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1999 Subaru Impreza Outback - Shake n' Shudder

I have a '99 Subaru Impreza Outback Sport with 158,000 miles. It runs great, looks good, and has been very reliable. I get this intermittent shaking/shuddering on acceleration and sometimes on tight turns at low speed. Any ideas?


  • edited July 2009
    Automatic or manual transmission?

    When the AWD transfer valve in a Subaru automatic transmission starts to wear out it doesn't allow the clutch pack to disengage during tight turns, and the vehicle will shudder as the front and rear wheels fight each other for traction.

    Insert a fuse in the FWD receptacle under the hood. This should temporarily disengage the AWD. If the shuddering goes away with the fuse inserted, you've found the culprit.

    Replacement of the AWD transfer valve and clutch pack requires removing the rear section of the automatic transmission. It's about a $700-800 job. Ignoring the shuddering can result in internal transmission damage, which costs even more.

    If your car has a manual transmission it uses a viscous coupling, rather than a transfer valve and clutch pack. Sometimes changing the transmission fluid will eliminate this shuddering with a manual transmission.

    So, is your car automatic or manual?
  • edited July 2009
    Automatic. Is it possible to just disengage the AWD for a while? What about the torque convertor? I've found some posts on Google suggesting that. Also, I've had the trans fluid and filter changed recently. Is there any other fluid I can change like the rear, etc.?
  • edited July 2009
    Are all 4 tires precisely matched as to brand, model, and size?
    Do all 4 tires have the same amount of tread wear (or does it vary from tire to tire)?

    If the answer to either or both of these question is "no", then it is very likely that you damaged the clutch pack for the center differential.
  • edited July 2009
    Thanks for the responses from both of you. Things seem to be pointing to the trans. I also had a mechanic look at the car yesterday. They found intermittent issues shifting from 1st to 2nd (automatic trans). They weren't able to high speed test drive but that's what they found on DC city streets. As far as the tires are concerned, I've also heard that mismatched tires could contribute to a trans issue. Right now, all tires are exactly the same make, model and size. The fronts are newer than the rear, though. Prior to me buying new tires in the front, there were different make tires between the front and rear. Same size but different makes. Thanks again for your responses. I got a quote yesterday for a rebuilt trans for $2200. I'm not going to be sinking that kind of money into this car right now. I'll see if I can get another opinion/quote. My concern is if I find someone who will do the clutch work for $800 and I end up having other trans issues. It's a shame. The car is a good city car for me right now.
  • edited July 2009
    My Subaru mechanic tells me there's no reason you can't insert a fuse in the FWD receptacle and drive the car that way. You'll have a front wheel drive Impreza, but that's fine.

    I'd try it and see if it makes a difference. Driving it while it's binding sure won't help anything, and can cause damage to the inside of the transmission case.
  • edited July 2009
    I will definitely give that a try. I can live with just FWD if that's the case. It sure beats $2200 bucks! :-) Do you happen to know where this receptacle is? Thanks again.
  • edited July 2009
    I stuck a 20amp fuse in the FWD socket in the main fuse box under the hood. It appears to have fixed the problem - no more shaking on tight turns or acceleration in the test drive tonight. I'll be driving a bit this weekend so it'll have a good long road test. And as per the Owners Manual, I get a FWD light on the dash indicating I'm in FWD. I can definitely live with this. If I get stuck in the snow somewhere, I'll take out the fuse to give me temporary AWD. Thanks again for sending me down this path - I didn't even have to buy the fuse.
  • edited October 2009
    It sounds like my wife's 1998 outback, auto trans, <40K miles, very conservative driven, has a similar problem.

    Where do I find the FWD fuse block ??


  • edited October 2009
    I found the fuse block.. Near the fire wall by the windshild wiper motor and behind the shock tower on the passengers side..

  • edited October 2009
    I would like to tap the wisdom of those on the forum. I don't expect to try to fix this myself as I have almost no AT experience or special tools but I would like to be knowledgeable when talking to a repair shop. Sounds like I have a similar problem.

    At low speed like pulling into or leaving a parking place and when turning our Subaru Outback has a pronounced drive line chatter or binding.

    1998 Subaru Outback, 2.5 L, Auto, Very conservatively driven ( wife's car ), less than 40K miles half of that on basically flat suburban roads in Arizona. There are very few times where the AWD actually served.

    Transmission fluid is full and clean ( Original fluid ). Tires are original and have equal tread ( ~ 2/3 of original ).

    Gas mileage has been approximately constant over the last several years. A test in a sloped parking lot I could move froward at 700 RPM ( AC fast idle ) in drive but would only hold position at 600 RPM ( normal idle ). In both cases there was no evidence of engine missing.

    Coasting in the parking lot, engine off, in neutral, and turning hard back and forth did not indicate any sort of CV joint binding. Likewise there was no CV joint noise.

    Putting a fuse in the FWD fuse socket seems to eliminate the low speed chatter.

    When I start the car the "AT oil temp" light comes on and soon after the engine is running goes out. ( It does not flash afterward. )


    What is the best guess at the problem ??

    What might I realistically expect for a repair bill ??

    Will leaving the FWD fuse in temporarily cause any harm ??


This discussion has been closed.