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  1. #1
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    3906 transmission mods???? and more mod??

    Is it just me or isn't the slipper clutch shaft on the older 3906 Maxx transmission more centered over the center drive shaft output then the newer 3908?, Ive never seen one in person, just in pics, I was wondering if anyone tried to use the newer 3908 parts in the older case? say someone had access to good machine shop equipment, do you think it could be done??? I'm starting on a E maxx crawler/torque monster for my nephew I got my hands on a couple of old style 14.4 dewalts at a great price ...free!! and after sorting through my leftover parts from my maxx build, I'm not too far from having another truck But im hoping to get the motors evenly positioned for good balance, that's why im looking for a transmission the is more "centered"
    (Rich)..If its stock.....leave it in the box!

  2. #2
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    Yes, it can be done I think, all the gears are the same diameter, just I think they have to be ground down in width. not sure about the output gears, but steel idler gears are a common upgrade, as is the 3903 input shaft which has the gears pressed on it.
    "American Muscle beats import any day of the week"

  3. #3
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    OK, Mr power was the yes for the input shaft is centered above the output shaft? I do believe the input shaft is longer on the 3908 tranning,because of how it sticks out the opposite side of the tranning. I figured I can cut it down to the proper length...or drill out the housing so it can stick through like the 3908, I figured Maybe that some of the spacers may have to be modified, longer or shorter for the different case size....next crazy question how will it mount to the 3908 chassis? I may go with a custom aluminum chassis, longer, maybe so the longer rear center shaft will work on the front too.... but then what body to use???? lol .. the only thing bad about custom jobs!!!
    Last edited by goalieman3037; 08-24-2012 at 08:56 PM.
    (Rich)..If its stock.....leave it in the box!

  4. #4
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    "American Muscle beats import any day of the week"

  5. #5
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    ok ......so I have some questions....why dosent any one want a two speed transmission any more? IF they are still going to use the 3906 transmission Most people change the idler gear to the new steel one, and lock it into 2nd gear, right? then how does the 3906 output gear hold up compared to the 3908 output gear? Now I know they used to make a all steal gear/ drive hog set for the 3906, I found one on ebay but they want $120 tooooo much for a truck I'm going to give to my nephew!
    he wants the two speed transmission...WHY?....I have no idea??? so how do I really upgrade the 3906 to be better/different?
    How crazy am I?
    step 1 input shaft
    my Plan is to mic the 3906 shaft length,and the position of the two gears that are on that shaft,I do have a old slipper setup that fits the 3906 hex shaft, so i will probably install it on the shaft so I can get a distance from the spur gear to the 1st internal gear too next cut down the length of the 3908 shaft and install the two 3906 gears on the 3908 shaft in the same position as they were on the 3906 shaft

    step 2- change the idler gears to the new steel one, but instead of sanding the gear thinner, I did see a forum somewhere , where they sanded a little of the center plastic guide that hold both idler gear shafts, it will depend on just how much needs to come off I will mic the old idler gear and the new idler gear and do the math if too much has to come off ill sand the gears instead

    now step 3 is where i want to try a few things that im not sure will work....
    1st I looked at the output shaft on the new summit 2 speed transmission, i like the X shape of the shaft where the drive hog rides, seems to me it would have a stronger hold over the square shaft, with less chance to strip/spin in the drive hog...so my next question is will the drive hog in the new summit transmission lock up with the older 3906 output gears? if so, I would use the summit output shaft,next I would have to use the 3906 shift fork shaft assembly because of the different transmission case, but will that shift fork fit the summit drive hog? looks like I may have to buy a few extra parts to see what will work unless someone out there know any of these questions???

    LOL why would I go through all of this????? to start with I like the fact that the input shaft is centered directly over the output shaft, which in turn will let me mount the motor so The weight is balanced evenly in the truck- 2nd I have a old 3906 transmission case, and my lhs has a bin full of older model close out parts (still packaged new) with most of the parts I need for 2-3 dollars for each part
    Last edited by goalieman3037; 09-09-2012 at 11:48 AM.
    (Rich)..If its stock.....leave it in the box!

  6. #6
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    what???? no input!!! lol
    (Rich)..If its stock.....leave it in the box!

  7. #7
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    i still use my two speed, high gear for short grass, low for longer grass it saves time changing pinions just flick a switch and carry on running.
    been a while since i done the idler gears, I think one needs sanded/grinded down, but i done the two as it done no harm. The plastic bit is where the bearing sits, above the idler gear on the input shaft, only the bottom bit of the lip needs removed, you'll see when you put the gear in how much needs to come off.
    I like the idea of trying the some summit parts in there.
    With trying get a good balance with the motor, will you be sacrificing that for a higher centre of gravity motor.
    Problems.The manual's good starting point. Simple

  8. #8
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    thanks trax I didn't know that it was the plastic where the bearing from the input shaft sits is where the issue was, that what I like about you guys, always a big help! my biggest question is if the drive dog from the summit will lock up with the 3906 gears... and the length of the output shaft I may have to just buys some and see whats up...actually Im going to mount them more to the left and right so the motors shafts are even with the spur gear shaft @ say it 9:00 and 3:00
    Last edited by goalieman3037; 09-17-2012 at 06:34 PM.
    (Rich)..If its stock.....leave it in the box!

  9. #9
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    remember that the small shafts that come with the new idlers are just slightly longer also and won't let the gearbox halves close. Using the old ones will do nicely. If you thrown the old ones out, taking about 1-2mm of the new ones should do I think.
    If only there had been parts that could change the size of the stock gears from the start that would of been great. As you know yourself, using second gear with a powerful motor will get you over most terrain with ease. I would of loved a low gear that's lower than the stock second, Then a second gear that is a lot higher than the stock second.
    Last edited by trax de max; 09-18-2012 at 03:31 AM. Reason: typo
    Problems.The manual's good starting point. Simple

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