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  1. #1

    Default How your manual transmission works

    Ok guys, here is how your manual [aka standard, 5 spd] works.

    Below is a pic of the internals of a Alltrac trans. Only the trans part, no transfer case for now.
    In your head, rotate the pic 90* counter clockwise.

    Input/Output Shafts and Shift Forks
    Now, see the 2 shafts with gears on them? Those are the input and output shafts. the one in the back is the input shaft. Power is input to it from the engine. You can see the other side of it sticking out into your bellhousing. The one in the front is the output shaft. Power is output from it to the differential.
    The fat gear on the bottom is of course the differential.
    Note the metal rods to the right. These are the shift fork shafts. The shift forks are attached to them. Note the shift fork on the bottom of the output shaft. It is the aluminum "wrapped" halfway around. This is the 1st/2nd [1/2] gear shift fork.
    Note the two "teeth" on the right side, right by the plier handles [red]. The shift levers connect to the shafts here. This is how the shafts are moved.

    The input shaft has 5 gears [Both 5th gears are not on the shafts atm. They have to be removed to take the case off]. The output shaft has 6 gears. One for each "speed", plus one to drive the diff ["Gears" are the ones with slanted teeth. ]
    For the moment, ignore the 5th gears and the diff drive gear.
    Each shaft has 4 gears left [remember, we are ignoring the rest for the moment]. Two are locked to the shaft [when the shaft rotates, the gears MUST rotate], and two are free spinning on bearings. 1st gear is on the lowest gear set, 2nd the next, and so on.
    For the input shaft, 1st and 2nd gear are slaved to the shaft, while 3 and 4 free spin.
    For the output shaft, 1 and 2 are free spinning, while 3 and 4 are slaved.
    Let's go back to the 5th gear[s] for a min.
    See the needle bearings on the top of the input shaft?[Remeber, the input shaft is the REAR shaft in the pic. Do not confuse the large bearing set on the output shaft with these. That bearing set is for the shaft itself.] And the splines on the top of the output shaft? These are for 5th gear[s]. 5th gear on the input shaft is free spinning [spins on those needle bearins], while 5th gear on the output shaft is slaved to the shaft [via the splines].

    Synchronizers [Snychros] and Hub Sleeves
    The hub sleeve is what locks the free spinning gears in place when needed.
    If you look at the shift fork on the output shaft, it is on the 1/2 hub sleeve. See the straight, fat metal teeth right above the fork? That is the top of the hub sleeve. The bottom is right below the fork. The hub sleeves are splined inside to the shaft they are on. So they spin WITH the shaft. They rotate inside the "tines" of the shift forks.
    The synchros help the sleeves to slide onto the gears easier/quieter.
    They are the brass you can see above and below the 1/2hub sleeve.

    How It All Works
    When you move the shifter lever, it moves the shift cables, sliding the pertinent shift fork shaft up or down. When the shift fork shaft slides, so does the shift fork on that shaft.
    Note 1st gear on the output shaft. See the slanted teeth?
    Notice right above these are a set of straight teeth? That is part of 1st gear. The hub sleeve has a matching set of straight teeth on the inside of it.
    When you shift into 1st, the 1/2 shift fork slides DOWN, locking 1st gear to the shaft [remember, the hub is slaved to the output shaft, so the normally free spinning 1 gear is now slaved to the shaft also.]
    Now, remember which 2 gears on the INPUT shaft are slaved to it?
    1 and 2.
    SO, we have the input shaft spinning [driven by the engine], in turn spinning the 1 gear on it [which is slaved to it]. This 1 gear is meshed to the 1 gear on the output shaft. The 1 gear on the output shaft is now slaved to the output shaft, via the hub sleeve, forcing the output shaft to turn also.
    Which in turn forces the diff to spin, via the diff gear on the output shaft [it is below the 1 gear, and is part of the output shaft.

    When you shift to N, all 4 normally free spinning gears on the two shafts are unlocked at the same time, allowing the 2 shafts to independently spin. Normally, when the vehicles drive wheels are on the ground, the resistance from this forces the output shaft to not rotate. Instead the 1 and 2 gears on the output shaft rotate [they are the free spinning ones], and the 3 and 4 gears on the input shaft rotate [they are the other 2 free spinning ones].

    BUT, if you lift the drive wheels off the ground, the slight resistance the free spinning gears have allows the input shaft to drive the output shaft via all 4 gears, in turn driving the diff, ect, ect.

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  2. #2


    I know this is explained in howstuffworks.com, but I thought I would set it out with actual pics here....
    I am going to try to get some detailed pics of the parts later, when I have time.
    I have a spare awd trans torn apart in storage....

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  3. #3


    Thanks so much. Call me retarded, but I never really understood how a tranny works. Now if you could only explain suspension to me.. I understand what individual parts do and how they work, but I don't understand how it all comes together.

    I also rotated the image:
    Morwan Osman
    Navy Gloss '90 Celica
    Self-hating Toyota fanatic and bench racer.
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  4. #4


    Heh... transversely (?) mounted engines like ours have much more complicated transmissions it seems.. I helped my friend rip the tranny out of his WRX and it is WAY less complicated because of it's mounted orientation.
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  5. #5


    Not really....
    Just the diff is added into the trans. Pretty much all manual trans have those 2 shafts.
    Just in a rwd, the output shaft drives the driveshaft, instead of the diff.

    The WRX is probably a little more complicated inside, as it has the front and center diff inside that small ass space....

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  6. #6


    Nah.. we took it apart it was much less "clustered" inside.. all the same parts I'm sure.. but .. yea easier to look at.
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  7. #7


    Dude, there's the same stuff in there....
    an input shaft, and output shaft, and a diff.....

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  8. #8
    Member BLAIRCROFT is on a distinguished road

    Join Date
    Mar 2005
    living in a van down by the river!!


    ok guys fight to the death.
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  9. #9


    nice write up. Thanks for posting.
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  10. #10


    Quote Originally Posted by BLAIRCROFT
    ok guys fight to the death.
    It wouldn't be fair...
    I have deadlier weapons....

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