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AWD not working


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19 replies to this topic

#1 mikec03

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Posted 27 December 2012 - 02:04 PM

I bought a 95 legacy with 200K miles last summer. Now with the snow, I realize that the all wheel drive is not working! It doesn't matter whether the FWD fuse is in or not. Other then the AWD, the car runs fine. I have a couple of ideas.

1. Someone disconnected the front propeller shaft. I checked that the rear shaft is still connected at the rear differential. It looks like it takes a lot of work to disconnect the front shaft so I wonder if anyone would bother. I can't get far enough under the car to see if its still connected to the transmission.

2. A gear broke in the transmission or in the rear differential.

Does someone have any ideas as the cause. Has someone lost the AWG due to a gear being broke? Has someone disconnected the front shaft, presumably because of torque bind?

Edited by Turbone, 27 December 2012 - 08:49 PM.


#2 johnceggleston

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Posted 27 December 2012 - 02:24 PM

auto or manual????

1. Someone disconnected the front propeller shaft. I checked that the rear shaft is still connected at the rear differential. It looks like it takes a lot of work to disconnect the front shaft so I wonder if anyone would bother. I can't get far enough under the car to see if its still connected to the transmission.

if the front section of the drive shaft is removed the trans will puke fluid, auto or manual. so this is not the situation.

2. A gear broke in the transmission or in the rear differential.

for the auto trans,
it could be just worn out transfer clutch discs in the rear extension housing.this is not uncommon.

or it could be a busted clutch drum. less likely but it still happens.

or it could be as simple as a busted rear drive axle.

you don't here much about the manual trans with NO AWD. but i guess it is possible.

try unplugging the TCU under the dash on the driver side. (it has 2 wide wire connectors, one with 20 pins and one with 16 pins, side by side.) this will put you in ''limp'' mode with reverse and 3rd gears only. and it SHOULD cause torque bind in tight circles on dry pavement. if no TB there is a mechanical problem in the transfer clutch, as mentioned above..

#3 86BRATMAN

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Posted 27 December 2012 - 02:46 PM

I've also seen the front speed sensor or the one in the guage cluster cause the car to not have awd if its an automatic trans.

#4 CoupedUpSubie

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Posted 27 December 2012 - 04:22 PM

Do you have good tires on it? Even with an AWD car crappy tires dont work in the snow.

#5 mikec03

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Posted 27 December 2012 - 05:06 PM

Johnc

Wow. How would anyone know that disconnecting the plugs to the TU would put the transmission into 3rd gear or reverse? This is incredible detailed knowledge.

It's an automatic by the way. No problem with speedometer.

Thanks, Ill try it and report. It will be a couple of weeks before I can get the car again.

#6 johnceggleston

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Posted 27 December 2012 - 06:07 PM

don't forget to drive the car up on the curb and then crawl under and check the drive shaft and rear axles.

#7 GeneralDisorder

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Posted 27 December 2012 - 10:17 PM

Johnc

Wow. How would anyone know that disconnecting the plugs to the TU would put the transmission into 3rd gear or reverse? This is incredible detailed knowledge.


Not really. That's pretty common knowledge around here. The transmission internally defaults to 3rd gear without it's computer brain to tell it otherwise. Reverse is not a computer selected gear ever so it's selection is entirely mechanical based on the selector lever. The forward drive gears are shifted via computer control and without the computer to intervene the state of the shift solenoids that govern pressure to the drum bands and clutch packs defaults to 3rd gear. That is their unpowered "at rest" state. So no computer = no electrical power = unpowered hydraulic state = 3rd gear.

GD

#8 johnceggleston

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Posted 28 December 2012 - 04:51 PM

Not really. That's pretty common knowledge around here. The transmission internally defaults to 3rd gear without it's computer brain to tell it otherwise. Reverse is not a computer selected gear ever so it's selection is entirely mechanical based on the selector lever. The forward drive gears are shifted via computer control and without the computer to intervene the state of the shift solenoids that govern pressure to the drum bands and clutch packs defaults to 3rd gear. That is their unpowered "at rest" state. So no computer = no electrical power = unpowered hydraulic state = 3rd gear.

GD


i knew it was common knowledge.

but i sure as hell didn't know why it defaulted to 3rd.

thanks

#9 mikec03

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Posted 05 January 2013 - 11:02 AM

UPDATE

I unplugged the TCU and the AT defaulted to 3'rd gear. There is no torque bind.

Both front and rear propeller shafts are in place.

With the AT in neutral and costing downhill, the rear wheels turn the propeller shaft at 4.11 shaft/wheel ratio, indicating that the rear differential is OK.

I'm getting the 16 flashes on the AT dashboard light.

Conclusion: Obviously the duty C solenoid is bad. But are the discs bad too? If the solenoid failed in the usual manner, then I would have to be getting torque bind, even if the discs are bad. Yes?

So is this a correct analysis: either the solenoid failed open, the tubing to the solenoid is leaking, the plate under the solenoid body is leaking at one of two gaskets, or a busted clutch drum.

#10 ivans imports

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Posted 05 January 2013 - 11:05 AM

a'm doing that fix thiss week 98 forester no awd i rest the clearance in the clutch pack and clean and check the awd valve body check the slip rings on tailshaft output. And energise the soiliniond and confirm it turns on and flows. a not working or slow working awd is caused by two mutch clearance in awd clutch pack or fliud transfer problems

#11 johnceggleston

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Posted 05 January 2013 - 02:46 PM

lets clear up a few things.

the AT Templight is flashing at start up. is this with or with out the TCU unplugged??
did it flash before you unplugged the TCU?
does it flash with the TCU pligged back in? if yes, read the codes.

the duyt c failure usually causes TBind. i do not remember ever hearing it cause no AWD, but maybe.

next test, jack up one side of the car, driver or passenger, both wheels up. unplg the TCU. place the shifter in N and start the car with the hand brake OFF. (it would be really good if the wheels that are on the ground are blocked.) turn the rear wheel by hand, if the front wheel truns the same then the mechanical parts are working.

both rear axles good?

#12 mikec03

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Posted 06 January 2013 - 02:56 PM

Thanks Ivan. It gives me hope that the problem is excessive clearance in the clutch pack.

I did find another post where the loss of the awd was caused by the shearing off of the "gear" that drives the clutch pack. This would be a disaster of course. http://www.subaruout...ansmission.html

The AT light flashing is the normal warning [maybe only on the late 90's] that the duty c solenoid is defective and it occurs with TCU plugged in. It flashes 16 times on start up.

Both rear axles are good.

So I don't know if I should go ahead and have someone pull off the transfer case and replace the duty c solenoid? If they find anything else wrong, it would be as cheaper to just put in a used transmission. Unfortunately, there is no guaranty that a used transmission is any good either. And there is no way to test them. As a confirmation, I see an old transmission on car parts that came from one of my old subarus, and it has torque bind!

#13 torxxx

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Posted 06 January 2013 - 02:58 PM

16 flashes indicates a fault in the transmission system. It does NOT indicate an problem with the Duty C. Its telling you to put the transmission in read mode and pull the codes off it.

As for your issue, either bad VSS, bad clutch pack or broken input gear to the AWD end of the transmission

#14 darsdoug

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Posted 06 January 2013 - 08:19 PM

You guy's are sharp.

#15 ivans imports

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Posted 07 January 2013 - 12:59 AM

one small thing was mocking up awd test bed to test valve body release valve so take the valve body remove the pin on the aluminum plug remove plug and valve take the spring that sits behind it and stretch it a bitt. thiss should increase the awd preshure. I will tset thiss thery tomorrow and see if it can be addjusted.

#16 ivans imports

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Posted 08 January 2013 - 10:29 AM

it helped but not enuff thiss gave it more awd for shure butt in thiss cars case the awd drum slip rings had worn into the housing and made a grove so even with the higher preshure the awd was losing its preshure. The repair worked but not the housing i only got about a 60% awd increase on a car that had no awd at all

#17 ivans imports

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Posted 09 January 2013 - 11:27 AM

Next step for me is a new clutch pack for a 95 svx as it uses the updated steels and better clutches and fitts from 89-98 awd 4eat tranys. As i bought a 95 svx and it has 0 awd so fixing awd on a different car today thiss is a real problem here in the snow

#18 malcamaro66

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Posted 14 January 2013 - 07:26 AM

Hey The awd clutches, c solnoid and awd valve body control are in the tail shaft housing. After romoving the exhaust, heat shields, drive shafts and cross member to tranny remove the tail shaft housing. take all parts to the bench. Take out the tail shaft with clutchs in it apply air pressure to hole in between the two seals on the shaft you should see the clutchs lock. then take a screwdriver and see if you can move them. If a. you dont see the clutchs move then the hole is clogged or b. ther clutches move after you apply pressure but they dont lock then the clutches are shot. If both are good then apply air pressure to hole in tail shaft housing case next to aluminum tube. should see air coming out of hole where the shaft was in the housing. if not remove tube blow air in tube if air comes out of tube, romove awd valve body and solnoid c. Remove filter/screen and see if theres a clog. also blow air in the same hole in case and make sure air comes through the hole where the valve block was. if air comes out of hole blow air in valve block and make sure vlave is not stuck. if it is then take valve block apart and clean valve reassemble and blow air through it again some times valve gets bent. if no air replace valve and the c solnoid. if the c solnoid goes bad it defaulfts to to full on awd all the time.

#19 ivans imports

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Posted 18 January 2013 - 11:42 AM

the problem turned out to be groved out tailshaft housing were they slip rings ride was to badly groved to seal

#20 mikec03

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Posted 21 January 2013 - 10:39 PM

Thank you guy for all the replies. I have learned a lot. I think what happened is that my subaru was operated with torque bind and eventually the transfer clutch hub sheared off or other serious problem. So I think that the risk of taking the transfer clutch off wouldn't be worth it. The cost of replacing the hub part, for example, would be prohibitive.

So I'll look around and maybe put in a whole transmission if I can find one that is a bargain.

I finally did find the procedure to access the tcu trouble codes but I haven't done it yet since I won't have access to the car for a couple weeks. The procedure is different from the one that works for the 99?-04 cars.




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