Kraton Kraton EXB rear diff blown again

[jondilly1974]

So I shimmed a brand new rear diff last night. Cleaned it all. Dry fit it with as many shims as I could get behind the pins. Cup side took .6mm worth and couldn’t get even another .08mm shim in there. On the gear side I could get .75mm of shims behind the pin. Both sides were firm and couldn’t pull them at all. Neither had resistance. Assembled it dry and it felt good, minimal gear feeling and no notchiness. Opened it back up and put 25k inside. After final assembly it was super smooth yet the outdrive cups were tight. It took one Kyosho shim on the ring gear side bearing. Everything felt like new. Went out and ran one pack with no issues. Half way thru the second pack it started clicking. Now I was bashing pretty fast at the construction site, but no ramp. Lots of donuts and cartwheels. Minimal air.

This was the result:

 

[Spoc85]

Stabbing the throttle while it’s cartwheeling is not going to do the diff any good.

 

[TooTall]

Did you take it apart? Is it input to ring stripped or internal breakage?

If the input pinion to ring is what is stripped, then check your diff case, bet you have a crack and it is flexing.

If it is internal problem again, then not sure, as mine is nice and snug just like you said, and I have ran10+ packs thru, standing backflips, ramp jumps, speed runs on grass, etc, and i've had no issues with 6s and a MMX8s/1717 combo.

 

[Cheez]

Putting this on watch ? wanting to learn.

 

[MrTitanium]

Take her apart? Curious as to what let go

 

[jondilly1974]

I can assure you it’s the sun gears again, but I will pull the diff here in an hour or so. Last time the input pinion and ring gear were flawless and I don’t expect a change there. Pics will be posted here soon. I will lay out every part for a photo.

 

[MrTitanium]

Just to make sure I understand, you’re running the EXB unit, not the V4, right?

 

[jondilly1974]

Just to make sure I understand, you’re running the EXB unit, not the V4, right?

Correct. I picked up an EXB center diff from JRC and put that in my center. Took the original center sun and planetary gears out and put them in the original rear cup (center cup was worn from a rock) and tried every combo of shims and plates that I could. The plates would either lock the diff or make it very notchy. I abandoned that effort before reading that you have to really cut back on shims if using the plates. I plan on trying the three star plate method when the next JRC shipment arrives later this week. I have another rear and front EXB diff coming. I just need the two more star plates and whatever gears I shredded today to get it back up and running. I don’t feel like swapping to the V4 again so I will just wait for the parts to come.

 

[MrTitanium]

I have another rear and front EXB diff coming...

Ahhhhhhh! So you’re the little bugger buying up all the LSD’s from Jen/Ted! I freakin’ knew it! ??

 

[jondilly1974]

Here are the pics. It’s the cup side sun gear again. I could find two of the broken teeth.

Shim values:

Top row (left to right)
.20 .25 .25 .15 Total .79

Bottom row (left to right)
.30 .20 .20 Total .68

 

[Vietnemesis]

Sorry it blew again. Thanks for posting the pics.

 

[Jamart85]

I'm assuming those sun gears are wobbling in the diff with just shims, minimal surface area compared to the plates? If the center and front are surviving and they use the same sun gears as the rear, the common denominator leads me to believe having shims only in the rear diff are at fault. Come on September EXB delivery! Tired of breaking and repairing my 20yr old Tmaxx classic ?

 

[MrTitanium]

@jondilly1974

Very interesting. No doubt that you know how to shim your diffs properly. So we can take that right off the table.

It would seem that material used for internal gears is questionable. Perhaps a question of hardness. Is there any way for you to check the gear’s hardness (rockwell)? Maybe run a file across the teeth to see how soft/hard the material is?

 

[Dscracing1320]

I can tell you right now its 100% not correctly shimmed. And if I'm understanding you put different amounts of shims on each side makes no sense. Not to mention running without the lsd plates after I told you they are a must. Killing me smalls lol

 

[Spoc85]

@jondilly1974

Very interesting. No doubt that you know how to shim your diffs properly. So we can take that right off the table.

It would seem that material used for internal gears is questionable. Perhaps a question of hardness. Is there any way for you to check the gear’s hardness (rockwell)? Maybe run a file across the teeth to see how soft/hard the material is?

You’re digging too deep mate........ This issue happens when you run your car during an Earthquake or it’s cartwheeling along the flat and you apply the gas to get it back onto it’s wheels.

 

[Surchaufeur]

I think once the diff strips the diff cup is gone is the plastic diff cup or the shims are oval?

 

[MrTitanium]

I can tell you right now its 100% not correctly shimmed. And if I'm understanding you put different amounts of shims on each side makes no sense. Not to mention running without the lsd plates after I told you they are a must. Killing me smalls lol

That’s kinda harsh.

Why would running different shim thicknesses on either side make no sense? Have you not witnessed the inconsistencies with the Arrma diff components?

You’re digging too deep mate........ This issue happens when you run your during an Earthquake or it’s cartwheeling along the flat and you apply the gas to get it back onto it’s wheels.

Not digging too deep at all. I question everything and that’s how trouble shooting is done. Merely changing parts and not knowing why they fail is not part of my vocabulary ?

 

[Surchaufeur]

Me on my kraton 4s when i cartwheel is appli little baby taps throttle and makes me not end up upside down most fo the time but if you gas it
Something fishy is happening bicketybam diff survives but jondilly just explodes
I will wait for my lsd hopefully this week they arrive at my hobbyshop wont run without them im making a beast before running it nphonestly theres almost nothing to upgrade other than the diff bulkhead, LSD, rear wing mounts and a wheelie bar i have soare rod ends and shock ends now+ the pivot ball thingy

 

[Dscracing1320]

That’s kinda harsh.

Why would running different shim thicknesses on either side make no sense? Have you not witnessed the inconsistencies with the Arrma diff components?

Are you serious or joking. A diff must be assembled symmetrically or the load will not be applied evenly throughout the teeth. I understand not everyone is a mechanic on here but sometimes I try and help and get guys trying to argue with my statements and if you think you know more than I do more power to you.

 

[Surchaufeur]

If its as durable as my k4s and less expensive in the long run might sell it im starting getting fed up of the clutch i think i nucked it againt by landing hard on my rear end after a 3 backflip jump that i panicked and tried to save it