A vibration all the time points to the rear driveshaft. How is the carrier bearing? Mine went bad recently and the replacement cured the vibration, though the yoke on the rear axle was also bad and I replaced that as well. A front axle driveline problem will likely not present itself in 2hi. I had forgotten to tighten 2 bolts on the t-case output to the front axle and didn't have any idea untill I needed 4x4 on the highway a few days ago....Just some food for thought. Jack the rear of the truck up and check the carrier bearing as well as the rear axle yoke. As for checking the front shaft u-joints, jack the front up on one side, have the wheel turned all the way in one direction and spin the tire by hand. Any u-joint issue will be easy to see/hear.

 

Great advice, thank you and I will replace the rear u-joints, The carrier bearing should be good as i replaced that this last spring. I will also check the u-joints in the front end by how you advised. Thanks again!

 

I have to weigh in here on a couple of things. My post count is not high here, but I am speaking from over 10 years of rockcrawling experience. I know what wears and breaks axles.

With all due respect, I have to say that 4wd on pavement is not that big of a worry to me unless you run lockers. I would also be skeptical that worn tires of the same original size would cause an issue.

I run a hydraulic ram on the tierod of my rockcrawler that assists the steering. When I am on the rocks I have both differentials locked in full time for periods of time (not like a detroit). Of course this is hard on axles, but 4wd on pavement with open differentials would cause a fraction of the wear of what this does. Now there is no reason to be in 4wd on dry pavement, but if it happens, there is no need to stress about it. It will cause the vehicle to handle a bit differently and yes it will strain the drivetrain a bit. If it is causing steering problems driving straight, there is something wrong.

Regarding the different tire sizes--there is a rule that allows for different gear ratios front to rear within a very small margin of error. (ex. 5.29s with 5.38s) This is no different that slightly different tire sizes. Also consider that stock open differentials allow the two hubs on each axle to spin at different speeds for turning purposes.

Finally I just drove my cummins for 300 miles in 4wd (really bad snowstorm) I was on dry pavement for a bit before I stopped to take out 4wd. My truck did not steer any different than it does in 2wd.

I hope I explained myself and that this is helpful in eliminating a few posibilities.

 

Leorn, Thank you for your input, I appreciate any and all ideas no matter what their post count states. Knowledge is not about how many times someone posts So you are saying that the tires should'nt the cause of any of this right? and it did do this driving straight so I am just trying to figure it out by checking one thing at a time. Do you think it could be the steering stabilizer? Thanks again!

 

In the rockcrawling community we call steering stabilizers a bandaid fix for other real issues, but I don't know enough about the stock cummins setup to know how important the steering stabilizer is.

If it were me I would have someone work the steering wheel back and forth slightly with the engine off and while I looked for joints that are worn (loose) -- or anything else that looked strange.

I am still learning about the crappy steering dodge gave us. The only thing I can think of that would affect steering differently in 4wd vs 2wd is if you were getting different amounts of power to each wheel like a broken axle shaft, or something rubbing on one shaft and not the other??? With a broken shaft I would think the spiders would just spin and no power would go to the front. I guess you could check for a broken shaft by putting it in 4wd and jacking up one of the front tires at a time and attempt to rotate it. With the other on the ground, you should not be able to rotate it very far at all.

 

I do not want to sound like a know it all but I do have over 40 years experience as a Master mechanic and have owned a 4 wheel drive shop in the past. You can in no way compare rock crawling to street driving. The maximum difference in ratios is 4 points (hundredths) and yes you can do damage driving on asphalt in 4WD. I have seen and repaired MANY vehicles that were driven on the street in 4WD. If you have a dually with the heavy diesel engine then there is a lot more strain on the driveline then with a gas engine and single wheels. Lockers have nothing to do with this, it is the speed differential between front and rear not side to side. When you turn the front wheels travel further than the rears. If the transfer case is locked in the wheels are all going to travel the same speed/distance. Something has to slip. In a diesel dually you have four tires worth of traction in the rear and a heavy engine right over the front axle for traction up front. Will the tires slip? Maybe. Will an axle break instead? Maybe. Do you feel lucky? Even going straight down the road you could have one tire with a little less pressure than the others or a little less tread and that tire is going to be spinning faster that the other three, where will the slippage be? Open rear or not all four tires are locked to the road and to the pinion, something will have to slip. Hence bad steering in this scenario. Just so you know, I have four heavy duty four wheel drive pickups, Chevy, Ford and Dodge. I also have a CJ-7 powered by a 454 with locked rears front and back. I know a little about what I am talking about. OH, I have also been four wheeling since 1968.


Rick

 

I don't see much difference between a high traction rock slab and high traction asphalt or concrete.

The rule of thumb I am familiar with is 2%. My example is 1.7% difference meaning that for every 100 revolutions the tires will ned to slip 1.7 revolutions or for every 100 inches 1.7 inches slip. (purposely not boring everyone to death with drivetrain slop, and shaft twist) We're getting into a lot of detail here, but facts these are the facts. The same thing would occur with different tire wear. Yes there is some stress and wear, but IMHO its not worse than a burnout if its not for a long distance. I have been doing infinitely worse things to the same set of axleshafts on dry sandstone slabs in my toyota on 40in tires on locked (e-lockers think spools) tiny toyota axles -- thats why to me 4wd on the street is not a significant source of drivetrain wear. I do agree that if you did it all the time that small amount of wear will add up and something will give. All drivetrain components wear out and require repair/replacement eventually.

Well put. I was trying to keep it short, but what you say is correct.

At the end of the day maybe your right and it is different tire wear/pressure, but my lesser experience training tells me that steering issues are generally related to alignment, suspension wear, steering component wear or an improper modification of one of those systems.

Good post Rick

 

OUCH! That sounds like a CAD unit not engaging nicely. If it sounded loud and bad, I would be concerned with the splines not being engaged fully and disengaging enough to clunk from one spline to the next.

There are vacuum lines that go from the vac pump back to the shift lever at the transfer case, then from there across the crossmember to the passenger side, and then to the CAD unit. Maybe one is leaking preventing proper engagement of the CAD causing some horrible sounding clunks?

BTW I have never bothered to pull a driveshaft to check a u-joint. When they let go they are pretty obvious, and can get pretty bad without hurting anything but the u-joint itself. Usually you get a funky squeak when engaging the clutch, and maybe some strange grinding/squeaking as they get worse, then when the needle bearings get really bad and disintegrate, a solid clunk on acceleration and deceleration, and sometimes a noticeable wobble from the driveline balance from not being in line due to the bad bearing.

Good luck with it.

As to driving on the pavement in 4x4 it does nasty wear to the engagement collar for the front driveshaft inside the transfer case. I am unaware of one actually failing, but it is SO ugly to look at I highly advise against normal on pavement 4x4 driving. Also driving with lockers offroad you have a major advantage over open diffs on pavement. On pavement with one leggers or a posi, there is precious little slop to absorb the differential of the front taking a wider sweep in corners.

Offroad with lockers, the locker itself has a significant amount of slop it absorbs. At least all ratchet lockers do. Lockrights and other lunchbox lockers you can "feel" this slop with the tires in the air. Spin the pinion flange and you will see what I mean. It's actually remarkable play. You can't really feel it from the wheel, because the locker will just ratchet with very little resistance. Detroit full case have a similar amount of "slop" but it's HEAVILY springload, so it's very hard to demonstrate. When you hit a slick spot or lift a tire, this stress is unloaded from the locker. Springwrap also soaks up a LOT of this F/R differential.

Either way high traction driving in 4x4 is hard on components.

 

Thank You all for this info. I am learning so much more than I figured i would and I am always glad to learn anything! Thanks again!