Kronos Help with noisy gearing

[Stormwind]

Hi,
On my last outing I noticed that my gearing was incredibly noisy and not sounding good at all.
After giving it a once over at home I found that I had lost one screw holding the motor mount to the body. I assumed that
this was the main issue due to the gearing being free to move around messing up the mesh.

I have replaced the screw and ensured the others at the bottom of the chassis have had Loctite applied.

I also removed a stone that was rattling around under the battery tray (I wonder if this made its way underneath the center diff at some point causing the vibrations that shook the screw out in the first place?).

Whilst I was at it, I also inspected the gearing and can't see any noticeable damage to either the pinion or spur gears.
However, after putting everything back together, the gearing is still very noisy.

My initial thoughts are that the meshing is now out of alignment (although to my n00b eye it looks fine). I have attempted to loosen the positioning screws to see if adjusting it makes a difference but I'll be darned if I can undo them at all. Have they used green loctite in the factory or something? Any tips on undoing these screws?
Is there any other places I should be checking?

 

[Jeffwazz]

Heat and well fitting tools are your friends when it comes to loctite. To concentrate the heat in the head, try a soldering iron with a large tip.
If it doesn't move easily, try heating again, it'll move eventually - just don't strip the head! That's annoying
Make sure the gear teeth are clean and meshed right, if it's still noisy, there might be some burrs or rough bits. And of course check the drive cups/shafts/bearings.

 

[KnowAir]

Have you checked the gear mesh between the motor pinion and spur gear? Something may have moved. I use a sheet of standard copy paper as a gauge. Check the mesh in several different spots by rotating the gears and rechecking as the gears are usually not perfectly round.

 

[Stormwind]

I've spent a few hours today trying to get to the bottom of this with no luck. I've managed to loosen the meshing screws and remeshed it several times and it is still happening. I also changed out my pinion to a brand new 14tooth that I had spare and its still doing it.

I've tried several different combinations of things, motor running by itself with no spur gear, sounds fine. Then with the spur gear attached, no center drive shafts in place, the noise came back. What was also strange was that I reattached everything including the wheels and found that as soon as there was the extra load, I can hear something slipping. Out of curiosity I tried jamming the pinion right into the spur and span it up slowly to see if that still occured and it did seem too.

Am I right in thinking that I need to pull the centre diff apart next to see what's what in there? I have been reluctant to do that today due to not having any new diff oil handy. Is it possible that one of the gears inside is worn and needs replacing? Would that fit these symptoms?

 

[DaniC]

I've spent a few hours today trying to get to the bottom of this with no luck. I've managed to loosen the meshing screws and remeshed it several times and it is still happening. I also changed out my pinion to a brand new 14tooth that I had spare and its still doing it.

I've tried several different combinations of things, motor running by itself with no spur gear, sounds fine. Then with the spur gear attached, no center drive shafts in place, the noise came back. What was also strange was that I reattached everything including the wheels and found that as soon as there was the extra load, I can hear something slipping. Out of curiosity I tried jamming the pinion right into the spur and span it up slowly to see if that still occured and it did seem too.

Am I right in thinking that I need to pull the centre diff apart next to see what's what in there? I have been reluctant to do that today due to not having any new diff oil handy. Is it possible that one of the gears inside is worn and needs replacing? Would that fit these symptoms?

What you've done here is exactly what I was about to suggest, you have isolated the rear and front and know you know it's the center diff.
How are the diff bearings? Could they perhaps be binding?
It's definitely worth opening up the diff and checking everything and rebuilding it.
Could you perhaps be setting that mesh too tight?

 

[KnowAir]

Is there any freeplay at the motor shaft itself? How about the output cups of the center diff? I used a Python 6s center diff in an Xray buggy that went south on me pretty quickly. The diff fit and worked perfectly for some time, then I started hearing some strange noises coming from the buggy about a month ago.
It only made noise at certain rpms..I discovered while the buggy was unweighted on a stand that the center diff output cups were wobbling excessively. Come to think of it, my 21 Kronos XTR did the same.. the XP(black) drive cups wear really fast in my experience. The center diff cups and shafts were really sloppy in the spur and diff cup at the other end.. I got the Swiss steel cups for the XTR under warranty from Corally, once I installed those, I haven't had a problem.
As to the Xray, I took the TC center diff out and replaced with a new diff from Xray. No more noises. So, it may very well be the center diff?

 

[Stormwind]

It's definitely worth opening up the diff and checking everything and rebuilding it.

I have the diff open and draining now. Just waiting on some brake cleaner to be able to dismantle it properly. I'll clean all the grease away to look properly.

Could you perhaps be setting that mesh too tight?

I tried with multiple meshing. What I believed to be correct, purposefully too tight and purposefully too loose as well just to see the differences (only at slow RPMs so I didn't kill anything).

Is there any freeplay at the motor shaft itself?

I'm not entirely sure what you mean by this.

How about the output cups of the center diff?

I can't say I ever looked too closely at my diff cups until now and have never replaced any on my other model. I have taken a look now whilst dismantling the center diff and noticed weird notches in them. I initially thought that they had worn but looking seeing as both center diff cups have them and seemingly like the rest of them do too, I can only assume that it's normal?

 

[Jeffwazz]

It's normal, in-so-much as that's how all drive cups wear. It's the pin in the driveshaft that kinda cuts into the cup, and gives more and more rattle, and as it cuts the notch deeper, stops the pin from sliding in the slot, will probably give the noise you're hearing.
Those cups are done - time for an upgrade to the Swiss spring-steel. The gearbox input cups are likely in a similar state, so would also benefit from the spring steel upgrade.

There's also some wear on the diff case - did something get stuck in there or is the diff not running true on the bearings?

 

[Stormwind]

Those cups are done - time for an upgrade to the Swiss spring-steel.

That would be these ones vs the parts listed the manual?

The gearbox input cups are likely in a similar state, so would also benefit from the spring steel upgrade.

These ones right? It's gonna be an expensive order

There's also some wear on the diff case - did something get stuck in there or is the diff not running true on the bearings?

There was stone lodged under the battery case that I assume has likely made contact with the housing at some point. Once I get my brake cleaner I'll pull it all apart, clean it up and reassemble to try and gather how it's looking. I'll probably buy some more bearings anyway when I replace the diff cups. Do you think the casing will need replacing as well?

 

[Jeffwazz]

These for the gearbox end of the centre driveshaft. If yours is like mine, then these will also have a fairly deep slot cut into them by the drive pin.

And as for the diff case, personally I wouldn't replace it. It's only a bit of the anodize missing.

Expensive? Yeah, especially when you add on a set of driveshafts as the pin will probably be worn as well.......

 

[KnowAir]

I agree, that diff needs a rebuild. The slots are pretty well worn out where the dogbones ride, as well as the spur looking pretty worn. As the teeth of the gears wear, they definitely do get noisier I find.
I was referring to the motor bearings in regards to freeplay of the motor shaft.
The swiss parts at each diff input and ouput, along with center driveshafts does sure add up.. IIRC, around $140.

These for the gearbox end of the centre driveshaft. If yours is like mine, then these will also have a fairly deep slot cut into them by the drive pin.
View attachment 4084

And as for the diff case, personally I wouldn't replace it. It's only a bit of the anodize missing.

Expensive? Yeah, especially when you add on a set of driveshafts as the pin will probably be worn as well.......

IDK if Jenny's rc ships overseas but, $110 for complete front, center and rear diffs (swiss)with gearboxes for $110 is a great deal.

 

[Jeffwazz]

Looks like a very good deal on the stuff from Jenny's.
Of course, need to factor in the exchange rates, shipping, possible import duty and the Royal Mail ransom demands, but for fully built front, rear, centre that's a very good deal

 

[KnowAir]

Looks like a very good deal on the stuff from Jenny's.
Of course, need to factor in the exchange rates, shipping, possible import duty and the Royal Mail ransom demands, but for fully built front, rear, centre that's a very good deal

IDK what is available in the UK, but have to imagine there are kit breakers? I'm not certain if the Asuga or other TC 6s buggies use the same gears and ratios in the diffs as the truggies or trucks. I think so. Arrma uses different gears and ratios between truggies and buggies, so worth checking with TC parts listings between models to be sure.

 

[Jeffwazz]

Fortunately there's a few kit breakers selling on eBay. Front/rear diffs seen to run around 40quid (for the Asuga with the Swiss outputs), centre for around 50quid (looked to be a exh outputs from an XP 6s). No doubt what you need will come up, but they don't seen to shift the same volumes as Jenny's.

 

[KnowAir]

Fortunately there's a few kit breakers selling on eBay. Front/rear diffs seen to run around 40quid (for the Asuga with the Swiss outputs), centre for around 50quid (looked to be a exh outputs from an XP 6s). No doubt what you need will come up, but they don't seen to shift the same volumes as Jenny's.

Does TC use the same ring/pinion ratios acrossed the 6s line? Including the Sketer too I think. Starting with the 2022 Kronos XTR, Sketer and now the Asuga, all 3 of these use the swiss spring steel outdrives. If gear ratios in the diffs are in fact the same, any of these from a kit breaker could be a great option to upgrade a 6s rtr.
I could've swore there was a change in center driveshafts between the 21 and 22 XTR, but then couldn't find an alternate part number for them.
That's my achilles now with my 21 XTR.. center driveshafts. I think the amount of offset of the center diff on the TC rigs is the biggest reason they wear so quickly.

 

[Jeffwazz]

Based on the teeth on the ring/spur gears, it's possible that the 6s line uses common parts. Not checked the part numbers, but the pictures do look very similar!
My Punisher is my first TC model, so not sure if there was a change in driveshafts or just the upgrade to the Swiss sitting steel cups. Either way, with the offset, something will wear - I expect that the Swiss steel will wear the driveshaft pins faster than the EXH cups. Not a new problem, my SavageXS has the same issue.

 

[KnowAir]

Based on the teeth on the ring/spur gears, it's possible that the 6s line uses common parts. Not checked the part numbers, but the pictures do look very similar!
My Punisher is my first TC model, so not sure if there was a change in driveshafts or just the upgrade to the Swiss sitting steel cups. Either way, with the offset, something will wear - I expect that the Swiss steel will wear the driveshaft pins faster than the EXH cups. Not a new problem, my SavageXS has the same issue.

Since I've swapped to the swiss parts on my XTR, and replaced center driveshats at the same time, I haven't noticed any change in the center driveshaft wear. They're wearing about the same I feel. The cups however are indeed much improved.
I have a Redcat Kaiju that seems to wear the front diff input cup and related forward portion of the center driveshaft rather quickly as well. On that, it's not the offset but rather the angle of the front differential housing that seems to be the culprit..along with questionable quality steel.. basically every year or so, I have to replace the input cup and center front driveshaft.

 

[Jeffwazz]

Good to hear that the Swiss cups don't wear the pins excessively.
And as to your Kaiju, I'd be more than happy with a year or two before replacement - the standard SavageXS cups would last me about a month before developing a very deep notch!

 

[chipster]

Hi,
On my last outing I noticed that my gearing was incredibly noisy and not sounding good at all.
After giving it a once over at home I found that I had lost one screw holding the motor mount to the body. I assumed that
this was the main issue due to the gearing being free to move around messing up the mesh.

I have replaced the screw and ensured the others at the bottom of the chassis have had Loctite applied.

I also removed a stone that was rattling around under the battery tray (I wonder if this made its way underneath the center diff at some point causing the vibrations that shook the screw out in the first place?).

Whilst I was at it, I also inspected the gearing and can't see any noticeable damage to either the pinion or spur gears.
However, after putting everything back together, the gearing is still very noisy.

My initial thoughts are that the meshing is now out of alignment (although to my n00b eye it looks fine). I have attempted to loosen the positioning screws to see if adjusting it makes a difference but I'll be darned if I can undo them at all. Have they used green loctite in the factory or something? Any tips on undoing these screws?
Is there any other places I should be checking?

I feel for you. I bought a new Python and wanted to fit a bigger pinion than the 13T it came with. I could not budge the grub screw at all and ended up grinding it off

 

[Stormwind]

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 ). 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.