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Thread: Putting together a decent 5mt transmission

  1. #1
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    Default Putting together a decent 5mt transmission

    For those of us without STis, our transmission leaves a lot to be desired. Our gears are only sufficient for near stock power levels, and the front and center differentials just plain suck. I've wanted to put together a "decent" transmission for a while now. I say decent because I don't plan on spending 6k+ on upgrading the 5mt. Recent events involving an axle seal leak that went unnoticed for months (huge skidplates require frequent inspection...) have made future plans more of a short term necessity.

    Front Differential: OBX. Cheap Chinese torsen variety diff. Good enough
    Gears: Stock, maybe RA. I already have late model gears, and I don't plan on doing any significant power mods for a while, so no real need to do much here.
    Center Differential: STi 20kgf unit for 5mt. Five times the viscous coupling of the stock center diff.

    I received my "like new never used" OBX differential the other day, so here goes. You buy one of these knowing that their are limitations present, and a small amount of work required to get the most out of your purchase; it's 1/3rd the price of anything comparable for a reason. OBX makes diffs for all sorts of cars, so there's already a lot of great info out there on how to deal with the shortcomings present. Read this pdf, and this pdf from this thread for a good idea of what's involved (AKA don't expect a step by step pictorial here EDIT: OK, I lied, check out post 8).

    Here's a closer look at what all was involved for me. First up, crappy belleville washers. These washers have a built in curve, and when stacked with opposing curves act as a spring. Junk included, with two of them already squashed permanently flat:



    Behold, junk bolts. These were actually of the correct grade, but were beyond rough shape.



    The only real rework I had to do involved the oiling holes drilled into both top and bottom halves of the case for the worm gears. The top half was properly countersunk, the bottom not so much. Top:



    The holes on the bottom case were obviously drilled after the pockets for the worm gears were milled out, as the blowthrough from drilling was poking into each pocket. Nothing a couple minutes with the dremel can't solve. Don't mind the sloppy countersinking, I was primarily concerned with removing the blowthrough, not with making pretty countersunk holes. You can also just make out that I touched up the knife edges of the worm gear pockets to get rid of some flashing.



    Everything was pretty straightforward assembly from here. I stacked the new belleville washers in the following order )()()( for max preload. A little bit of oil on the belleville washers and a steady hand are required to get everything together without the washers moving around. Ready for the top half to go on:



    And here it is all bolted together, ready to go into the transmission.


    A couple of general notes... I cleaned off whatever oil they used at the factory, and lightly coated all internal parts with 75w90 transmission oil. No need to make a mess, I just didn't want anything getting rusty. Also, if you look closely you will note that this diff has halves that do not completely mate, leaving a ~1mm gap. Don't go all crazy on the bolts expecting the halves to suck together! Finally, you may have noticed that this is a stub axle only design. This means for late model owners like myself, you will need to replace your male axles with those of the stub axle variety. No big deal... new axles, stubs, and new axle seals are required to make the change.

    Next up will be acquiring the center diff, and swapping the new diffs into the transmission.
    Last edited by lorenkb; 07-31-2010 at 11:29 PM.

  2. #2
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    Do you know of any place to get replacement spring washers?
    92 legacy (t)wagon
    "If you know you can do something, I don't think it takes a lot of courage to do it." -Roger Clark

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    Indeed I do. Rich Bryant sells them as a complete set along with new bolts, or you can source your own from McMaster-Carr.

    I'm debating picking up a new set of bolts and redoing them... none of them came even close to stripped going in, but it's obvious there are some defects on one of the case halves doing damage to a couple of bolts as they thread in. If I do pull it apart again I'll measure the belleville washers and post the appropriate McMaster-Carr part number.

  4. #4
    Dirty Member FlatBlack's Avatar
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    Yeah!! Another OBX user.

    I've been using a rear unit in my Datsun, I will for sure be getting one for my Subaru when the time comes.

    As long as you do the modifications properly, they work fantastic. Mine was $500 after initial carrier cost, upgrade 'kit' and shop cost for installation. A Quaiffe diff [that this is a rip-off of] costs $1600 just for the carrier.

    Re: Case fitment

    I'm not sure if the Subaru front diff is any different, but the RWD R200 carrier DOES connect firmly with properly stacked washers. RBryant's site even states that you should get between 1 to 1.5 turns of the bolts from when the case is tensioned from the washer stack.

    Lots of pictures on our R200 OBS install

    http://forums.hybridz.org/index.php?...-installation/

    I didn't get a picture of my case after the upgrade kit/washer stack trial and error, but the case sides are touching each other.

    Would you mind posting your new washer stack configuration?
    - Mat
    78 Datsun 280Z Terbeaux, L28ET, MegaSquirt Extra V3.57, Evo FMIC, 275/40/17s, Helical LSD, etc...
    05 Subaru Forester XT - 5MT, EJ257 hybrid
    96 Subaru Impreza Outback Sport - EJ22/5MT, GrpN TM, GD WRX Springs/Struts/RSB


    Quote Originally Posted by Lancia037Rally View Post
    Besides, if Travis wants to drive around in a circle on a bunch of yahoo's bumpers, he lives not far from the DC Beltway and can do that 24/7.

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    Quote Originally Posted by FlatBlack View Post
    I'm not sure if the Subaru front diff is any different, but the RWD R200 carrier DOES connect firmly with properly stacked washers. RBryant's site even states that you should get between 1 to 1.5 turns of the bolts from when the case is tensioned from the washer stack.
    I double and triple checked. It's not from washer stackup, it's a physical case limitation. I verified that a completely compressed washer stack (both old and new) would clear the center housing. After that checked out I started measuring the case. The lip on the lower half of the case is taller than the machined recess in the upper half of the case. I'm hoping this is by design for proper bearing spacing, because if not this thing isn't going to fit worth a damn.

    Quote Originally Posted by FlatBlack View Post
    Would you mind posting your new washer stack configuration?
    Max preload, )()()(

    No specs on the washers themselves until I open the case back up.

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    Dirty Member FlatBlack's Avatar
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    Quote Originally Posted by lorenkb View Post
    Max preload, )()()(

    No specs on the washers themselves until I open the case back up.
    Thanks for that, the R200 OBX is a crap shoot, I had to test 3 different stack configurations before settling on the one that gave me about 1.25 turns.

    Different stacks might be useful as a base for other members who are doing this. Thanks for doing this write-up/documentation
    - Mat
    78 Datsun 280Z Terbeaux, L28ET, MegaSquirt Extra V3.57, Evo FMIC, 275/40/17s, Helical LSD, etc...
    05 Subaru Forester XT - 5MT, EJ257 hybrid
    96 Subaru Impreza Outback Sport - EJ22/5MT, GrpN TM, GD WRX Springs/Struts/RSB


    Quote Originally Posted by Lancia037Rally View Post
    Besides, if Travis wants to drive around in a circle on a bunch of yahoo's bumpers, he lives not far from the DC Beltway and can do that 24/7.

  7. #7

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    awesome info!

    I already have a collection of center diffs, now just need to source a front. I'm subscribing to this for sure.
    Chris Lynch
    2010 Honda Fit Sport (FOR SALE)
    1996 Ford Ranger 2.3L
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    I got bored, was bugged about a couple of things that were present during the rebuild, so I tore the diff apart again. I also took a lot more pictures and measurements this time

    Here's some specs on old and new hardware.

    Bolts (old and new): M8x1.25, 45mm length, grade 12.9
    Old Washer OD: 1.104" (28mm)
    Old Washer ID: .590" (15mm)
    Old Washer Thickness: .045" (1.14mm)
    Old Washer bowed height: .055 - .090" (1.4 - 2.29mm)
    New Washer OD: 1.101" (28mm)
    New Washer ID: .660" (16.76mm)
    New Washer thickness: .057" (1.45mm)
    New Washer bowed height: .085" (2.16mm)

    The old washer thickness has a range because they were all over the place. I'm assuming they all started out around .090" and got squished down to varying degrees during assembly. The new washers on the other hand were all .085 - .0845" even after assembly and disassembly.

    Here's what the new bolts looked like after being pulled. Some minor - moderate damage is going on here, being caused by the upper case.



    To figure out what was going on, I sacrificed one of the old bolts for an alignment pin, opposite the factory alignment pin location. Once assembled and clamped together with two of the old worn out bolts, the problem became pretty obvious. The upper case was slightly clocked compared to the lower case holes. This was causing the bolts to rub against the upper case when threaded in, filing off a portion of the threads.



    The culprit here is poor tolerance on the notch milled away for the alignment pin. You can even see where the alignment pin was worn flat on one side by the harder case during initial assembly.



    Out with the dremel once again, and I took a very small amount of material off the offending pin alignment section.



    With the following dimensions, there was just enough wiggle room during assembly to get the clocking of the cases close enough. At this point each bolt could be threaded in by hand. For reference, the original milled slot was ~.32" compared to the final .33"



    This leads into another thing I wasn't happy about. Here you can see one bolt completely tightened, and another ready to be threaded in. There is very little thread engagement here...



    With the cases fully bolted together, the exposed bolt length (to the bottom of the head) is 1.42". Total length of the bolt is 1.76", meaning there is only .34" thread engagement. I went back and checked each hole for max thread engagement depth. Values ranged from .982 - 1.192" exposed bolt length. This means that with the worst case hole, I can go to a 1.988" bolt. It just so happens that this is a tad over 50mm McMaster-Carr to the rescue, M8x1.25x50mm, grade 12.9, all for a grand total of 8 bucks per pack of 25.

    Right, so with all that sorted out, I figured I might as well take enough pictures to put a decent assembly sequence together. First off, you have to disassemble, and odds are that even with the bolts pulled, you are going to have to pry the cases apart. So get to prying! Pry a little, rotate, repeat.



    Here are all of the internals. Don't worry about keeping track of which gears go to what side. The great thing about this particular diff is that you can't put it together in more that one way (unlike other OBX diffs).



    Now would be a good time to repeat as much of the above tweaks/mods/madness as you care to. Clean everything with your favorite degreaser, and apply a light coat of transmission oil.



    Drop in the lower output shaft and the corresponding worm gears. Don't worry, only one set of worm gears will work. It doesn't matter if you put the worm gears dimple up or down, I just kept them all dimple up for ****s and giggles.



    Now would be about the time to start worrying about the belleville washers.If you bought your washer/bolt kit from Rich Bryant, you can skip this portion. If you didn't, or just have an irresistible urge to measure things with a caliper, play along. Go caliper crazy on the following parts:



    I ended up with the following:
    Spacer gear keeper height: .954"
    Thick spacer gear height: .517"
    Thin spacer gear height: .34"
    Thick spacer lip depth (symmetrical sides): .17"
    Thin spacer lip depth: .168"
    Washer bowed height: .085"
    Washer Thickness (compressed height): .057"

    Now, here are the important parts. You need to make sure that a fully compressed stack of belleville washers won't cause the spacer gears to protrude out the sides of the keeper, keeping the case from completely bolting together. You also desire a stack of washers that are thicker than the total spacer lip depth, giving a preload to the differential.

    Add up your total lip depth: .17"+.168"=.338"
    Add up your total washer stack: .085*6=.51"

    Our washers when stacked will be larger than the total lip depth; good. This is easily seen when you assemble the washers and spacer gears (note that each washer is opposite the next, so you have a )()()( pattern!)



    Now lets make sure the thing will still bolt together all the way. We will need to find the additional height due to a fully compressed washer stack, and make sure we still stay within the keeper height.

    Add up your total spacer gear height: .517"+.34"=.857"
    Add up your total compressed washer stack: .057*6=.342"
    Subtract the total lip depth from the compressed washer stack depth, and add in the spacer gear height: (.342"-.338")+.857"=.861"

    Looks like we are good to go, with our total compressed washer/spacer combo coming out to .861" compared to the total allowable height of the keeper at .954". If one were so inclined, you could expirement with different washers to get more or less preload. The wider the compressed stack of wahers the more preload.

    I hope you've gotten your caliper fix, as it's time to finish assembly. In goes the keeper



    Followed by the lower spacer gear. I treated the thick spacer as the lower, but I don't think this matters. Note that for our differential, unlike other OBX models, this is a symmetrical part.



    Next up are the belleville washers. It really helps later on if you oil up the washers.



    Top it off with the upper spacer gear. Use an appropriately sized drillbit, or allen key wrapped with tape, to align the washers.



    In go the next set of worm gears. Once again, dimple up or down, it's your choice.



    Next up, the output shaft.



    From here, the upper case goes on, and you get to have fun with bolts. This part takes some patience, so take it slow. The upper case is a press fit, and likes to go on crooked. To make life even more interesting, with this style of OBX diff, there is no way for you to keep the belleville washers aligned during assembly. If you were paying attention and added some oil to the washers, they should stay put during final assembly. Get each bolt started, and 1/2 a turn at a time start to cinch them down. Others have said to use a star pattern while tightening, I just went in a circle. Double check every now and then that the case is going on straight, and use your trusty prybar as necessary to correct. Once each bolt is snugged up nice and tight (not torqued yet though!) you can pull one at a time and apply a bit of blue loctite. Torque to 30ft*lbs.

  9. #9

    Default Re: Putting together a decent 5mt transmission

    Awesome stuff Loren. Good job for all of us that your hobby is Subarus and not, say, building armies of evil robots.
    Phil

    '03 Evo VIII : '90 Corrado G60 : '05 Legacy GT wagon : '11 Fiesta hatch : '77 Capri 2.8

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  10. #10
    Dirty Member FlatBlack's Avatar
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    Quote Originally Posted by lorenkb
    Drop in the lower output shaft and the corresponding worm gears. Don't worry, only one set of worm gears will work. It doesn't matter if you put the worm gears dimple up or down, I just kept them all dimple up for ****s and giggles
    Great information, but I'm jumping in to double check something again...

    There ARE two different ways to put these diffs together.



    You need to assemble the gears the "right" way so the planetary gears hit the case on acceleration and not the washer stack.

    The Quaiffe is designed so that the washer stack ONLY sees force from the planetary gears on decel.

    Yours is assembled properly, but to everyone else who does this, make sure the gears are flipped the proper direction.
    - Mat
    78 Datsun 280Z Terbeaux, L28ET, MegaSquirt Extra V3.57, Evo FMIC, 275/40/17s, Helical LSD, etc...
    05 Subaru Forester XT - 5MT, EJ257 hybrid
    96 Subaru Impreza Outback Sport - EJ22/5MT, GrpN TM, GD WRX Springs/Struts/RSB


    Quote Originally Posted by Lancia037Rally View Post
    Besides, if Travis wants to drive around in a circle on a bunch of yahoo's bumpers, he lives not far from the DC Beltway and can do that 24/7.

  11. #11
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    That's the nice thing about this particular model OBX though, there isn't two different ways to put it together.

    The diff you have pictured has the final drive gears swappable, which will reverse the direction that the worm gears drive under torque. This model has the stubs built into the final drive gear, and they are different lengths. The stub coming out the top of the case is a lot longer than the bottom stub (bottom = ring gear attachment). If the stubs look correct (AKA both are showing out the side of the case) then it's assembled properly without question.

    Now, if OBX ever gets around to making a version that works with male axles, the story will change...

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    The new hardware I ordered from McMaster-Carr arrived this morning. Everything was a perfect fit.

    New Bolts (5 mm longer): M8x1.25 50mm length, grade 12.9. Part# 91290A448
    New Belleville Washers: 28mm OD, 14.2mm ID, 1.5mm thickness, 2.15mm height. Part# 96445K278

    The bolts came in a pack of 25, the washers in a pack of 12. Grand total shipped to my door was $20 and change including tax.
    I verified that the new washers have the exact same stackup as the upgraded washers from Rich Bryant. I didn't bother swapping them out though. So, I have 12 spare washers and 16 spare bolts if anyone needs some

  13. #13

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    Dayum Loren.

    For as much knowledge as you have...why has it taken you so long to get your vehicles functioning?

    I've gotta re-read this a few more times (given the little that I know about diffs). Thanks a ton for the great write-up amigo.

  14. #14
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    I guess knowledge is a poor substitute for being lazy, and never seeming to have enough cash for two projects at once

  15. #15
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    Well, I'm still waiting on more parts, can't pull the transmission until we cut the subframe up a bit (a story for another thread...), and curiosity won over. So, I opened the diff up again a couple days ago and took some more measurements related to the worm gears.

    I measured the total depth of each worm gear pocket, and the height of each worm gear. This is the price you pay for buying a cheap diff:

    Lower case pockets: 1.894, 1.899, 1.900, 1.888, 1.897
    Lower worm gears: 1.851, 1.853, 1.856, 1.851, 1.853
    Upper case pockets: 1.924, 1.909, 1.910, 1.918, 1.923
    Upper worm gears: 1.854, 1.848, 1.851, 1.852, 1.853

    While the worm gear tolerance is "OK", the pockets leave a lot to be desired. Even with matching the long worm gears to the deeper pockets, both upper and lower cases are running a ~.01 spread in pocket/gear tolerance. While the diff will no doubt function, the pockets with the least clearance will have to wear down before the rest of the worm gears start to engage their pockets. No wonder there are reports of having to do several oil changes after the initial install to get rid of metal dust in the oil.

    While I had the diff apart, I took a close look at the worm gears themselves. I hadn't noticed before, but there were several gouges spread across multiple worm gears.

    Although the edge of each worm gear was beveled, the "leading edge" of each tooth was rather sharp, and some were downright deformed. Here's a before/after shot.



    I also took the time to nock down the nipples left over when they faced off each gear (center of the non-dimpled side of each worm gear)



    Here you can see where I had to clean up a couple of gouges on the face of a tooth.



    I didn't bother taking a picture, but I also cleaned up each leading/trailing edge of the final driveshaft teeth. While all of this took quite a while, I'm hoping it will cut down on the inevitable metal dust/paste creation during break-in.

    With all that done, I think I've pretty much beat this dead horse into a pulp... The sooner I can get ahold of the rest of the parts needed for this build the better!

    EDIT: Oh yeah, and I put the diff back together with the belleville washers I sourced from McMaster. Perfect fit.

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