legacycentral bbs

Why would the central differential on a Legacy automatic lock up the moment the engine is started?
Is this familiar to anyone?
The car was built for the Japanese home market, and imported to UK. It is a 1994 legacy estate-car / station-wagon with twin turbo and automatic gearbox.
According to the man who is working on the car:
"The only difference putting in the diff lock fuse makes is that the warning lamp on the dash comes on for the diff lock."
He explained to me:
" The turbo cars have permanent 4wd, with a central diff. When you engage low ratio it locks the central diff also. The auto cars don't have a low ratio, but to get them out of sticky spots you can insert a fuse in a fitting under the bonnet, and this hydraulically locks the central diff. "
This suggests that there is some sort of (electronic or hydraulic) control unit somewhere which is triggering the diff lock. But where? And why? Is there a solution? What should we / he do or try next?
What other information would I need to supply for someone to be able to advise me how to solve and fix this problem?
Thanks in anticipation.
Don

Sounds like you need to stop talking to this guy. He has alot of information backwards!

The center differential in ANY automatic legacy is activated elecronically using hydrolic pressure. When the car is started the pump is running (the transmission pump is connected directly to the engine NOT through the TC).

Functionally there is no difference between Turbo and NA.

The fuse under the hood is intended to send 12 volts to the solenoid that controls the center differential. This causes the clutches to fully disenguage giving you FWD.
Its only meant to be used when you have a flat tire.


You forgot to mention the most important detail in your post, what problem are you having exactly?

BTW, its actually very useful that the differential locks in this way. Many tests can be performed including verifying the front and rear differential ratios match.

The problem is that the centre diff locks as soon as the engine is started, and, because it's locked up, the transmission winds up when doing tight corners at low speeds causing one or two wheels to shudder and scrub. Putting in the fuse or taking it out makes no difference to the way the car behaves. With the car on a wheel-free hoist this is easily demonstrated. The only difference is the warning lamp.
Is the control for this inside the box or external?

how would it make no difference? If the fuse is in for fwd the rear wheels dont get power. How are you testing this on a hoist?

domhnall: You know what a "red herring" is?

You problem has nothing to do with the center differential lockup when the engine is running. The failure is the center differential itself. Search on here and on Nasioc for torque bind.

If you leave the FWD fuse installed long enough it WILL release once pressure has dropped (unless yours is really gone).
The problem is known by subaru and the fix invlolves a whole new center differential. From what I remember 96+ transmissions have the fix from the factory.