Hi Andy
I left it too late to check mine and as such am currently waiting for a new IRD and VCU to arrive so I can replace them
Basically the VCU mounted mid way on the rear prop shaft allows the front and rear shafts to rotate at slightly different speeds if necessary under normal road conditions. If the front wheels spin the rotation is faster at the front of the VCU and the viscous plates bind tighter and delivers more torque to the rear shaft. When the rear wheels match the speed of the front again the VCU plates relax a little and allow any shaft wind up to disperse.
If, like mine did, the VCU is seized then the shaft winds up putting extra pressure on the gears of the IRD and rear diff. This is not good when on a good traction surface (dry road) as you can't lose the difference through wheel spin and eventually the IRD and /or the diff will sh*t itself.
The good folk on here have covered the subject and I take no credit for their tried and tested methods. I have only thanks and respect for their knowledge and assistance which has given me the confidence to undertake what used to appear to be fairly daunting proceedures.
TO TEST THE VCU you need to establish if it can allow the front and back shafts to rotate indepenently. Paint a mark front and back and take a drive on a slippery surface to get them wheels slipping. Ming suggested a golf course but we don't have any near me, only a sandy beach and rough tracks through the mountains. There is a small chance when you stop to look the marks may have lined up again so do it a couple of times if in doubt.
BTW it's not the two drums that move so mark the shafts. If in doubt put a spot on the rear shaft, drums and front shaft.
Apparently the VCU can fail seized and unseized in which case in which case you don't get 4WD, but you should be able to notice that fairly quickly.
Good luck my friend.
Now can anyone tell me what the good equivalent is for MTF 94 for me gearbox?
