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3 spd auto - 4wd problems
Posted 21 November 2003 - 11:09 PM
Anybody out there an expert on these things? I'm not, although I've been a mechanic most of my life. I replaced the burnt out 4WD clutches on my 87 and 93 Loyale wagon. Basically a 1 hour job and $25 in parts. I then experimented a little in an attempt to make them fully engage with no slip. I discovered that the 4WD is much stronger when the transmission modulator gets zero vacuum (which is like being at full throttle). I'm tempted to put a vacuum switch on the dashboard. In the mean time, I experiment further by adjusting the modulator for higher pressure. This is done by installing a longer actuating pin. Easy to make from an old drill bit.
Got both wagons working well in 4WD mode now, but curious if any one else has jerked around with these "bad" Subarus. By the way, my 87 and 93 Loyale wagons both get around 17 m.p.g. on the highway in winter driving. My 92 Loyale wagon with 5 speed stick gets 27 m.p.g. and my 85 with 5 speed gets around 25. Of course, better yet, my crappy little 89 Justy 4WD with 5 speed gets around 34 m.p.g. and runs like a little rocket. A crappy rocket perhaps, but a rocket just the same.
One more comment on the 3 speed automatic Subarus. I bought two to them cheap because both owners were told that they needed transmission rebuilds. Neither one would go into high gear. After a little research, I fixed them both in an hour. Seems these transmissions are prone to suffering from stuck governor valves. Open the hood, pop the spare tire out, and the valve comes right out. Take it apart, hone it a little with emory cloth, clean it up, and all works well.
Posted 22 November 2003 - 07:59 AM
The FT (full time) 4wd trannies you speak of are the 4EAT model
the 3 speed are called 3AT.
The govenor fix on 3ATs is pretty well documented, called by some "morning sickness" as in the begining stages it happens when the tranny is cold. Not quite as simple to get out on a turbo model.
The FT 4wd system is operated by a duty solenoid feeding the hyd pressure to the clutch pack.
The trick used by some is to circumvent the duty solenoid signal sent by the tranny brain (TCU) with a constant 12v signal via a dash switch. This then emulates the "diff lock" switch in the manual FT trannies.
Thanks for the tips and keep up the good work.
Posted 22 November 2003 - 06:03 PM
I'm not sure I know how a perfect running 4WD drive with an automatic is supposed to behave. My service manual states that it is designed to slip at low throttle (i.e. high engine vacuum). Taking that into consideration, and also . . . the fact that it's easy to drive around with the 4WD accidentally on without knowing it. With the sun shining, it hard to see the indicator light. And, if the clutches slip, a person might not notice that the cars is in 4WD. With a standard shift, I think anyone would notice since there is no slip, except, perhaps at the tires and the drivetrain growls on pavement. So anyway, I can see how these clutches get burnt out. After putting new ones in, I can now hear them chatter if I engage 4WD on a hard road and turn.
I turned up the pressure to the clutches by removing the modulator, and taking out the original acutating rod which was 1.375" long. I made a new one out of a drill bit to a length of 1.425 and the 4WD works much better.
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