1995 Explorer 4wd front end shakes a lot when in auto 4wd mode

[Tedybear]

I swear everyone is going to get sick of hearing from me eventually.

Planning on the maintenance, but wanted to get some feedback on this one issue:

Going down the road the "Auto 4wd" is supposed to be able to be engaged "on the fly". (not the 4wd low range. I've not tempted fate with that one yet)

Well, I'm not much into flies. I come to a stop and switch on the auto 4wd. The transfer case does it's thing. The truck moves forward and is riding very rough, almost like I'm driving a flippen Sherman Tank! Lots of shuddering and noises like the front end is ready to blow apart.

I can put it back into 2wd mode and the ol' girl settles down and goes down the road fairly smooth and with out issue.

I did note the front diff was a hair low on fluid. It's been topped off. (I'll likely drain and refill that as well once I manage to find something useful to suck the old fluid out with)

Here's my concerns, and if someone could tell me if they could be related?

Speed sensor is inop below 2,000 RPM. (No one seems to have access to the wiring information. I'm fairly sure it's a bad wire...)

I'm running 235 75 15 on the rear. 235 70 15's on the front axle. (All I have for the moment until I can afford to put new tires all around this on the stock wheels)

Could any of those two issues create my "Rumble-Shake-rattle-n' roll"?? It feels like the front end is shaking itself apart--until I go back into 2wd mode. Then the ol' girl does okay.

I checked the U-Joints on the front drive shaft. Seem to be fine without any play or clunks.

Next few days I'll be nipping up another set of jack stands so I can get all 4 wheels off the ground and seeing if I can recreate those issues/shudders/noise. Also need to locate what I'm sure is a bad wire to the speed sensor, just wish I knew where those two wires are plugged into. (Yeah I know where they wind up on the end of the transfer case....It's the other end I need help with)

Any ideas are welcome!

Thanks!! I'll check for responses tomorrow morning.

S-

 

[429CJ-3X2]

I'm not going to be of much help here, but running different size tires in 4WD is a no-no. That is the same as having slightly different gear ratios front and rear. You also shouldn't be using 4WD on dry pavement. Both the different size tires and 4WD on dry pavement could/will cause binding in the front end.

Shifting into/out of 4WD on the go is no problem, just don't shift while you're accelerating. I lift my foot off the gas when I do it just to be sure. You can hear or sense when it shifts and then you can continue driving normally.

There is a specific procedure to shift into or out of 4WD LOW. You must be stopped for one thing, so you can't do it on the go either intentionally or accidentally.

 

[manimal]

If it were mine, I would disconnect the front driveshaft at the front diff yoke, and check all U-joints for binding.

Then I would pull the front unit bearings to expose the front CV shafts, at which point you can grab the end of the shaft and move it around to check the CVs for binding.

Pulling the bearings isn't a big deal, just time consuming. You can either replace the shaft nuts or re-use them with red loctite and torque to 150 ft-lb or so. I also mark them with a dab of white paint to check back later to see if they have backed off. Mine never have when reusing with red loctite..

Although the Control Trac TC's fluid coupling allows for some difference in speed between front and rear axles in 4-Auto, it's generally not a good idea to run different sized tires on the front vs. the rear. It is an absolute no-no when using 4-Lo.