Used Kraton 6s diff - rebuild failure

[lee82gx]

Ok, introduction:
1. I bought a used Kraton 6s, it had very heavy wear on the diff outdrives front and rear.
2. Center diff looked ok - FWIW
3. I figured I'd service and rebuild all 3 diffs with fresh Oils, per original specs.
4. Center diff was just topped up with 100k fluid and re-assembled. I think I put too much and it oozed out of the screw holes as I screwed down the diff case to the spur gear.

3 x 6s packs later, after quite a bit of WOT, I gently tapped a goal post at <3km/h, walking speed, on the bumper.

After which I heard a weird gear mesh sound and in about 3 minutes, lost drive, the spur was turning but the wheels struggled.

I guessed since both front and rear wheels struggled to turn it was the center diff. And here is the post mortem:

First photo shows the sun gear worn. This is at the diff case side.

I noticed the screws were not tight - could this be due to my overfilling with fluid? The diff oils were squeezing out during my screwing in process.
I did not screw so tight until "11" but was probably "just tight".

I've ordered a new set of gears but due to my location - Malaysia will need easily 2 weeks ETA.

So, now I have a lot of time and nothing much to do while waiting for the new part.... so questions:
1. The wear does not look too bad?
1.1 When I re-assemble and try to spin the outdrives with the spur gear clamped, I'd lose the mesh if I backed out the screws by maybe 1mm, does this mean If i re assemble and tighten I can get them to mesh again?

2. Looking at the 2nd photo, I don't think I damaged the planetary gears, and I didn't show the spur side sun gear and that was fine also.
2.1 I highlighted a gap when the planetary gears are seated down, there seems to be a 0.7mm gap between the backer piece and the top surface of the diff case.
2.1.1 Is this normal? Is it supposed to be flush or a bit down?

3. Do you guys reckon I can shim up the sun gear by 0.7mm upwards base on 2nd picture, re-gasket and tighten and use it again?

4. I need to purchase and irreversibly use a new gasket as I damaged it during this disassembly....cheap me would not like to spend another dime if un-necessary.

Should I roll the dice?

THis is my first metal gear heavy oil filled diff (I have only previously played with 1/10 touring with ball diffs) that has ever blown, I'm kinda bummed, is this a regular feature with 6s 1/8 cars? To think that there are 3 diffs to maintain.....??

 

[SrC]

You might be able to work with what you got. IDK. But clearly these are worn to some extent. Who knows how much wear and abuse these had. Best to start out with 3 new diffs. Shim Front and Rear as well. For oil, Run 60k Fr/500k center/20-30k rear. Stocker 10k/100k/10k oils are way too thin for bashing.
I replace all the 4 Sat and 2 Sun gear "shims' with Mugens #E0206 diff shims. The stocker shims plain suck. ( all 3 diffs) I then shim the main and input gears for correct backlash (Fr+Rr ones)

https://www.amazon.com/MUGEN-Differential-Washer-M-Spec-MUGC1206/dp/B000BMPK2U/ref=sr_1_fkmr0_1?crid=2KZKF257A6LUI&keywords=mugen+washers+e0206&qid=1696312645&sprefix=mugen+washers+e0206,aps,60&sr=8-1-fkmr0

These are for standard "Open 6s diffs". ( Not EXB LSD diffs)
I install the 4 screws several threads in, during the fill process. So no oil gets into the threads. Take your time filling, Less of a mess this way. Less wasted oil
I fill to the top and place the SUN gear into the diff, which pushes out any excess oil, Wipe off the excess, then place the Main gear in place and screw it on. Less waste this way. The tiny grub screw if removed from the diff case/cup will also release any excess oil under pressure after you tighten it all up. Remove the grub screw and turn the diff by hand a few turns, any excess oil will drip out. Then reinstall the grub screw snug. Just don't strip the grub's threads.
After I've done about 60-80 of these diffs, over the years, it all became muscle memory. Watch some videos, if need be. Takes some practice. Arrma 6s diffs tend to be needy. If done the way I explained, they should last 20+ packs/runs, before changing out the oil/maintenance, replacing the BB's etc. Your mileage may vary.
Good luck.

BTW, it's also a good idea to smear some grease onto the output cup shafts before inserting them. They will wear less and last longer. When these wear out, the sat and sun gear alignment gets all jacked up.

Edited.

 

[lee82gx]

You might be able to work with what you got. IDK. But clearly these are worn to some extent. Who knows how much wear and abuse these had. Best to start out with 3 new diffs. Shim Front and Rear as well. For oil, Run 60k Fr/500k center/20-30k rear. Stocker 10k/100k/10k oils are way too thin for bashing.
I replace all the 4 Sat and 2 Sun gear "shims' with Mugens #E0206 diff shims. The stocker shims plain suck. ( all 3 diffs) I then shim the main and input gears for correct backlash (Fr+Rr ones)

https://www.amazon.com/MUGEN-Differential-Washer-M-Spec-MUGC1206/dp/B000BMPK2U/ref=sr_1_fkmr0_1?crid=2KZKF257A6LUI&keywords=mugen+washers+e0206&qid=1696312645&sprefix=mugen+washers+e0206,aps,60&sr=8-1-fkmr0

These are for standard "Open 6s diffs". ( Not EXB LSD diffs)
I install the 4 screws several threads in, during the fill process. So no oil gets into the threads. Take your time filling, Less of a mess this way. Less wasted oil
I fill to the top and place the SUN gear into the diff, which pushes out any excess oil, Wipe off the excess, then place the Main gear in place and screw it on. Less waste this way. The tiny grub screw if removed from the diff case/cup will also release any excess oil under pressure after you tighten it all up. Remove the grub screw and turn the diff by hand a few turns, any excess oil will drip out. Then reinstall the grub screw snug. Just don't strip the grub's threads.
After I've done about 60-80 of these diffs, over the years, it all became muscle memory. Watch some videos, if need be. Takes some practice. Arrma 6s diffs tend to be needy. If done the way I explained, they should last 20+ packs/runs, before changing out the oil/maintenance, replacing the BB's etc. Your mileage may vary.
Good luck.

BTW, it's also a good idea to smear some grease onto the output cup shafts before inserting them. They will wear less and last longer. When these wear out, the sat and sun gear alignment gets all jacked up.

Edited.

SrC,
thanks for the informed reply...
Your point here being 20+ runs per re-install, do they really wear out so quickly? What is the actual wear? THe oils getting filthy or the gears just stripping the metals?

I think I more or less know that I should not fill to the brim by now, the Manual is faulty.

I'd like to understand the use of thicker oil for the purpose of bashing - it makes it last longer between servicing? I don't really need great cornering agility with these trucks, they just need to maintain a straight line under heavy acceleration.

I have a complete center diff coming by order, do you recommend to immediately flush out the oil and replace with 500k? Or can I be lazy and run 20+ packs and then use the service interval to change oils?
thanks again.

 

[SrC]

Welcome to AF.

 

[Sandracer_NL]

Welcome to the club!
What @SrC above said.
Don’t re-use a damaged gasket as oil will find a way out of your diff.
Arrma gaskets are quite thin and you need to be careful when working with them. You could have a look at Tekjo gaskets (sold on Ebay) which are, if I recall correctly, about 50% thicker.

 

[djrahbee]

SrC with the great info! I always clean the screw holes out from every diff I rebuild with some kind of spray, with a straw on the can, like terminal cleaner. Also you could look into EXB diffs with an open setup. I don't run any BLX diffs.

 

[Hector_Fisher]

When re-assembling your diff, did you check to make sure the slot in the cross pins matched each other? I've had issues before where the pins spun during re-assembly, the slots no longer matched up, and I was not able to close the diff case all the way (with the spur), so i was getting binding and bad mesh when rotating the outdrives.

 

[lee82gx]

When re-assembling your diff, did you check to make sure the slot in the cross pins matched each other? I've had issues before where the pins spun during re-assembly, the slots no longer matched up, and I was not able to close the diff case all the way (with the spur), so i was getting binding and bad mesh when rotating the outdrives.
View attachment 325159

Yes, this was obvious enough to me.

 

[lee82gx]

Welcome to the club!
What @SrC above said.
Don’t re-use a damaged gasket as oil will find a way out of your diff.
Arrma gaskets are quite thin and you need to be careful when working with them. You could have a look at Tekjo gaskets (sold on Ebay) which are, if I recall correctly, about 50% thicker.

I measured the thickness of the stock gasket which is around 0.50 to 0.40mm thick, now wouldn’t a 1mm thick gasket require extra shimming of the sun gear to close up the gap? I was under the impression thinner is better.

 

[Sandracer_NL]

You shouldn’t use additional shims to compensate fir gasket play. The shims under the sun gear should eliminate lateral play of the diff cups. Shim just enough so that there is minimal lateral play and you won’t feel any binding/friction when turning the output cup by hand. If you need force to turn it, you’ve overshimmed it.

Know you’ve mentioned the thickness of the stock gaskets I’m pretty sure the Tekjo ones are around 0,7mm.
I always turn the four diff screws with minimal force close to all the way down. Then one by one turn them just a tiny bit (about 1/8th of a full turn) and after each one I turn the diff cups by hand.
At some point you may start to feel the gears starting to bind a little. Just undo that last tiny turn on that screw and it the binding should be gone.
After a couple of diff maintenance times you’d probably do everything by feel and know when you‘ve reached that point just before binding.

 

[SrC]

I measured the thickness of the stock gasket which is around 0.50 to 0.40mm thick, now wouldn’t a 1mm thick gasket require extra shimming of the sun gear to close up the gap? I was under the impression thinner is better.

Excellent point to be made.
I have tried doubling up stock gaskets because for the life of me, I couldn't get one diff correct. Felt way too tight and binding with one gasket. I know that I just really needed a new diff cup. It was worn out ( plastic stocker one) 2 gaskets, and it worked. But yeah I can see how more gasket thicknees can also pose a problem. Worth a try to see. Many use the Tekjo's. I think Basher Queen also has her own gaskets??
I always stayed with the stocker ones, myself.
The Tekjo "bulkhead gaskets" are probably worth it. I never used them. I use a bead of grease and it works well enough. I don't run in the wet anyway. But in theory you do need to seal the bottom of the bulkhead where it meets the chassis. The Arrma 8s bulkheads have an o-ring type seal on its Fr and Rr bulkheads. Makes sense.

 

[SrC]

SrC,
thanks for the informed reply...
Your point here being 20+ runs per re-install, do they really wear out so quickly? What is the actual wear? THe oils getting filthy or the gears just stripping the metals?

I think I more or less know that I should not fill to the brim by now, the Manual is faulty.

I'd like to understand the use of thicker oil for the purpose of bashing - it makes it last longer between servicing? I don't really need great cornering agility with these trucks, they just need to maintain a straight line under heavy acceleration.

I have a complete center diff coming by order, do you recommend to immediately flush out the oil and replace with 500k? Or can I be lazy and run 20+ packs and then use the service interval to change oils?
thanks again.

Clean out the OE oil out the gate. Use Car Brake spray cleaner to clean out old silicone oil. The best way. Every gear and all into a glass container. Rebuild using 500k. (center) The stock thinner oils causes "Diffing out". The tires can blow out easier because of this. The center diff gets quite hot as well. 500k keeps it cooler by not spinning the Sat and gears too fast. The oils I suggest, will make the rig come alive more as well. More power to the ground.
Diff oil will darken with use, Normal, because the gears are only Cast pot metal and the worn metal turns the oil dark and silvery in color.. Not tragic, but a routine preventive maintenance keeps the diffs lasting longer. Diffs will have a slight break-in period, and will run smoother after a few packs. Factory always underfills them as well. And I don't trust what is in there. I found loose metal fragments in new Unused diffs before. It bricked one of my new diffs.
Bless these diffs with your own two hands and these diffs are good for a while. We all drive differently. So your milage will vary.
The factory assembles these super fast. There is little to no Quality control. A known thing with these China made Arrma's. Seems HH has lost control of their Outsourcing for any years IMHO. But otherwise Arrma's are great RC's. I am a diehard kit builder, so I rebuild these when new out the box before even running them. They are considered RTR's, but honestly when you do run them as is out the box, the drivetrain will fall apart fast. Just look at all the threads here at AF in regards. New guys with their very first Arrma. Been that way for years and years. Me included. With my very first 6s Outcast. It was a disaster, because I opened the box charged some packs and checked over nothing, Blew out diffs. Tire blowouts etc. Oils were very low. The outsource factory is cheaping out with the diffs oils. I say HH is getting robbed. And so are we.
And many other China produced RTR RC brands are this way. Just part of China's FAST business Mfr'ing culture. And it's unskilled slave labor force unfortunately.

 

[lee82gx]

Sorry guys I don't want to divert too much from the topic. Before I go balls deep into this, can you help me truly -
1. I am now 41, have 2 young but uninterested kids. between that and my wife and a 1:1 job and upcoming Rheumatoid arthritis, I no longer have the time and energy to wrench. Back in the days I literally slept in nitro infused clothes.
2. I think that the used kraton 6s intro has smacked me into reality, there is a lot of maintenance required....to achieve this kind of speed, kinetic energy and tumbling about. I was really attracted by Kevin Talbot who ensured all of us that we can whack the 6s system to the moon and back and repeat this without necessary wrenching. Silly me.
2.1 Much as I like, I do not envision re-building 80 diffs so that I can do it by muscle memory - Mad respects to those in this passion, and teach freely here.
3. I already have a typhon 3s which appears so much more friendly everytime you look at it, save for the fact that I can barely move it around on 2 inch high grass.

Is there another model that I can enjoy, with much lower maintenance even at lower speeds? As long as it can move around on sites like these:

I have given up on doing mad jumps and backflips and what not. But I do not want to "crawl" at 5km/h. How about 40km/h top speeds?

I don't mind spending on a new kit. Here are the options in my country:
1. Tamiya - I know - the horror of ABS plastics
2. Arrma (obviously)
3. Traxxas
4. Losi
5. Corally (only 1 dealer in the whole country, yikes)
6. Serpent (same as above)
7. Chinese XYZ/ABX/MJX/HBX etc brands
8. Repair my kraton and take it easy, go 4s etc.

FYI, I tried to start a new thread but Arrma admins have nuked it.

 

[Sandracer_NL]

With terrain like that (rocks) I‘d go for something with fairly big tires. A 6s running on 4s should bring the amount of maintenance required down. You’ll have no problem running (faster than) 40kmh on 4s..

 

[SrC]

The 6s line of Arrmas are just as easy to work on as the 4x4 line. If not even easier IMHO.
Unfortunately what you are looking for may not exist? All RC's need to be wrenched on. Wrenching is 80% of the hobby. 20% is the driving aspect. Keep driving like Talbot does and well you will ultimately be disillusioned with this Hobby. TBH, Talbot is not really any great RC role model for newcomers at all. . He has some entertainment value. But mostly for the "Clicks". And he always Baits many into the hobby, no doubt. Making RC look easy. KT loves RC for sure, just that he loves all the $$$ he makes from his Videos even way more. He makes it look easier than it really is. He has the coin to keep spending on RC's . He needs that new content to make a living. For the shock value it offers. It is not like he portrays it to be. The Break, Fix, Repeat thing is overrated greatly. Many get sucked into this logic. And go broke quickly. No need to.
A Tekno MT410 KIT has better quality diffs and drivetrain.
I haven't serviced their diffs since the original build, and many years since then. But this costs way more. And a bit more tedious to work on. You pay for what you get in this hobby.
Doing this hobby for 35+ years and also work on my scale 1:1 cars for many years. My hands get swollen from Arthritis as well. I get you.
Learn the 6s diffs well, and they will take care of you. If you drive more mellow, rig will need way less wrenching, short of normally worn parts being replaced. We all need to find the limits of our driving skills along with the durability limits of the rig we are driving. After 100+ hours of wheel time, your skills will be much better.
When we find that limit , we can get way much more mileage out them. Less wrenching.
Arrma's tend to be the least expensive brand, when it comes to OE Replacement parts in general.
Never run in the Wet stuff, if you don't like the wrenching thing and spending more Coin. You will be adding insult to injury needlessly, along with your wallet.
The more you wrench, the more easy they get to work on. What took you an hour or more , eventually takes you only 10 minutes. Trust me. You end up developing shortcuts. Proper tools really do matter. Speed you up greatly. I use a Milwaukee M12 power driver, for example. Saves me 50 % of my time. And also spares my hands. MIP Hand Hex drivers are very comfortable for my hands. Way Less fatigue.
Just some thoughts and ideas.
Enjoy.

 

[Surchaufeur]

Bruhh just get exb diff and ditch the rtr. If you wnat get the metal cup for ur rtr diff. But the rtr diffs are cheese they can last torture or explode its internal for no reason

 

[parcou]

Welcome!

 

[lee82gx]

The 6s line of Arrmas are just as easy to work on as the 4x4 line. If not even easier IMHO.
Unfortunately what you are looking for may not exist? All RC's need to be wrenched on. Wrenching is 80% of the hobby. 20% is the driving aspect. Keep driving like Talbot does and well you will ultimately be disillusioned with this Hobby. TBH, Talbot is not really any great RC role model for newcomers at all. . He has some entertainment value. But mostly for the "Clicks". And he always Baits many into the hobby, no doubt. Making RC look easy. KT loves RC for sure, just that he loves all the $$$ he makes from his Videos even way more. He makes it look easier than it really is. He has the coin to keep spending on RC's . He needs that new content to make a living. For the shock value it offers. It is not like he portrays it to be. The Break, Fix, Repeat thing is overrated greatly. Many get sucked into this logic. And go broke quickly. No need to.
A Tekno MT410 KIT has better quality diffs and drivetrain.
I haven't serviced their diffs since the original build, and many years since then. But this costs way more. And a bit more tedious to work on. You pay for what you get in this hobby.
Doing this hobby for 35+ years and also work on my scale 1:1 cars for many years. My hands get swollen from Arthritis as well. I get you.
Learn the 6s diffs well, and they will take care of you. If you drive more mellow, rig will need way less wrenching, short of normally worn parts being replaced. We all need to find the limits of our driving skills along with the durability limits of the rig we are driving. After 100+ hours of wheel time, your skills will be much better.
When we find that limit , we can get way much more mileage out them. Less wrenching.
Arrma's tend to be the least expensive brand, when it comes to OE Replacement parts in general.
Never run in the Wet stuff, if you don't like the wrenching thing and spending more Coin. You will be adding insult to injury needlessly, along with your wallet.
The more you wrench, the more easy they get to work on. What took you an hour or more , eventually takes you only 10 minutes. Trust me. You end up developing shortcuts. Proper tools really do matter. Speed you up greatly. I use a Milwaukee M12 power driver, for example. Saves me 50 % of my time. And also spares my hands. MIP Hand Hex drivers are very comfortable for my hands. Way Less fatigue.
Just some thoughts and ideas.
Enjoy.

First of all I love hearing from experience. I am hard necked but once in a while I listen.

I can buy a MT410 and even build it right, most likely, if I am motivated enough. But - there is only an online retailer for Tekno in my whole country and ordering spares will also be a 3-4 week affair. Is it worth it to take a risk? Is there any parts worth getting in advance?

suppose, I do get a Tekno MT410, do you think if I don't stunt the vehicle, don't send it to the moon but rather more like fast crawl style using the 6S BLX system with 4s power and just retire my Kraton - Would it involve just as much wrenching?

I reckon I have the juice to build a fresh kit - Its one of the joys afterall. I just don't enjoy emptying the same 3 x diff cases every dozen packs to have to end up shimming the sh!t out of every diff - "Feeling it like Beethoven" before deciding to close the bulkhead. One mistake and at is another 3 weeks + more money down the drain. My rear bulkheads have started to strip at the screw bosses by the way....

You are right - the right tools and necessary care to do it right is always important - just as in any endeavour be it cooking or cleaning. I have plenty of good tools that have survived from my previous life racing 1/10 EP on road.

 

[SirCrashALot]

After 20 or so packs it is also time to replace the front and rear input bearings. If you don't, the input gears will get bad and cause way more damage.
Wear and tear and the inevitably required service intervals will be greatly reduced when running the 6S cars on 4S, or just 3S.