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How on earth did this happen? rear diff gearbox issue?

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tetsuo

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I'm guessing this might be user error vs tekno failure, but I can't see how this bearing would have been pushed out along w/ the outdrive. Rear didn't seem to be slipping, but I could sometimes hear that ugly slipping gears noise. Took off the body and this is what I saw:
that_bearing_isnt supposed_to_be_out_there.jpg


The set screw seemed tight but I suppose things might have slipped? Looking at the pic, I'm thinking the sound that I thought was slipping gears was actually the outdrive eating into the receiver box and screw. So did I botch something here or did parts just slip? I used loctite and can't imagine turning that set screw any harder than I did w/o breaking the driver or stripping the screw.

[edit/update] Nope - gearbox case and bearing failure. Ring gear has minor nicks but seems reusable. Pinion is chewed up. Rear diff is fine, but center diff failed. These things failed together in mine just as seen here: https://www.teknoforums.com/threads...t-a-inner-bearing-in-diff-case.421/#post-4978 [/edit]
 
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For that to happen either the inner bearing blew out and or the plastic ridge that keeps the inner bearing in place was damaged and the bearing has slid forward.

To fix you may need bearings at the very least. It may have been caused by bad bearings and they over heated and melted the housing in the bulkhead. That being said you may want to check the bulk head and see if it needs to be replaced.

Hopefully you caught it in time so there was no damage to the ring and or pinion gear.
 
Thanks for that break-down. That all makes sense. Will have to see what state things are in when I get a chance to put it on the bench later. Fingers crossed.
 
And this might be a stupid question, but what is the _minimum_ amount of dissasembly required/recommended to get the rear diff out of there? I feel like I'm going to have to take apart most of the back end to get to it but maybe I'm overthinking it.
 
I'm guessing this might be user error vs tekno failure, but I can't see how this bearing would have been pushed out along w/ the outdrive. Rear didn't seem to be slipping, but I could sometimes hear that ugly slipping gears noise. Took off the body and this is what I saw:View attachment 4623

The set screw seemed tight but I suppose things might have slipped? Looking at the pic, I'm thinking the sound that I thought was slipping gears was actually the outdrive eating into the receiver box and screw. So did I botch something here or did parts just slip? I used loctite and can't imagine turning that set screw any harder than I did w/o breaking the driver or stripping the screw.
Was the grub screw loose? Or maybe maybe not tightened on the flat part of the shaft and it slid back a little. This happened to me on the front diff but was saved in time.
 
I can see the end of the pinion still where it should be. I don't think his grub screw slipped.
 
How much mileage do you have on the Diffs? While you're in there might be a perfect time to upgrade the diff case with a nice shiny M2C aluminum case. I added the M2C Aluminum case on the center diff when I needed to add fluid and check the spur gears. Figured I was in there why not splurge a little for some M2C bling. Upgraded all Tekno aluminum center diff mounts too.
 
How much mileage do you have on the Diffs? While you're in there might be a perfect time to upgrade the diff case with a nice shiny M2C aluminum case. I added the M2C Aluminum case on the center diff when I needed to add fluid and check the spur gears. Figured I was in there why not splurge a little for some M2C bling. Upgraded all Tekno aluminum center diff mounts too.

I've only had the MT410 running for a couple weeks. Admittedly I've been thrashing it almost daily in my back yard, but I have no idea how/why this failure occurred. It wasn't the diff case, but the gearbox. Once I got the rear end taken apart, I pulled on the outdrive to check for play and was able to pull it out completely as seen here - you can even see a ring of plastic between the bearings that was previously part of the gearbox (TKR5016B)

plastic_failed_IMG_20200503_221011.jpg


I do confess that I was "rocking" the car with forward/brake/forward to self right the vehicle a number of times. Perhaps that was enough to impact that ring of plastic enough times to break through? Can't think of what else would have done this.
 
Where the bearings still good or are one or both shot?
The bearings seem gritty to me, so I'm going to replace them to be safe. The diff itself is fine. Well, the REAR diff is fine. Turns out the center diff was seized up, and I noticed that it was leaking from a crack in the case. Turns out two spider gears split in my center diff.

I'm wondering if me self-righting the car (hitting throttle / brake /throttle / etc) a few times was the cause of this carnage? It's only 4s, but it's in the grass where things hook up HARD unlike on dirt. I also never adjusted the "punch" setting on my ESC, and castle is immediate-full-power by default. The last time I was into this hobby was with an RC10 B3 back in 2002-2003 and having so much power/grip that you could grenade your internals was never really a concern! :D
 
Yeah that gritty feel could have attributed to them over-heating and then softening the plastic enough so that the forces of an impact broke the little ridge.

I have seen the same thing happen to the spindles when you dont check your bearings enough. I dont think that "bullet proofing" the rear bulk head is totally necessary but more so bearing maintenance.
 
Yeah that gritty feel could have attributed to them over-heating and then softening the plastic enough so that the forces of an impact broke the little ridge.

I have seen the same thing happen to the spindles when you dont check your bearings enough. I dont think that "bullet proofing" the rear bulk head is totally necessary but more so bearing maintenance.

I dont know - it's all pretty new. I'd only run about 8-10 packs through it and really the only abuse is medium sized jumps off a small ramp and using throttle/brake to flip it back over when it's upside down and having the rears come down in the grass at or near full throttle (seen others do it, but it looks to be brutal on the drive train). The new bearings arrived today and feel a touch smoother, but like I said, I'm really only replacing the others out of an abundance of caution. I'm also not going to try to flip this thing right side up w/ the throttle anymore just in case that was it. Going to back off the punch setting of my ESC as well, now that I know that's even a thing! :)

On a related note - the manual says nothing about oiling any of these bearings, and the steps for the gearbox assembly only have grease going on the ring gear. What kind of maintenance is really expected on sealed bearings like these?
 
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I dont know - it's all pretty new. I'd only run about 8-10 packs through it and really the only abuse is medium sized jumps off a small ramp and using throttle/brake to flip it back over and having the rears come down in the grass at or near full throttle (seen others do it, but it looks to be brutal on the drive train). The new bearings arrived today and feel a touch smoother, but like I said, I'm really only replacing the others out of an abundance of caution. I'm also not going to try to flip this thing right side up w/ the throttle anymore just in case that was it. Going to back off the punch setting of my ESC as well, now that I know that's even a thing! :)

On a related note - the manual says nothing about oiling any of these bearings, and the steps for the gearbox assembly only have grease going on the ring gear. What kind of maintenance is really expected on sealed bearings like these?
I know that when I ran my MT410 on higher grass everything runs hotter on the truck. This also goes for my Arrma vehicles. I Always look for short grass or no grass now. High grass and high traction wheels will cause drivetrain issues for sure. Probably going to slowly wear down the motor and esc too in the long run.
I never run two lipo packs back to back without allowing some cool down time to keeps temps at check. This is a force of habit of running nitros in the past. Rule of thumb with nitros is one full tank run time equals same time for cool down but I usually only waited 10-15 minutes if weather was not too hot.
 
This is why most people have multiple rigs, run one then let it cool and run the other..?
 
OK.. somewhat tangential question: can I re-use the set screw (TRK1603) on diff coupler/pinion? I have the new bearings and gearbox housing, and started to put things together and then realized that it might make more sense to use a new set screw to "bite" into the pinion shaft. ARGH! Dont want to wait on more parts :D
 

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