One of my rear axles is shifting (?) on the M923A0

[TwistedOaks]

(Forgive the narrative, but who doesn't like a good narrative...)

So the last 3 months have been an incredible learning experience. The Green Iron disease is a real thing... don't underestimate. Ever since I brought home "The Dog" (named by my 6yo daughter), there's been a random vibration when driving/braking/moving. Loaded/unloaded, didn't seem to change - but like I said, it was also random. Sometimes it was there, sometimes it was smooth as ... well as smooth as the M939 gets under the best conditions. I always attributed it to G177's on split rims, which were of unknown history and age.

Last weekend, Av8tor hooked me up with some nearly new 1600r20 on Combat Rims at an incredibly reasonable price (and he's only 2 hours from me, which was a bonus - and yes, that thread is coming soon). I was hoping, probably naively, that aside from the upgrade and "killer beast" stance, this would alleviate the vibration. Nope. Got worse... WAY worse.

All along, occasionally, as I am maneuvering out of my driveway, a random "clunk" is heard. I, again naively, assumed something was rolling around in the toolbox or the bed.

Now mind you, EVERY DAY I've tasked myself with some added project. This evening, I got my replacement Budd Nuts from Big Mikes (along with a speedo ratio adjuster, and a new socket... for the new impact driver, for the new 1/2" hose, for the new belt drive 70 gallon compressor all of which was required - at least when reporting to the wife - to put on the 500lb behemoth wheels and tires ). As I backed the Dog into my maintenance area, I heard the clunk, and dismissed it. It wasn't until the 6yo (who loves nothing more than watching me drop things, and look consistently frustrated) says "Daddy, why aren't the back wheels straight?" Huh? Whaaaat?

I'll be strung for hamhocks...she's right! WTF is that?! When I look at the rear wheels, one set appears to be offset by about 6 inches left/right from the other set. I can't tell which set it is, but think it's the forward axle. Then, I parked the truck, hearing the clunk again, I immediately got out, and ****ed if the wheels weren't perfectly aligned again!

So now, I'm asking people that are confirmed more knowledgable than me (and since it's not something covered in any of the TM's that I can find)... WTF is that?! I'm guessing the bobbers will have the answer faster than I can figure out. Any help to point me in the right direction would be greatly appreciated... But here's some photos...


Passenger Side


Driver Side


After re-parking, clunk, back in place!

 

[gimpyrobb]

Its cause your driving with sandals.

 

[TwistedOaks]

Down here in FLA, it's the law.

 

[infidel got me]

rear axle

I would start by checking the dog bone mounts. These are a weak link on the truck and can have similar results as to what you have pictured. Usually they pop off, but you may have one that the rubber bushing is worn out and letting the axle shift. With a constant clunking sound it should be easy to find. Duplicate what you did before pics. and have someone watch for what is shifting/moving around. Good luck!

 

[Floridianson]

Yep sandals will do it every time also all of my trucks do it not a problem. Now if it was shifted when you were driving straight down the road you should worry.

 

[Swamp Donkey]

The clunk you hear is most likely the spring end moving side to side in the spring pocket. There is extra room in the pocket to allow for articulation without binding the spring. A slight offset of the axles can result and both are normal. The picture below shows the space on either side of the spring end.



It would be a good idea to check the condition of the trunnion bearings though. This can he done by removing the cover in the picture. To check for trunnion play, chock the truck well and place the jack under the center dogbone mount. Jacking here will take the weight of the truck off the spring. You only raise the truck enough to unload the spring. With the spring unloaded there is enough room in the spring pockets to move it around a little. There should be no side to side play. The bearing nut and lock nut behind the cover are the same sizes as the wheel bearing nuts.



Getting to that cover would've been a lot easier with the 11.00x20's, lol.

 

[gimpyrobb]

Its just slop in the dog bones. The rubber allows some flex, nothing to see here, move along.

Many of the mv 6x6s do it.

 

[gimpyrobb]

Ahh yes, there can be slop in the trunion might check that too, but from your pics, I doubt it.

 

[TwistedOaks]

Yep sandals will do it every time also all of my trucks do it not a problem. Now if it was shifted when you were driving straight down the road you should worry.

If it wasn't for these HEMTT seats, I'd probably be more agitated by the vibration.

 

[silverstate55]

If your torque rods all look OK (which they seem to be, by your photos), then that is normal flexing of the rear suspension during turns and whatnot. Every one I've driven with rear torque rods (vs. Hendrickson or air-ride) all do the same thing. And the offset of the tires is normal, after I replaced all 12 ball joints in the torque rods of my Deuce, it does it more now than ever before, every time I turn the wheel.

 

[silverstate55]

if it wasn't for these hemtt seats, i'd probably be more agitated by the vibration. :d

SHOWOFF!!

 

[TwistedOaks]

Its just slop in the dog bones. The rubber allows some flex, nothing to see here, move along.

Many of the mv 6x6s do it.

What I neglected to mention, when the vibration starts, it wants to shake the whole truck down (obviously worse since the 1600's). To a point of requiring speed reduction to no more than 20MPH at which point it doesn't subside until I shift lanes.

 

[silverstate55]

What I neglected to mention, when the vibration starts, it wants to shake the whole truck down (obviously worse since the 1600's). To a point of requiring speed reduction to no more than 20MPH at which point it doesn't subside until I shift lanes.

Just wait until you put a load in the back, and get some serious torque hop from the rear suspension between 30-40mph....

Those 16.00 tires are far heavier than what used to be on your truck, so that extra weight is forcing the suspension to flex a little more when the intermediate axle starts scrubbing in turns, or when backing up. Any imbalances will be felt at higher speeds, so look into getting some balancing beads and start with those.

And these trucks will always ride rougher when empty; put something in the back that will flex the springs & tire sidewalls a little to calm things down.

 

[Swamp Donkey]

If the new 16.00's aren't touching then the lower dog bones are most likely still in place. If an upper dogbone came loose then the axle could roll forward or backward and cause a u-joint to bind. I got a bit in depth about the clunking and forgot about the vibration.

That, and the horrible memory of Gimp's sandals at last year's rally.

 

[gimpyrobb]

That, and the horrible memory of Gimp's sandals at last year's rally.

View attachment 622591

I don't wear sandals, you were probably thinking of my thong!

 

[Swamp Donkey]

Trucks....yes, that's what we were talking about. Trucks!

 

[Floridianson]

What I neglected to mention, when the vibration starts, it wants to shake the whole truck down (obviously worse since the 1600's). To a point of requiring speed reduction to no more than 20MPH at which point it doesn't subside until I shift lanes.

Yes the 1600's can be a ruff ride and if out of balance also takes many miles to heat up and relax. I run about 40lbs to get a better ride but when I turn I can feel the tire stick but the side wall give. I just lean to the other side so the truck does not tip over. LOL

Also #2 lets see the air ride seats installed!!!!!!!!!!!

 

[KaiserM109]

Guys, as the owner of an M923A1 that's been rode hard andput up wet, this seriously worries me!

The only time I have ever had a vehicle exhibit symptoms like this was with an F100 and there WAS something wrong with it and it WAS dangerous. After trips to 2 major front end alignment shops a little back-water shop identified and fixed the problem. It was one of Fords better ideas, a nut on the track bar that couldn't be tightened because of a bracket welded over it. That little back-water shop was the last stop before the junkyard.

What alarms me with this thread is that the problem sounds to me to be real and serious and nobody has come up with a legitimate sounding answer, just silly ones. My truck is 25 mi. away from home in a storage yard and I can't get up there right now to look at it. I follow these threads in order to get a heads-up on problems I might encounter, so I will be watching for better answers.

These trucks are big and old and dangerous and have often had poor or no maintenance. If we are going to maintain our right to own MVs, we need to take all these problems seriously.

 

[gimpyrobb]

What alarms me with this thread is that the problem sounds to me to be real and serious and nobody has come up with a legitimate sounding answer, just silly ones. My truck is 25 mi. away from home in a storage yard and I can't get up there right now to look at mine. I follow these threads in order to get a heads-up on problems I might encounter, so I will be watching for better answers.

These trucks are big and old and dangerous and have often had poor or no maintenance. If we are going to maintain our right to own MVs, we need to take all these problems serious.

Aside from the 1600s being crappy for balance, the only things it could be have been identified. The dog bones and trunion.

 

[1bonehead]

I have a very hard time reading black writing on dark green background.

I I think the suggestions provided are sufficient to get the owner started down the right path. I would be interested to know if the trunion bearing is bad.
Please let us know what you find out