91 Legacy - Sudden on and off AWD engagement

[fmerkel91]

1991 Subary Legacy - I used to ski and thought the Legacy AWD would be a real boon to driving up. It acted odd > When going up hill under power (freeway or near freeway speed) the front wheels would lose traction, spin way up (verified by the tach), and SUDDENLY the AWD would kick in. Traction would be good, then just as suddenly the AWD would dis-engage and the process would repeat itself.

 

I thought it was poor tires, never having had AWD before. I was not sure HOW AWD should act.  My previous ride was a 4WD Toyota Tercel that you engaged with a lever. Personally I thought it was great and worked quite well but was obviously different.

 

Quit skiing so the car seldom gets in snow anymore, but occasionally in our driveway on a slope one tire will end up on wet grass. When loaded (I scuba dive now so the load is not trivial), when trying to take off it will spin > then suddenly engage. Engagement is not smooth, more like revving up the car a middling amount and putting the automatic transmission in gear.  Now I have GOOD tires and fairly new all around.

 

Recently I took it in for it's first CV joint replacement (160K). The shop (Subaru only) indicated the transmission had a problem with the rear not engaging correctly. Well, how about that. They also said that otherwise it was fine and probably not worth the trouble of tranny repair. I agreed since the AWD is about 95+% not necessary. If I didn't know there was a problem, there is almost nothing other than this odd and occasional behavior to indicate it.

 

Then talking with a dive buddy that runs a Transmission shop indicted it could be electrical with the throttle sensor providing input to gradually engage the AWD. I did some searching and find there appears to be a bunch of such sensors.

 

Anyone know where to start on this issue and what to check and where? I don't have anything to check computer codes nor do I have any CEL issues.

 

Note-While researching I found out about the FWD fuse. I JUST put it in and will be taking it on a 100 mile test trip this afternoon. A trip around the block indicated normal driving behavior and a new FWD red icon on the dash.

Appreciate any help.

Fritz

Edited January 31, 2016 by fmerkel91

[porcupine73]

Hi, first question I would ask is - condition of the automatic transmission fluid, i.e. when was it changed last? What type was used? The reason I ask is the way the transfer clutch works I believe it needs the fluid to be good, i.e. good dynamic friction properties, else I think it's going to get grabby, because the difference between slipping and not slipping it can't module it very well otherwise and will get grabby. But that assumes mechanically everything else is good. If it doesn't have torque bind, like feeling like the brakes are in in slow speed cornering near idle then that is good. But then again if the shop indicated they detected some kind of problem that might be indicative of something that me sitting in an armchair can't know or see.

Edited January 31, 2016 by porcupine73

[wtdash]

HI,

My '90  engaged 4WD after a delay. Fixing the transfer clutches resolved it. It's not an easy fix, but doesn't require pulling the trans. You can R&R your existing clutches or buy new.

 

What's the car worth? I'd just drive it w/the FWD fuse in.

 

If you DO want AWD, you could install the center diff lock switch (10 mins of work) which would override the TCU's control. This has caveats, so read up.

 

TD

[fmerkel91]

I bought the car with 40K on it in '95. Previous owners were the kind of people that did their maintenance as prescribed at the dealer. I'm not sure if there was a problem then since it only shows up when AWD is really required, which is rare.

I immediately put in the aftermarket filter and had the tranny flushed as was recommended for the '91; done by an independent Subaru dealer.

Drove it for a good while after that before finding there was a problem, that I didn't recognize AS a problem at the time.

 

Tranny fluid was changed again this summer at another independent Subaru shop that has given me good service over the lifetime of the car. Don't know what was used. They are the ones that told me there was a problem, so I tend to believe them....but, there seems to be this possible issue of a less costly and much easier fix of some of the throttle sensors? Maybe......?

There is no binding issue that I can tell.

 

As a '91 and no longer a skier it's not worth putting much more than a couple hundred $$ into this, certainly not a thousand+.

 

[if you DO want AWD, you could install the center diff lock switch (10 mins
of work) which would override the TCU's control. This has caveats, so
read up]

 

That could be of interest. Got any links handy? I assume this would need to be treated like the old style 4WD that was engaged ONLY on slippery surfaces when really needed. I assume AWD was developed for people that didn't know when to engage and disengage 4WD and ruined transmissions, which is probably most people.

[AK_Kev_007]

I know this is an old thread but I'm wondering if there has been any progress?