Center Diff Destruction (Pics Attached )

[IrieWheeler]

Just buy a new center diff on Jenny's RC. Alternatively buy a new alu center diff with all the parts.
You might want to invest in a dusty cover, would have prevented this.

https://jennysrc.com/collections/ar...fferential-diff-50t-spur-gear-kraton-ar106048

Thanks for that heads-up!

By the way, do you know if there's a specific aluminum cup that can be used for LSD's, do the Arrma and Hot Racing cups contain spider gears, sun gears and LSD plates properly? This diff thing is highly confusing for an autistic n00b. Can LSD plates be used in all aluminum cups or is the composite cup needed? I've seen the exploded view and the LSD plates must take more space than the 2 shims in BLX diffs under the sun gears? Anyway, don't mean to assault you with these questions but a n00b adrift in a sea of Arrma diff details is a bit of a plight. Thanks a lot if you have a spare minute though, cheers.

I use this Arrma option part. Others use Hot Racing.
METAL DIFF CASE (ARA220050) | ARRMA - Designed Fast, Designed Tough (arrma-rc.com)


200k CST or 500k CST. whatever you can find. I prefer 500k/center in my Noto and Kraton 6s. Running larger wheels/tires gets 500k IMHO.
@

I feel bad for asking two people the same question but are these Arrma aluminum cases compatible wit LSD components, is there enough room in the case? Just looking at pictures the aluminum case looks more squat than the composite cases but it's so hard to tell being clueless like I am and havin no reference. Thanks a lot if you get a minute, cheers.

 

[SrC]

EXB LSD/Open 29mm diffs do not have any alloy option cases/cups that I know of yet.
EXB 29mm diffs do not cross over with the RTR diffs in any way. Just that they both fit in a standard 6S bulkhead.
Maybe others will comment on this one.

 

[IrieWheeler]

EXB LSD/Open 29mm diffs do not have any alloy option cases/cups that I know of yet.
LSD diffs do not cross over with the RTR diffs in any way.
Maybe others will comment on this one.

Thanks again Sir! That's what I suspected. I thought "open" diffs were standard BLX/non-limited slip (shims only), but appreciate you clearing-up the cup thing.

 

[SrC]

The Kraton EXB for example uses 3 29mm diffs. But only the front and center are setup as LSD. The rear diff is shimmed to be open. Its just a matter of differnt shims/plates. The RTR older diffs, if yo want to call them that, are all fully open diffs.

 

[Rcproponent]

The metal diff cases are on preorder now...
https://www.horizonhobby.com/product/metal-diff-case-29mm/ARA311061.html

Also note that the newest kraton exb rear diff now has a “shim/spacer” installed in place of “shims” behind the big sun gears. . haven’t had an issue with mine yet and I’ve run it on 8s multiple times.

the new Mojave is supposed to have LSD in all 3 diffs. I have not split my diffs yet so I couldn’t verify that yet.

 

[IrieWheeler]

The Kraton EXB for example uses 3 29mm diffs. But only the front and center are setup as LSD. The rear diff is shimmed to be open. Its just a matter of differnt shims/plates. The RTR older diffs, if yo want to call them that, are all fully open diffs.

Thanks a lot for the help with these nagging questions. I saw a recent YT video of an American gent who bought a Mojave EXB roller and it had an LSD rear diff in it. I wonder if Arrma even knows what it's doing anymore? Cheers!

I do want to praise and recognize the virtuous, all the R/C afficionados who have been maintaining and tolerating their less-than-tolerant diffs in their Arrma cars so we could get to a point whereby fewer people are having problems with the diffs. Thanks Arrma and bless you all!

 

[SrC]

The Mojave EXB does use LSD F/C/R. The Kraton EXB has an open one in the rear. At least the first release batches did. And that rear open diff was an issue because it wasn't shimmed properly without the LSD plates to make it an open design. Maybe Arrma made them all LSD like the Mojave EXB?
The Standard parts for the Kraton EXB lists LSD diffs designated for both front and rear. I guess you could use LSD in the rear. No issue. Depends how you like it. Nothing holding you back from trying it that way.

 

[Rcproponent]

The Mojave EXB does use LDS F/C/R. The Kraton EXB has an open one in the rear. At least the first release batches did. And that rear open diff was an issue because it wasn't shimmed properly without the LSD plates to make it an open design. Maybe Arrma made them all LSD like the Mojave EXB?

The newest exb open diffs have a shim/spacer..

the early fix for this was to put lsd plates or shims in there to stop the thing from exploding. But now they have the spacer in there. Seems to hold up well ??

 

[jkflow]

@oddworld take a very good look at the 2nd picture, your diff mount is now defective as well, the bearing has eaten into it which results in the spur being at an angle, you will need a new one (ARA320499 - CENTER DIFF MOUNT)

Center diff, the alu housing is blank and you will need all diff internals plus spur gear. For Arrma Alu the standard shims are included.
You would there new an existing good diff to be used with the metal housing.

 

[IrieWheeler]

Bought an Arrma Aluminum case in anticipation of rebuilding the rear with it on my soon-to-be-mine Mojave BLX V2 but it would be a nice surprise if I didn't need to as @Rcproponent eluded to.

By the way, any of you making diff pins out of 2.25mm drill blanks like a few on YT? Looks like the stock pins have at least a few thousanths of play in the outdrive and on both sides of the sun gear slot, quite a lot of slop for such a high sheer stress point?

 

[oddworld]

Thanks @jkflow

Where are you looking? Within the second picture, left or right side? Top or bottom?

 

[jkflow]

Tried do draw some line on the spur/pinion, see how that is not square? It is caused by the bearings eating into the diff mount (2nd pic). The damage is on both sides of the bearing, I bet its wobbling.

 

[oddworld]

Thanks. Looks like I need a new metal center diff mount. Would you recommend Arrma, Hot Racing, other? A link would be much appreciated. These parts all start to look alike after awhile.

 

[jkflow]

Stock is ARA320499 - CENTER DIFF MOUNT - plastic
https://www.ebay.com/p/5031770580

HR - Alu
https://hot-racing.com/?partnumber=ANN38A02;c=926

PPS - Alu
https://practicalproto.com/collections/frontpage/products/arrma-v4-6s-blx-differential-mount

I have stock plastic and never had an issue. I'd go with PPS for the bling but all comes down to cost and shipping.

 

[oddworld]

@jkflow you've got eagle eyes to spot that. Appreciate you pointing it out, because as I mentioned - this is my first RC car and I would have probably kept the existing mount in place (causing yet another failure down the line).

I purchased the PPS diff mount. Damn that's shiny.

Question for you. I have 100k diff fluid at home already. Think that's okay for center diff?

 

[SrC]

Tried do draw some line on the spur/pinion, see how that is not square? It is caused by the bearings eating into the diff mount (2nd pic). The damage is on both sides of the bearing, I bet its wobbling.


View attachment 112191


View attachment 112192

Good eye. I see that now also. Clearly there is lateral and radial runout between the spur and pinion. Loose motor mount screws at the chassis can cause this as well. But undue wear results unfortunately if not caught in time. Revamp/renew all related parts. Teardown all inspect and clean. Just needs some TLC. Looks like it has 20+ hours of runtime.

 

[SrC]

Tried do draw some line on the spur/pinion, see how that is not square? It is caused by the bearings eating into the diff mount (2nd pic). The damage is on both sides of the bearing, I bet its wobbling.


View attachment 112191


View attachment 112192

Yeah the heat melted that. Get an alloy upright replacement mount. The bearing is toast also from the heat. Happens like that. Get one from PPS. I like mine. I think its better than the HR version I have also. An alloy top plate over the diff Assy. would make it complete while you are there. Will reduce temps greatly if all is alloy like the motor mount is.

 

[jkflow]

Diff fluids are not an exact science. I run 500k in the middle and 50k/30k fr/r.
Sometime 50/50 but you want to be higher in the middle or you tires will balloon.

 

[oddworld]

See those MX2.8 tires? There's a reason they're threaded with blue 150lb fishing line.... I was seeing a gigantic balloon effect. It was fun for awhile, but tended to make the car flip backwards in a wheelie.

 

[IrieWheeler]

Those PPS motor mounts look skoooooooookkkuuuuuuuuum!

edited because I can use all the dignity I can get these days.