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  1. #1
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    Subaru 5MT gearbox - anyone knows these boxes? Identify this part?

    Currently repairing an Impreza 5 speed manual box with a friend. Come across something I’ve not seen before which is also the part that’s failed. Can anyone identify/explain this part?

    ?8830FA7B-BE7E-4437-A02B-EBB64500D0CB.jpeg

    Loose thin ring sat between the main helical constant mesh gear and the gears teeth that engage with the sliding collar. Ie it’s in the middle of the gear assembly inboard of the synchro ring. Only there on 3rd gear.

    You can see it’s all chewed up. What’s it for??
    Lloyd B
    Current: Crendon #54 in build - 427 Side Oiler/Cobrajet Heads/Dual 600cfm Holleys/4 speed toploader/Vintage cast knock on wheels
    Dedion Dax/Clarkson 383 Chevy with roller 4/7 swap cam, AFR195 heads - SOLD

  2. #2
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    I believe that's called the "expense ring" .. because it's expensive.

    .. no idea, really. I did try a quick look on the EPCs I could find, but not knowing which Impreza (and there are so many chassis codes to choose from!) I didn't have much luck finding it on any diagrams either. Ah, wait:
    [img]https://www.rallispec.com/images/pro...synchro5mt.jpg[/img]

    There it is, but it doesn't seem to have a name! Does show you what it should look like, though.. and it looks like it's just a spacer between the helical gear and the synchro teeth? Or maybe it's meant to prevent the teeth from engaging too far when the synchro ring is worn?

    Right, another look at the 5spd EPC and it doesn't look like it's available as a separate part - only as part of the 3rd & 4th gear set.. Here's where I was looking - might not be the right car, but at least it was a 5spd gearbox - http://opposedforces.com/parts/impre...llustration_2/
    Last edited by aaronjb; 11-11-19 at 09:07 AM.
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  3. #3
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    At a glance that looks like a baulk ring.
    They are designed to facilitate the synchromesh action by acting as a brake before the selector dog engages the gear.
    Andy
    A S motorsport Ltd. 01379 688356 mob; 07909531816 web; asmotorsport.co.uk email \"andrewsoar@yahoo.com\"

  4. #4
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    Second look after a proper read and I can see what you mean now.
    That looks like a ‘fence’ plate to prevent over travel of the selector dog. Presumably nipped by the other pair gear teeth.
    So that would indicate excessive movement of either the selector dog or the shaft set I guess.

    A
    A S motorsport Ltd. 01379 688356 mob; 07909531816 web; asmotorsport.co.uk email \"andrewsoar@yahoo.com\"

  5. #5
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    I find gearbox internals are very much like beautiful women...… best left alone, otherwise they can get very expensive, very quickly.
    Regards

    Craig Perry

    No, I'm not "repairing" it, I'm fine tuning its performance.

  6. #6
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    Quote Originally Posted by cperry View Post
    I find gearbox internals are very much like beautiful women...… best left alone, otherwise they can get very expensive, very quickly.
    Manual boxes aren't too bad.. automatics are just filled with black magic though and need several ritual sacrifices to ensure they'll still work once reassembled

    Lovely informative video on gearboxes, btw: https://www.youtube.com/watch?v=aHtshoUVhEU (highly addictive channel .. I do love the title of one video: "So you've taken your classic car apart. Now what?" )
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  7. #7
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    Having been trained in and then eventually teaching agricultural engineering I used to get occasionally arm deep into gearboxes.
    I actually used to really like the work but that was quite some time back. Electro hydraulic 32 speed shuttle gearboxes and the like are quite interesting as are the hybrid mechanical / hydraulic drives now common in top end stuff.
    Most of it is just following stage instructions really. Easy if you have the right manual.
    I remember one of my first jobs was rebuilding a john Deere gearbox that had bee damaged by the farm staff where it resided pushing the two halves of the tractor back together with a forklift after doing a home clutch replacement. It had to have a new casing and all of the internals swapped. A lesson learned - don’t force the gearbox back on. Get things aligned properly.

    Best of luck with your part search.

    A
    A S motorsport Ltd. 01379 688356 mob; 07909531816 web; asmotorsport.co.uk email \"andrewsoar@yahoo.com\"

  8. #8
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    Quote Originally Posted by dinosoar View Post
    I remember one of my first jobs was rebuilding a john Deere gearbox that had bee damaged by the farm staff where it resided pushing the two halves of the tractor back together with a forklift after doing a home clutch replacement.
    Ah, farm maintenance.. if you can't fix it with bailing wire, get a hammer. If you can't fix it with a hammer, get a bigger tool! (No offence to any farmers out there - I grew up around them and, in reality, many are very smart people indeed!)
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  9. #9
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    Hi fellas

    Thanks for that. We couldn't find anything online either and were scratching our heads even though I used to rebuild gearboxes as part of my living many moons ago.

    It looks like we came up with the same idea in the meantime that it must be a collar to stop over travel of the 3rd/4th sliding collar. 3rd gear is the only one small enough to cause a problem (sounds odd but the box alternates the synchro hubs on input and layshaft so 3rd is actually the smallest gear with a sliding collar heading towards it).

    Seems a pretty crap idea, why not simply stop the selector fork over travelling in the first place but hey ho?!

    In the bin with 3/4th and new straight cut gears going in, which have no collar so we'd better figure out why its over travelling.
    Cheers again, useful hive mind on here when you can't figure something out auto engineering wise!
    Lloyd B
    Current: Crendon #54 in build - 427 Side Oiler/Cobrajet Heads/Dual 600cfm Holleys/4 speed toploader/Vintage cast knock on wheels
    Dedion Dax/Clarkson 383 Chevy with roller 4/7 swap cam, AFR195 heads - SOLD

  10. #10
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    Funny - I looked at the various straight cut options (it was easier to find pictures of those!) and noticed none of them had the fence .. but figured you'd want a stock replacement rather than drop a new gear set in. Evidently I was wrong
    My DeDion build diary..
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