Truck violently bouncing

[Indyharleyguy]

Hi I've got the violent bouncing when I hit 40 MPH. I slow down to 20 MPh and it stops. It last maybe 5 minutes then it stops. It drives fine after that. It seems to only happen when it's cold? I've already had the transmission filter and fluid replaced, the vacuum gauge on the top of the engine to shift better replaced. Any thoughts on what's causing it to bounce?

 

[Mullaney]

Hi I've got the violent bouncing when I hit 40 MPH. I slow down to 20 MPh and it stops. It last maybe 5 minutes then it stops. It drives fine after that. It seems to only happen when it's cold? I've already had the transmission filter and fluid replaced, the vacuum gauge on the top of the engine to shift better replaced. Any thoughts on what's causing it to bounce?

.
What kind of air pressure are you running in your tires?
I am guessing it starts after sitting overnight?

.

 

[NY Tom]

Tires would be my guess too.

 

[cucvmule]

Square tires from sitting over the winter? How much use does the truck get. Age of tires become a hazard also after many years in the weather.

Could also be death wobble from many things from one thing or combination of several.

Do you think it is engine related; motor mounts check out ok? How are the propeller shaft u joints.

 

[chucky]

Yea when i hit 40 my vehicles violently rocked as well but you will notice with time your vehicle barely rocks at all !

And then you wished it did again !

 

[NY Tom]

I say it because have a similar problem with my deuce truck sits for a month and then shakes pretty good for the first 5 minutes or so once I hit 45 mph. After some driving it calms down until the next time out. Hot weather reduces this. Tires are not new but in good shape.

 

[nyoffroad]

To me it sounds like flat spots on the tires from sitting, it can happen overnight. Could you have an old set of bias belted tires? Those things would flat spot and run rough for about 10-20 miles before warming up and rounding out.

 

[canadacountry]

be lucky you don't have a trailer, as I was telling someone about cold cummins engine - the same trucking book author also mentioned that having to deal with flat spots on tires till they had warmed up was one thing but to back into an equally-frozen trailer was double the punishment with two sets of flat spots in different places!

 

[Indyharleyguy]

.
What kind of air pressure are you running in your tires?
I am guessing it starts after sitting overnight?

.

Yes it does start after sitting overnight. I have HumVee tires on it. It does ride a little rough right after driving but this is a different feeling to me,. I'll have to check the pressure.

 

[Indyharleyguy]

Square tires from sitting over the winter? How much use does the truck get. Age of tires become a hazard also after many years in the weather.

Could also be death wobble from many things from one thing or combination of several.

Do you think it is engine related; motor mounts check out ok? How are the propeller shaft u joints.

I was thinking transmission until the fluid get run a little bit? I have been driving a few times a week for the last 6 months.

 

[Indyharleyguy]

.
What kind of air pressure are you running in your tires?
I am guessing it starts after sitting overnight?

.

yes seems to happen after sitting a few days. I'm going to check the pressure after it stops raining in Indy area

 

[Indyharleyguy]

Square tires from sitting over the winter? How much use does the truck get. Age of tires become a hazard also after many years in the weather.

Could also be death wobble from many things from one thing or combination of several.

Do you think it is engine related; motor mounts check out ok? How are the propeller shaft u joints.

i'LL CHECK. iF IT WAS U JOINTS WOULDN'T

Square tires from sitting over the winter? How much use does the truck get. Age of tires become a hazard also after many years in the weather.

Could also be death wobble from many things from one thing or combination of several.

Do you think it is engine related; motor mounts check out ok? How are the propeller shaft u joints.

I'll check these out. If it was u joints it wouldn't stop would it?

 

[chucky]

i'LL CHECK. iF IT WAS U JOINTS WOULDN'T

I'll check these out. If it was u joints it wouldn't stop would it?

Unless maybe its out of balance at the same speed/ mph Im playing with a rear shaft on a jeep i jacked up so angles changed but still get the vibration on take off in 1st so if you havnt messed with the height i bet its the flat spot after sitting

 

[nyoffroad]

Hummer tires are available in radial and bias belts, look and see what you have when checking tire pressure. IIRC the 16 inch tires are radial and the 16.5 are bias, may be wrong on that. Doubt it's the U joints, they will normally click and vibration doesn't go away.

 

[87cr250r]

M1008? That's the death wobble. The Dana 60 axles are especially prone to it. Kingpins and bushings are worn out. Drop your tire pressure to 30 psi or less and it will go away. This is a test, not a solution.

 

[cucvmule]

i'LL CHECK. iF IT WAS U JOINTS WOULDN'T

I'll check these out. If it was u joints it wouldn't stop would it?

Yes they can be intermittent as they begin to wear from non greasing issues. They can open up clearance one or both sides and as the propeller spins it will spin balance to the center and will act normal. I see it more on stock non greaseable u joints front axle shafts and as the front propeller constant velocity joins go bad.

I always keep new upper nylon kingpin bushings around as they are a wear item and with bigger tires they go bad faster because of the added stress. I use the nylon as they take abuse and shock better than the bronze bushing. When GM was the only supplier I would buy bags of 10 pair.

Between the draglink, tie rods and upper bushing are likely 70% of death wobble issues. Other areas of concern: steering damper, 2 with larger tires, spring bushings, loose worn bearing races in rotor hubs. And possibly the most overlooked on the front axle, the frame housing, bushing that the rear spring shackle bolt goes through. Most times they are worn very bad sometimes clear through.

 

[Indyharleyguy]

M1008? That's the death wobble. The Dana 60 axles are especially prone to it. Kingpins and bushings are worn out. Drop your tire pressure to 30 psi or less and it will go away. This is a test, not a solution.

Yes, it is an M1008. It's hopefully stopped raining in the Indianapolis area and will check the PSI today. Thanks.

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