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  1. #1
    RC Racer
    Join Date
    Dec 2011

    Post 3906 to 3908 Conversion

    I want to convert my Emaxx 3906 to a 3908. I have a 2200kv MMM on it along with the esc. Almost everything is upgraded to RPM and CVD's all around. From my research I found out that I will be needing:
    -3908 Chassis along with battery hold down
    -3908 Transmission
    -Center Drive-shafts

    Is there any way I can convert my 3906 transmission to fit the 3908 chassis?(The motor plate has been modded to fit my MMM) I'm a little confused about how the dual servos will be set up. Let me know what parts I will need for the servos. If I'm missing anything for the conversion, let me know.


  2. #2
    RC Racer
    Join Date
    May 2005
    Chatsworth GA
    You will need a bellcrank setup for the 3908 (TRA3941 and TRA3968) and a matching servo to the one you have already. You will need the lower chassis brace set (TRA3921) also tranny skid (TRA3920).

    When you assemble the truck, make sure both servos are connected to the receiver, and your steering trim is set to center. Turn on the radio, and then the esc. This will set the servos at center. Turn off the esc, and the radio. Mount the servos into the chassis. Mount the servo horns (TRA3968) to the servos parallel to the lower chassis braces. When you install the bellcrank set, there is a turnbuckle (TRA3941) that goes from one servo to the other. After you install the complete bellcrank set, power on the radio and receiver once again, and listen to the servos. If they are buzzing, then they are fighting against each other. Adjust the turnbuckle untill the servos are no longer buzzing. Not adjusting the turnbuckle correctly will cause you to burn out your servos. If you have an aftermarket servo with at least 200oz/in of torque, then forget everything I just posted, and put the servo on the same side of the chassis as on your 3906.

    With brushless power I got tired of replacing center driveshafts. Even with revo shafts it would twist the ears off of the shafts at the u-joint every run. I suggest the TRA5151R steel CVD upgrade. $40 is a little high, but can be found at for under $30 shipped.

    As for the tranny, You could build a small adapter plate to mount the 3906 tranny, buy a complete tranny on ebay, or build one using part #s found in the PDF here
    Buying a complete tranny from ebay is the easiest and cheapest drop-in option.

    Part numbers included for your conveniance.
    Last edited by Ninja; 03-07-2012 at 11:50 AM.

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