Kraton New Kraton 6s EXB back diff failure on first run

[Crypto]

Today I received my new Kraton 6s exb and not even through a full battery pack the back diff gave out. I notice it was pulling left when giving it power so I stopped and inspected the back diff. I couldn't rotate the back wheels in opposite directions. The diff was locked up. This evening I got the back diff out and found what was wrong. The big gear on part ARA310985 had the pin holders on the back sheered off. The pin and the washers were also damaged a bit.

How could I have done this so fast? I was just ripping up and down the street and trying to do wheelies in the grass. I was using a brand new GenAce 6800 Mah 120c battery. No jumps other than going off the grass and onto the street which is just a small drop. Is flooring it too much for it to handle?

 

[cancelthefuture]

Today I received my new Kraton 6s exb and not even through a full battery pack the back diff gave out. I notice it was pulling left when giving it power so I stopped and inspected the back diff. I couldn't rotate the back wheels in opposite directions. The diff was locked up. This evening I got the back diff out and found what was wrong. The big gear on part ARA310985 had the pin holders on the back sheered off. The pin and the washers were also damaged a bit.

How could I have done this so fast? I was just ripping up and down the street and trying to do wheelies in the grass. I was using a brand new GenAce 6800 Mah 120c battery. No jumps other than going off the grass and onto the street which is just a small drop. Is flooring it too much for it to handle?


View attachment 417954

Reach out to Horizon support, they will probably send you a new diff. I fried my Outcast 6s EXB center diff on one of the first runs and they sent me a new one.

 

[Crypto]

Reach out to Horizon support, they will probably send you a new diff. I fried my Outcast 6s EXB center diff on one of the first runs and they sent me a new one.

Did you change how you drive the Outcast after that? How did the new one hold up?

 

[cancelthefuture]

Did you change how you drive the Outcast after that? How did the new one hold up?

No I didn't change it at all, but I will say it's a good idea to open all the diffs from factory and add more fluid. Arrma has a bad habit of underfilling the differentials which won't help matters. The new one was better but still weaker than I would've hoped. The limited slip diffs in general have given me a lot of headache.

 

[RCbuzz]

Oh wow, that in looks like it skipped right over the sun gear.

This is really frustrating to see, I wish Arrma would use keyed spacers on open configuration diff's.

If you run open, the spacers do not "capture" the sun gear, although, this situation might have been a shimming issue as the pin on the out drive should have have been able to skip over that sun gear.

Check out these threads:

Mojave Thread 'Engineer's Mojave EXB Build'

Dec 12, 2020

Well, I couldn't resist the siren song of another EXB and here she is.

First things first, I went through and checked the differentials - all of them weren't bad, but still needed a top off. I swapped the front diff fluid for 30K, added some 200K to the center diff and rebuilt the rear diff and filled it up with 10K diff fluid.

I realize Arrma's fix was to add the diff plates as well as the large washer - and a solution proposed on this forum was to use 12x18 shims from McMaster-Carr. The were some posts here of how people had snapped off some of the metal ridges on the back of the sun...

• Engineer
• Replies: 7
• Forum: RC Build Logs

• 
• 

Kraton Thread 'Kraton EXB LSD Diff to Open - Thx again to the Members'

May 1, 2022

All I wanted to say was thanks again to the guys here who found a fix to the early Kraton EXB LSD rear diff.

Nothing against LSD diff users this is not a post to convert anyone only to say after months of using their solution the results are still grand for me to date. Thanks to @BashingBrian early solution here. Then shortly later I found @HZRDOS solution taken from something discovered from @Engineer and Hzrdos created here what I still use today.

My rig was purchased in Oct 2021 and it did come with all LSD. I gave all LSD a run with stock oil, changing...

• parcou
• Replies: 20
• Forum: Arrma 6s BLX

• 

 

[hobo]

No I didn't change it at all, but I will say it's a good idea to open all the diffs from factory and add more fluid. Arrma has a bad habit of underfilling the differentials which won't help matters. The new one was better but still weaker than I would've hoped. The limited slip diffs in general have given me a lot of headache.

I had that happen on my talion EXB but it was after a lot of run time. I've been servicing my diffs on my old HPI vorza and the diffs are so much more beefy than the arrma diffs and never had a problem with them for years. been hearing people having a lot of problems with the EXB diffs lately it must be the extra power from the new ESC and maybe the 16t pinion

 

[Barmaleus]

Ouch, looks nasty.
This must never happen with a brand new car, imo. It is time for Arrma to iterate on the diff design and make them beefier.

Also, one of the reasons why I want to move to aluminum diffs - to minimize the risk of blowing the internals. Composite material is not on par with metal.

 

[Crypto]

Ouch, looks nasty.
This must never happen with a brand new car, imo. It is time for Arrma to iterate on the diff design and make them beefier.

Also, one of the reasons why I want to move to aluminum diffs - to minimize the risk of blowing the internals. Composite material is not on par with metal.

I don't know what to do. Upgrade to the aluminum diff casing? Get the limited slip diff plates and use the circle plates to reenforce the sun gear? Chalk it up to I did something stupid? Current plan is to see if Horizon will give me a new diff and I guess see it happens again. If it's this easy to blow a diff I have concerns if the 6s exb is right for me.

 

[Barmaleus]

@Crypto
Sorry, I am not really in a position to give good advice. I got my 6s model about 2 months ago and before that only had 4s experience. Hope more experienced folks chime in. But I really don't think a diff should behave like that. Even if you go full throttle.

If I were you, I'd document what happened, contact Horizon and absolutely expect them to send a new diff.
When you get a new diff from them (imo, they MUST send a new one), do take some time to open it + the other 2 diffs and check the amount of oil in them. My 4s model had outrageously little oil inside and I was happy I opened them and topped up before the first bash.
My 6s Kraton had an OK amount of oil, but I still added some in all 3 diffs before doing the first run.

My 5c.

 

[Neelis]

I don't know what to do. Upgrade to the aluminum diff casing? Get the limited slip diff plates and use the circle plates to reenforce the sun gear? Chalk it up to I did something stupid? Current plan is to see if Horizon will give me a new diff and I guess see it happens again. If it's this easy to blow a diff I have concerns if the 6s exb is right for me.

This video's might answer all your questions.

 

[Garcbomber]

That's just a case of poor mesh with too much axial play along the planetary set allowing the sun gear to swivel, easily snapping those cast ears on a forward/reverse transition. One of the drawbacks of eliminating the friction plates is no support behind the output pin.

 

[Mopsik_Klopsik]

Easy fix: https://www.arrmaforum.com/threads/open-exb-29mm-diff-planetary-sun-gear-reinforcement.71302/

 

[Crypto]

Easy fix: https://www.arrmaforum.com/threads/open-exb-29mm-diff-planetary-sun-gear-reinforcement.71302/

Interesting, what keeps the 12x18 .1 and .5 shims in place? The ears on the sun gear is what keeps the 1.9mm shim in place but if the circle LSD plates take t hat up those other shim are just floating there. I could see them slipping to the side.

Horizon is sending me a new diff, but I also ordered parts to rebuild the stock diff with a aluminum case. As Garcbomber said, something allowed the sun gear to lift off it's seat on the pin and then the sun gear ears were toast. Hopefully the aluminum case will mesh the planetary and sun gears better. If not I might have to add 12x18x.1 shim directly behind the sun gear?

 

[SirCrashALot]

I don't know what to do. Upgrade to the aluminum diff casing? Get the limited slip diff plates and use the circle plates to reenforce the sun gear? Chalk it up to I did something stupid? Current plan is to see if Horizon will give me a new diff and I guess see it happens again. If it's this easy to blow a diff I have concerns if the 6s exb is right for me.

Your best bet is to be easy on the throttle and brakes when running on pavement.
The grip is so good, you can stress the drive train a lot. I never had this problem, probably because i run in the dirt. Dirt allows the wheels to slip, resulting in less stress.

 

[hobo]

Your best bet is to be easy on the throttle and brakes when running on pavement.
The grip is so good, you can stress the drive train a lot. I never had this problem, probably because i run in the dirt. Dirt allows the wheels to slip, resulting in less stress.

I used to run on pavement a lot still do in winter and never had problems with the blx diffs no jumps or anything though. it was off road I sometimes would get breaks with all the jumps but not enough times to be bothered about it. I would break the pins more than anything so would buy cobolt drill bits and use as pins which worked. all this was with the stock systems

 

[Neelis]

Interesting, what keeps the 12x18 .1 and .5 shims in place? The ears on the sun gear is what keeps the 1.9mm shim in place but if the circle LSD plates take t hat up those other shim are just floating there. I could see them slipping to the side.

Horizon is sending me a new diff, but I also ordered parts to rebuild the stock diff with a aluminum case. As Garcbomber said, something allowed the sun gear to lift off it's seat on the pin and then the sun gear ears were toast. Hopefully the aluminum case will mesh the planetary and sun gears better. If not I might have to add 12x18x.1 shim directly behind the sun gear?

Did you watch the video I shared? That shows how to deal with play inside the diff, how to shim it and which parts you need.

 

[Mopsik_Klopsik]

Interesting, what keeps the 12x18 .1 and .5 shims in place? The ears on the sun gear is what keeps the 1.9mm shim in place but if the circle LSD plates take t hat up those other shim are just floating there. I could see them slipping to the side.

Horizon is sending me a new diff, but I also ordered parts to rebuild the stock diff with a aluminum case. As Garcbomber said, something allowed the sun gear to lift off it's seat on the pin and then the sun gear ears were toast. Hopefully the aluminum case will mesh the planetary and sun gears better. If not I might have to add 12x18x.1 shim directly behind the sun gear?

Diff case is roughly the same diameter as the shims. It's what keeps them in place. They won't be able to move by much.

 

[Crypto]

Did you watch the video I shared? That shows how to deal with play inside the diff, how to shim it and which parts you need.

I did watch the video. He added one extra shim under the sun gear then put it back together and it was too tight so he took it out, which I think that left him at the stock configuration for inside diff. I'm going to rebuild my diff in the aluminum case and I'll see how it feels. One thing I didn't mention is when I was taking my stock diff apart the screws were not all that tight, but being a plastic case perhaps that is expected. I'm smoking the hopium that the aluminum case helps keep the assembly tight together. The simplest explanation is that the plastic diff case just allows for to much expansion.

Did you see the other guy who posted that he bought a new Kraton and did the exact same thing in 3 mins? I wonder if a bad batch of diffs made there way into the new EXBs.

 

[Garcbomber]

I question Arrma/supplier's casting quality. There seems to be an inconsistency with those gears, anytime I have a tooth or back ear let go I'll upgrade to Vitavon's machined gears. Especially if it's going in a rear end.

 

[flyxii]

Exb v2
today during an oil change both pins holding the cups came apart in 3 pieces....