E MAxx diffs
 

Hey guys, I bought a set of E Maxx 3908 diffs for my big block Maxx. I have done some research and found that I will need longer pinion shafts, so I bought some for a 4909 T Maxx so I can use my dogbone center rear shaft with a better fit. The diffs I bought are complete and removed from a new RTR E Maxx. I do have a few questions about these diffs though. First do they need shimming or should they be alright in stock form? Also, are these diffs the sealed ones and if so, do they come with oil in them already? Also, what weight for the front and back is a good starting point if I decide to tune them in?

Yes they are sealed diffs. I would recommend shimming to get the most life out of them, they'll last much longer. For diff fluid, I'd recommend a 10k - 50k front and rear, the thicker you go the of a "posi track" you create or the more "drive" you create. Hope it helps!

Yes that did help, thank you! I'm thinking I'll start on the lighter side with 10k fluid and go from there. This will actually be my first set of sealed diffs ever, so I'm actually used to less posi effect.

I've heard of shimming the diffs, but I'm not sure how it is done really. Do you just put washers on the pinion shaft or on the output shafts too? Also, does anybody make a shim kit with varying thicknesses of washers?

i picked up shims from lowes, but ive used shims from team associated before and they come in different sizes

Hmmm I have a clutch bell shim kit that could possibly work. There are many different washers in it. Do you have a part number for a kit? I can't seem to find them, or what size washers are needed?

The diffs come with 30k fluid in them. Personally I liked my big block Maxx with the 30k so I'd at least try them out with that fluid.

As for shimming the diffs, the plastic cases fit the diffs pretty tight on the output side. So you really only need to shim the pinion. Ditch the Teflon washer and get some 8x6x.2mm shims to fit on the pinion. This size shim will only contact the inner race of the bearing and not hit the bearing shielding. This size can also be used to shim the spider gears if needed but the Emaxx diffs usually don't have too much play. You want to place them between the pinion gear and the first bearing. Assemble the diff including the drive cup or center shaft. Then pull out slightly on the pinion drive cup to make sure it's up against the bearing and turn to check the mesh. Once you're satisfied with the pinion depth, see if you can push the pinion in. If you can push the pinion in this obviously changes the pinion depth and mesh. Add shims behind the drive cup on the assembled diff until you can't push it in anymore.

Excellent info, thanks a lot! 30K seems plenty thick enough for me. So basically the pinion is the only thing to worry about. That's easy enough, I've gotta swap it out anyways so that's as convenient as can be. Do hardware stores carry washers of that size or do I need to go to the LHS or order some?

30k is like water in a maxx. I run 100k in my maxx with 1/8 buggy diffs, and 500k in my maxx with stock diffs.

Wow, that's some thick oil, sounds more like axle grease! I'm used to old school un-sealed diffs lubed lightly with automotive grease. Whenever i re lubed them, they only got half filled or so. This will be my first set of sealed diffs on a truck ever, and I don't know how this truck will handle really, either. I've driven it with it's current chassis set up, but it was powered by a TRX 2.5R. It is now powered by an LRP .28 and weighs a lot more too so I can only imagine it will be kind of sluggish compared to a stock chassis set up. Still, happy to hear everyone's set ups, it gives me an idea of what the average weights used are. Is yours a big block, too?

That weights MaxxGabeiel listed are for a more powerful brushless setup, I believe 6s in his case. Everybody likes something a little different and the weight also depends on the amount of power, the tires and the surface being run on. The truck is going to feel different going from grease to 30k, either way I think it's a good starting point for a big block. If you notice you're ballooning tires in the turns you can always increase the weight of the fluid.

I'm not sure where exactly to get the shims, I doubt a hardware store has them as .2mm thick is really thin. Try searching tower for them, McMaster Carr, etc.

You have to change out diff oil every once in a while anyways so start with 30k, and try 100k next time and see which you prefer. Im willing to bet you will like the heavier weight a lot more, but everyone is different.

For shims I usually just figure out what size I need and then get them from an rc parts seller with cheap prices and cheap shipping like omnihobby. Brands dont matter, just sizes.

How to shim a stock diff
http://farm9.staticflickr.com/8407/8...99390c86_z.jpg

Good advice guys, I'll go that route. I'll be watching for tire ballooning and power unload while accelerating through corners quite closely after the break in. Kind of like shock oil I guess, I've got a buddy that runs 80 weight with stock springs in all 8 shocks on his T Maxx. I've tried it in mine, and I don't like that heavy of oil with light springs. To each their own I suppose. I found some 6x8x.2mm shims on Ebay, 10 for like $6 from Omni. How often do you usually change it for regular maintenance? With the unsealed diffs I usually re lubed them once a year during my annual winter tear down, or after 1 gallon burned, whichever came first.

That's awesomely perfect! Thanks a lot for that, cheers:)

I do the same with my rigs, they all get a winter tear down. Every gallon is excessive, when new you can get 2 gallons through before they'll need any fluid added to them. I generally put all new seals on my diffs every other year during winter teardown.

Yeah a good winter tear down is a great time killer, good time to upgrade stuff if you want to as well. Wow, 2 gallons I would have never thought they could go that long between tear downs, this upgrade gets better and better.

I got the diffs in the mail today! They were quite cold sitting in the mail box, but after playing with them a little I noticed the pinion slop they have. I never really noticed that before in diffs. There is a slight bit of fluid around the pinion bearing, is there fluid in the housing too or is that just some grease slipping past the o ring? I'm still waiting on the shims to come, but I got the 4909 pinions already. I'll post some pics of the size difference in size between the E Maxx pinions and the T Maxx ones when I get it apart.

Hey guys, posted this as an update on my big block build thread, but thought I'd post it here too for those seeking info in the future. I got my 6x8x.2mm shims and set to work on the diffs. I put the 4909 T Maxx pinions in, and started with 1 shim. To my surprise, 1 shim made the diffs too tight. I removed it and re assembled the diff. With no shims it actually felt fine. Just a hair of play in and out on the pinion, and almost no slop felt when I turned it and held the ouput shafts still. It went this way for both of the new diffs. In comparison, my old Pro .15 diffs that came out of the truck had a fair amount of play and slop. Strange, it seems I got a really tight set of diffs:D I did have to shim the outside quite a bit though. The 4909 pinions are a few mm longer than the E Maxx ones are. I ended up getting some 6mm ID washers from the hardware store and using those in conjunction with my diff shims. I used the smaller diff shims against the outer pinion bearings to space the larger washers away from the bearing. Without the smaller shims, the larger washers would contact the outer edge of the bearing instead of just the inner rotating part. With everything tight on the outside, the gears still felt quite nice so I'll leave it like this and check it out next winter to see if they wear in at all and need shimming then.

Here are a few pics, one is of the E Maxx diff with the 4909 pinion installed next to the old Pro .15 one, there's also a pic of the longer 4909 pinion next to the E Maxx one and of the shimming done on the outside of the pinion. Good amount of info here for anybody looking to upgrade a non extended Maxx to the newer style sealed diffs. What I did allows the use of any old style center shafts and requires no grinding on them for fitting. This mod also applies to the newer 4907/4908 3.3 T Maxx diffs as they share the same exact pinion shaft as the E Maxx diffs do. Great and fairly inexpensive upgrade for anybody using the older style un-sealed diffs. The E Maxx diffs fit perfectly in my bulkheads, too. The oil in the new diffs makes the diffs feel more like a posi diff than the old grease filled ones did, so I think it will help a lot in cornering and off road driving too!