Started last evening on our drive to JPN lessons. It seems the tcase/4hi isn't completely disengaging. The lever is in 2hi position, but the 4wd light on the dash flickers in and out. And if I step on the accelerator, speed over 40kph I get the high piched whining grinding sound. I could not exactly tell what rpms that triggered it, but mmm maybe over 1500. So, I can'y drive over 40kph.

This is a '96 Isuzu Wizard, 3.1TD. Anyone know of inherent or common problems with the tcase/front diff? Is this a cold weather act up? It was .5*c.

The only problem I have seen is the needle bearing disintegrating on the input shaft from the tranny (this assumes the same t-case as the petrol engines in the US have). There's been a couple of those in the last year. Strawmeyers had a nice lengthy thread about it here if you want to search it out...

HERE is that thread... but I don't think that is your issue if you are correct that the truck is partially engaged in 4WD. If those needle bearings were locked up, I'd imagine the t-case would be in Hi/Lo at the same time, not 2WD/4WD. <img src="/forums/images/graemlins/confused.gif" alt="" />

Here's a picture to go along with the rest of this reply:


The bottom-left 'rod' (shift rail) and its attached shift fork go the mainshaft where the needle bearings Steve is referring to are. This engages either high range or low range (the needle bearings are under the low-range gear). This shift fork is 'hard mounted' to the shift rail with a spring pin; so you are physically pulling it into high or low range.

The bottom-right shift rail and its associated shift fork go to the front output shaft and engage 2WD or 4WD. This shift fork is not 'hard mounted' to the shift rail; but instead is able to slide back and forth on it. You are physically putting it into 4WD when you shift the t-case, but when you shift the t-case into 2WD you are just moving the shift rail itself and a 'return spring' is what actually pulls the shift fork back (thus disengaging 4WD).

If your t-case is the same as mine and the problem is the t-case staying in 4WD, my guess is something is preventing that spring from pulling the shift fork fully out of 4WD such as the spring being fatigued or unseated.

My only issue with your diagnosis is that, if the truck was partially engage in 4WD, you should here the grinding all the time and not just above a certain speed or RPM. <img src="/forums/images/graemlins/confused.gif" alt="" />

Yeah, I agree the symptoms are a little contradictory...the rpm-noise thing suggest bearing, but the 4WD sticking doesn't, unless the lack of bearing is preventing the shift fork from moving properly...but as Sean says the bearing that usually goes out would affect the Hi/lo fork, not the 2WD/4WD fork.

I guess the other needle bearing on the front output could go out, though it is rarer because it is fully immersed in oil and therefore always well lubricated.

Hey guys, thanks for the replies. Sorry I've not gotten back sooner, it's been busy.

The night this problem occured, I tried to squirrel through the neighborhood to get home. In that time, I put the tcase in 2hi, but something would not completely disengage as that's when the whining would sound when I reached 40kph or over a certain rpm. So, I was literally crawling. I turmed to a side street, put the tranny in reverse in hopes that would fully disengage the tcase. However, as I put the truck in D again, the trouble persisted. The 4wd indicator on the dash was also flickering in and out. That corresponded with the whining noise.

When I put the tcase in 4hi, it would get into 4wd. So then I'd go to 2hi, but it seemed the tcase/somewhere would not completely disengage (though I don't rightly recall if the tires were still locked in 4wd or not).

By this time I was just about home and had random traffic to contend with so I couldn't much troubleshoot anymore, so I bopped along at 35kph, then backed it in the garage and left it for the next day. Next morning, I get up to take it to the shop to get checked out and fixed if need be, but that never happened because the truck was behaving fine. I put the truck in 4wd (hi), it got into 4. I dropped it down into 2hi, it dropped down just fine. I used 4wd tonight in the ice, again, using it when needed then dropping to 2hi and it went well.

Needless to say, I'm at a loss. I've had no further trouble with the truck. I'm rather embarassed that I don't know this system at all, I'm not much help figuring this out, am I? <img src="/forums/images/graemlins/confused.gif" alt="" /> I sound like a complete auto newbie lol The dealership that sold me the truck resprayed black undercoating ***** on everything before it was delivered to me so labels and radomn identifying marks are no longer visible <img src="/forums/images/graemlins/angry.gif" alt="" />

I'll read through the recent tcase post suggested above in a bit (my mind isn't settling now to read it) <img src="/forums/images/graemlins/lol.gif" alt="" />

Try looking here. http://www.planetisuzoo.com/article...ing_the_Isuzu_Shift_on_the_Fly_Mechanism

Also it helps if you do your shifting in neutral, if your front axle disconnect is sticking. You can also try backing up a bit then putting it in neutral.

Joe

It sounds like it's bound up.

This has happen'd to mine before,I could shift into what ever I wanted to but the whole system was in a bind,
even with front hubs unlocked etc.
When it does it again,lift one of the front wheels off the ground and see if this allows it to "unbind"

I'll try the Neutral if it occurs again.

Thanks for the link and the troubleshooting tips.