Quote:
Originally posted by Jack
I will put in the fuse and then try the grass thing. Thanks for the idea.
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If you put in the fuse and
then try the grass thing, your front wheels will spin even if there's nothing wrong with the car. Putting a fuse in the 'FWD' slot effectively makes the car forget about the rear half of the drivetrain and
no pressure is applied to the transfer clutch.
It sounds like you're a little fuzzy on how the whole thing works. I'll give you a little explanation.
Instead of having a center differential or viscous coupling between the front and back halves of the drivetrain, the SVX has a multiplate clutch. When the TCU senses a difference in the signal from the two speed sensors in the transmission (one for the front and one for the rear) that suggests the fronts are spinning, it applies pressure to the transfer clutch. It does this by using duty solenoid C. Since it's a solenoid and simply on/off, it applies more or less pressure (more or less torque to the rear) by fluttering on and off at different frequencies. This allows more or less hydraulic fluid to act on the piston that's pushing the transfer clutch together.
The difference between the signals received from the two speed sensors doesn't just happen on a slippery surface. When you turn, the front and rear wheels take different paths and therefore spin at different speeds. So even on a dry surface there's a difference between the signals from the front and rear wheels and the TCU has to operate duty solenoid C to compensate. If duty solenoid C doesn't work right, the transfer clutch binds up. This will tear up your transfer clutch pretty quickly. Eventually, the clutch will be totally worn and the binding will go away - but so will your AWD. Your car will effectively be FWD because duty solenoid C doesn't work and there's not enough clutch material left for it to work with anyway.
Randy's recommended procedure works because you're putting the front wheels on a surface where they will slip and the rears on a surface where they won't. If your car is working properly, the fronts will barely slip before the rears push you forward. Now, the important thing to note here is that the fronts really shouldn't slip much at all. I've driven much less elegant MPT clutch-operated AWD cars, and they slip a considerable amount before the rears help out. Not so with the SVX - it should be nearly instantaneous.
But I think that his recommendation is better for diagnosing a bad transfer clutch - because the TCU
can't tell you that it's worn and unable to use it. It
can tell you about electrical problems like duty solenoid C. If it gives you that code, then no extra diagnosis is required and you just need to replace it. The only other option is to drive around with that FWD fuse in until you
do fix it, because (as I explained) you're going to tear up your transfer clutch if you don't.
Whew, that was longer than I meant it to be. Anybody feel free to point out any mistakes I made.
Anyway, my wife's Legacy has a bad duty solenoid C. I will fix it, but in the meantime I put in the FWD fuse so it doesn't tear up the transfer clutch.
PS My recommendations assume that the TCU is good. It sounds like yours is working fine, which is why I made that asumption.