Better diffs for the 3905
 

I tried to search, but didn't find info about this subject - many threads for the older 3906 though.

So, I'm having a decent BL setup for the new E-Maxx 3905 including LMT 1940-7, MGM ComPro 12018-3 and 8000mAh lipos for 4S, 5S or 6S setup.
I'm looking information/help for upgrading the differentials - something that wouldn't cost a million (200$ max.), don't need major modifications and would be a bit durable than the original diffs.
Links to needed parts/part numbers would be greatly appreciated.

I guess you can use the same upgrades as for the 3906. Some Maximizer diff cups with Robinson gears should be able to stand up to the power, and then mount them in some alu housings.

Have you run the stock diffs with the brushless setup yet?

The bellow links helped me a lot with my diff up grades... I hope they'll help you too.

http://www.rc-monster.com/forum/showthread.php?t=9153

http://www.rc-monster.com/forum/show...=hv+conversion

http://www.rc-monster.com/proddetail...d=RCMdiffshaft

http://www3.towerhobbies.com/cgi-bin...?&I=LXJBE9&P=M

The 16.8 diffs are supposed to be stronger than the older diffs, even stronger than the 4 screw diffs that came on the 3.3. I would try them first and if they don't hold up, replace them with UE diffs.

You can stay within you budget with used UE diffs - check ebay, look for seller named billytrucks123.

I use the UE 8-spider. Not cheap, but have never looked back since...

Yes, I have run the truck with this setup. Even had a spool in the rear, but that seemed to be a bad idea...

http://janezki.pp.fi/grfx/maxx_3905/...020592_640.jpg

http://janezki.pp.fi/grfx/maxx_3905/...020593_640.jpg

http://janezki.pp.fi/grfx/maxx_3905/..._twist_640.jpg

And all of the above only with 4S and on snow.

Few teeth were also chipped from the ring gear, so I swapped the front diff (which was as new) to rear and vice versa.

The 3905 diffs are supposed to be quite a bit stronger than those with the 3906, so maybe I'll just order new pinion/ring gear set for the other diff and wait and see how much the stock diffs can handle.

For the moment only real problem are the center driveshafts - broke two of the fronts only today... :oops:
They are out of stock from almost everwhere I have looked, but fortunately one can be made out of a 3.3 plastic driveshaft.

I've seen Kershaw Designs is making steel shafts, but the company is not known to me.
The price isn't too bad, dunno about shipping to Scandinavia though.

Kershaw is okay- think RCM in a shed, with not so many cool tools to use....

I love my UE ultralite cases with HB 1/8 buggy diffs- works out cheaper than using the UE 6 spider diffs (HB diffs are 6 spider too).

If you do try to repair your stock diffs, make sure they are shimmed. I have the older Emaxx and they didn't shim those diffs, kinda doubt they are shimming the new ones either - takes too much time.

If the pinion is spaced too far away from the ring, no amount of strength is going to prevent them from getting stripped. With you loosing ring gear teeth, sure sounds like a shim prob (lack of)??

Aluminum bulkheads may help. And shimming is a must. Ant reason you swaped uot the stock sliding driveshafts for cvds?

Neil, I almost fell out of my chair laughing about the RCM in a shed comment! That was funny. Dan at kershaw does a decent job, but it usually takes a while for him to ship stuff.

From what I gather the 3905 diffs are the same as the ones in a revo so maybe u can find some revo upgrades to use? I have an e-revo and am still running stock diffs but am currently twisting the output shafts on the tranny, two so far both going to the rear. First one was what came in the Gmaxx tranny I bought and I ordered a hardened alum. one and snapped that in about 2 minutes! Thought the first was steel but it had been replaced w/ the aluminum already. Ordered a steel one and gonna give that a try, if I still have problems I'm gonna go to the plastic center shafts (with some creativity and mixing of 3905 and revo parts) I'm sure I'll get this problem solved! BL has massive amountsw of power and will break parts that nitro won't bother!!!LOL

Duster_360: Yes, I shimmed the stock diffs when I opened them. The teeth have better contact now.

lincpimp: CVD's for two reasons mainly, durability and space for the OFNA 9.5 shocks.

E-Revonut: I've studied the exploded views and there are some minor differences in the diffs, but it shouldn't be impossible to use Revo stuff in a creative way... :smile:

If you want a set and forget diff, i advice you to use the FLM 1/8th bulkless with hotbodies diffs. You can use them with output shafts instead of cups, so you can use the excisting 3.3 spec driveshafts.

Both are available from Mike's store.

A spool isn't helping a high speed truck (such as 5/6S) running stable at straights.

The maximizer cups and integy housings are nice too, but they are not tweakable with diff-oil so you are rather limited in your choice of slip.

They also don't offer the strength that the 1/8th conversion will give you.

The 1/8th bulkless also replaces another weak link in the design; the bulks. they tend to break sooner or later. (at the shocktowers or where the bulk is mounted onto the chassis)

I'm building (slowly it seems...work) an flm Emaxx running a 125b, 8XL on 6S a123s. I chose to go with the flm hybrids with 1/8th diffs (the ones sold to go in UE diffs) cause I didn't want trouble. I'm using UE TI centers, but went with RCM output shafts so I could run 3.3 cvds with the GorillaMax suspension I bought.

I've built several sets of trx based diffs using flm diff cups (they're cheaper and I like the guarantee) with the modded ring gear and 3mm screws. I put them in the cheapest alum cases I can find - I've used gpm, integy and GA (ebay). The alum case is a must to keep them from twisting which lets ring pull away from pinion and causes it to eventually strip. This is an intermediate solution - they've held on any nitro I've put them with, up to a 28 with no probs. BL makes so much more torque, I'm not sure how long these will last, may depend on gearing to some extent.

I'm getting ready to try a set of these in my Emaxx (older one) - the stockers are gone. I run a pr of brushed S600 motors in this one on 14cells. Its enough that I can twist the plastic axle shafts easily. I 'm hoping these diffs will be strong enough.