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Help! Random grinding/squeal from somewhere...

That's really interesting - I'd not even thought about it having a VC, I assumed in my innocence that it just had a normal central diff lock. I'm guessing if the VC is acting up it could be catching unnecessarily or inappropriately, and acting like a locked diff. If it was happening now and again, this would also explain some drive line shunt on the road, I guess. The question is, does a failing VC also start to make nasty noises? Interesting....
 
Okay - bit more info - had 10 mins free this morning so just nipped out and jacked up a front wheel, stuck in neutral and (apart from finding a bit of play in NSF wheel bearing - joy - another job) I found I could turn the wheel, though it took a fair bit more effort than I would have expected. So the VC (assuming it has one) is definitely not completely locked solid, so does this mean its "good"?

Out of devilment value, I used the centre lock switch, and this worked perfectly (i.e. suspended wheel locked solid, apart from the usual play in the driveline). I'll get some time back end of the afternoon to do a little more digging...
 
Hi Clive - I'd say maybe 1/4 inch top and bottom (we're running 285/75/16s). But I've had wheel bearings go before and nothing that sounds quite like this... thats not to say that isn't it, but.... looks like I am coming up with quite a list of little fixes - hopefully one of them will flush out what the problem is. Either that or I'll sell it buy Janet a Kia haha!
 
Funny how this item ended up double threading as I'm wondering if I have the other type of broken VC!

Dave s it would appear by the year of your truck that you do have a vc and as Dave2000 suggests =go try it!
 
Funny how this item ended up double threading as I'm wondering if I have the other type of broken VC!

Dave s it would appear by the year of your truck that you do have a vc and as Dave2000 suggests =go try it!
I did - see posts above ;-)
 
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I think you can only properly test it by trying to drive it with no cdl and no front propshaft. you shouldn't notice any difference at first then it will drive like your clutch is slipping and then it wont drive at all after a few miles.
 
Huh? Now I'm confused. Will the VC scavenge enough power to drive the rear axle if its working properly? I can understand it driving the back axle if its knackered and locked up, didn't appreciate a "good" one would do that. And if it was good, wouldn't the test you've suggested just have cooked it?

I know very little about these VCs - they may operate on black magic for all I know...
 
Well in my experience it did, I slid off a rock one day and shattered the front right drive flange on another rock and so had no drive. I used CDL toget home and then took it off. Had a look at the damage the next day and decided it didn't look so disruptive and wondered if I had just not selected gear properly in my hurry so took it for another drive. No problem for a few miles then going up a steep hill it began to loose drive until it stopped. So put on the cdl and off it went. I then suspected it was the VC kicking in and so tried it again later that day with the same result. So it can provide a substantial amount of drive on an unladen truck. Obviously once it heats up the fluid looses viscosity and slip occurs. I think the old discos had them as well.
 
I can only assume that if it looses the fluid somehow that it then can seize
 
The VC heats and the silicone thickens and expands, thus the sheering is less and hence there is drive. Continual slipping will eventually heat and expand the silicone beyond its working parameters into a globby mess, this eventually hardens.....VC toast!

Regards

Dave
 
Huh? Now I'm confused. Will the VC scavenge enough power to drive the rear axle if its working properly?

Yes it will drive the axle but will feel like a bad clutch, speed about 15 mph but by then you are starting to heat the VC unnecessarily, so don't push your luck, suffice to say it can move your LC it is working. If your LC moves as if with both propshafts connected, then your VC is cooked.


Regards

Dave
 
Cheers Dave - that makes sense. Based on jacking up the front wheel, I'm sure the VC isn't completely locked solid, though I do wonder it its some how breaking up or otherwise misbehaving (can they grind/jangle when breaking up - who knows?!).

Based on all of the comments, I think my starting point is to pull the front prop off - that will answer the question as to whether or not its that worn UJ, plus I can check out the VC as you describe. If that doesn't clarify things, then I guess I'll just work through the known faults (brake pads, front UJ and NSF wheel bearing, probably in that order) and go from there. Those bits and bobs need doing anyway, so may as well get it sorted out...
 
Funny how this item ended up double threading as I'm wondering if I have the other type of broken VC!

Dave s it would appear by the year of your truck that you do have a vc and as Dave2000 suggests =go try it!

Sorry guys, it just struck me as I read it...
 
That amount of play in the wheel bearings will give no noise nor other symptoms other than a little bit of excessive brake pedal travel after maneuvering round a car park where a lot of work on the steering forces the wheels hubs and discs sideways, removing the play and pushing the pistons in to the calipers.

Not a good idea to rely on the VC to drive the car. It's designed to work in the background to transfer a different amount of power to the front c/w the back. It's working a lot of the time during routine driving but within it's own capabilities.
 
I’d put the wheel bearing higher up the list and you may need a new stub shaft as bearings rotating on the shaft can wear it to the point the bearings aren’t properly seated.
 
Thanks guys. TBH I plan to do all three jobs in quick succession - main reason for doing one at a time is so I can definitively identify the culprit! The joys of running a 20 year old truck...
 
You’ve certainly got plenty to be getting your teeth into that could be causing the grinding. You could have a seized bearing turning on the stub axle. Without hearing the sound it’s difficult to say.
 
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