M1078A1R Offroad Behavior/Question

[GCecchetto]

Over the weekend I went to look at an M1079 van body for sale that was located on a very remote ranch. The road up to the ranch was tight, steep, loose rocky, rutted, and full of tight switchbacks. To be honest, it was getting close to about as much as I would want to do with my truck offroad. That said, the truck drove up it easily with zero issues, aside from fallen trees constantly folding the mirrors in, all the poison oak dragging down the side of the truck, and the constant kidney punches from the front coilover shocks. The turn around at the ranch required side hilling in the red on the inclinometer, but I know that's set up to show the limits at the max GVWR, so I'm sure there was still a good safety factor there.

Overall, I was pleased how the truck did and 1st gear still felt low enough despite the ECO Hubs. On the way back down however, in the switchbacks, I was getting a significant clunking and jerking that felt very much like binding U-joints, and quite frankly felt like something wanting to break. It really didn't feel like something you could let happen for an extended period of time without something bad happening.

Go up the hill under power, turning full lock, no issues, but under engine braking going back down made me wonder if something was wrong. I was in Mode, so the center diff was locked, but the surface was loose, so shouldn't have been an issue like being locked and making tight turns on pavement. At the bottom of the hill down from my house, there is a turn that is a slow full lock turn and I have never felt this happening there where I am not in Mode. I should have thought to take it out of Mode to see if it still happened, but didn't think about that until we were back down and out through a locked gate.

So, pinging the brain trust here to see if any of you have experienced this and to see if I maybe have an issue to address.

Thanks

 

[GeneralDisorder]

Locking the center does cause the driverain to bind - even on loose surfaces - rocks, etc - the axle will stll bind since it has no differentiation so the driveshafts are going to unload when the binding overcomes the friction - there will be *less* friction on loose rocks but not zero so it's still going to happen.

Have you rebuilt the driveshafts and replaced the u-joints?

When the drivetrain binds or experiences unusually strong gravity in a directions other than nearly straight down it can also pull the engine and transmission off to the side if the mounts are old. Had a 2007 A1R locally that had a HORRIBLE noise that sounded like the transmissions was eating itself alive on some downhill left turns, etc - found it was totally shot engine mounts allowing the power pack to be in hard contact with the frame and thus the cab causing severe NVH.

DELETE the coil springs. They are stupid and pointless.

 

[GCecchetto]

Locking the center does cause the driverain to bind - even on loose surfaces - rocks, etc - the axle will stll bind since it has no differentiation so the driveshafts are going to unload when the binding overcomes the friction - there will be *less* friction on loose rocks but not zero so it's still going to happen.

Have you rebuilt the driveshafts and replaced the u-joints?

When the drivetrain binds or experiences unusually strong gravity in a directions other than nearly straight down it can also pull the engine and transmission off to the side if the mounts are old. Had a 2007 A1R locally that had a HORRIBLE noise that sounded like the transmissions was eating itself alive on some downhill left turns, etc - found it was totally shot engine mounts allowing the power pack to be in hard contact with the frame and thus the cab causing severe NVH.

DELETE the coil springs. They are stupid and pointless.

I haven't had the driveshafts rebuilt yet, but have spoken to a shop about it. Plan do have it done when I get back from vacation and can get back on the list of stuff to do. Next up is the trans flush and convert to Transynd, so I'll pull both driveshafts and get them rebuilt and balanced. I have new U-joints, and the joints in the truck seem tight, but obviously the truck puts more load on them than my hands do, so there may be some play.

You've definitely changed your opinion on the coilovers since I first said I wanted to delete them! Glad it has turned out as positive as I thought it would.

 

[Ronmar]

How are your sway-bar bushings and brackets. Steep downhill would shift the weight forward and perhaps put them in a different orientation to make some noise?

 

[GCecchetto]

How are your sway-bar bushings and brackets. Steep downhill would shift the weight forward and perhaps put them in a different orientation to make some noise?

Top and bottom sway bar bushings are new. This was definitely something to do with a rotational drive component, ether in the front knuckles or possibly driveshafts as GD eluded to. I'm guessing you haven't experienced this with your truck off road?

 

[GeneralDisorder]

Deleting the springs turned them into a simple shock - other than *not* buying a new thing - I did "delete" them in the sense that they aren't a coil over anymore. It was a free modification that ended up making a lot of sense. I'm still technically using the stock parts though so I'm calling that keeping them.

Ron makes an excellent observation. Those are universally shot and made a lot of noise before I replace them. Same with the coil-overs actually. The spring protection "sleeve" thing is just incorrigible with its scraping and squeaking as it rubs on the coils. I even swapped in BRAND NEW coil overs just to see and they did the same thing. And there's a specific idle RPM that causes them to ring constantly like a tuning fork. Super annoying. Glad they are gone.

 

[GCecchetto]

Guys, this was a forward and back lurching, just like a 4x4 typically will with the center diff locked when in a full lock turn, which I wouldn't normally worry about. But in this case, there was a significant clunking noise with it that really sounded like binding u-joints. Didn't do it going up hill, just going down.

Definitely nothing to do with sway bar bushings, which as I said are new, and definitely not the sleeve on the coil springs.

 

[Keith Knight]

I’ve driven mine over 34,000 miles and hundreds of off road miles. Yes the front axle steering u joints clunk when in mode! Makes a terrible noise. It doesn’t even require full lock turning I’ve experienced it in half turn primary when there is good traction. This past fall I replaced the drive shaft u-joints, front axle steering u-joints, and all drive line seals. And still every time in mode I turn a little too far to the left or right, even on gravel it clunks. So unless I truly need it to be in mode I keep it in normal and manual down shift to 1st. Switch to mode when I’m rock crawling the switch it back out. Kind of the same concept as if you had a selectable front locker. Use it then disengage it.
I have a trusted friend that snow plows with his and never noticed it until he took it out west and experienced the clunking. In mud you won’t experience it many times as well. When I was rebuilding them I looked for a problem or solution and could not come up with one. It acts as if the u-joint is not perfect centered with the king pins. There are spacers that are supposed to do that but they all measured the same thickness. So maybe something was machined out of spec. But no way of knowing.

 

[GCecchetto]

I’ve driven mine over 34,000 miles and hundreds of off road miles. Yes the front axle steering u joints clunk when in mode! Makes a terrible noise. It doesn’t even require full lock turning I’ve experienced it in half turn primary when there is good traction. This past fall I replaced the drive shaft u-joints, front axle steering u-joints, and all drive line seals. And still every time in mode I turn a little too far to the left or right, even on gravel it clunks. So unless I truly need it to be in mode I keep it in normal and manual down shift to 1st. Switch to mode when I’m rock crawling the switch it back out. Kind of the same concept as if you had a selectable front locker. Use it then disengage it.
I have a trusted friend that snow plows with his and never noticed it until he took it out west and experienced the clunking. In mud you won’t experience it many times as well. When I was rebuilding them I looked for a problem or solution and could not come up with one. It acts as if the u-joint is not perfect centered with the king pins. There are spacers that are supposed to do that but they all measured the same thickness. So maybe something was machined out of spec. But no way of knowing.

Okay, thanks for the info, guess I won't worry about it and stay out of Mode as much as I can. Interesting that I didn't feel it at all going up, only back down. I guess it's just another of the semi-sorted design elements of these trucks I really need to read the operators manual as well, I always stop, switch to neutral, then engage mode. If it can be done on the fly, it would make your strategy more practical. sometimes stopping is the kiss of death.

 

[Ronmar]

Top and bottom sway bar bushings are new. This was definitely something to do with a rotational drive component, ether in the front knuckles or possibly driveshafts as GD eluded to. I'm guessing you haven't experienced this with your truck off road?

No I have not, but have not done much off-road with it save wheeling around the property and pulling a few stumps…

 

[Skyhawk13205]

Okay, thanks for the info, guess I won't worry about it and stay out of Mode as much as I can. Interesting that I didn't feel it at all going up, only back down. I guess it's just another of the semi-sorted design elements of these trucks I really need to read the operators manual as well, I always stop, switch to neutral, then engage mode. If it can be done on the fly, it would make your strategy more practical. sometimes stopping is the kiss of death.

I usually try to shift when driving straight on a low traction surface. I have a couple of situation where I shift on the fly, such as making a hard turn then driving up a steep hill. I think the weak point of the drivetrain would be the splines in the differential, front axle u joints or the c7 clutch pack slipping and burning itself up which I don’t really see happening unless you have low clutch pressures. I think a big concern for the locking transfer case is the c7 clutch pack seal rings wearing out and producing low clutch pressures and not locking the transfer case, a completely latent fault that is not observable or reported until you get stuck.