wrong!
how would measuring "pressure" determine whether the VCU was working correctly.
Because whether the VCU is slipping or not is not what damages the drivetrain. It is when it doesn't slip when it should do that does. Therefore the way to tell if the VCU should slip is by measuring the pressure it is applying to the transmission.
Its a bit like the 1 wheel up test - that measures the force needed to slip the VCU when the car is stationary - which is in effect the pressure the VCU is applying. Obviously you can't do the 1 wheel up test when driving down the M1 - but if you could measure the pressure its applying to the transmission, it is essentially the same thing.
The term in the 1 wheel up test is 'force', I termed it 'pressure' - they may technically be different things - but that's what I'm meaning.
A correctly working VCU will only exert so much force/pressure on the drive train when turning, a tight one will raise that force/pressure - so the bearings fail and teeth get stripped.
Measuring heat wouldnt show much as it is heat that makes theVCU operate.
Agreed, that's why I mentioned not testing the VCU.
Lack of heat might be an indicatore, but as I stated before, measuring the difference in rotational speed of the two halves of the VCU would give a more meaningful measurement because one that gave little or no slip would give little or no variance and one that slipped all the time would give a high variance. More importantly though, either woukd be a relatively constant output. If a VCU was working correctly then the variance would be changing irregularly. This would be easy to ascertain with non contacting sensors too - a problem with most feedback systems.
Yes, you could measure the rate of slip, but you would need to analyse what was causing the slip and whether it slipped sufficiently before tightening to apply damaging force/pressure on the transmission.
That's why I'm thinking to measure the force/pressure, either as a guage or when it exceeds a damaging level, throw up a warning/LED. It may be that damaging levels are different for short durations (eg turning or pulling away off road) and long durations (eg open road)
and its a big BUT, whatever system woukld need to be cheap and reliable, otherwise it might be cheaper to change the VCU more regularly.
Absolutely - regardless of whether its a "VCU Replacement" or "VCU Monitoring", its got to be cost effective. If you could "measure" it, it wouldn't just save expensive repair bills, but could save on replacing the VCU when its still OK, and give you warning when it's getting towards the end of its life so you can plan for it financially.
The costing side of it is why I was wondering if you could tell the force/pressure exerted on the transmission by the temperature of a bearing and then whether you could cheaply mount (glue!) a temp. sensor on the outside of the IRD/Diff case by the bearing to pick it up.
