Auto trans set in park, car lunges when key turned off

[dsc]

When I come to a stop in my 1994 Legacy wagon, put the car in "Park", and turn the key off, the car sort of lunges. It's similar to what happens when you put a car in "Drive", keep your foot on the brake, and turn the key off. This lunging effect goes away when I disable the AWD by installing the FWD fuse. What causes this? Should I worry about it?

[ciper]

Sounds like you have too much 4wd a the time you stopped and the tension built up in the drivetrain is letting loose when the pressure to hold the car in gear is released.

Imagine a rubber band, while driving your front and rear move at different speeds. If you just made a turn before stopping the tension is built up. Once the tranny goes into neutral the driveshaft can spin freely in relation to the front wheels so the car moves forward.

[Legacy777]

Not sure I follow.

So after the engine is off....the car moves?

When do you release your foot from the brake pedal? Before or after you shut off the car?

The car will move slightly with just the car in park......but it shouldn't lurch, or feel like it's wanting to move.

Try some different combos of letting your foot off the brake before & after you shut off the car

[ciper]

My other legacy does this sometimes. The car actually moves forward as if you just put it in gear.

On a completly flat surface or even with the car on a hill so that it would roll backwards the car will move forward when the key is switched off.

dsc: Does your POWER light ever flash when you turn the car on in the morning?

[dsc]

Try some different combos of letting your foot off the brake before & after you shut off the car

I will do that and then report back.

Ciper's description is pretty much on target. The lunging (which is probably too strong a word for what I am trying to describe) happens when I stop the car, put it in park, take my foot off the brake, and then turn the engine off. As the engine stops, the car lunges. It is as if one set of drive wheels is locked up in park, but the other drive wheels are still trying to push the car. It is the same effect as when you leave the car in drive and turn the motor off with your foot on the brake. The transmission puts tension in the drivetrain which then gets released when the motor shuts down. That is the amount of lunging I am trying to describe. There is nothing dangerous happening. I am just worried that I am damaging the drivetrain by continuing to drive it in this condition.

Another thing about this car that may or may not be related is that it seems to scrub the tires when you turn a tight circle at low speeds, particularly in reverse. There also seems to be a lot of resistance in the drivetrain. If you are rolling very slow (less than 5 mph), with the car in drive or reverse, and take your foot off the gas, the car STOPS. There is no coast to it.

[totech]

Are your front and rear tires the same size and manufacturer?

They have to be identical - even pressures.

Subaru's need rotating too!!

[Legacy777]

Ok,

Do this. Go to a parking lot, turn the wheel all the way to the left, slowly drive around in circles. Do the same thing with the wheel all the way to the right.

See if the car feels like it is "binding" or lurching.

Now do the same things with a fuse in the FWD fuse holder. If your problem goes away, then yeah you probably have some wear within the clutch plates.

If so, I would recommend changing the tranny fluid, possibly having it flushed. I think there is an additive you can buy from the subie dealer to help.

[dsc]

I did that very test on the way home last night and it did exactly as you describe. I will change the tranny fluid and check at the Subaru dealer on the additive. I looked into having the tranny flushed. The guy said that he did not like the look of the fluid and that flushing might do more harm than good. I don't know the history on this car, but I would bet the transmission fluid was never changed. Otherwise the car is really sweet. The air suspension went bad so I put new struts (with junkyard springs and hardware), new strut tops, new ball joints, and new tie rod ends. The more I drive it, the more I like it.

Thank you for your help.

[Legacy777]

Yeah....these trannies will have big problems if you don't change the fluid. We changed the fluid on my buddy's RS....it was absolutely disgusting.......

And yeah....if the tranny wasn't taken care of....flushing it sometimes can cause more problems then help.

I will probably change mine out at next oil change......just for posterity's sake. I need to replace that rubber hose that connects the power steering pump to the return line......mine oozing......and probably should change the diff fluid.....since I never have done it....hahahaha However that stuff is like molasis anyway......

[entirelyturbo]

DON'T flush it, then! Just change the ATF. By flushing it, you will only unclog all the leaks that the gunk has stopped up. Same thing with old radiators...

Legacy777, diff oil doesn't necessarily need to be changed, I understand. But can't hurt, I did mine. Of course, when it drains into the pan, feel around for any metal shavings to check diff condition, you will almost assuredly not find any, but better safe than sorry...