Undo the bolts in such a way that the fluid drains off the corner of the pan, not all across the long edge, and get a bigger catch pan.

Much cheaper and simpler than installing a drain plug.

 

Well, I replaced the tranny pan with no problems and was happy to see that the inside was squeaky clean with no crap stuck to the magnet. Only a minor mess on the shop floor when I moved the catch pan to get to the filter, forgetting that there's a bunch of fluid trapped by the filter still. Oh well, that's what they make rags for.

Back to the original problem, I swapped out the transfer case motor / sensor for a rebuilt one. Changed the fluid while I was at it, fired it up and have the exact same problem. Transfer case fluid was clean as well, so I don't have any reason to believe that something is broken there.

On to the front diff, pulled the front cover and checked things over. Oil was reasonably clean with no metal / dirt fragments in it. I looked at the diff as best as I could with a light / mirror and didn't see anything obviously broken, but then again I've never really done any diff. work so this thing could be trashed and I wouldn't know the difference.

Refilled it with synthetic lube and don't notice any difference. Visual inspection of the driveshaft doesn't show anything out of the ordinary.

Troubleshooting ideas? Also, If I need to replace the front diff, is it better to do the whole unit (case & all) or can I just install the diff as an assembly? What years would interchange in case I need to source one from a scrapyard?

Thanks for any and all advice!

Bob

 

Sounds like your front diff is in good shape, but without pictures I can't confirm other than it sounds good.


I'm thinking, sense you replaced the shift motor and shift sensor that your problem might be electrical and thus bringing into play the TCM (Transfer Case Module). There would be only one way to diagnose this correctly however, to stop installing non needed parts I would shoot for the old school diagnostic and look for volts being distributed between the wires or harnesses to ensure that the signal is being received.

You need to Download a manual and look through the diagnostic or electrical schematics. http://www.mediafire.com/?fqnnjdzq252

 

Hydra,

Thanks for the link to the manual, I'll grab it and study.

Not sure on it being electrical or not, as the motor definately does move to 2 independant locations when you rotate the switch, I can hear it move as well as feel it by placing my hand on it while someone else moves the switch. (car turned off, ignition on, trans in neutral).

To help prove some of my ignorance on 4WD knowledge, let me ask a few stupid questions.

What actually changes when going from 4HI to 4LO? Going strictly from memory, when in 4 HI I was able to drive relatively normal and nothing sounded differently other than the truck having the feel of more of a drag on it. (aka "heavier" steering feeling). When in 4 LO there was a severe drag on it, and turning the wheel you could feel a substantial wheel "hop" from the front end. I don't see how anything can actually change in the frint diff. from HI to LO, so why the wheel hop difference? I assumed that while in 4LO the gearing is also changed to the front end?

Is there a way to mechanically test the front diff / transfer case to try to isolate the problem? How can I tell if the drivetrain is in 4HI or 4LO independant of what the indicator light is telling me?

Maybe I've just lost too many brain cells over the years.

Thanks!
Bob

 

Update:

Hydra, thanks again for the link to the manual. I read the front axle & transfer case sections closely and now have a MUCH better understanding of what's going on in there. I now see clearly that there's no way the motor could have been "over driving" it into 4 LO because it's rotating in the opposite direction from 4 HI. I'll chalk that one up as a $175 lesson learned.

Now it's back to my original problem..... when in 4HI on a snow or rain covered road the truck has a noticeable "wobble" above 20mph, as well as there is a drivetrain "whine" coming from somewhere (very difficult to tell exactly where) that goes away when going back to 2WD.

Switching between all modes of drive is normal, also no codes are being thrown. Reading 10+ volts at the motor connector when engaging 4WD switch. Reading the resistance across the 4WD switch (connectors removed) I get proper ohms at the different positions. I don't really have an easy way to read the output channels of the drive motor position sensor (short of hooking up a scope to it) but according to the charts if it was moving out of position it would kick up a fault / prevent the motor from moving anyways, so I think it's safe to say that it's good.

Tires & suspension are eliminated (new tires, new upper & lower ball joints, shocks, alignment).

I'm still suspecting a transfer case issue somewhere but would really like to troubleshoot this better before I go dropping it.

Ideas?

Bob

 

Open the diff up. It is a lot easier than digging into your T-Case. Your truck is pulling from one side to the other. The place it will be doing that from is the front diff. the T-Case is sending power to the front and rear, the diff is dividing that power from left to right.

 

Common sense also told me to look into the front diff, but when I pulled the cover things were clean & nothing seems amiss. There's no noise coming from the diff when in 2WD either. I'd think if there was a problem I'd get a whine all the time?

Is there specific troubleshooting for a front diff beyond tearing it down and checking clearances?

Bob

 

I'm not great with gears but my gut is screaming front end. It may be one or both of the CV shafts binding. When the t-case isn't engaged it may unload without you feeling feedback. After engaging 4wd the shafts are unable to unload through an idling driveline and now you end up with this side to side pulling. Maybe none of this makes sense. I've been up with my wife all night helping her with her math and I'm dead tired now.
(And no we weren't multiplying. )

 

Hmmm.... this may make more sense than you think. I just noticed the problem after I changed upper & lower ball joints, so I had the CV shafts off. I replaced the boot on one side (I punctured the original accidentally) and everything appeared normal. I very rarely use 4WD though, so I can't confirm that it's related. Anyways, thanks for the thoughts, it gives me a little bit more to dig into. Bottom line is I need to determine where the noise is coming from when 4HI is engaged and start from there.

Get some sleep, maybe the homework selection will be better tonight!

Bob

 

+1 Sounds like a front end issue.