M939A2 / M923A2 bucking/bouncing at 25 to 35 mph

[Alexsha]

Under 25 and over 35 mph my truck is pretty smooth. At 25 to 35 I get some severe bouncing/bucking. This is on flat roads. Would this be a wheel balancing issue? Wheels out of round? Shocks/springs? I know these trucks are not smooth rides, but the bouncing is pretty intense.

 

[73m819]

What is the air pressure in the front tires, is the front axle OUT of front wheel drive (never mind if the light is on or not) that you know for sure ???

 

[MuleMac01]

Make sure your truck has the C.t.I.s counter weights on the front tires and that there opposite of the c.t.I.s valve on the tire.

 

[Alexsha]

What is the air pressure in the front tires, is the front axle OUT of front wheel drive (never mind if the light is on or not) that you know for sure ???

55 psi in front passenger. 62~63 psi in front driver.

Later today I'll take it out and engage/disengate the front axle, but I'm fairly sure it's not engaged.

Make sure your truck has the C.t.I.s counter weights on the front tires and that there opposite of the c.t.I.s valve on the tire.

Yes, CTIS counter weights are present and opposite the valve.

 

[TacticalDoc]

tag...for follow up

 

[porkysplace]

Similar thread
[h=1]Bull ride question[/h]

 

[Alexsha]

Similar thread
Bull ride question

I saw that thread, but this bucking/bouncing happens regardless of the road and at slower speeds. after I go over 35 it's much smoother.

 

[VPed]

Then just speed up or slow down

 

[Alexsha]

Then just speed up or slow down

I would, but the speed limits around here are 30... right in the middle.

 

[QUADJEEPER]

I have the same issue around 40 mph with my 109. I have 11.00 XL's all around. Front axle not engaged. Run 60 lbs. front and 50 rear.

 

[Jason O]

You likely have one or more tires out of round. My truck felt like it had Fred Flinstone tires until I had them buffed/ shaved to bring them in true. I lost a good bit of tread in the process but it was worth it.

 

[VPed]

O.K. then, I'll try to be more helpful. Both my deuce (on 395s) and my 5 ton have bouncing issues at certain speeds that I can affect with tire pressure. Airing down usually will work to reduce my vibration below 40 mph. But I have to air down quite a bit so I limit this to when I will not be going faster. If I have highway time in my plans, I go with higher pressures and avoid the vibration speeds.

I do not have CTIS but I did read a thread that indicated that the counterweights are actually a little too heavy to properly balance against the CTIS valve. Maybe you can pull a front hub cap and jack up that tire. This might show you which is the heavy side and that can guide your remedial actions.

 

[71m109a3]

I have the same issue around 40 mph with my 109. I have 11.00 XL's all around. Front axle not engaged. Run 60 lbs. front and 50 rear.

My 109 does too. I have 9.0 NDCCs and have swapped them around and replaced a few to no avail.

 

[joesco]

My Super Singles, Michelin 14-20's do the same thing. Brought it to the local truck tire shop and they suggested re-groving them for $150.00 per tire, which would bring them back to new.

My guess is that the more I drive him, the uneven wearing will "may ", as the BBTB (Big Boy Toy Budget) is depleted!

 

[MuleMac01]

Rotate the tires if that doesn't help balancing beads, and put about 1,000 pounds in the back should smooth it out nice. Most of the trucks have had the same tires for years and sat on them for years... out of rounds tires is a big problem. Mine does it at 55-60Mph but smooth as glass below.

 

[QUADJEEPER]

During my brake and wheel bearing service, I spun the tires with the axles out and didn't see any major out of round tires. Too much bearing drag to check for balance issues. I have tubes, so not keen on putting anything in the tires for balance. Anybody have any experience with Centramatic balance plates? They mount to the lug pattern behind the wheels.

You likely have one or more tires out of round. My truck felt like it had Fred Flinstone tires until I had them buffed/ shaved to bring them in true. I lost a good bit of tread in the process but it was worth it.

 

[Tinstar]

Mine does that also if I haven't driven it for a while.
Slow speed and short trip will not smooth out the flat spots.
A nice trip that allows the tires to heat up and higher speeds always works for me.

Remember all of that truck weight on that one tire spot over time will not make it happy.

 

[bchauvette]

When we took Ken's M923 wheel off the back side of the rim was loaded with caked on hard dirt!

 

[lindsey97]

quadjeeper-- I have centramatics on one of my dump trucks and I think they work wonders on my steer axle. do not have them on my m923a1.

 

[QUADJEEPER]

Thanks Lindsey97, I think my bounce is from the rear, so I may try a full set if they have them in the correct bolt pattern and when (if) I can save up for them. As for the flat spotting Tinstar, I have driven over 90 miles in one run without smoothing out. And no terra firma attached either Bchauvette. Someone told me that all 109's did that. I'm not convinced. Yet.

quadjeeper-- I have centramatics on one of my dump trucks and I think they work wonders on my steer axle. do not have them on my m923a1.