Kronos Help with noisy gearing

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
Stormwind said:
Just an update on this.
I have replaced my pinion with a brand new 12T one (I'm gearing down since it's summer and the grass gets long real quick :p). I have finished changing my drive cups as suggested above (I've not bothered changing the driveshafts since I replaced the rear center one not long before, whilst it has a slight bend in it (again) - bought it to replace a bent one already :( ).

I have pulled the center diff apart, cleaned it up, nothing looked particular broken or badly worn so rebuilt it.
Since the noise is still occurring even with those new cups, I'm possibly thinking that I will replace the spur gear and may as well get new planetary gears and bearings too whilst I am at it. It looks like as soon as rear drive shaft has any load on it, the gearing slips at the minute.

Currently though, I have not refilled the diff with fluid. I have some, just not bothered refilling it since I didn't want to waste any if I was gonna replace the spur gear anyway.
Could this possibly be the whole issue all along? When I drained the diff in the first place, there wasn't particularly all that much liquid that drained off in the first place, just a small amount of gunge really.
Click to expand...
I can't speak from experience because I've never ran a diff with no fluid, but I would say that does explain the increased noise...
 
Without fluid, the diff is going to be "diffing" (if you get what I mean) a lot. As the internals are quite small straight cut bevel gears, they'll be noisy and a bit rattly if not immersed in diff syrup.
It'll probably be much quieter when it's filled. My rear driveshaft has also got a slight bend, but it's not noisy.
 
I've gone ahead and filled it this afternoon, it used a lot less fluid than I thought it would to be honest so I'm not gonna be too bothered if I end up pulling the diff apart again and draining that off.
It's hard to tell if it has really helped the noise but it certainly hasn't helped the slipping. I'm starting to think that it may be the back diff now. I'll probably pull both front and rear diffs apart in the next few days to double check those. Once I have all the wheels on and giving it a slow ponder around the front garden the amount of slippage is unreal. I'm just envisioning gears stripping as it goes :S
 
Ahhh, it might also be the diff case screws backing out - my centre diff did this - which will cause the crown mesh to go loose, and also the internal planetaries to skip and slip.
I guess the front and rear diffs need attention as well.
The internal gears are quite well made, so they might have survived a bit of skipping without (too much) damage.
 
There should be some physical indication if it's the gears slipping inside the diff I would think? Rounded teeth. Curious, with the diff removed is there excessive freeplay of the input shafts?
I recently pulled a Corally center diff out of my Xray buggy that I ran for about a year. The front and rear output shafts had considerable freeplay, the diff was basically empty. Just wet inside. I don't think it was actually skipping teeth but it sure was noisey. The noise came and went at different rpms too. The TC diffs seem to have high quality steel gears though. On mine, I think it was the XP cups/shafts that did it in. They wore, then the fluid leaked out. Interestingly, when I installed the swiss cups in my XTR center diff, it too was wobbly with XP cups, then nice and tight after installing the swiss parts. Holding up well still, I just swapped the cups, no reshimming or anything.🤷‍♂️
 
The Swiss centre cups were a straight swap for the black EXH cups. As above, I didn't need to do any additional shimming, and they just seemed to be a better fit through the case and spur gear seal.
 
Jeffwazz said:
The Swiss centre cups were a straight swap for the black EXH cups. As above, I didn't need to do any additional shimming, and they just seemed to be a better fit through the case and spur gear seal.
Click to expand...
Yes, that's what I was trying to say☝️
I will likely do the same with the Python 6s diff I removed from the Xray. Buy the swiss cups, clean everything up and reassemble with new bearings. It has a 46t spur, but that's okay, it's still a good diff to have on hand. Like I said, I had it in an Xray buggy and I'm confident it would drop right into an Arrma 6s as well. I picked the Python center diff from JRC for $25. That's likely what the spur gear alone sells for?
 
KnowAir said:
Yes, that's what I was trying to say☝️
I will likely do the same with the Python 6s diff I removed from the Xray. Buy the swiss cups, clean everything up and reassemble with new bearings. It has a 46t spur, but that's okay, it's still a good diff to have on hand. Like I said, I had it in an Xray buggy and I'm confident it would drop right into an Arrma 6s as well. I picked the Python center diff from JRC for $25. That's likely what the spur gear alone sells for?
Click to expand...
Even more. Not sure on the exchange rate these days but the spur gear for Kronos (52T) is selling for £28 at the minute. Hence why I'm trying to avoid buying one if I can :LOL:
 
Got my replacement centre diff today, installed it raring to go and...... still happening.
Something is slipping and making a horrendous noise and it certainly sounds like it's coming from my centre diff still. How could a brand new diff be slipping? Is my pinion too far out or what?
When I roll the car, everything seems free and I can't really feel anything locking up. As soon as I try to let it push it on it's own power, slippage.
I haven't put loctite in the motor mount screws again just yet but I still tightened the screws pretty tight by hand so I can't imagine that the motor has moved out.

When I find the time I will try removing each centre driveshaft in turn to see if it happens in particular with either. I'm sure I already did this before switching out the diff and it happened with both. Ultimately I think I'm gonna have to pull the whole thing apart (again) to try to get to the bottom of this. My current theory is that either the front or rear diff is to blame? Something isn't as free as it should be and the centre diff is struggling to drive it?
 
Have you checked the pins in the wheel hexes? Not sure that would make any noise but would definitely give a slip as it'll put all power to the wheel with the least resistance. That said I assume a wheel would have fallen off by now, but maybe a pin for the a diff out drive? Or even a front or rear pinion gear stripped, that'll chatter and possibly seem like it's coming from the center diff even though it isn't, I'm just spit balling here, all worth checking if you haven't already
 
Last edited:
Have you tried isolating the front/rear input cups yet?
By sliding a 1mm hex key through the slot, you'll be able to load up the wheels (against the locked out input gear) and check out the front/rear diffs, crown gear and input gear, bevel gears etc. It'll also show up broken hex pins etc, and allow you to hopefully get to the bottom of this.
 
So I did some more testing over the weekend and definitely confirmed it was the backend that was slipping.
Pulled it all apart and noticed that the spur gear in the rear diff was likely the culprit here.

Bought a brand new rear diff off a kit-breaker on ebay and you can see the difference:
IMG_20230719_123527.jpg


Popped the backend together again and voila! Good as new :)

Now I just need to fit my upgrades and rewiring. Always work to do 😂



Thanks for all your help guys!
 
Crikey, that's well worn! With that uneven wear it almost looks as of it was running off-axis.
 
Stormwind said:
So I did some more testing over the weekend and definitely confirmed it was the backend that was slipping.
Pulled it all apart and noticed that the spur gear in the rear diff was likely the culprit here.

Bought a brand new rear diff off a kit-breaker on ebay and you can see the difference:
View attachment 4264

Popped the backend together again and voila! Good as new :)

Now I just need to fit my upgrades and rewiring. Always work to do 😂



Thanks for all your help guys!
Click to expand...
Your crown wheel only had gums...... 🤣
 
Stormwind said:
So I did some more testing over the weekend and definitely confirmed it was the backend that was slipping.
Pulled it all apart and noticed that the spur gear in the rear diff was likely the culprit here.

Bought a brand new rear diff off a kit-breaker on ebay and you can see the difference:
View attachment 4264

Popped the backend together again and voila! Good as new :)

Now I just need to fit my upgrades and rewiring. Always work to do 😂



Thanks for all your help guys!
Click to expand...
Did you check the bulkhead/diff casing for damage. If your original diff got damaged like that, it’s likely there is a crack in the casing which causes the gears to slip.
 
Klappars said:
Did you check the bulkhead/diff casing for damage. If your original diff got damaged like that, it’s likely there is a crack in the casing which causes the gears to slip.
Click to expand...

I didn't notice any when I fit the new diff nor when I just changed out the pinion but then again I wasn't specifically checking for any cracks. Everything looked OK.

I'll certainly give it a detailed look over when I find another 2 hours to strip it down again to swap my diff round.
 
Back
Top