Granite Killed a rear diff already!

Goofy

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Wasn't expecting to kill some bearings a diff after about 8 packs, but here we are! Handful of bearings are seized up or really gritty, so I'm guessing this went downstream and stripped the gear on the rear diff.

I don't have a long enough 2mm so I cant split the housing, but you can see all the ground up plastic and some missing teeth.
PXL_20221223_192620396.jpg


Couple of questions stemming from this (as I also killed some bearings on my Fireteam).
  • Are the stock bearings garbage at keeping out sand/dirt/etc.? I typically hose these off after use and hit with an air compressor. Perhaps my maintenance could also use some work?
  • Should I replace with stock plastic gearing or move to metal? I do very basic bashing with my daughter; no crazy jumps, just around parks and a local quarry.

Thanks!
 

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For $11.00

This set is very handy to have around >
https://www.amazon.com/HRB-Screwdri...-Helicopter/dp/B07QGZW57K/ref=sxin_25_ac_d_rm

... Couple of questions stemming from this (as I also killed some bearings on my Fireteam).
  • Are the stock bearings garbage at keeping out sand/dirt/etc.? I typically hose these off after use and hit with an air compressor. Perhaps my maintenance could also use some work?
  • Should I replace with stock plastic gearing or move to metal? I do very basic bashing with my daughter; no crazy jumps, just around parks and a local quarry.

Thanks!

You mean light rinse with a hose or blast it off under pressure?
 

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I recently did the same thing on my Senton 3s during a meetup. Check out my post here of the results. I recommend replacing the stock diff input and ring gear with the Hot Racing Helical gear setup!
 

Goofy

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For $11.00

This set is very handy to have around >
https://www.amazon.com/HRB-Screwdri...-Helicopter/dp/B07QGZW57K/ref=sxin_25_ac_d_rm



You mean light rinse with a hose or blast it off under pressure?
Light rinse with a hose as I was under the impression that was the preferred method.
I recently did the same thing on my Senton 3s during a meetup. Check out my post here of the results. I recommend replacing the stock diff input and ring gear with the Hot Racing Helical gear setup!
Skimmed over your post, did you take each bearing apart to clean and grease them? I'm on the fence on doing this vs buying a kit from JimsRacing or FastEddy.
 
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Tex Koder

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Light rinse with a hose as I was under the impression that was the preferred method.

Yes, that should've been fine.
Doesn't sound like you're doing anything out of the ordinary..

Maybe lube up the joints and bearing areas with some WD-40 Dry Lube..
1671827497198.png
 

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Are the stock bearings garbage at keeping out sand/dirt/etc.? I typically hose these off after use and hit with an air compressor.
Yes the stock bearings are garbage.

Careful with the air compressor near bearings. With a dirty bearing and high enough pressure, you may be pushing dirt into the bearing.
 

parcou

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Wasn't expecting to kill some bearings a diff after about 8 packs, but here we are! Handful of bearings are seized up or really gritty, so I'm guessing this went downstream and stripped the gear on the rear diff.

I don't have a long enough 2mm so I cant split the housing, but you can see all the ground up plastic and some missing teeth.
View attachment 264555

Couple of questions stemming from this (as I also killed some bearings on my Fireteam).
  • Are the stock bearings garbage at keeping out sand/dirt/etc.? I typically hose these off after use and hit with an air compressor. Perhaps my maintenance could also use some work?
  • Should I replace with stock plastic gearing or move to metal? I do very basic bashing with my daughter; no crazy jumps, just around parks and a local quarry.

Thanks!
Hello and welcome!

Been there. The stock bearings are not the best but even with the better JimBearings or whatever, I buy a basher in the dirt, sand, rocks, etc is going to get dirty. I keep plenty not worth the trouble to clean I just replace it. Also after each bash, I look over the rig and turn the tires to listen for crunchy bearings. I replace those. The wheel/hub bearings I remove after 3-5 runs to clean and inspect...replace them if needed. Then I lube with silicone spray.

The bearings in the rear between the power module and the diff get dirty fast, so needs to be checked often. Nothing you did wrong, just depending on the dirt level need to be checked more often. When it comes to eating gears shimming is important here. In some cases, the plastic yoke covers the diff flex and adds to the issue so a metal HR yoke helps no flex keep all the other items stock.
 

Goofy

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Hello and welcome!

Been there. The stock bearings are not the best but even with the better JimBearings or whatever, I buy a basher in the dirt, sand, rocks, etc is going to get dirty. I keep plenty not worth the trouble to clean I just replace it. Also after each bash, I look over the rig and turn the tires to listen for crunchy bearings. I replace those. The wheel/hub bearings I remove after 3-5 runs to clean and inspect...replace them if needed. Then I lube with silicone spray.

The bearings in the rear between the power module and the diff get dirty fast, so needs to be checked often. Nothing you did wrong, just depending on the dirt level need to be checked more often. When it comes to eating gears shimming is important here. In some cases, the plastic yoke covers the diff flex and adds to the issue so a metal HR yoke helps no flex keep all the other items stock.
Interesting take. So you'd replace the yoke and keep the plastic input and diff gears? I thought lubing exposed parts would attract more dirt and grime?
 

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These drivers are fantastic for the price. I’ve used them for over a year and they are still very solid. The stock diffs are good and will last, but you have to watch over them. They need to be maintained on a regular basis, the bearings checked, and the plastic gears re-greased.

You also need to see if this shim needs to be moved or removed. The cars come with a shim on the non-ring gear side of the diff. After a certain amount of use the shim will need to be removed. After further use the shim will need to be put on the ring gear side. I check mine every 4 to 6 weeks and service as well as move the shim if necessary. I only like a tiny bit of play between the input gear and the differential.

There is an issue with the plastic differential yoke flexing. The hot racing diff yokes are great, just pricey at 35 bucks. I’ve been trying this brand for a couple of months and it is just as good as hot racing. It’s only a few bucks cheaper but every little bit matters. If you wanna go with a metal differential and you’re staying on 3S power the 4S metal differential is really good. It may be a bit weak for 4s power but plenty strong for 3s and can be bought off jrennysrc.com for $38. You also need a metal input gear.

There are also CNC metal differentials. You can build one using the interior gears from a stock differential for a round 40 bucks in parts, or buy a complete one for 75 I think.

C882D519-3D9A-41E8-BAEF-C4D9B585FE80.png


65B3A48C-3DE3-4914-B4C3-AB767096AC7B.png


3DF3231C-C986-4235-ABF1-AF02DDCFD835.png


32287C79-C7F3-44FC-BAB9-13C6AAE792BA.png
 
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parcou

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Interesting take. So you'd replace the yoke and keep the plastic input and diff gears? I thought lubing exposed parts would attract more dirt and grime?
@Velodromed answered it best....good vet there I've learned a lot from that guy!

I have some old posts about your issue when I had the same issue. What killed it for me:

1. As Velodromed said, I was not or did not know as a newbie to keep checking my diffs as they wear to shim and keep the mesh right....it does change over usage

2. Using the metal yoke with the plastic stock diff and input was great for me. I could tighten down on the yoke screws, which is tricky with the plastic yoke. Then I could move the shims to get the best gear mesh and the comfort of knowing the metal yoke was not going to flex. It's a good replacement for the stock stuff.

Nothing wrong with the metal diff, but starting with the metal yoke is a good first step.... and/or closer watch and maintenance on the stock stuff.
 

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Stock bearings are OK for most, however hosing off the car after each use leaves the unsealed bearings prone to water intrusion and stagnation, which means they will rust up and grind to fine powder. Sealed bearings, steel diffs, and aluminum diff carriers are my recommendation.
 

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Skimmed over your post, did you take each bearing apart to clean and grease them? I'm on the fence on doing this vs buying a kit from JimsRacing or FastEddy.
I've already replaced the stock bearings, but yes, I cleaned out the bearings and re-greased them.
 

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How do you shim these and go about getting the mesh correct? Is there a shim kit available? I still have the stock diff's in my Granite.
Thanks in advance
 

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How do you shim these and go about getting the mesh correct? Is there a shim kit available? I still have the stock diff's in my Granite.
Thanks in advance
Good question

Took me a lot of time and videos to get it right and post here. For this rig, I find it best to have the diff housing in my hand assembled in the yoke and with the input gear in. I can spin and feel to determine if the mesh is good or if I need to add or remove shims from the crown gear side.

It needs to be assembled to get it right.

Shim, they are various sizes, and you will collect them over time. For this diff:
https://www.amainhobbies.com/arrma-washer-4-12x15.5x0.2mm-ara709052/p707217
 

BgSkyRC

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Good question

Took me a lot of time and videos to get it right and post here. For this rig, I find it best to have the diff housing in my hand assembled in the yoke and with the input gear in. I can spin and feel to determine if the mesh is good or if I need to add or remove shims from the crown gear side.

It needs to be assembled to get it right.

Shim, they are various sizes, and you will collect them over time. For this diff:
https://www.amainhobbies.com/arrma-washer-4-12x15.5x0.2mm-ara709052/p707217
Thanks for the quick reply. So do you want the mesh like you would do for the Spur gear then, not to loose and not too tight? Maybe I need to play around with it and get a feel for it, by taking the shim out and feeling it and vise versa. I appreciate the link to the shims.
 

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Thanks for the quick reply. So do you want the mesh like you would do for the Spur gear then, not to loose and not too tight? Maybe I need to play around with it and get a feel for it, by taking the shim out and feeling it and vise versa. I appreciate the link to the shims.
Correct like the gear doing it the same. I had to do the same. Put it all together with no shim and compare the feel. Then add 1 or 2 shims to see how it feels and sound. It's hard to see the mesh completely with the yoke on but it needs to be assembled in your hand to spin and test for proper mesh. But I can feel how much rocking I have when I turn the input gear.

You have the process right (y)
 

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So I took both front and rear diff's out, they both had 1 shim on the non gear side under the bearing so closest towards the crown gear. So this would be for a looser fit correct? Either way, not happy with the quality, you have to barely tighten the yolk almost leaving it loose for a smooth feeling, if you tighten them up where the case half's touch it is very notchy feeling and only in one spot in rotation, it's like something is out of round so to speak but can't see it. I have had only one run on this totally stock and on 2s no bashing, due to weather out here. Bearings are good and internals on the diff look good to with the planetary gears. I noticed on You Tube a lot of people shredding the diff gears on there Big Rocks also and getting the metal set posted above. I ordered the HR yolk and both metal diff and pinion, spendy but hope it resolves this issue. It's a great truck other wise I like it. I'm new to RC cars, been flying heli's for the past 8 years and needed a change, fitment with heli's is crucial specially in the drivetrain, so this is dissapointing, at least I cant crash it and cost me hundreds of dollars to repair and parts flying off in a 30 foot radius! Sorry Goofy, I'm not trying to Hijack your thread, you just had the perfect post, I was going to post the same topic and see you beat me to it. :D
 

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So I took both front and rear diff's out, they both had 1 shim on the non gear side under the bearing so closest towards the crown gear. So this would be for a looser fit correct? Either way, not happy with the quality, you have to barely tighten the yolk almost leaving it loose for a smooth feeling, if you tighten them up where the case half's touch it is very notchy feeling and only in one spot in rotation, it's like something is out of round so to speak but can't see it. I have had only one run on this totally stock and on 2s no bashing, due to weather out here. Bearings are good and internals on the diff look good to with the planetary gears. I noticed on You Tube a lot of people shredding the diff gears on there Big Rocks also and getting the metal set posted above. I ordered the HR yolk and both metal diff and pinion, spendy but hope it resolves this issue. It's a great truck other wise I like it. I'm new to RC cars, been flying heli's for the past 8 years and needed a change, fitment with heli's is crucial specially in the drivetrain, so this is dissapointing, at least I cant crash it and cost me hundreds of dollars to repair and parts flying off in a 30 foot radius! Sorry Goofy, I'm not trying to Hijack your thread, you just had the perfect post, I was going to post the same topic and see you beat me to it. :D
All good! I'm learning too 😁
 

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@Goofy ,
I never allow my BB's to get wet. Chromium BB's will rust. In minutes you can see them turn rusty brown. They are donefore at this point. Can't undo that.
With my FT for instance, before I drive it, I removed every BB and repacked them with 1/3 grease. (automotive Bearing grease)
Many new BB's were just Dry upon removing the seals. I think this is why many are having BB issues. Good to have spare sets of BB's on hand. Just part of the hobby to replace them here and there. Well before they contribute to more damage, i.e. stripped gears. Lube the Gears well also. Sometimes the factory doesn't install enough. Even the Diffs can be low on oil.
 

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@Goofy ,
I never allow my BB's to get wet. Chromium BB's will rust. In minutes you can see them turn rusty brown. They are donefore at this point. Can't undo that.
With my FT for instance, before I drive it, I removed every BB and repacked them with 1/3 grease. (automotive Bearing grease)
Many new BB's were just Dry upon removing the seals. I think this is why many are having BB issues. Good to have spare sets of BB's on hand. Just part of the hobby to replace them here and there. Well before they contribute to more damage, i.e. stripped gears. Lube the Gears well also. Sometimes the factory doesn't install enough. Even the Diffs can be low on oil.
This is something I'm learning post-ownership; QC isn't that great. At this point I plan on checking both diff fluids, tossing some red tack in the case, and probably replace each stock bearing while I'm at it.
 
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