[perkinstouch]

I have a 99 Outback and when I jack all 4 wheels up and put the car in drive only the right front and left rear wheels spin. is that how these older awd cars are suppose to function? I thought Subarus were symetrical awd and all 4 tires are supposed to turn at the same time.

 

[rasterman]

Heh, flawed test, common mistake.

Your car is properly delivering torque to both front and rear axles. The differentials on each axle are allowing independence between left and right sides. Your front right decided to turn first, so it got all of the front torque. Your rear left happened to move first and got all of the rear torque. Because both front and rear are open differentials, this is normal.

Once there is some resistance to motion on the wheel that is turning, torque gets reflected to the opposite side of the car. It is not easy (and probably dangerous) to simulate this resistance with the car on a lift, but it's your car, your lift, your life.

If you did the same test to a FWD car you are just as likely to see only one of the front wheels move.

You might investigate further to see if there is a dragging brake on the left front & right rear, causing all the torque to go across the diff to the opposite side... but all in all this sounds like normal behavior.

 

[perkinstouch]

great thanks. When I bought the car the perosn said it was only working in FWD and might need a rear differential thats why I was trying to test it. But sounds like its working fine I might have lucked out.

 

[plain OM]

Hopefully it's okay; however, the "raised wheel test" also unfortunately doesn't indicate if the AWD transfer clutch is "fully" functional. It might have enough friction to transfer the small amount of torque needed to turn the rear wheel (or wheels) when raised, but not when on the ground.

The scientific way to check it would be to put the car on a four wheel dynamometer, and then load the rear to see if the torque delivery to the wheels is maintained.

For us average users, a real situation, such as a slippery uphill slope will do -- stop the car on the slope, in gear, and have a second person watching both rear wheel from a distance. Try to accelerate rapidly, intending to get the wheels to spin, rather than move the car. If the AWD is working properly, when one or both front wheels are spinning, at least one rear wheel will be spinning as well. If neither rear wheel seems to be doing anything, then the AWD isn't working properly.

As a preliminary, turn the key to ON but don't start the car. Make sure that the AT Oil Temp light, the check engine light, and the AWD (or FWD) light come on. Then, start the car; all three should go out, and none come back on or flash at any time.

Your AWD car has an auxiliary fuse socket at the right rear of the engine compartment. It should be labelled for the AWD or FWD fuse. When there's no fuse in the socket, the car should be in AWD mode. When a fuse is installed, the car is forced into FWD mode, and the warning light should come on in the instrument panel.

 

[perkinstouch]

Hopefully it's okay; however, the "raised wheel test" also unfortunately doesn't indicate if the AWD transfer clutch is "fully" functional. It might have enough friction to transfer the small amount of torque needed to turn the rear wheel (or wheels) when raised, but not when on the ground.

The scientific way to check it would be to put the car on a four wheel dynamometer, and then load the rear to see if the torque delivery to the wheels is maintained.

For us average users, a real situation, such as a slippery uphill slope will do -- stop the car on the slope, in gear, and have a second person watching both rear wheel from a distance. Try to accelerate rapidly, intending to get the wheels to spin, rather than move the car. If the AWD is working properly, when one or both front wheels are spinning, at least one rear wheel will be spinning as well. If neither rear wheel seems to be doing anything, then the AWD isn't working properly.

As a preliminary, turn the key to ON but don't start the car. Make sure that the AT Oil Temp light, the check engine light, and the AWD (or FWD) light come on. Then, start the car; all three should go out, and none come back on or flash at any time.

Your AWD car has an auxiliary fuse socket at the right rear of the engine compartment. It should be labelled for the AWD or FWD fuse. When there's no fuse in the socket, the car should be in AWD mode. When a fuse is installed, the car is forced into FWD mode, and the warning light should come on in the instrument panel.

I will test it more this weekend. thanks.