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Thread: 3906 with a 775

  1. #1
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    3906 with a 775

    I bought a titan 775 a few years back to put into my Min-E-Maxx build (p2de) and since the motor won't physically fit in a magnum 272 tranny, the motor has sat in a case unused since. I would like to use the motor in my spare 2906 emaxx, but I am not sure how to go about mounting the beast into the truck. Is there an aftermarket motor plate that will allow me to mount a 775 into a 3906? Will the tranny handle it? Should I just try to swap a summit transmission into the old school maxx? I don't really want to sink a ton of money into the truck since I have to buy an EVX2 to power the motor, so if there is a cost effective option, I'd like to go that route.
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  2. #2
    RC Champion PowerToTheMaxx's Avatar
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    I thought it just mounted up, but if not the dual 700-HO plate from KD might work. If you are hard on it you will have tranny issues, but thats just how 3906s are. Swapping in a new tranny is a lot of dremeling to make it fit, you can upgrade the idler gears in the 3906 and greatly increase the durrability if you wanted to do that. Much easier than new tranny. Cheaper too.

    Ya, summit uses same motor plate as Revo, Revo uses same motors as MAXX, old and new maxx have same sized motors i believe... Maybe im wrong but i dont think so.
    Last edited by cooleocool; 01-04-2014 at 01:58 PM. Reason: merge
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  3. #3
    RC Champion trax de max's Avatar
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    the old maxx uses a different mount and tranny to newer maxx. The summit motor isn't ontop of tranny like the 550's.
    It's not impossible to make it fit, just takes some creativity. I installed an 820 using the stock 3906 mount. But needed some cutting to it and then limited to gear sizes because of the shape of tranny and size of motor.
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  4. #4
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    It is possible too mount a titan 775 motor with the stock motor mount, drill new holes in the mount and shaw the transmitipns case or plastik.

    I have gear mine 20/68 and it runs great.

  5. #5
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    I was really hoping to just put in a specific motor plate and not have to slot new holes. I tried that on the Min-E-Maxx and it destroyed a perfectly good transmission case. I also don't want to be locked into one particular gear ratio either if I just use one set of holes and not a sliding mount like the 3906 already has. Its a shame that traxxas doesn't offer a retrofit kit (hint hint) as I'm sure that this would be a pretty common swap with genuine traxxas parts.
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  6. #6
    RC Champion trax de max's Avatar
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    It would of been a good swap a few years ago, but people are choosing the dewalt motor now for the brushed option upgrade. and since it's not a traxxas product I don't think they'll make it, then they have to think, how many people will buy it.I've had dewalt in mine for 3 years.
    Snoopmaxx built a nice motor mount when he done the 775 install in his 3906.
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  7. #7
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    Well it looks like I have three options. Option #1: hand fabricate a new motor plate from 3mm aluminum to mount one 700 class motor. I don't really want to do that much fabrication on such a precise part, I'm fairly sure that all I'll do is create a lot of scrap material and not a functioning motor plate. Option #2: adapt a summit motor plate to the stock 3906 plate. I think this might be the most cost effective option since I already have the summit plate left over from my Min-E-Maxx project. I can use a countersunk screw between the summit plate and the motor to hold the motor in a fixed position and have the summit plate attach to the stock motor adjustment holes to adjust gear mesh. Option #3 is to buy a Kershaw Designs replacement motor plate to hold one or two 700 class motors. I just found out this morning that they offer conversion kits for the 3906 while looking at their site for some short course parts. The dual motor plate is $20 and the single motor adapter piece is $15, both of which are cost effective ways of achieving a workable piece.
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  8. #8
    RC Champion PowerToTheMaxx's Avatar
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    Id go with the KD one, just because its probaly going to be the cleanest. If you run a 72T spur gear you do not have to shave the tranny (thats how Dan at KD does it). On the new MAxxs, you have to shave the chassis to fit the big spur, but i think the old MAxxs can take a 72T spur without modification.

    Based off my memory, not sure its compleatly accurate
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  9. #9
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    I have a 72t in it already so that will help keep costs down. Now I just need to find a smoking deal on an EVX2. I dug the 775 out of storage today along with the 3906. One the Mrs. gives me the ok to buy some parts, I'll be set. Looking to gear the truck way down and use it as a trail/ slow speed basher. With my impaired vision, the size of the truck makes it easier for me to see and follow if it is moving slowly.
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  10. #10
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    I tried the summit mount and without removing 75% of it I don't think it will work. I guess I will be ordering the KD kit after all. The 775 will hit the transmission with the 14t gear that I have now, so I will need to get another pinion along with the mount. Are the 775's pretty sensitive to being over geared? I think I will be getting a 20t if that's not too high. I already have CVD's front and rear and the steel Traxxas center shafts, and I am hoping to upgrade the idler gears when I install the 775. What part # are the traxxas upgraded idlers? Thanks for the help!
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  11. #11
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    You could also buy the e maxx brushless motor mount, and drill some holes in it.

  12. #12
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    With my vision as bad as it is, I'd destroy a perfectly good Traxxas heatsink motor plate in the process.
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  13. #13
    RC Champion trax de max's Avatar
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    I think the easiest way to go is with the full 820 kit from kershaw designs. Any other way and you'll need some sort of work.
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  14. #14
    RC Champion PowerToTheMaxx's Avatar
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    Full 820 is a lot of money tho. Not sure id do that. 775s are sensitive to overheating, I dont know what gearing people usually use. I believe my 700 is geared at 19/72, Id imagine the 775 would do that or maybe a little smaller cause its more torque and less speed than a 700, id try 18 personally, or buy a set of pinions, u can get them 5/$15 if you look the right place, just make sure they have the 5mm shaft size.
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  15. #15
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    I have been studying the KD webpage and I think I'm going to try to build my own adapter plate out of 3mm 6061t6 aluminum to adapt the larger bolt spacing of the 775 to the factory motor plate. It looks relatively simple to do. If that doesn't work I'll just spend the $15 on the Kershaw piece.
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  16. #16
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    Try to contact snoopmaxx he has done a mount or search this site

  17. #17
    RC Champion trax de max's Avatar
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    Yea snoopmaxx made a nice motor mount, I'm sure the measurements and drawings are also on this site what he did.
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  18. #18
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    Morten SnoopMaxx
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    c",)

  19. #19
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    Thanks guys, that gives me some ideas. Snoopmaxx, did you do any mods to the trans internally to handle the extra torque of thhe 775?
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  20. #20
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    Yeah I did the topshaft and idler gear mod on my 3906 E-Maxx




    However
    My solid axle truck with 2650kv, 14,4v and Clod size tyres has a completely stock 3906 gearbox


    Morten SnoopMaxx
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    c",)

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