Kraton EXB Rear Diff Discovery ---UPDATES!!

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TooTall

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Ok so, while looking to shim rear diff, I realized what might be a contributing factor to why some people have had problems even with 3 shims under each sun gear.

Background Info:

This pic shows the exploded view on Arrma site, notice the diameter of the shims in the diagram, it appears to me it was designed to have 2 shims of the smaller diameter and 1 shim or the larger diameter when you look at it visually.
1596214137920.png

So that would be according to the break out part numbers two ARA709059 and one ARA709060.
Now looking at this part of Jason's post on FB:
1596214306371.png

From that one can conclude that the ARA709060 are 0.2mm shims and the ARA709059 are 0.3mm shims.

From those two diagrams I reason that the initial designer targeted 0.8mm of shims under each sun gear based on drawing visual size and such.

So then I noticed that both part numbers on Arrma and Horizon sites listed the shims as both 0.2mm.
1596214561569.png

So I set out to figure out if it is a typo, so I pulled my rear diff and measured the shims under the ring gear sides sun gear, and determined that the larger diameter shim is the one that is 0.2mm and the smaller diameter shim is 0.3mm.
Therefore this part list should be this:
1596214666368.png


So then I noticed that on both the exploded diagram and on the reference image Jason posted the part numbers were backwards as compared to physical dimensions as compared to the visual representation.
It should be :
1596214834693.png
1596215201436.png

I verified that my rig has two of the larger diameter(0.2mm) and one of the smaller diameter(0.3mm) shims under the sun gear.

So my conclusion is that Arrma somewhere along the line reversed the part numbers and the bill of material then ended up with 0.7mm of shims rather than 0.8mm under each sun gear.

So that variance X 2 for the pair of sun gears, leaves a 0.2mm narrow on correctly assembled diffs based on part numbers.

Does anyone know if that is enough to cause teeth to break? (I'm not an expert on diff shimming.)

So my recommendation is to buy a pack of ARA709060 0.3mm shims and put two of those and one of the larger diameter ARA709059 which should add up to close to 0.8mm of shims (measure each to validate and also test feel of diff without fluid) which is what I believe the Arrma design engineer targeted.

Also to note, I had already ordered and received a pack of ARA709059 and measured it, it was the larger diameter like it should be and it was 0.2mm.

I have notified Arrma (JD) about the part number swaps and he said they will get it updated, he didn't really say if that missing 0.2mm would cause issues, he feels more are failing from the extra shim missing due to QC issues.

Hope this helps some of us and saves us from blowing a diff, I know I will be shooting for the 0.8mm total shims and testing the mesh before filling by feel.

TT



Updates: I rebuilt my rear today using the shims as I suspect the designer meant them to be used, (two 0.3 and one 0.2) for a total 0.8mm under each sun gear. the 0.8mm fits beautifully, and the diff felt perfect both empty and filled.

For the heck of it before filling it, I built it back the way it came to me (two 0.2mm and one 0.3mm) and it felt and sounded a little too loose, so maybe with big power motors it is enough to break tops of teeth off.

I highly recommend everyone build it with 0.8mm.
 
Last edited:
Ok so, while looking to shim rear diff, I realized what might be a contributing factor to why some people have had problems even with 3 shims under each sun gear.

Background Info:

This pic shows the exploded view on Arrma site, notice the diameter of the shims in the diagram, it appears to me it was designed to have 2 shims of the smaller diameter and 1 shim or the larger diameter when you look at it visually.
View attachment 92186
So that would be according to the break out part numbers two ARA709059 and one ARA709060.
Now looking at this part of Jason's post on FB:
View attachment 92187
From that one can conclude that the ARA709060 are 0.2mm shims and the ARA709059 are 0.3mm shims.

From those two diagrams I reason that the initial designer targeted 0.8mm of shims under each sun gear based on drawing visual size and such.

So then I noticed that both part numbers on Arrma and Horizon sites listed the shims as both 0.2mm.
View attachment 92190
So I set out to figure out if it is a typo, so I pulled my rear diff and measured the shims under the ring gear sides sun gear, and determined that the larger diameter shim is the one that is 0.2mm and the smaller diameter shim is 0.3mm.
Therefore this part list should be this:
View attachment 92191

So then I noticed that on both the exploded diagram and on the reference image Jason posted the part numbers were backwards as compared to physical dimensions as compared to the visual representation.
It should be :
View attachment 92192View attachment 92194
I verified that my rig has two of the larger diameter(0.2mm) and one of the smaller diameter(0.3mm) shims under the sun gear.

So my conclusion is that Arrma somewhere along the line reversed the part numbers and the bill of material then ended up with 0.7mm of shims rather than 0.8mm under each sun gear.

So that variance X 2 for the pair of sun gears, leaves a 0.2mm narrow on correctly assembled diffs based on part numbers.

Does anyone know if that is enough to cause teeth to break? (I'm not an expert on diff shimming.)

So my recommendation is to buy a pack of ARA709060 0.3mm shims and put two of those and one of the larger diameter ARA709060 which should add up to close to 0.8mm of shims (measure each to validate and also test feel of diff without fluid) which is what I believe the Arrma design engineer targeted.

Also to note, I had already ordered and received a pack of ARA709059 and measured it, it was the larger diameter like it should be and it was 0.2mm.

I have notified Arrma (JD) about the part number swaps and he said they will get it updated, he didn't really say if that missing 0.2mm would cause issues, he feels more are failing from the extra shim missing due to QC issues.

Hope this helps some of us and saves us from blowing a diff, I know I will be shooting for the 0.8mm total shims and testing the mesh before filling by feel.

TT
Thanks for the write up. I will probably be tearing mine down after a bash today to thicken my fluids anyways. I will measure and verify mine and see if it matches yours. I have some Mugen shims I can add to mine and see if it binds. I will add as many as I can to see what it can take before binding. ??
 
Thanks for the write up. I will probably be tearing mine down after a bash today to thicken my fluids anyways. I will measure and verify mine and see if it matches yours. I have some Mugen shims I can add to mine and see if it binds. I will add as many as I can to see what it can take before binding. ??

Are the mugen ones 6mm hole? I thought they were 5mm.. The outdrive shaft on the exb is 6mm. If so that would be good info to have.
 
Are the mugen ones 6mm hole? I thought they were 5mm.. The outdrive shaft on the exb is 6mm. If so that would be good info to have.
Dang. Never even put that much thought into it. There goes that plan ??‍♂️
 
Added updates after rebuild with 0.8mm.

TT
 
Somebody mentionned this to Jason already, and it seems it is a typo, on the spare bag it is the right thickness.

Capturethick.JPG


60 = 0.2mm and 59 = 0.3mm.
 
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Somebody mentionned this to Jason already, and it seems it is a typo, on the spare bag it is the right thickness.

View attachment 92462

60 = 0.2mm and 59 = 0.3mm.
I mentioned it to him Thursday evening, he said he would get it changed, problem is if you look at the diagram, the smaller diameter shim is shown as 059 and should be 0.3.

059 is actually the larger diameter one and is 0.2 when it comes. (I know I ordered and received them already.)

The 060 is the smaller diameter and it 0.3.

Like I said they reversed the part numbers along the way somewhere, and the assembly used the part number and ended up with 0.7mm instead of the 0.8mm. (that's my theory)

TT
 
I mentioned it to him Thursday evening, he said he would get it changed, problem is if you look at the diagram, the smaller diameter shim is shown as 059 and should be 0.3.

059 is actually the larger diameter one and is 0.2 when it comes. (I know I ordered and received them already.)

The 060 is the smaller diameter and it 0.3.

Like I said they reversed the part numbers along the way somewhere, and the assembly used the part number and ended up with 0.7mm instead of the 0.8mm. (that's my theory)

TT
Brilliant. I have spare exb diff parts on the way... got both sized shims and will be rebuilding once I get em. I have done quite a few short runs in my yard and neighborhood and no issues. I was going to tear down diffs prior to running it but I said meh, and ordered diff parts instead so I could drive it ??
 
Yo this is gooooood stuff. I think your 100% right. Honestly problems have logical answers and it makes total sense. I guess I gotta order shims. Pretty lame but oh well.
 
So there is a good chance the stock diff is dodgy? Absolutely unacceptable afaic... "Bullet-proof" is the whole point of buying this thing(for some of us, it having come out a short time after we'd just bought a V4...)

They're not available here in Europe yet anyway, but I personally would absolutely not buy one if I had to mess with the diffs to get them as they should be out of the box... Not at Horizon pricing..(and its recent abysmal - and yes, IMO inexcusable, regardless of corona - availability and support...)

This car would be far more desirable IMO if it were a kit and €100 cheaper.. Especially if you have to tear it down anyway to fix diffs... :rolleyes:
 
Have anyone seen statements from Arrma if they will fix the ones that haven't been shipped to B2B (LHS I guess)? I really hope this issue will be fixed for the EU preorders that haven't arrived at LHS yet (even though they might already have been packed) but maybe that's not realistic? It annoys me that I am waiting for something that MIGHT be broken at arrival :/ Still keeping my preorder though...
 
Have anyone seen statements from Arrma if they will fix the ones that haven't been shipped to B2B (LHS I guess)? I really hope this issue will be fixed for the EU preorders that haven't arrived at LHS yet (even though they might already have been packed) but maybe that's not realistic? It annoys me that I am waiting for something that MIGHT be broken at arrival :/ Still keeping my preorder though...

Same here, i still keeping my pre-order. I just ordered the slipper plates as they are already available in EU.
Not sure if i read that right. But is a shim missing from the factory? Or would mine be ok until i change fluids?

Many different things can happen. You can have missing shim, you can also have the wrong shim thickness if the shim reference and thickness aren't good...The only fast solution i see for the moment is to buy a set of slipper plates and rebuild the rear diff. with them, it cost only 6$.

Arrma has corrected the shims references and sizes on the website :
https://www.arrma-rc.com/part/ARA709060
https://www.arrma-rc.com/part/ARA709059
 
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Same here, i still keeping my pre-order. I just ordered the slipper plates as they are already available in EU.


Many different things can happen. You can have missing shim, you can also have the wrong shim thickness if the shim reference and thickness aren't good...The only fast solution i see for the moment is to buy a set of slipper plates and rebuild the rear diff. with them, it cost only 6$.

Arrma has corrected the shims references and sizes on the website :
https://www.arrma-rc.com/part/ARA709060
https://www.arrma-rc.com/part/ARA709059

Looks like they corrected the thickness of ARA709060 in the graphic on their website but they still missed the 0.2mm listed under Specifications and INCLUDES.
 
So it’s obvious that since it’s been corrected on the website faster then they can answer a email that it was a issue. Seems like best case scenario you have the 3 shims but you still have the wrong total thickness in the back only. It’s basically a must that you take it apart as soon as possible to shim it. Add 10$ to the truck plus diff oil which is kinda lame but ultimately HAS to be done. When I get my shims I will take mine apart and confirm if I had two or three and I’ll also measure them just to make sure this is a problem with more then a few.
 
So my decision is which would be best long term:

1) V4 rear diff and input
2) Add shims to rear open EXB diff
3) Add LSD plates to rear EXB diff

Are there any other options? How would you rank these personally?

I think I would go 3, 2, 1 myself. ?
 
2,3,1 for me. The diffs with the wider gear and higher angle cut is what makes this car in my opinion. And I want an open rear this is would just spin out with a lsd in the back. Maybe I’m wrong but that’s what I think
 
So my decision is which would be best long term:

1) V4 rear diff and input
2) Add shims to rear open EXB diff
3) Add LSD plates to rear EXB diff

Are there any other options? How would you rank these personally?

I think I would go 3, 2, 1 myself. ?

i will go 3, from the feedbacks it is the more safe solution to have the diff. working without issues.
 
I ordered my shims yesterday so I’ll checking to see what’s going on with it.
i will go 3, from the feedbacks it is the more safe solution to have the diff. working without issues.
It seams that the initial “just see if you have 3 shims” was wrong. The issue is incorrect thickness so even when you have three your off a total of .2 which is equal to missing an entire shim. In another thread someone put it together both ways and could feel a big difference with the correct 3 vs the incorrect 3. I think if you make sure you actually have .8 on each side you will be fine.

I’ve ran 20 hard packs through mine and half were on concrete just beating it and I haven’t had a diff issue and if I can add another .2 I think it would be fine. This is all speculation but this is my personal experience
 
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