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Guest Message by DevFuse

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AWD Switch, very cool

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32 replies to this topic

#1 Guest_truk_*

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Posted 30 October 2002 - 01:32 PM

I have a 96 OBW 2.5 Auto, and found myself switching on and off the AWD when doing highway driving to improve mileage a little. But after a while of opening the hood to put a fuse to cut it off, I decided to put in a switch.

If you're not using the cigarette lighter, then Radioshack has a round switch that fits in the hole. Take out the complete lighter body, then replace it with this round switch. Add tape or glue behind it for a snug fit. I split one of the wires coming out of the AWD fuse box (back of engine bay, passenger side, if you didn't already know) and ran the two 16 guage wires from there, through the wall (black rubber plug about 6 inches below hoodline, drivers side) into the center console and hooked it up to the switch. Flick it on or off, and the FWD light will appear below the speedo. I even printed out a small round label to cover the switch, and it looks great, like there was an option for this. I'll try to get pics up on here.

Anyways, this was pretty easy to do, and will not hurt the car, according to the research I have done. A few bucks and a maybe 30 minutes will do it. Only possible for autos, remember.


#2 Guest_Mike W_*

Guest_Mike W_*
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Posted 30 October 2002 - 08:54 PM

Interesting idea. So what kind of highway milage are you getting in 2wd and AWD?

#3 Guest_SSJCody_*

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Posted 30 October 2002 - 09:50 PM

How did you get the cigarette lighter out? Do you have an actual lighter or the 12V plug for phones and stuff? Just wondering because I'm trying to get mine out so I can put in my new stereo.

#4 Guest_Legacy777_*

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Posted 30 October 2002 - 10:20 PM

Your mileage will most likely not be that much better. You still drag along the rear drive train........so it's dead weight rather then powered weight.

At highway driving, the affects of the dead weight vs. the 10% rear power is not going to be much different.

IMO......I wouldn't waste my time on it.....but that's me.

If you wanna switch something....switch the Duty C solenoid....when disconnected...ECU goes into a default mode.....it'll allow you to go to 50/50 split between front and rear.

#5 Guest_sirveaux_*

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Posted 30 October 2002 - 10:52 PM


Could you explain more how this works? In an auto, under normal circumstances the split is 90/10 right? Is there a reason why one wouldn't want to run it 50/50 all the time?

#6 Guest_whippet_*

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Posted 30 October 2002 - 11:27 PM

I put in a switch on the dash of my wife's 93 LS. I used a rear defroster switch from a 90 Legacy. I put it on the right side of the steering column. It looks like the factory did it. Needed a relay to use this switch. If you don't you need a pretty hefty switch to take the current. Like Josh has stated before didn't notice much if any improvement in gas milage. Did notice less traction though, but can put it AWD easy.


#7 Guest_truk_*

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Posted 31 October 2002 - 02:24 AM

Mike, about the numbers, I have noticed a move up to almost 27 mpg on the highway when in FWD. It usually runs around 25. Of course, more tests are needed to figure if there really is a difference. But, in my opinion, any little bit helps when you want to save a penny. Acceleration feels stronger when in FWD, so I do wonder how much less machinery is actually used.

Perhaps someone could shed some light. I couldn't find much about location of the transfer clutch in the archives. So, the driveshaft going to the back is still turning when in FWD? Only the rear diff. is disengaged? If this is true, then there wouldn't be much gain, if any. I would think something like a clutch would be in the AT housing area. Haynes isn't much help, and I havn't been under there much lately.

Josh, as far as a switch for the solenoid, isn't this car 50-50 in the first two gears in normal driving, and then power will go mostly to the front? I thought I had read that before somewhere on the board. Perhaps this is switch is a waste of time, but don't we all like to tinker?

Cody, the cigarette lighter I have on my 96 has three main parts--the lighter, the cylinder, and the housing behind it. The housing should screw off, so the cylinder can be pulled out the front. What is left is a hole about an inch in diameter.


#8 Guest_Legacy777_*

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Posted 31 October 2002 - 08:58 AM

To sorta answer questions posed.....in no particular order.

The way the rear wheels gets their power is through an extension housing that gets bolted on the back of the transmission. It is actually pretty simple. The housing has a set of clutches in there, with solenoid and other misc. stuff.

There is a tranny fluid line that goes back to this housing. When ECU detects a difference in speed between the front & rear speed sensor, it will then send a signal to the duty c solenoid on the extension housing, and will allow more pressure to go to the clutch pack....in sense....allowing more torque to be given to the rear wheels.

This design allows a maximum of a 50/50 torque split.

As far as moving parts....when you disable the AWD....you simply take away the line pressure to clutch pack. However the rear wheels are still going to turn, which in turn drive the rear drive shaft.....so that's your dead weight...so-to-say.

As mentioned, the ECU has a fail-safe mode for the duty c solenoid. When it doesn't get a signal, or bad signal, it puts the torque split up to 50/50.

This is why some people notice torque bind when the duty c solenoid or associated parts go bad.

I think that the AWD map puts the torque split in 50/50 in 1st gear.....2nd gear....it's possible, but I'm not sure.

As far as advantages for running 50/50 split all the time.......there probably isn't any. But if you do some back road driving, mudding...trails, or snow.....it may give you a tad more of an edge because you don't have to wait for the power to kick in.....it'd already be there.

Oh.....here are some pictures from the FSM that show the rear extension housing for the AWD system.

(they are big, so I'll just make them links)

<a href="http://www.main.experiencetherave.com:8080/images/AWD_transfer_system1.jpg" target="top">Picture 1</a>
<a href="http://www.main.experiencetherave.com:8080/images/AWD_transfer_system2.jpg" target="top">Picture 2</a>
<a href="http://www.main.experiencetherave.com:8080/images/AWD_transfer_system3.jpg" target="top">Picture 3</a>

#9 Guest_Legacy777_*

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Posted 31 October 2002 - 09:06 AM

I'm goin to archive this when we're done playin......so have at it..

#10 Guest_truk_*

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Posted 31 October 2002 - 12:43 PM

Aha. That is something I didn't think about, the fact that the drive shaft is being turned, but from the reverse direction in FWD (by way of rear tires) All parts are still moving. I would think, then, that 10% transfer in AWD to the rear at highway speeds would almost make the system neutral, the torque on the driveshaft being somewhat equal between the output of the transmission and the rear diff. That sounds better for the whole mechanism over the long haul, but wish I knew how much torque it takes to turn the driveshaft from the rear diff., Perhaps just a little less than when in AWD?

Who wants to do the test?


btw, josh, your links seem to go the same page.

#11 Guest_truk_*

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Posted 31 October 2002 - 01:00 PM

Another question: Is it possible to lock the AWD at 10% transfer to the rear? I would probably have to be a Subaru ECU designer to do that.


#12 Guest_Legacy777_*

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Posted 31 October 2002 - 01:22 PM

Ok.....links fixed....I changed the display text, but not the actual link when I orig did it.

No there's really not a way to fix torque split at 10%....

#13 Guest_mrtoyou7747_*

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Posted 31 October 2002 - 04:45 PM

Recomend you add a fuse (10 amp) just in case. Slight chance of fire if it shorts the solenoid shorts out.

#14 Guest_wjmgl10_*

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Posted 31 October 2002 - 07:20 PM

links are still not working for me....

#15 Guest_truk_*

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Posted 31 October 2002 - 07:25 PM

About the fuse, wouldn't the fuse inserted in the location to flip on the FWD be considered "inline?"


#16 Guest_Legacy777_*

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Posted 31 October 2002 - 07:42 PM

if you want to disable the AWD, you make an open circuit where the FWD fuse is at.

You either just put a switch in, and flip it on to disable the AWD......or use a reverse pole relay setup.....either way, I'd probably leave a fuse in the FWD fuse holder, and just splice a switch inline with the FWD fuse.

The links should work now.....had some security issues I had to take care of on the server.

#17 Guest_truk_*

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Posted 31 October 2002 - 10:34 PM

Yeah, that was my setup.

Anyone know how heavy the rear driveshaft is? I just want to get an idea of how much energy would be required to turn it.

One thing I really have noticed when in FWD is that the car shifts with a little more jolt than when in AWD, especially when going into 2nd. Not a smooth shift at all. Kind of annoying. But, I don't do much driving around town in FWD.


#18 Guest_slideways34_*

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Posted 01 November 2002 - 02:52 AM

The rear driveshaft wieghs about 20-25 lbs (estimate), i took it out not long ago.

As far as the torque spilt, it is 90/10 all the unless there is a slip. When i had my 90 AWD automatic, i could notice hte clutch pack engaging. If the front wheels were on sand and the rear was on solid ground, i did notice the front wheels slip for a tiny fraction of a second, and then the car would move.

#19 Guest_drOutback_*

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Posted 01 November 2002 - 07:45 AM

Quote Legacy 777...I think that the AWD map puts the torque split in 50/50 in 1st gear.....2nd gear....it's possible, but I'm not sure.

I think it only puts the AWD in 50/50 split in first gear. Which is also why I think people get stuck sometimes. They leave the tranny in drive so that when the wheels start spinning on a really slippy hill the tranny shifts through the 1st-2nd-3rd-4th gears causing less power to get to the wheels. If you lock the tranny in 1st or 2nd when the wheels slip, the trans won't be able to shift up by sensing the wheels speed.

#20 Guest_spagemurray_*

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Posted 02 November 2002 - 10:18 PM

I take it this for auto trans only?

#21 Guest_mangolango_*

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Posted 03 November 2002 - 01:35 AM

Can I lock the AWD to 50/50 all the time?

#22 Guest_drOutback_*

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Posted 03 November 2002 - 10:01 AM

yes i meant that it would happen with an auto trans.

#23 Guest_Legacy777_*

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Posted 03 November 2002 - 02:27 PM

I don't know if you'd want to have 50/50 all the time.......mileage would probably be less, and would create more wear and tear on the transmission and such.

#24 Guest_SSJCody_*

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Posted 03 November 2002 - 06:54 PM

Why is this whole switch thing only possible for automatics?

#25 Guest_wjmgl10_*

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Posted 03 November 2002 - 09:49 PM

I tohught it was, but there is not mention of it in the haynes manual, it does say "on automatic models, diable awd before towing..." or similar to that effect.

i guess the rear clutch disables when the key is turned off....i dunno.

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