. Especially for what you have into it.

[redtruck]

my guess is tires it happens on my freightliner FL80 whenever I get over about 75,000 miles on them, plus they start to cup some on the insides.

[wilson1010]

TJ DW yields to the three fixes: lower control arms, new front tires, alignment. secret is figuring out which one is the real problem so you don't have to spend $800.

[trkklr77]

I'd bet that it's a bad tire...


im thinking the same, i wore the fronts out from windy road driving with smaller flat bed [c6500 26kgvwr]. they wore all lumpy and high/low spots, new tires = problem solved for me.

[64Trvlr]

Have you checked the king pins yet?

[Robert]

im thinking the same, i wore the fronts out from windy road driving with smaller flat bed [c6500 26kgvwr]. they wore all lumpy and high/low spots, new tires = problem solved for me.

You fixed the cause of the DW, but not the cause of the cupped tires.
A new set of shocks would keep the tires from wearing funny ;)

[70~K5]

Have you checked the king pins yet?

+1 Every time I've had DW on a semi its been kingpins. If you can slide your hitch forward and put more weight on the front axle it may go away.

[Matty Moe]

I would guess it's your steer tires, my FL70 dose the same thing when they are worn out!

[rockmup]

King Pin bushings or spring eye bushings.

Either one is alot of work but not much money. Just bushings if your lucky

[yager]

figure it out yet?