Kronos XTR First 6s run... Complete failer

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Caleb90

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Did my first 6s run. Lasted about 5minutes. Thing is stupid fast, hard to control. Snapped the front drive shaft, and cooked the center diff. Seemed to have alot of cogging off the start. Truck would jump and bounce, go no wheres making a racket. Then it would finally get going. I just put over size tires on, so i will try gearing down i guess. Pretty dissapointing afternoon

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Also do they make front cvd rebuild kits? I broke the pin in one of the cvd axles. Luckly i had a spare axle on hand
 
Moral of the story: Check your rollout if you decide to run much bigger wheels/tyres and adjust the gearing accordingly. Stock gearing is designed for stock wheels/tyres.

That diff looks seriously overheated and for the shaft to sheer off like that, something must have been fouled/jammed up.

Also worth noting: If it ain't broke, don't fix it! 🤣 Besides the fact the stock tyres balloon like crazy, they hook up pretty good on a variety of surfaces. And they're nice and light.
 

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Caleb90 said:
Thinking the drive shaft broke, as a result of the diff cup wearing a groove in it. Center diff is my fault for running it with just the rear drive shaft
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It's more likely that a pin from your CVD came loose, jamming the transmission and shearing the front centre drive. The heat generated in the diff was from the subsequent permanent diffing out, due to no front drive.
 
Yeah, wow!! You like it well done eh? LOL. Sorry, I couldn't resist the lame joke.
My guess is something has been amiss for a while possibly? Since your esc had been thermalling on 4s previously.
The center diff in these Corally's are waay off center to the chassis..the front center driveshaft and cups take a beating as a result..my guess is one side of the front center diff outdrive is severely worn and the opposite looks fine? They tend to wear unevenly at both the front center diff and front diff input cups.. my Redcat Kaiju does the same.. I don't know of any real fix for it. Just gotta keep a close eye on wear and try to replace before they get too bad.
Hit up jrc for a center diff. I recommend going with either sketer or kronos xtr if they have them.
They should have the upgraded swiss steel cups which are bronze in color..they're holding up better than the black XP RTR pieces mine came with.
Sorry about the breakage. It really may have just started due to the diff cups wearing unevenly, then progressively got worse. That center diff should be replaced IMO. JRC makes it cheap enough.

.. I lifted this photo from @RCproponent . He has a build thread over on AF for the Kronos xtr. Nice build BTW (x2)👌
What I wanted to point out is the wear on the front driveshaft on his broken XTR.. I think the groove in this driveshaft eventually happens with all the TC 1/8 rigs..need to change the shaft and cups before failure.
 

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KnowAir said:
Yeah, wow!! You like it well done eh? LOL. Sorry, I couldn't resist the lame joke.
My guess is something has been amiss for a while possibly? Since your esc had been thermalling on 4s previously.
The center diff in these Corally's are waay off center to the chassis..the front center driveshaft and cups take a beating as a result..my guess is one side of the front center diff outdrive is severely worn and the opposite looks fine? They tend to wear unevenly at both the front center diff and front diff input cups.. my Redcat Kaiju does the same.. I don't know of any real fix for it. Just gotta keep a close eye on wear and try to replace before they get too bad.
Hit up jrc for a center diff. I recommend going with either sketer or kronos xtr if they have them.
They should have the upgraded swiss steel cups which are bronze in color..they're holding up better than the black XP RTR pieces mine came with.
Sorry about the breakage. It really may have just started due to the diff cups wearing unevenly, then progressively got worse. That center diff should be replaced IMO. JRC makes it cheap enough.

.. I lifted this photo from @RCproponent . He has a build thread over on AF for the Kronos xtr. Nice build BTW (x2)👌
What I wanted to point out is the wear on the front driveshaft on his broken XTR.. I think the groove in this driveshaft eventually happens with all the TC 1/8 rigs..need to change the shaft and cups before failure.
Click to expand...
@Caleb90 I have all that in stock if you can't find it anywhere else. In the vendor section I have a coupon code for 10% off too. Hope you get it running.
 
KnowAir said:
Yeah, wow!! You like it well done eh? LOL. Sorry, I couldn't resist the lame joke.
My guess is something has been amiss for a while possibly? Since your esc had been thermalling on 4s previously.
The center diff in these Corally's are waay off center to the chassis..the front center driveshaft and cups take a beating as a result..my guess is one side of the front center diff outdrive is severely worn and the opposite looks fine? They tend to wear unevenly at both the front center diff and front diff input cups.. my Redcat Kaiju does the same.. I don't know of any real fix for it. Just gotta keep a close eye on wear and try to replace before they get too bad.
Hit up jrc for a center diff. I recommend going with either sketer or kronos xtr if they have them.
They should have the upgraded swiss steel cups which are bronze in color..they're holding up better than the black XP RTR pieces mine came with.
Sorry about the breakage. It really may have just started due to the diff cups wearing unevenly, then progressively got worse. That center diff should be replaced IMO. JRC makes it cheap enough.

.. I lifted this photo from @RCproponent . He has a build thread over on AF for the Kronos xtr. Nice build BTW (x2)👌
What I wanted to point out is the wear on the front driveshaft on his broken XTR.. I think the groove in this driveshaft eventually happens with all the TC 1/8 rigs..need to change the shaft and cups before failure.
Click to expand...
I put all the swiss diff cups in a while back. Last time i had the center diff out, i remember seeing and thinking the front diff wear was going to be a problem
 
If there was one thing I could ask TC to change in their design is the position of the centre diff. Just moving it back 10mm would make a huge difference. There's a least 4cm to spare at the back of the stock motor. But it would require different sized back and front driveshafts, and the front chassis brace would need to be redesigned.
 
I feel like it's the offset that's the biggest issue personally. I have a TT MT4 monster truggy from about 10 years ago that has at least as short a front driveshaft. It doesn't have the wear issue though..the center diff is dead centered on the chassis. Unfortunately it's just something we have to work with and replace parts as needed.
@Caleb90 , sorry I missed the swiss cups in your pics. I've measured temps of 180-190f on the center diff cup during summer, but unless your phone is rendering the color wrong that diff is seriously cooked!!
 
KnowAir said:
I feel like it's the offset that's the biggest issue personally. I have a TT MT4 monster truggy from about 10 years ago that has at least as short a front driveshaft. It doesn't have the wear issue though..the center diff is dead centered on the chassis. Unfortunately it's just something we have to work with and replace parts as needed.
@Caleb90 , sorry I missed the swiss cups in your pics. I've measured temps of 180-190f on the center diff cup during summer, but unless your phone is rendering the color wrong that diff is seriously cooked!!
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Picture made it look worse. All that brown was burnt on diff grease from when it blew the paper gasket out. I got it cleaned off of there. Didnt look bad inside and will be putting it back together
 
Caleb90 said:
Picture made it look worse. All that brown was burnt on diff grease from when it blew the paper gasket out. I got it cleaned off of there. Didnt look bad inside and will be putting it back together
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Good, glad to hear that. That's the very reason for the aluminum cup, to withstand the heat.
I'm sure it would be possible to move the center diff closer to center, just requires some new holes in the chassis plate and appropriate length center shafts.. but then IDK how the t2t brace would work. I don't have one, so wouldn't be an issue for me. If I were adept at welding I could shorten the center driveshafts and I bet it would help cut down the wear.🤔
 
KnowAir said:
Good, glad to hear that. That's the very reason for the aluminum cup, to withstand the heat.
I'm sure it would be possible to move the center diff closer to center, just requires some new holes in the chassis plate and appropriate length center shafts.. but then IDK how the t2t brace would work. I don't have one, so wouldn't be an issue for me. If I were adept at welding I could shorten the center driveshafts and I bet it would help cut down the wear.🤔
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I'm not sure it's that simple, at least not on the 2022 XTR. If you move the centre diff towards the middle you'll see the front driveshaft will hit the chassis brace. What needs to be done is reducing the angle at which the driveshaft connected with the drive coups, moving the centre diff towards the middle is one way, but moving it back is another way too. But the front brace issue will happen in both cases regardless.
 
DaniC said:
I'm not sure it's that simple, at least not on the 2022 XTR. If you move the centre diff towards the middle you'll see the front driveshaft will hit the chassis brace. What needs to be done is reducing the angle at which the driveshaft connected with the drive coups, moving the centre diff towards the middle is one way, but moving it back is another way too. But the front brace issue will happen in both cases regardless.
Click to expand...
Yours definitely right, it is quite invlved the more I think of it.. stock up on center drive parts is the best bet I suppose..👍
 
Got these in the drive cup. Pretty good. You have to make them a bit shorter but that is easy 2 do

Screenshot_20220511-093422.jpg
 
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