Kraton EXB Rear Diff Discovery ---UPDATES!!

[Yas]

I don't have the gears in person so please correct me if this is incorrect, but I really don't think shimming up these gears is going to help!

As @jym73 said, the shims sit on the inner diameter of the gear, which isn't even a flush surface. Shims are circular in shape, yet this gear is shaped as a cross where it comes in contact with the shims. Under torque, the gear will twist at an angle because the gear has no support on it's outer diameter, which will result in a poor mesh and cause it to chip. This is surely a design flaw ??

In reality what is needed is a flush gear of which shims will fully contact the gear's flat surface area. Or just add the LS plates to pack up the area it leaves when left out and have an LSD in the rear instead

Image courtesy of @Cirasa

 

[jym73]

I don't have the gears in person so please correct me if this is incorrect, but I really don't think shimming up these gears is going to help!

As @jym73 said, the shims sit on the inner diameter of the gear, which isn't even a flush surface. Shims are circular in shape, yet this gear is shaped as a cross where it comes in contact with the shims. Under torque, the gear will twist at an angle because the gear has no support on it's outer diameter, which will result in a poor mesh and cause it to chip. This is surely a design flaw ??

In reality what is needed is a flush gear of which shims will fully contact the gear's flat surface area. Or just add the LS plates to pack up the area it leaves when left out and have an LSD in the rear instead

Image courtesy of @Cirasa

View attachment 92683

Imho the side/sun gear can't twist that much at an angle because it goes on a pretty big axle. The EXB outdrive axle is bigger than the RTR, as for the pin which drive the gear. But, with the tolerance of the hole in the gear plus the tolerance of the axle in the diff. case guide, yes, the gear can slightly move maybe.

What would worry me more is when i see that the side gear can break sometime on the RTR and when i see the small amount of material to drive the gear by the pin, it look more weak than the RTR and look like it would break more easily.

 

[Buckwhea7]

Unfortunately, the active diff plates (310984) are sold out worldwide... I just chewed up my rear diff on the EXB. First run! Pretty lame! I wasn't doing any standing backflips, donuts, self-righting, or landing on power. Literally just cruising around a gravel lot, maybe ten minutes. If the shims won't fix it and the LSD's are sold out for god knows how long, what's the answer here? There must be something. Duperbash and RC Dude81 aren't having problems, and they are bashing 100 times harder than I just was. Please advise.

 

[JDarby05]

Unfortunately, the active diff plates (310984) are sold out worldwide... I just chewed up my rear diff on the EXB. First run! Pretty lame! I wasn't doing any standing backflips, donuts, self-righting, or landing on power. Literally just cruising around a gravel lot, maybe ten minutes. If the shims won't fix it and the LSD's are sold out for god knows how long, what's the answer here? There must be something. Duperbash and RC Dude81 aren't having problems, and they are bashing 100 times harder than I just was. Please advise.

I had trouble finding some as well. I managed to find one left in stock online and after i purchased it. It switched to out of stock but it has been a hit or miss with the same situations on different sites. I might get the item or an email saying... were sorry but this item is sold out and there was an stock error etc etc lol. Sucks when that happens

 

[jondilly1974]

You can always swap in the V4 diff and pinion. Just make sure to shim the ring gear side bearing to make it tight.

 

[razorrc]

I understand what you are saying but if they know there is varying degree why do they all end up with .7 so far and not some with .8 and some with .7. Can you share what is going on with your front. It might help someone avoid a huge problem. The fronts show one of each shim so hows is yours different? Also what is the third shim you are taking about ordering is it a external shim? most people want to take care of this so you don’t end up spending money and wasting time so please elaborate and help us.

Also yes is only .1 but again thats on each side and they mesh the same gear assembly. Anyone who knows how finicky these dang diffs are knows leaving out an entire .2 shim CAN make the difference. Maybe not every single time but yes .2 in a diff like this with huge power motors being installed does make a difference. I think if it didn’t make a difference they would not have released a statement about it on Facebook I think they would just tell you to shim as needed. FYI I normally don’t post much but this has turned into a pain for a lot of people who just spend some good money on a new truck so this is important
Also the .7 OR .8 is something he posted after the fact on Facebook. If you look in the manual that comes in the box it specifically shows the 3 shims of two different part numbers that equal up to .8. It doesn’t say Anything about different combos or anything

My point was more a commentary that what's printed in the manual and what a car actually needs can be different, and I don't get mad at the manufacturer for that. It's really hard to produce plastics to within 0.1mm of spec at a low cost. That's why there are shims -- shim as needed. I'm not disagreeing that it needs shims or that 0.1mm doesn't make a difference. Now maybe they could've put in some verbiage like "shim as needed" in the manual (that's what other manufacturers say), but quite honestly the average Arrma buyer can't be bothered and wouldn't even know what to do with that anyway. The last 4 kits I built had to be shimmed differently than what the manual said. That's just... the nature of the hobby.

My Kraton 4S had the rear diff shimmed too tight. That's the way the manual says it should be built, but mine definitely needed shimming to the other side. No big deal, these things were designed to be shimmed as needed, not YOU MUST FOLLOW THE MANUAL.

My EXB front diff has too much side to side play in the whole diff externally. It needs an external shim (12x15 or whatever), that's the third one I ordered.

 

[Buckwhea7]

You can always swap in the V4 diff and pinion. Just make sure to shim the ring gear side bearing to make it tight.

Thanks dude! Killer suggestion! I didn't think of that. I'll do that until they figure out the EXB BS. I emailed HH. I saw on YT, some people that got ahold of HH with the same problem are being sent an entire new LSD diff to replace. Hopefully, that will be my case, as HH seems to be going that route for the fix now. If the LSD fixes the problem with the rear diff, that will be awesome! My only question is, is there any downside to running full LSD? Handling? If that's key, why didn't they come that way to begin with?

 

[razorrc]

Thanks dude! Killer suggestion! I didn't think of that. I'll do that until they figure out the EXB BS. I emailed HH. I saw on YT, some people that got ahold of HH with the same problem are being sent an entire new LSD diff to replace. Hopefully, that will be my case, as HH seems to be going that route for the fix now. If the LSD fixes the problem with the rear diff, that will be awesome! My only question is, is there any downside to running full LSD? Handling? If that's key, why didn't they come that way to begin with?

The diffs are pretty simple. Thicker fluid/LSD plates don't allow the left/right wheels to turn at different speeds as much. This is good if you're trying to go straight. It's bad if you're trying to turn. When your car goes around a corner, the outside wheel has to spin faster than the inside wheel because it's following a longer arc around the corner (has to travel further in the same amount of time). This is what a differential is for.

 

[Yas]

My only question is, is there any downside to running full LSD? Handling? If that's key, why didn't they come that way to begin with?

Using an LSD in the rear whilst under throttle at lower speeds and low rear wheel traction will make it more likely for the car to oversteer and spin out whilst cornering

Using an LSD in the rear whilst under throttle at higher speeds and high rear wheel traction will make it more likely for the car to understeer and continue straight whilst cornering

 

[Adawg]

Razor I totally hear you. Honesty I’m not that upset about it but I don’t wanna sugar coat it and I want to help people fix it before it actually damages something. It’s become more of a mission which is why I’m posting these pictures. I already know what I’m gonna do but I want others to see. That’s what this is about

as for the comment about the shims not pushing the sun gear because it’s not flat on back that is completely wrong. If you look at the back of all sun gears they have a cut out for the pin anyway. That’s what the discs go into. As for them not pushing the sun gear into the planetary gears check out this picture. Again the first 2 out of 3 discs for the lsd sit into the gear and don’t add any thickness to the sun gear and have no effect on mesh. If you look at the other gear you can see the shims ride on top of it and add thickness which is why you need the correct shimming to get the correct mesh. This I’m 100% sure please just look at the pictures

 

[Jimbobjr]

The more I read about these diff the more silly they seem. Nearly 1mm of shims to make up for that assembly is hilarious. They should’ve just made an insert for the open one or redisgn it. All those little plates, what are they thinking? Guys are going to be hosing these things up left and right and then won’t be able to get them back together. Horizon better hire some more help for the service phone staff...wait til they start putting these in the rtr’s...

 

[OLIVERH]

I can’t decide weather to cancel my exb order or on it’s due here in the UK on the 24th August, but it will be my only rc so don’t want the rear diff blowing out on the first run then be waiting ages for a fix ?‍

 

[Lingerfelter6]

Razor I totally hear you. Honesty I’m not that upset about it but I don’t wanna sugar coat it and I want to help people fix it before it actually damages something. It’s become more of a mission which is why I’m posting these pictures. I already know what I’m gonna do but I want others to see. That’s what this is about

as for the comment about the shims not pushing the sun gear because it’s not flat on back that is completely wrong. If you look at the back of all sun gears they have a cut out for the pin anyway. That’s what the discs go into. As for them not pushing the sun gear into the planetary gears check out this picture. Again the first 2 out of 3 discs for the lsd sit into the gear and don’t add any thickness to the sun gear and have no effect on mesh. If you look at the other gear you can see the shims ride on top of it and add thickness which is why you need the correct shimming to get the correct mesh. This I’m 100% sure please just look at the picturesView attachment 92704View attachment 92705View attachment 92706

Thank you, I tried to explain this, but it upset some ppl. Maybe I didnt do it right. That said, there may be a problem with the space. If you were to place the shims on table top, with the sun gear at the top of stack (pretty much flipped over from your pic) and apply pressure to one end of sun gear, does it move? this would represent a situation when fully assembled, and one planetary gear exerts more force on the sun gear. The opposing side from where you apply the pressure, does it lift?

 

[BashingBrian]

They should’ve just made an insert for the open one or redisgn it. All those little plates, what are they thinking?

@Jimbobjr .. I'll place my pre-order with you now for when you make an insert..???
Seriously though, they should have just made the rear diff differently with a solid spacer or something..?

 

[Adawg]

Thank you, I tried to explain this, but it upset some ppl. Maybe I didnt do it right. That said, there may be a problem with the space. If you were to place the shims on table top, with the sun gear at the top of stack (pretty much flipped over from your pic) and apply pressure to one end of sun gear, does it move? this would represent a situation when fully assembled, and one planetary gear exerts more force on the sun gear. The opposing side from where you apply the pressure, does it lift?

exaclty you are 100% right. To be honest I’ve been a member for years and haven’t posted much but this got my passion flowing. It’s more about trying to convey what I’m looking at right in front of my face. It’s logical, makes sense, and you can see if.

you guys are right they should have made a insert or something.

I plan on trying .8 on each side and probably also try .8 on one side and .9 on the other. I’m curious how it will feel compared to the front. I might clean all the internals thoroughly and you can basically shim one side and fully assemble it but don’t put the top sun gear in and leave it open. Then use a caliper and measure how high the planetary gear sits in the case and compare the rear diff to the lsd diff. Whatever the difference is multiply by two and you will see how close they would be to each other assembled. Hope that makes sense.

 

[Rcproponent]

And of course, now the parts for the “fix” are unavailable ANYWHERE ??‍??‍???

 

[Adawg]

So for me I want to rebuild a open diff. These are the parts I needed after messing up the sun gear

ARA709059 - .3mm shim
ARA709060 - .2mm shim
ARA310985 - planetary gear set

if you wanna do lsd then you need to add the lsd pack set to this. Please check for yourself don’t just order this stuff. Also make sure you only damaged the sun/ planet gear set.

 

[Yas]

Razor I totally hear you. Honesty I’m not that upset about it but I don’t wanna sugar coat it and I want to help people fix it before it actually damages something. It’s become more of a mission which is why I’m posting these pictures. I already know what I’m gonna do but I want others to see. That’s what this is about

as for the comment about the shims not pushing the sun gear because it’s not flat on back that is completely wrong. If you look at the back of all sun gears they have a cut out for the pin anyway. That’s what the discs go into. As for them not pushing the sun gear into the planetary gears check out this picture. Again the first 2 out of 3 discs for the lsd sit into the gear and don’t add any thickness to the sun gear and have no effect on mesh. If you look at the other gear you can see the shims ride on top of it and add thickness which is why you need the correct shimming to get the correct mesh. This I’m 100% sure please just look at the picturesView attachment 92704View attachment 92705View attachment 92706

?‍ tune the shims if you think it will solve the problem (I'm positive it won't!) Your pictures are helpful because it confirms that the shims don't cover the surface area of the gear, like the LS plates do

There's a reason why HH are sending out LSD diffs as replacements, instead of "correctly" shimmed open diffs!

 

[SrC]

Drove my truck for about ten minutes on 4s and the diff was destroyed. Took it apart and I had six of the .2 mm shims.
Arrma must not drug test and gets that labor on the cheap cheap.

QC gets watered down during later production runs. Volume becomes more critical. I say HH should build a 30 Acre ISO production facility here in the States for Arrma-RC manufacturing.
If SAE AS9100 Aerospace standards were used we would be paying 20 times+$$$ for the price for our Arrma Toys. And the diffs would never break. They could even be used on Mars Lunar Rovers. Imagine Big Air on Mars???

 

[SrC]

Has anyone with an EXB considered/ experimented with going back to Standard Open 6S diffs?? Does the limited slip at Front and Center really make a difference? The LS diffs appear more robust. The design is nice. Is the execution? Are they that much better?
Anyone?