Big Rock Diff case gear and input gear stripped. Why?

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Ragga

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Arrma RC's
  1. BigRock
Hey fam,

Just wondering what would cause the input gear and differential case gear to strip like this? I don’t jump. I mostly drive in grass fields going full speed and I don’t go full throttle right away. I ease into it. Anybody know why it happens. Or just wear and tear?

Thanks

D616B41E-AF41-4436-8982-95193AEAFFB5.jpeg
 
1. If your slipper clutch is too tight it can really wreak havoc on the rear diff. But the wheelies are fun 😁

2. Use plastic safe grease (avoid white lithium, some variants have been known to soften the plastic gears)

3. Check diff mesh, one of mine blew up because arrma put the shim on the wrong side and the mesh was way off.

3.b Ensure diff bearings are pressed on all the way to ensure proper diff mesh.
 
What kinda grease is that? Hopefully not lithium. Doesn't look like the stock stuff I found in mine.
 
Time for parts. Use Super Lube for the new parts. FWIW, if batteries drain quicker while running in grass, then odds are there's some strain being put on the rear diff as well. Granted it's not as much stress as landing a jump under throttle but it's generally gonna heat up the gear more. How old is the vehicle, how many packs have you run through it? How meticulous are you with maintenance, slipper adjustments, are you running larger/heavier tires? Many things can contribute to this wear, in the end its just a plastic gear and will eventually fail. Just chalk it up to the cost of having fun.
 
1. If your slipper clutch is too tight it can really wreak havoc on the rear diff. But the wheelies are fun 😁

2. Use plastic safe grease (avoid white lithium, some variants have been known to soften the plastic gears)

3. Check diff mesh, one of mine blew up because arrma put the shim on the wrong side and the mesh was way off.

3.b Ensure diff bearings are pressed on all the way to ensure proper diff mesh.
I was thinking slipper. I watched a video where you put your screw driver in where the screw for the slipper is then move the truck slowly forward until wheels stop. So maybe too tight?

Also, not sure what the diff mesh is. I’m kind of new to this. Do you mean where the gears come together? Make sure they mesh well and are in line with each other?

Thank you for this info!! I will check all.
 
I was thinking slipper. I watched a video where you put your screw driver in where the screw for the slipper is then move the truck slowly forward until wheels stop. So maybe too tight?

Also, not sure what the diff mesh is. I’m kind of new to this. Do you mean where the gears come together? Make sure they mesh well and are in line with each other?

Thank you for this info!! I will check all.
Loosening the slipper clutch is a safety measure that can protect your diff allowing "slippage" when binding or poor mesh is happing but doesn't solve the problem. To chew teeth away given your relatively tame driving things have to not mesh well. If the slipper is on lock down and all the force of the motor is transferred to the diff then over time plastic gears can wear down but this seems like an alignment/mesh issue in the diff. If you've been running for years or running it a ton with a tight slipper i guess this could be "time wear" but again, seems more like something wasn't meshed well or some junk got in there causing poor mesh. When you get new stuff in there check that mesh of the input to the crown teeth by spinning by hand feeling for any binding or catching, running on the bench at low power (use throttle trim so both your hands are free) and looking and listening for binding. Check for play between the gears, check if differential is "sliding" back and forth side to side in the housing. Small shims can make a lot of difference so have some on hand to take play out. Check the new gears regularly early on for wear. hopefully it was something in the gears themselves and not your diff casing or chassis or something causing miss-alignment.
 
2. Use plastic safe grease (avoid white lithium, some variants have been known to soften the plastic gears)

What kinda grease is that? Hopefully not lithium. Doesn't look like the stock stuff I found in mine.

Interesting. I have read on various forums that people recommend white lithium grease. Never knew this wasn’t safe for plastics. Looks like I opening some diffs today.

I was using Lucas oil Xtra Duty grease but then put on some white lithium because I felt that was to thick for the diff grease.
 
Loosening the slipper clutch is a safety measure that can protect your diff allowing "slippage" when binding or poor mesh is happing but doesn't solve the problem. To chew teeth away given your relatively tame driving things have to not mesh well. If the slipper is on lock down and all the force of the motor is transferred to the diff then over time plastic gears can wear down but this seems like an alignment/mesh issue in the diff. If you've been running for years or running it a ton with a tight slipper i guess this could be "time wear" but again, seems more like something wasn't meshed well or some junk got in there causing poor mesh. When you get new stuff in there check that mesh of the input to the crown teeth by spinning by hand feeling for any binding or catching, running on the bench at low power (use throttle trim so both your hands are free) and looking and listening for binding. Check for play between the gears, check if differential is "sliding" back and forth side to side in the housing. Small shims can make a lot of difference so have some on hand to take play out. Check the new gears regularly early on for wear. hopefully it was something in the gears themselves and not your diff casing or chassis or something causing miss-alignment.
Awesome. thank you I will check all.
Awesome. thank you I will check all. Also truck is fairly new. Bought it in august 2021. Have not driven too much.
Loosening the slipper clutch is a safety measure that can protect your diff allowing "slippage" when binding or poor mesh is happing but doesn't solve the problem. To chew teeth away given your relatively tame driving things have to not mesh well. If the slipper is on lock down and all the force of the motor is transferred to the diff then over time plastic gears can wear down but this seems like an alignment/mesh issue in the diff. If you've been running for years or running it a ton with a tight slipper i guess this could be "time wear" but again, seems more like something wasn't meshed well or some junk got in there causing poor mesh. When you get new stuff in there check that mesh of the input to the crown teeth by spinning by hand feeling for any binding or catching, running on the bench at low power (use throttle trim so both your hands are free) and looking and listening for binding. Check for play between the gears, check if differential is "sliding" back and forth side to side in the housing. Small shims can make a lot of difference so have some on hand to take play out. Check the new gears regularly early on for wear. hopefully it was something in the gears themselves and not your diff casing or chassis or something causing miss-alignment.
Also the truck is only 8 months old. So it must be what you said. How are you doing your slipper clutch though? I put screwdriver in, roll truck forward till the back wheels stop. Then lock tight it. I immediately stop right when those wheels stop. No further. Maybe too tight?
What kinda grease is that? Hopefully not lithium. Doesn't look like the stock stuff I found in mine.
I used marine grease that’s safe for rubber and plastic.
 
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Time for parts. Use Super Lube for the new parts. FWIW, if batteries drain quicker while running in grass, then odds are there's some strain being put on the rear diff as well. Granted it's not as much stress as landing a jump under throttle but it's generally gonna heat up the gear more. How old is the vehicle, how many packs have you run through it? How meticulous are you with maintenance, slipper adjustments, are you running larger/heavier tires? Many things can contribute to this wear, in the end its just a plastic gear and will eventually fail. Just chalk it up to the cost of having fun.
Super lube. Ok will try that. Truck is 8 months old. About it 20 packs. I just put new diff oil in about a month ago. I’m pretty good about maintenance. But looking back when I first serviced I did notice some plastic coming off of the gears.
Time for parts. Use Super Lube for the new parts. FWIW, if batteries drain quicker while running in grass, then odds are there's some strain being put on the rear diff as well. Granted it's not as much stress as landing a jump under throttle but it's generally gonna heat up the gear more. How old is the vehicle, how many packs have you run through it? How meticulous are you with maintenance, slipper adjustments, are you running larger/heavier tires? Many things can contribute to this wear, in the end its just a plastic gear and will eventually fail. Just chalk it up to the cost of having fun.
Oh also running 2.8 Pl badlands. Slipper I adjusted once by putting screw driver in and rolling truck forward until the wheel locked. But stopped as soon as the wheel stopped. No further. Then lock tightened it.
 
Truck is 8 months old. About it 20 packs.
8 months, 20 packs, is actually some pretty good wear on the truck. What may have happened is your input and a ring gear wore down overtime and finally stripped out.

The trucks come from the factory with a shim opposite the ring gear side between the bearing and the diff. Every 8-10 packs are so I check to see if I need to switch that shim to the other side or just remove it altogether. It’s a good idea to open up the differentials anyway every 10 runs and re-grease. Otherwise dust infiltrates the differential housing and gunks up the grease. Then the gunk compacts between the teeth and screws up the mesh.

Superlube is great, it’s a food grade synthetic lubricant. I stay away from grease/lube made from petroleum products. Those can soften plastic and I don’t like the smell lol.
 
For grease I have been using Super lube for yearsView attachment 212800 zero problems. Are you making any soft to hard transitions? That screwed me up before.
Nice. Will try that thanks.

What do you mean soft to hard transitions?
8 months, 20 packs, is actually some pretty good wear on the truck. What may have happened is your input and a ring gear wore down overtime and finally stripped out.

The trucks come from the factory with a shim opposite the ring gear side between the bearing and the diff. Every 8-10 packs are so I check to see if I need to switch that shim to the other side or just remove it altogether. It’s a good idea to open up the differentials anyway every 10 runs and re-grease. Otherwise dust infiltrates the differential housing and gunks up the grease. Then the gunk compacts between the teeth and screws up the mesh.

Superlube is great, it’s a food grade synthetic lubricant. I stay away from grease/lube made from petroleum products. Those can soften plastic and I don’t like the smell lol.
Oh ok. Will definitely check more often! Thanks!
 
Nice. Will try that thanks.

What do you mean soft to hard transitions?

Oh ok. Will definitely check more often! Thanks!
Like from low traction to high traction (dirt to grass for example).
 
Nice. Will try that thanks.

What do you mean soft to hard transitions?

Oh ok. Will definitely check more often! Thanks!
Like from low traction to high traction (dirt to grass for example).
Or also like landing a jump while hard on the throttle.
Basically any scenario that would create a shock stress in the drivetrain.

Interesting. I have read on various forums that people recommend white lithium grease. Never knew this wasn’t safe for plastics. Looks like I opening some diffs today.
I've seen conflicting information on the interwebs about white lithium grease affects on plastics. From what i understand, alot of that comes down to what sort of additives, cleaners, or stabilizers you put into it the specific white lithium grease formula. Some white lithium greases are supposed to be safe for plastics:
https://www.amazon.com/Permatex-80345-White-Lithium-Grease/dp/B000HBNV58
Ultimately just do research before you buy anything. As long as it's safe for plastic, and is a grease, you should be good for use in the diff.

FWIW, i use the superlube.
 
Or also like landing a jump while hard on the

I've seen conflicting information on the interwebs about white lithium grease affects on plastics. From what i understand, alot of that comes down to what sort of additives, cleaners, or stabilizers you put into it the specific white lithium grease formula. Some white lithium greases are supposed to be safe for plastics:
https://www.amazon.com/Permatex-80345-White-Lithium-Grease/dp/B000HBNV58
Ultimately just do research before you buy anything. As long as it's safe for plastic, and is a grease, you should be good for use in the diff.

FWIW, i use the superlube.
That’s actually the exact same White Lithium Grease I had covering my diffs. I already dissembled the granite. Wasn’t for nothing though as a couple of bearing were not spinning great on the drive shafts.

I have seen many people recommend mobil 1 synthetic grease. I think I will give that a try since it readily available at the auto parts store. Appreciate your input.
I haven’t had issues since getting the hot racing diff yokes and good bearings. I use red n tacky grease. We run 4s
That’s exactly what I upgraded to for both front and rear. Added some FastEddyBearings and it so much smoother.
 
Nice. Will try that thanks.

What do you mean soft to hard transitions?

Oh ok. Will definitely check more often! Thanks!

This can also simply be spots in the grass with "dips" where one or more wheels will suddenly not have traction and start spinning quickly, then have traction again suddenly. It can easily be from braking as well where you go from grass to either grippier area of grass or to a paved path with throttle or brakes on. Both can cause shocks to the drivetrain. Loosening your slipper will help prevent all of these things from damaging your diffs. Grass is a very difficult surface for RC rigs because the traction can be high or low with a ton of variation. High drag, high traction, and high variation in surface grip is very hard on drivetrains. It also generates a ton of heat.

The grease in your picture seemed to have a bunch of dry dust or gunk in it. I would clean and seal up that housing as best as possible and put fresh Superlube on the ring and pinion. Ensure that the mesh between the ring and pinion is set properly and that the pinion is aligned with the ring gear for maximum contact. You may need to shim the input gear on one side or the other to get it right. Shim the input gear to get the pinion lined up properly with the ring gear, and shim the diff in the case to get the mesh right.
 
This can also simply be spots in the grass with "dips" where one or more wheels will suddenly not have traction and start spinning quickly, then have traction again suddenly. It can easily be from braking as well where you go from grass to either grippier area of grass or to a paved path with throttle or brakes on. Both can cause shocks to the drivetrain. Loosening your slipper will help prevent all of these things from damaging your diffs. Grass is a very difficult surface for RC rigs because the traction can be high or low with a ton of variation. High drag, high traction, and high variation in surface grip is very hard on drivetrains. It also generates a ton of heat.

The grease in your picture seemed to have a bunch of dry dust or gunk in it. I would clean and seal up that housing as best as possible and put fresh Superlube on the ring and pinion. Ensure that the mesh between the ring and pinion is set properly and that the pinion is aligned with the ring gear for maximum contact. You may need to shim the input gear on one side or the other to get it right. Shim the input gear to get the pinion lined up properly with the ring gear, and shim the diff in the case to get the mesh right.
Ok yes I totally understand about driving on grass now. There are dips and and all that stuff so that makes sense. I will do all what you said. Very helpful. Thank you!
Like from low traction to high traction (dirt to grass for example).
Yes for sure.
 
Super lube. Ok will try that. Truck is 8 months old. About it 20 packs. I just put new diff oil in about a month ago. I’m pretty good about maintenance. But looking back when I first serviced I did notice some plastic coming off of the gears.

Oh also running 2.8 Pl badlands. Slipper I adjusted once by putting screw driver in and rolling truck forward until the wheel locked. But stopped as soon as the wheel stopped. No further. Then lock tightened it.
Big tires and normal wear. For a point of reference, I probably ran 25 packs through my BRCC before it gave up a diff running Granite wheels and loads of jumps.
 
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