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RobCavendish

New Member
I've been studying my Borg Warner transfer box lately, mainly due to the fact that the VC unit has seized and broken numerous parts of the transmission; until that is, it was identified as the problem.
My question is this: Why has this transfer box got a differential in it at all? Why is the VC unit not driven directly by the morse chain, as the purpose of the diff, that is to divide the torque equally between the two props is effectively over ruled by the VC. This seems a stupid question on the face of it, but the more I think about it the less convinced I am that the diff has any purpose at all. Anyone have a simple explanation?
 
RobCavendish said:
I've been studying my Borg Warner transfer box lately, mainly due to the fact that the VC unit has seized and broken numerous parts of the transmission; until that is, it was identified as the problem.
My question is this: Why has this transfer box got a differential in it at all? Why is the VC unit not driven directly by the morse chain, as the purpose of the diff, that is to divide the torque equally between the two props is effectively over ruled by the VC. This seems a stupid question on the face of it, but the more I think about it the less convinced I am that the diff has any purpose at all. Anyone have a simple explanation?
Click to expand...

The diff is there to correct rotational differences front to back. So the transmission does not wind up and do exactly what has happened to yours. The VC is there to ensure the rear/front wheels cannot spin independently giving true four wheel diff lock automatically.
 
it splits the torque evenly to both axles otherwise one would be locked to drive while the other taking less than 50% of torque until vc locked,vc locks diff in effect so that either axle can take advantage of vc
 
On some psuedo 4 X 4's a VCU is used in place of a diff and splits the torque unevenly front to rear. On the P38 the VCU is simply a diff lock that prevents excessive rotational differences between front and rear drive shafts.
 
Ok, thanks to everyone who has replied and I understand what people are saying, but this doesn't justify the diff being there totally to me. Datatek seems to have the best explanation and I'm interested in the applications that use solely a VC, as this seems a reasonable course of action.
I also understand that the diff is there as a torque splitter, but the VC overrrides this and means that even if the diff wanted to split the torque differently it would not be able to, clearly in a poor traction situation this is good, but again, when can the diff really do it's job?
Wammer's point about wind up is true, but, as I said before the diff is rendered useless by the broken VC and is unable to do the job it is given. Even when the VC is working it soon overrrides the diff and renders it incapable of working as a normal diff does.
I'm still unconvinced as the diff is always slave to the VC, the diff can only do what the VC allows it to, so why is it there?
There are some great discussions on this forum, thanks everyone :)
 
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A VCU used as a centre diff never provides full power to the wheels with traction until the other pair of wheels have already lost traction, it also dissipates power as heat like a torque convertor. In the case of Nissan, it is not recomended to run in 4WD full time and it is prone to failure if the front/rear tyres have different amounts of wear.
On the P38 the centre diff provides a 50/50 torque split, the VCU efectively limits the amount of slip permitted on the axle that that is losing traction. The exact opposite of the way a VCU works when it is used in place of a centre diff.
 
think someones on the windup.... :hysterically_laughi

can you go back to your 2wd eurobox please and stop messin about
 
gtland said:
Touche` Having any joy reading the runnes of that old driver unit Datatek?
Click to expand...
I have got 80% of the potting off, from what I can see so far it all looks pretty simple. Been concentrating on digging my service pit so I can change my gearbox:D
 
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