How To: Traxxas E-Maxx 3906 Steel Idler Gear Upgrade

[@inspireonex]

1:43 where are the friction pegs?

[@1i-rc]

Gone the way of the dodo, at least for me. The slipper is locked and I use a bit of shoe-goo to hold the slipper disc's to the hub which in turn helps lock the assembly together and reduces the chances of slipping as there's usually a bit of Adhesive making contact with the spur on both sides. If I was more confident in my drilling ability I'd convert the top shaft to use a revo slipper but as of now I don't have the nerves to do it.

[@inspireonex]

@@1i-rc gotcha

[@GyuHobbyRC]

Wow !!!! 😃 It's a great video. 😎😎 Thank you for sharing great information and great videos. 👏👍👊✌️

[@travisbaker7600]

Why did you have to grind off the lip? What was is interfering with?

[@1i-rc]

The lip hits the case if it is not ground off. Once ground the gear is the same thickness as the stock plastic gear and allows everything to spin freely. Thank you for your comment and for watching!

[@bobgeldoff9413]

so are these the same as the gearbox in the t-maxx nitro engine?? can i swap out the top fixed gear out and thats it???i wanna do a electric conversion and i have to do something with the top gear. can i just leave it as is?? it should bite anyway right??? what would it do if i dont change it???

[@1i-rc]

In that case you'll need a forward only conversion (part #4994x) to replace the forward/reverse output assembly and then decide how you want to deal with the 2-speed. If you want to keep it, great, adjust the shift point to where you like it and you're done. If you want to eliminate it you'll need to remove the first gear set and replace it with spacers to keep the second gear set aligned. Any tube that fits over the shaft will do (arrow shafts might be a good choice, as is brass or aluminum tube from the hobby shop); this will keep the gears from moving side to side.

[@ButtedorFrank]

that's so awesome ! I have a 3906 emaxx I just dug out of storage and made brushless and I was scared about snapping things in the trans. what about the bottom two big gears ? they don't break easy ? they can stay plastic ?

[@1i-rc]

The bottom 2-speed gears aren't commonly available in either steel or aluminum like these idler so I didn't really mention them. They are pretty tough though and if they are going to break it's going to be around the gear selector area simply due to torque breaking wither the selector pins or the hollowed portion of those bottom gears. When running the HV Maxx brushless system back in the day we didn't break a 2-speed gear but that's not saying it can't be done.

[@1i-rc]

That sounds awesome! I remember Radio Control Car Action doing a twin motor, all wheel drive TA03 back in the late 90's that used drivetrain components from a TA03F and TA03R and looked like it came from the factory that way. I want to switch this car to a custom machined carbon chassis at some point but wanted to use a stock chassis first just to show it could be done. Thanks for watching and for the comment!

[@BlackTownie999]

Is there a place to get 𝒂𝒍𝒍 replacement guts for this transmission? I'm tryin to get together a parts list to build a trans since I can't seem to find one new from traxxis.

[@1i-rc]

Unlimited Engineering used to produce some steel gears but short of finding them used on Ebay I don't see many options. With the age of the truck and its other weak points most people didn't bother making the jump to steel gears. Brushless and lipo were in their infancy at the time of the E-Maxx 2.5 (the first wide update after the original release, circa 2006-7) and even with those early setups the weak point was the slipper, diffs and center shafts. I originally ran a 4.5t Novak HV Maxx brushless system in my 2nd 3906 and never broke any of the transmission internals but managed to shred a few diffs, countless spurs (spinning through a locked down slipper) and even shattered a pinion.

[@jaredsayrc4947]

I'm rebuilding two emax 3906 and it seem slow since putting on Big Joe's tire

[@1i-rc]

If you are still running the Titan 550's (or most brushed motors for that matter) there are two issues that arise when using the Big Joe's. First is that they are heavy and that increase in rotating mass puts more stress on the motors, ESC and batteries. Second is their overall height effectively raises your gearing, again putting more stress on your electronics. Gear down a tooth or 2 on the motors and that should restore some of the "pep" to your truck. I love the look of my Big Joe's and they are great for cruising around but they are a workout for the Trinity Pro motors that I have in the truck currently. This truck may be getting a 775/EVX2 combo in the future and when/if it does I will update everyone on how that soup can of a motor gets along with the Big Joe's.

[@19Herofade92]

Question. Should there be grease on the gears? or is that only for the diffs? As far as other traxxas transmissions go they all have grease on the transmission as well.

[@1i-rc]

In the follow-up video I did make mention that I used a coating of Lucas Oil Red-n-Tacky on the gears to keep friction and heat down. I should have linked that video to make mention of that, sorry about that! Edit: I just updated the description with a link to part 2.

[@19Herofade92]

@@1i-rc Noob question. can you shift while in motion or only when at a stop? i dont want to strip my gears from shifting when not suppose to thanks!

[@1i-rc]

@@19Herofade92 The E-Maxx can be shifted while in motion, just remember to let off of the throttle during the shift to ease the load on the bottom drive gears and shift selector. Those pieces are plastic and, while robust, may not hold up to full-throttle shifts. Plus if you are on the throttle when the selector disengaged 1st gear the transmission will rapidly free-spin for a split second in between gears making the engagement of 2nd much more strenuous than it needs to be.

[@jamesrodriguez7771]

Nice video but I have been running brushless in my emaxx first generation with 2speed for years since I got mine 15yrs ago and My trans has been just fine haven’t had any issues was running 1/8 castle esc and 2650kv motor on 3s and 4s but mostly 3s it was crazy fast on 4 but 3s was perfect did backflips on acceleration but recently swapped out my 1/8 system to my 550 size 3150 kv motor and think this is more better all around motor kv for mine

[@1i-rc]

I'm glad to hear that your 3906 is still going strong! In my experience the idlers have been a weak point, even on 775 brushed power, but another benefit is parts availability. The 3905 idlers that I modified are from a newer generation truck and are easier to find. Plus these should be the last set of idlers a person should ever have to buy for the old 'Maxx! In my coworkers E-Maxx (back in 2007) with the original Novak HV Maxx brushless system idlers would get chewed up after roughly 1 month of running and that system only ran on NiMH power!

[@warmrollsforthetable]

running a Novak brushless esc setup on my 3906, runs great in 2023

[@murdernovaltr]

Wow!Great video!Let me know if you ever get to make it fully brushless ready with all gears metal.I have one and i use it at 50% speed because im afraid to strip the plastic gears:(

[@1i-rc]

From the research I've done there are no bottom 2-speed gears for the 3906 currently available unless a set from Unlimited Engineering pops up for sale. I wish a larger company would step up and make a batch of them.

[@bobgeldoff9413]

he got fired