Subaru Manual Transmission Repair

Subaru manual transmissions are pretty well built and have minimal problems. When failure occurs there are usually just a couple of things that fail. The most common problem is bearing failure causing the transmission to be noisy and if it’s excessive your trans will sound as if someone has put rocks in it. The other failure that is common is the viscous coupler. In Subaru MT transmissions the viscous coupler acts like a limited slip differential, but instead of allowing slip from the left and right tires the viscous coupler allows slippage of the front to rear wheels. This is for turning only because the front and rear tires while turn at a different rate in turns. The viscous coupler will also slip if the vehicle is under a heavy load going straight and when this occurs the power will be mainly transferred to the front wheels. Most of the time viscous coupler failure is on a WRX model, where the snap ring breaks out of the viscous coupler case. When this occurs there is no power transferred to the rear wheels.

These transmissions are pretty simple to repair, so if you would like to perform your own repair I will give you some tips to help you along the repair procedure. If after reading this you decide that the equipment needed and/or this seems like a little too much…

MDH Motors Specializes in Subaru MT Transmission Repair

Contact us today for an estimate!

Do it yourself Subaru MT Transmission Repair

Do it yourself required tools

  • Shop press
  • Split bearing puller (large and medium size)
  • Press fittings Tip: use different size exhaust pipe and old bearing races.
  • 55mm 6 point socket (mid or deep)
  • 44mm 6 point thin walled socket ( shallow OR deep)
  • Air Tools (1/2” Impact Gun)

First off, separate the transfer case unit from the main transmission case. After that is done, the biggest part that makes this easy is how you split the case and dis-assemble the transmission. The left side of the case will hold you input shaft, counter shaft, differential and shift forks and the other side is just part of the case. Just remove two of the four bolts holding the counter shaft main bearing from the side of the case your removing (at rear of case where transfer case unit was). Always mark the shim that is behind this bearing. It may not seem necessary, but upon re-assemble you can easily mix up how this goes and the holes won’t align correctly.

Now that this is done the rest is pretty self-explanatory, remove your shafts and press on and off the bearings that need replaced. I always recommend replacing all ball bearings and seals. There are some small flat bearings and round bushing type bearings that are OK to re-use. Use your split bearing puller and array of exhaust tubing to remove and press new bearings to the shafts. I use an assortment of 1’ to 3 ½’ exhaust tubing in ½’ increments for the job and also have some roll cage tubing that is more heavy duty for pressing some stubborn bearings. Another good tip for substituting your press fittings is to keep the bearing races. They can become very handy for certain needs, especially if you have a welder. You can then weld and fabricate special press fittings exclusively for certain jobs such as this.

When you get to the differential, do not move or adjust the carrier bearing adjusters. Replace the seals from the inside of the case, and if you want to replace the large O-rings in the differential carrier bearing preload adjusters just mark them. The service manual will tell you to use special tools such as dial indicator to adjust backlash. I have been working on these transmissions for over 10 years and have never had a problem doing it this way when replacing the differential carrier bearings. Another thing to look for that I see sometimes is these bearing races sometime have a tendency to spin in the case. Especially if the bearing is worn, causing drag. To resolve this problem just take a pointed punch (I use a spring loaded one) and ping around the case where the race fits. This will cause the race to fit tight again, cool huh. No need to replace the transmission case.

Hope this was helpful

This post was written by: Martin Hand

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Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.

109 Comments

  • Lindsay says:

    I’ll take a stab at this.
    My ’02 Impreza RS has had an issues with the transmission.
    While getting ready for work one early morning, it sat with the engine running while I scraped the frost of the windows. As it was idling, the engine cut out with a sound to that of stalling.
    I get back in and try to restart it, but as I did, the car jerked forward as if it was in gear, but was not.
    After some inspection and guesses, the third and fourth gear seem to be immobile.
    Only when the clutch pedal pressed down does it not stall out, as I release the clutch pedal slowly, the engine begins to stutter as if it’s about to stall.
    Any ideas on what thre transmission may have an issue with?

    • Martin Hand Martin Hand says:

      Yes I have seen this before, the gears are probably seized on the main shaft of the transmission. Not sure why this happens but the transmission will need removed disassembled and repaired.

      • Lindsay says:

        Yeah, we’ve done the hard part of taking it out. It’s been opened up and is exposed for us to make any repair needed. Also, a small note, a small bit of yellow-ish white plastic came out while the transmission fluid was being drained. It looked as if it was snapped off from where ever it came from. i’ll look more into it this coming weekend.
        Many thanks for the reply Martin!

  • I have a 2003 Subaru Outback wagon with a 2.5 L and 5speed manual transmission. My problem seems to be with the transmission in that after highway driving for 20-30 minutes I will notice front wheel clunking noises at low speeds when steering. You can actually see the wheel jump during rotation while observing outside the vehicle while someone else drives. I replaced the power steering pump, the CV joint (complete unit both sides). And front wheel bearings with ball joints with no difference. Any ideas or suggestions as to what might be wrong?

    • Martin Hand Martin Hand says:

      Sounds like you’re explaining a tire related problem try rotating the tires front to rear and see if this makes any difference

      • artbruce says:

        Viscouse coupler is shot (internal silicon is compromised from overheating) and needs replaced.
        Quote “This is for turning only because the front and rear tires while turn at a different rate in turns”. Hence the clunking noise as the viscouse coupler is not acting as a slip diff any more and the shorter arc your rear wheels are making in a turn are causing the binding at the front wheels.

  • Andrew says:

    Hi Martin/MDH:
    Ive got a 2010 outback with 6spd mt and 115k. the center diff (viscous coupler) is binding badly after hwy driving for >=30 min. The dealer quoted me $3k plus for the repair, which is nearly half of the car’s kbb value!
    i would like replace the center diff myself, im quite mechanically inclined and have done head gaskets, but would still like some sort of hardcopy visual reference…like parts diagram with torque specs….any idea where i could find such? or do you have pictures of the guts to a ty765 gearbox?

    also, besides uneven tire wear, what could cause the viscous coupler to fail prematurely?

    Great site! lots of helpful info! Keep it up!

    -Andrew
    Spring Valley, MN

    • Martin Hand Martin Hand says:

      Call your local Subaru dealer and have them email you diagram this is how you’ll have to order your parts anyways. Also can try a transmission manual like ATSG https://www.atsg.us/atsg/

      • Andrew says:

        score! thru the subaruoutback.org forum i managed to download pdf of MY2010 Legacy factory service manual for free!!
        From reading thru said manual, it gives 4 main steps to replace center differential:
        1. remove the entire transmission from vehicle
        2. remove transfer case from transmission
        3. remove extension case from transfer case
        4. remove transfer driven gear to expose center differential

        This leaves me with 2 questions:
        – are steps 1 & 2 necessary? ….can i just remove the extension case housing and transfer driven gear to replace the center diff?
        – what, if any, other items should be replaced while i’m in there besides center diff bearing?
        (subaru dealer recommended needle bearings, snap rings and remeasuring for shim washers)

        Thanks for your earlier response…i made a donation in return. 🙂

    • dave says:

      The tire size is the main cause of the viscous coupler to fail early. Check out ste viscous couplers if you need to get it replaced

  • Kody says:

    Ive got an 01 legacy gt wagon with a 2.5 and a manual trans. recently my car has begun leaking transmission fluid in extremely high quantities (over .5 quarts per day) and the transmission has begun to pop and knock/grind after about 2000-2500 rpm under light load (in any gear) was wondering if there is any known potential cause or if I’ve more than likely grenaded the tranny… thanks for your time!

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