3906 diff

hi all...alot on here have discussed the fact that t/e maxx diffs dont take much punishment, well heres why.
in the first pic you can see the pinion, clearly can be seen the contact is not full, just a small tip of the tooth has worn off the blacking and takes all the grunt of your motor


and the same story on the diff ring


just a small contact area on the outside edge, the small washer you can see is an attempt at shimming the pinion into the ring gear. in fact the pinion is actually machined with runout so one side has more contact than the other side, QUALITY!! gears cut by crackheads, see ya all...

oh by the way these gears have around 30 runs on them!!

[JERRY2KONE]

All I can see is a couple of blury photos. I can make out that one pic is a pinion gear and the second is a ring gear, but I do not see anything else to varify anything that you pointed out. Any chance you can post up better pics of your explanation?

[suicideneil]

I can see the wear pattern in the first photo- the very edge of the teeth is shiney and worn = very small amount of contact between ring & pinion when meshed normally. The 2nd photo isnt so clear, cant see the wear very well. I wonder if anyone at traxxas HQ is even aware of this though? It wouldnt take too much to change the gears a bit, then they wouldnt wear out after a few dozen runs- post a thread up on the trx forum and see what happens....

[Rnemhrd]

There are about 5 problems with those diffs besides the gear mesh. If you are going to keep using traxxas diffs get the 3905 diffs. They are a little better, and can be found new on ebay fairly cheap. Otherwise get 1/8 scale diffs and forget about it.

hi all...took some more pics with my digital camera. this time its the front diff as rear diff is back on truck. seeing as you need a good camera to take close up shots these may be a bit weired looking cause they where took through an engineers eye glass to add to the magnification.

basically the smooth shinny surface is the contact point. these gears are the original 7 year old front diff (3906) so no chance of your diff ever wearing in, just wearing out.
the previous post pics where rear diff (3905) which does not mesh or wear better. both these diffs have been modded to take m3 c/sunk screws.









see how the contact on the bigger ring gear is such a small area on the tips of the teeth that the corners are chipping off, these chips just go around in the diff and just add to the murder going on in the casing, i think 8th scale diffs and hybrid bulks are on my next shopping list from monster,
i trust the teeth are cut correctly on these larger 8th scale gears??
thanks all...

[George16]

What you're seeing are the results of the pinion moving in and out (too much play) of the mesh. That's why it's so important to shim these diffs in order to attain the minimum contact patch (at least 80%). Shim them properly and you'll be good to go.

Anyway, I still have to destroy the stock nitro diffs on my converted revo. I shimmed them nicely and it's still able to withstand running on 5S with my Castle 2200Kv motor. The rest of my trucks (buggy, truggy, supermaxx, gmaxx, and predator use 1/8 scale diffs).

[JERRY2KONE]

Lito hit it right on the head. Your pinion gear was not shimmed in correctly to increase the contact area between the two gears. Plus are you using plastic casings? That can also give you flex in your diff which will cause early wear on your gears. Most of the guys in here run the 1/8 scale gears in their setups just because they are made heavier, stronger, and seem to be better machined in general. Still you can make the stock type gears work if you shim them correctly. There have been plenty of threads posted eluding to this fact and showing exactly how to do this.

hi all...yer i see what your saying the larger gear is moving away from the pinion due to too much power haha. but i shimmed the pinion and its still quite well adjusted. must have movement else where. yes i am still running plastic cases and yes i know about flex on those (had a xtm mammoth st) . i have got ally fastlane bulks tho so it should be fine but i will re-assemble and check.
thanks all...

[redshift]

Some diehard Maxxers just won't admit flaws lol. Chris I have at least 3 pinions that are in worse shape than those, same thing, angular contact is just off, plain and simple. And the rear edge of the teeth is razor sharp, fronts are more or less untouched.

That, combined with excessive pinion 'rock' from undersized bearings that are also too close together. Shimming will not fix this, you have to consider at least the pinions as expendable. My spurs actuallly have never shown wear, they are significantly harder than the pinion. Which of course makes them somewhat brittle, I've seen more than one spur chunk itself. Just strange that ONLY my pinion gets whooped.

I have tried shimming, and it only makes the gear contact crunchier, that's both with spool, and diff. The RRP ring/pinion were supposed to be better, but they still cant overcome the rock issue. One of these RC co's needs to make a physically larger diff to tolerate the stress, or at the least a little longer pinion shaft for better bearing spacing.

[JERRY2KONE]

[QUOTE=redshift;345090]Some diehard Maxxers just won't admit flaws lol.

Flaws? What flaws? We don't have no stinking flaws.

If you try to setup a big block V-8 into a VW bug with the original drivetrain things are going to get broke plain and simple. If the drivetrain matches up with the powerplant things will run great. If not then the operator is doing something wrong, or your setup is flawed.

hi all...well your both right. firstly to make a precision bevel gear is a costly business with lots of expensive tooling, plus the fact the smaller you go the harder it is to produce, so redshift is right the gears are flawed they are not cut with multiple passes (as the correct procedure) they are a compromise between a correct cut and a cost effective gear. so cash rules there ...

also jerry is right that these gears where never designed to take a mm combo on 6s...

so you will need a bigger gear to take the extra power brushless will give out.
my personal experience is although these were shimmed it did noting to prevent chipping and wear. yes i run plastic cases but they are held with ally bulks so there should be no movement... but there is, i found the ally bulks have worn over the past few years and so have the cases,
fitting new cases still did not solve this as there is still a 1-2mm gap between each side of the diff casing.
this will be taken up by the expanding gears under power. so yes the gears are moving apart under power in this case.
so hybrid bulks are the solution with 8th diffs fitted to them...

bye all...

[redshift]

[QUOTE=JERRY2KONE;345124]

Originally Posted by redshift

Some diehard Maxxers just won't admit flaws lol.

Flaws? What flaws? We don't have no stinking flaws.

If you try to setup a big block V-8 into a VW bug with the original drivetrain things are going to get broke plain and simple. If the drivetrain matches up with the powerplant things will run great. If not then the operator is doing something wrong, or your setup is flawed.

Yeah, like grabbin too much throttle... I agree with all that Jerry, except Traxxas has at least two 6S capable rigs on the market. The ERBE and the 3908 BL Maxx. The 3905 diff cup was a decent improvement over the 3906, but they have yet to address the ring and pinion.

I'm tearing mine up with pussy 4S/9XL "power" haha.. what these things must look like after about a minute on 6S........

[JERRY2KONE]

Yeah, like grabbin too much throttle... I agree with all that Jerry, except Traxxas has at least two 6S capable rigs on the market. The ERBE and the 3908 BL Maxx. The 3905 diff cup was a decent improvement over the 3906, but they have yet to address the ring and pinion.

I'm tearing mine up with pussy 4S/9XL "power" haha.. what these things must look like after about a minute on 6S........[/QUOTE]

Oh I agree with you Redshift. The issues I have are with the poor quality that Traxxas and all the rest of the manufacturers are providing in these RTR rigs. It does not take a rocket scientist to figure out that the ring & pinion systems they are putting into their vehicles is subquality in design and material. I guess it is like most of the mechanical stuff throughout history. The manufacturers purposely build inferior stuff into the vehicles just to rake in the money on after market repair parts or upgrades that should have been part of the original design in the first place. It is disgusting how poor some of this stuff really is. Why can't one honest manufacturer put together the perfect vehicle and rake in the money on the merits of such a piece of craftsmanship. Sure the average Joe would not know the difference, but the majority of us diehard R/C hobbiests will revel in the support. To build any really good R/C vehicle you have to buy the rig from one guy, order the drivetrain from someone else, and the motor from another, and the ESC from someone altogether different. It is just plain stupid the way these guys think from the manufacturing point. These are not full size killing machines with rediculous Gov safety regs to uphold. They are higher priced toys for us big kids. And sure there is a learning curve for the younger croud, but that is just the way life is. Being a good mechanic is not a birth given gift for most, it is a learned skill.

hi all...totally agree guy's, ive allways said nearly all manufacturers make bare minimum products. but to last longer than 5 mins hard use they need x2 what you had spent for a mega list of upgrades.
my girl bought me a rc heli for xmas and ive spent the last month trying to learn to fly with a gyro problem on my heli, got pi#/ed off with it and sent it back for repair or refund, whichever.
and the problem is that most of the electronic stuff we buy today is made in countrys where there is unskilled cheap labour and there are no standards to which products are being made to.
again its all down to money.
i dont know about your country but the u.k needs to think really hard about all the stuff(c@ap) we import, we should be making that stuff to keep the cash in the u.k to a good standard.

ok sorry ive finnished my rant now bye all.

[suicideneil]

There was a time when alot of stuff had 'Made in England' stamped on it; those times are saddy over. It like you said; money- cheaper to make stuff overseas as the labour is cheaper & quality is 'good enough' most of the time.