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  1. #1
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    Question 3906 Trans Gear questions

    I've got a question, the low speed gear, 1st, has a little more noise in it, than 2nd and I'm wondering if that is normal? This was crashed hard and rebuilt before I bought it, which trans gears usually are the ones that give up? Also, can you put a differant gear in, to get more spread between 1st and 2nd? I thought I read that a few days ago, differant gears were available at one time. Thanks guys.

  2. #2
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    I don't believe there are other gears available for the 3906 maxx. And the gears that give are usually the idler gears(in the middle) but this is remedied by grinding down 3905 idlers and replacing them. I don't think 1st gear should be louder unless there is a stripped or almost stripped gear in there. Although it could just be because it turns more in 1st gear.

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  3. #3
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    Thanks Chopstx, it definitely has a "tick" in 1st, but not in 2nd. I can hear it when I'm accelerating moderatlly and deccelarating. It's not the spur or pinions. I haven't looked yet on Ebay to see how much a "new pull" trans is yet.

    Sooo would these gear sets be worth installing? I'm thinking putting new lipos in it will finish off whatever is ticking lol.
    Traxxas Input Shaft Drive Gear Assembly EMX TRA3993 Metal??
    http://www.ebay.com/itm/Traxxas-Inpu...item1e797707b9

    Metal idlers
    Traxxas New Idler Gear 20T:EMX TRA3996X
    http://www.ebay.com/itm/181118422858...84.m1438.l2649
    Last edited by cooleocool; 05-07-2013 at 09:27 AM. Reason: merge

  4. #4
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    Those idlers are what you need, however the need to be ground down so they are skinnier so they fit. Also, reuse your old shafts. Just pop the bearings out of the old gear and put em in the new one. The new shafts are too long.

    I don't have that input shaft on mine, just the original so i don't know about that

    Actually nevermind that is the original. Traxxas also makes a 'lightwieght' input shaft that is supposed to help somehow but I don't have it or know of anyone that has it.
    Last edited by cooleocool; 05-07-2013 at 09:27 AM. Reason: merge
    2wd Slash VXL
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  5. #5
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    Cool that's what I was thinking, mostly a drop in with metal gears, I actually pulled the parts numbers from the exploded views of the 3906 trans. Then looked on Ebay for those numbers.
    http://img24.imageshack.us/img24/8198/screenshot3cb.png

  6. #6
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    you sure it's not the diffs making the noise.
    I think U.E. did the output gears years ago. Anyhow this is how the idlers should look.Originally the teeth are wider than the bore like a lip. Just grind it flat on both sides.


    From what i remember you only need to shave one gear, but i done two while it was there.
    Problems.The manual's good starting point. Simple

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    Thanks dude. I ended up over at UE linking to their gears this morning. $40 is a little steep to me though.

    http://www.unlimitedengineering.com/...ore/13407.html

  8. #8
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    just use the traxxas 3996X grinded down for idlers. But it was the larger output gears and drive dog what i was thinking, I'm sure it was u.e. that used to make them. Last set i seen was on fleEbay last year.
    more info click
    Last edited by trax de max; 05-07-2013 at 05:43 PM.
    Problems.The manual's good starting point. Simple

  9. #9
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    Quote Originally Posted by trax de max View Post
    just use the traxxas 3996X grinded down for idlers. But it was the larger output gears and drive dog what i was thinking, I'm sure it was u.e. that used to make them. Last set i seen was on fleEbay last year.
    more info click
    I saw those lol, talk about rare. I think I'll go with idlers and see how it holds up.

  10. #10
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    You'll notice lots of noise after changing. I still use the stock input shaft with the dewalt only part inside the tranny I changed was the idlers. Maybe 2 year now.
    Problems.The manual's good starting point. Simple

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    Cool, that's what everyone has written, that just changing the idlers pretty much takes care of things. Does that brushless transmissions have steel in them? Like the 3908's?

  12. #12
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    I don't understand the question, the brushless tranny is the 3908/3905/3903
    Problems.The manual's good starting point. Simple

  13. #13
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    Yes, the new spec transmissions, which are shared with the full size revo and Summit families, minus the 2 speed in the summit, is steel input and idler gears, with plastic/nylon output gears. The size of the gears is also increased, so there is more surface area and harder to strip.
    "American Muscle beats import any day of the week"

  14. #14
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    That's what I meant, the differances in the brushed and BL. Thanks PTTM

  15. #15
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    But you can NOT put a new spec tranny in a old chassis
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    Lol I figured as much. I have read quite a bit on retrofitting and it's a chore lol. I'm not running a Mamba and figure the idler replacements will work fine for me.

  17. #17
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    I am running a mamba and for the past 10 or so runs my steel idlers and tranny as a whole have held up great. I did put some grease in there though.
    Last edited by Chopstx; 05-08-2013 at 08:18 PM.
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  18. #18
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    Ya, the old trannys are pretty good once the idlers are upgraded, although the slippers suck and require upgrade as well.
    "American Muscle beats import any day of the week"

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    Yes you are right and for that I used Robinson racing's slipper. Very nice
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  20. #20
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    Haha, just finished running the double 8K lipos. Already have a few casualties lol. Frt body mount is gone right off the bat, and it took one of the wheelie wheels and folded it right up after ten minutes lol. Bwahahaaaa this is going to be fun lol. Slipper was screaming off the line, haven't even checked it yet, center may be gone. 1/8th turn out too lol. You don't really steer this, you just kind of herd it, sort of lol. As soon as you let go of the throttle, it straightens right up and acts nice.



  21. #21
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    Becarefull with battery placement, Nearly touching the motors aint good, You may want to angle them out a bit more, Or make a new battery tray. Some nitro tubing on the screw threads might be better to, so that it acts as a sleeving, incase the lipo rubs on them.
    Problems.The manual's good starting point. Simple

  22. #22
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    +I agree, I actually did what I was originally thinking of, I trimmed the outer rib on the battery trays so they would lay flat. The higher COG was giving me grief lol. I will dremel the motor mount so I can tuck them inboard farther, but they extend past the outside edge about 3/8 of an inch right now, but fit fine longways. I was thinking that the main braces carry the main load and short of slight twisting, I would try this. The fact it's all aluminum from front to rear helps with the twisting and flexing part. I ran it and actually tried to flip it, much better now. My only other option was a COG chassis and the batteries would hang on everything it ran over. To counter the extra weight of the batteries, yes it matters lol, I put 80w in the rear shocks. 60w wasn't cutting it, still getting way to much rebound from it.

    I actually video the truck and then play it back to see what improvements I can do to handling. So much easier than doing it on the fly. This vid is my son driving it for the first time, driving a nitro is differant than an E Maxx, plus he had bandaids on his fingers lol. But you can see how much rebound is happening from having the 60w in them. So we go to 80w on the rear, the 2nd gen Integy's are handling it just fine. Now the bats are laying lower and flat, with slightly thicker oil, to control the increased weight and mass.


    I got my FLM bulkhead braces in last night and got them installed, took care of some of the integy issues with screws bottomed out and the connections being loose. I had to drill the Integy bulkhead brace holes, they were too tight and the screws were threading down those, instead of the braces. So I drilled them slightly larger to let the screw pass through to the X brace, then they snug right.
    Eta
    I have some 20Tooth pinions coming this week and my trans parts are here, so I'll be replacing the idlers and some bearings also. I'm getting almost an hour runtime on these batteries, and that's hard driving. I figure it this way, if I go brushless in the future I have the batteries to do it with.

    I also have another set of wheels and tires coming, that I bought from a member here. The cleets are fine in a straightline, but have 0 traction sideways, the cleets slide and I found out, tend to roll under, causing it to dig in and flip, not sure if their is foam in them or not. In the vid, you can see them tear the ground from doing this, the wheel is almost touching as it corners hard. The other tires should help on this lol.
    Last edited by Oldrcguy; 05-15-2013 at 01:34 PM.

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