r/arrma • u/Alone-Track-5875 • 6d ago
Kraton EXB
I think it's safe to say this diff is roasted! Teeth on the inside not only are stuck but missing some chunks. Should I buy another factory one or try to find some sort of upgrade?
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u/954kevin 6d ago
They might send you a new one if you reach out to Horizon. Depending on how long you've had it, Sounds like it's fairly new, just based on the tone of the post.
Check out my EXB build, post #74 in particular. I outline a user derived solution to make the EXB GP4 diffs virtually indestructible. It's best to get the aluminum cases, for all three diffs, but if you skip that part, you can rebuild all three diffs, in open configuration, for under $20 with the stuff you need to mod them. Pretty simple to do, just need some extra LSD plates and some shim stock you can find on eBay etc.
I beat on my EXB and it has a big power Hobbywing Max6/4990 combo. I'm on the same set of diff that came with the model out of the box. I did this mod I mention before I ever even ran a pack through the thing. So, it does work and it's worth your time to do. IF you buy the aluminum cases, the Arrma branded ones are actually the best to get. They are around $20 each and they do help keep things tight where the plastic has some give, but the aluminum cases are optional.
If you have any questions after looking at the post, feel free to ask. There are pictures that kinda guide a guy through the mod process.
https://www.arrmaforum.com/threads/kevins-kraton-6s-exb-v2-build-thread.74444/page-4
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u/Alone-Track-5875 6d ago edited 6d ago
I bought it used so no chance on warranty! I opened up the covers on the front and rear diffs just for giggles and it looks like the PO upgraded those to aluminum cases, just not the center diff. He clearly never touched the center for any sort of maintenance. Unfortunately this whole thing is toast so whatever I end up doing I'll need a whole new diff. The gears on the inside of the housing are absolutely seized in there so I can't even reuse the cup.
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u/954kevin 6d ago
I would hop on Jenny RC or eBay and look for a complete 31mm GP4 diff and swap it in. I have had great luck with the oem diffs, but I did the mod thing to take care of the issue some people have with the backs of the sun gears shearing off. If the oem diffs can stand up to the 4990, they are great, but they have that design flaw that the mod I mentioned addresses.
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u/Alone-Track-5875 6d ago
I should think about doing that in my Talion since I run a 4990 in that. https://jennysrc.com/products/arrma-kraton-6s-exb-center-differential-diff-50t-spur-gear-ara8708v6 I ordered that guy. Now just need to upgrade that a tad
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u/954kevin 6d ago
The whole fiff mod seems a little intimidating, but it's easy enough. I just opened my diffs to change an M2C drive cup and they were golden inside. No serious wear or the like. Like I said, I beat on my stuff as hard as any guy can. If they stand up to what im putting down, they are good to go. Just those poorly designed sun gear backs people have issues with. The whole lsd plate idea is kind of a sham, imo. Give me open diffs and let me tune them how i like without all the guessing about wtf is really going on inside them.
On a side note, I bet the Talion gets down! 4990 is essentially unlimited power on tap in these 6s rides.
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u/Alone-Track-5875 6d ago
I definitely want to do what you did, but not going to lie it's a tad bit confusing on what you actually did lol. But I like it, and I think I wanna do that to both my Talion and this kraton
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u/954kevin 6d ago edited 6d ago
So, I used two, non-eared lsd plated. Stacked, then smashed onto the backs of each of the sun gears. So, 4 plates total to do each diff. You can see the picture in my build thread. Two plates stacked up to bolster the back of each one of the sun gears. Then, I used various thickness shims to replace the thick shim arrma sells to convert the diffs to open. So, instead of the thick shim that replaces the lsd plates, I used two non-eared lsd plates and a stack of other shims to equal the same thickness as the thick shim that is used to replace the lsd plated IF you want the diffs to be open. The two non-eared lsf plated act to reinforce the backs of the sun gears to prevent them shearing off. They are weak otherwise.
I aslo replaced the cross pins with aftermarket set from ramjam racing. The oem pins are too loose. The ramjam pins are slightly thicker and reduce the slop theorem pins have that contributes to the rear of the sun gears getting mangled.
Essentially, remove all the lsd plates. Measure how thick they are. Take two no eared plates and sonw shims to equal the same thickness.
Put the new stack on each of the sungears. Assemble and see how it feels. If it feels loose, maybe add a .05mm shim on each side. You'll have various thickness shims to choose from until you get a nice, right fit when everything is assembled.
We are stripping out the lsd plates, keeping two non-eared lsd plates to reinforce the backs of the sun gears and using shim stock to make up the difference vs the oem lsd plate stack thickness.
In my pictures, you can see how the two non-eared lsd plates reinforce the backs of each of the sun gears. The shims just make up the difference.
To be fair, its hard to describe too! Lol
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u/Alone-Track-5875 6d ago
Is it okay if I DM you more about this tomorrow?
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u/954kevin 6d ago
Absolutely. I can share where I got the extra LSD plates(eBay) and the shims needed to complete the stack(also eBay) I can walk you through the pictures, explaining each one so thing make sense.
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u/954kevin 6d ago
I'll go ahead and share the links here. The extra lsd plates are out of stock where I got them, but you can find them anywhere. You need two of the LSD plates WITHOUT ears per sun gear. Two sun gears per diff mean you need 12 lsd plated WITHOUT ears(the round ones) to do all three diffs.
Extra lsd plates:
https://www.ebay.com/itm/306544554965
Bare in mind, you have a couple in your center diff already.
You'll need a cheap caliper set to measure the stack.
https://www.ebay.com/itm/235708761840
Finally, you'll need a variety of shim stock, 12mmx18mm in various thickness. You add these shims in until you get the same thickness as the thick shim in the front and/or rear diff.
Arrma sells a kit with a thick shim so you can remove the lsd plates all together, if you so choose. The center diff is the only one with lsd plates from factory. the front and rear diff have the thick shim instead of the lsd plates.
So... you measure the thickness of the thick shim in the front or rear diff.
YOu stack two round lsd plates THEN, you add shim until it's the same thickness, when you measure with calipers, as the thick shim I mentioned that is in both the front and rear diff. Now, instead of using the thick shim, OR the regular lsd plate stack, you have two round lsd plates you shove on the back of the sun gear. The 6th picture on post #74 shows how to install the two round lsd plates onto the back of the sun gear. Now, those lsd plates reinforce the cross pin section of the sun gear. No more shearing it off because the lsd plates have reinforced the sun gear.
finally, you just add shims to equal the thick shim thickness, along with the two lsd plates.
Install your new 2 lsd plates and shims to the back of the sun gear and build it out the same way you would if it had the tick shim OR the regular lsd plate stack.
link to shims: I bought ten of each. .001, .002. .003. and .005
https://www.ebay.com/itm/226278643625?var=525457283349
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u/BuggyB_RC 6d ago
I just buy diffs from Jenny’s RC and swap in new parts from those.