Granite Broke my First Diff Input Gear

[Adamator]

Hey all

Had a bit of bad luck with my Granite the last few weeks. Started with my rear diff. I had to replace it as a screw got stripped that connects the driveshaft and I couldn't recover it. Got a replacement from Jenny's RC. Although what happened might have been avoided, it was a good experience in that it got me kind of familiar with accessing the Diffs.

Then I managed to crack the slipper set and stripped another spur gear. I replaced the slipper set and took the opportunity to upgrade to a metal spur gear.

Weather has been bad here, so I had not used my Granite in days. But I had a chance today to take it to my favorite spot, a BMX Park. It was the first time I had ran it since replacing the Diff, slipper set, and upgrading to the metal spur gear. Almost immediately I knew something was up as when I gunned the throttle, I had almost no power. Still being only a few months into this hobby, I wasn't entirely sure what was going on but I was pretty sure I could hear the slipper. I took my truck back to my car (I had brought my tools thankfully) and adjusted my slipper. (I adjusted it based on the popular method that floats around on this site.) That seemed to fix things and I had a good run for almost all of my 5000 mAH 3S Lipo. I was mostly just doing laps on the rc track that is there. Near the end the same problem seemed to return but this time much worse. I had almost no rear power at all.

https://share.icloud.com/photos/0yyGYpduIrrSgLXfpRAG5UNyg

I wasn't sure what was wrong this time but decided to just pack it in and head home. Later took things apart and found I had indeed stripped out my first Input Gear. Based on how often I hear these break, I have been fortunate that this is my first one and I got the truck at the beginning of June.

Getting to the point of my post. In taking my Diff out and inspecting it, I noticed something on the exploded diagram I had somehow missed before. There is (I think) a shim on the outside of the diff case, part AR709052.

I don't have that piece on my diff and if I did, it's long gone unfortunately. (Or if it's still on there, I definitely do not see it.) I wanted to ask how important that shim is? and could it missing be what caused me to strip my first Input Gear after all these months?

If not, what are some other common things that cause them and how can I (Hopefully) avoid it?

Thank you.

 

[travykat]

Ive broke 2 rear input gears and let me say its deff not the shim & that shim is located underneath the bearing on the diff case supposed to be on the gear side of the diff but that can't be it my guess is well for me my driving style i rip it on turns and constantly give it full throttle out of turns kinda tryna make it drift type of style driving & make sure theres ample lube i use red & tacky from Lucas oil inside where the input & yoke is
Idk if that answers anything you asked lol

 

[SrC]

Shims are generally not optional. If missing just replace it. Just buy them. Why try to guess if it matters or not. It was there . You need it.

 

[parcou]

Hey all

Had a bit of bad luck with my Granite the last few weeks. Started with my rear diff. I had to replace it as a screw got stripped that connects the driveshaft and I couldn't recover it. Got a replacement from Jenny's RC. Although what happened might have been avoided, it was a good experience in that it got me kind of familiar with accessing the Diffs.

Then I managed to crack the slipper set and stripped another spur gear. I replaced the slipper set and took the opportunity to upgrade to a metal spur gear.

Weather has been bad here, so I had not used my Granite in days. But I had a chance today to take it to my favorite spot, a BMX Park. It was the first time I had ran it since replacing the Diff, slipper set, and upgrading to the metal spur gear. Almost immediately I knew something was up as when I gunned the throttle, I had almost no power. Still being only a few months into this hobby, I wasn't entirely sure what was going on but I was pretty sure I could hear the slipper. I took my truck back to my car (I had brought my tools thankfully) and adjusted my slipper. (I adjusted it based on the popular method that floats around on this site.) That seemed to fix things and I had a good run for almost all of my 5000 mAH 3S Lipo. I was mostly just doing laps on the rc track that is there. Near the end the same problem seemed to return but this time much worse. I had almost no rear power at all.

https://share.icloud.com/photos/0yyGYpduIrrSgLXfpRAG5UNyg

I wasn't sure what was wrong this time but decided to just pack it in and head home. Later took things apart and found I had indeed stripped out my first Input Gear. Based on how often I hear these break, I have been fortunate that this is my first one and I got the truck at the beginning of June.

Getting to the point of my post. In taking my Diff out and inspecting it, I noticed something on the exploded diagram I had somehow missed before. There is (I think) a shim on the outside of the diff case, part AR709052.


View attachment 175897

I don't have that piece on my diff and if I did, it's long gone unfortunately. (Or if it's still on there, I definitely do not see it.) I wanted to ask how important that shim is? and could it missing be what caused me to strip my first Input Gear after all these months?

If not, what are some other common things that cause them and how can I (Hopefully) avoid it?

Thank you.

I am not the best at explaining this....but in short the shim on the ring gear side helps to push your spur gear and input gear teeth closer together for a better mesh. It all varies per RC if you need one or some or if over time the mesh needs to be adjusted as it loosens over time.

Some newer rigs I have seen posted did not come with a shim on the ring gear side. Being new it may have been tight but overtime or runs it can get loose. One of those things you want to check after a few battery backs to see if the mesh is still good.

How I check mine is with the diff out of the RC. I have the yoke on and I spin the diff and listen to the sound to feel how close the mesh is. You can play around with it to feel and hear differences when you add 1,2,3 shim to the ringside to see how the teeth feel and sound.

Keep this in mind as well if you bash hard. The plastic yoke does flex so allows little movement. I think a wise and cheap upgrade with keeping the plastic diff ring gear as well as the plastic input gear is to get the HR metal yoke. Tightens down good and you will not get any yoke flex and much longer life out of your plastic gears....still remember to shim that as well but it will be a great upgrade. Only needed for the rear diff.

 

[SrC]

^^^ This.
@parcou knows 4x4's well.

 

[Adamator]

Thanks all. So it turns out I have that shim after all! I swear it was lost but apparently not. In any case, one less thing to worry about.

I have extensively watched videos and read about the motor mesh, but are there any tips for the Diff mesh? Once I get my new input gear, I of course want to put things back together best I can.

I was going to consider upgrading to an all metal input gear but looking into it, it seems you have to upgrade the whole diff to go along with it. Can anyone confirm if that’s true? If so, I think I’ll just get another regular input gear for now. Maybe get a spare as well.

 

[travykat]

Thanks all. So it turns out I have that shim after all! I swear it was lost but apparently not. In any case, one less thing to worry about.

I have extensively watched videos and read about the motor mesh, but are there any tips for the Diff mesh? Once I get my new input gear, I of course want to put things back together best I can.

I was going to consider upgrading to an all metal input gear but looking into it, it seems you have to upgrade the whole diff to go along with it. Can anyone confirm if that’s true? If so, I think I’ll just get another regular input gear for now. Maybe get a spare as well.

You can get a metal input gear by itself and yea you need the diff gear and diff housing

 

[Adamator]

You can get a metal input gear by itself and yea you need the diff gear and diff housing

But can I use the metal input gear with the stock diff gear and housing?

 

[Kla912000]

But can I use the metal input gear with the stock diff gear and housing?

Yes you can use the metal CNC diff input gear with the stock plastic diff ring gear and diff case, BUT, it is generally recommended to replace and use the metal ring gear also when upgrading to the metal CNC input gear.

 

[Grimbles]

^^^ This.
@parcou knows 4x4's well.

+1 @parcou - spot on

 

[travykat]

But can I use the metal input gear with the stock diff gear and housing?

Yea you can but im sure you can guess metal on plastic doesn't last long

 

[parcou]

But can I use the metal input gear with the stock diff gear and housing?

OR...start with the cheaper option and leave the stock diff as is and use HR metal yoke. I agree with all the others that posted on this question.

I was cool with what I just stated until I begin to use my rig outside of what it was designed for. As soon as I put belted tires on...right away I begin to strip rear gears and/or begin to change the punch settings. Belted Trenchers are heavy so metal gear ring and metal input helped me a lot with the CVD driveshafts...but I was out of factory specs doing this. So you really have to build to how you bash if I left it stock and wanted a bit more strength a better yoke would have been fine to reduce flex keep a consistent mesh.

Looks like you are getting there. Search this forum lots of talk on this subject

 

[Adamator]

Yea you can but im sure you can guess metal on plastic doesn't last long

That was kind of my thought as well. I decided to get a regular Gear for now. I’ll see how long it lasts.

****

What are some common reasons input gears get stripped and can any of them be avoided or mitigated?

 

[travykat]

That was kind of my thought as well. I decided to get a regular Gear for now. I’ll see how long it lasts.

****

What are some common reasons input gears get stripped and can any of them be avoided or mitigated?

I cant say for everyone but my senton witch is I bieleve same internals as the granite but i have a gpm rear yoke & i use red&tacky in my rear & also the metal rear hubs & upgraded bearings& gom tierods but honestly i feel like it could be your driving style for me im constantly ripping it out of a turn i gas it kinda like im tryna drift it

 

[Adamator]

I cant say for everyone but my senton witch is I bieleve same internals as the granite but i have a gpm rear yoke & i use red&tacky in my rear & also the metal rear hubs & upgraded bearings& gom tierods but honestly i feel like it could be your driving style for me im constantly ripping it out of a turn i gas it kinda like im tryna drift it

View attachment 175939

View attachment 175940

Nice upgrades and thanks for the reply. This might be an ignorant question but how do the metal yokes help? (Yokes are the orange things in your photo right?) my yokes haven’t been a problem.

I’d be surprised if my issue was my driving. Simply because I don’t drive my car hard. If anything I’m being more careful lately with all the things I have broke.

What is red&tacky?

 

[GRC]

Red & Tacky is grease. You should definitely be greasing the outer gears of your differentials. I also grease the edges of the shock tower's diff housings to prevent dirt from getting in and chewing up the gears. If grease alone doesn't solve the issue, you can try the following. Don't try them all at once. Try one at a time and see if you're still stripping input gears/diffs.

A common reason of stripping gears is landing jumps under power. If the wheels are spinning under power in the air and then abruptly get stopped when landing, it can strip gears.

I think another major cause of rear diffs and input gears stripping is rear end flex, which happens during bumpy driving and especially when landing jumps. The input gear and rear differential connection gets bent and the gears strip each other. Every time I've stripped the rear diff was immediately after landing a big jump. (I'm not landing under power, I land in neutral)

A metal diff yoke reduces this flex because it holds both the differential and input gear together with less flex than the plastic yoke. I have the Hot Racing metal yoke in the rear and I do think it helped reduce rear input gear/diff damage.

However, I jump pretty high, so I still managed to strip rear diffs on hard landings. I got the 4s tower to tower center brace. It most definitely reduces rear end flex. So far so good, I have not stripped the rear diff since.

The final solution would be to get the metal diff gear and metal input gear upgrade. But it's expensive, often out of stock, and I'd like to avoid the extra weight. So far the metal yoke and center brace are enough. If I strip another rear diff, I'll try the metal diff/input gear upgrade.

 

[BulletRCs_NZ]

Nice upgrades and thanks for the reply. This might be an ignorant question but how do the metal yokes help? (Yokes are the orange things in your photo right?) my yokes haven’t been a problem.

I’d be surprised if my issue was my driving. Simply because I don’t drive my car hard. If anything I’m being more careful lately with all the things I have broke.

What is red&tacky?

red&tacky is grease.

Diff oil is better

I have a box full of stripped diffs and input gears. I have the CNC steel diff set in one of my 3s rigs and it's solid. Hasn't stripped yet and I like to send em! But the composite one, well rebuild one just yesterday. Steel diff sets are expensive but back in stock.

 

[Adamator]

Red & Tacky is grease. You should definitely be greasing the outer gears of your differentials. I also grease the edges of the shock tower's diff housings to prevent dirt from getting in and chewing up the gears. If grease alone doesn't solve the issue, you can try the following. Don't try them all at once. Try one at a time and see if you're still stripping input gears/diffs.

A common reason of stripping gears is landing jumps under power. If the wheels are spinning under power in the air and then abruptly get stopped when landing, it can strip gears.

I think another major cause of rear diffs and input gears stripping is rear end flex, which happens during bumpy driving and especially when landing jumps. The input gear and rear differential connection gets bent and the gears strip each other. Every time I've stripped the rear diff was immediately after landing a big jump. (I'm not landing under power, I land in neutral)

A metal diff yoke reduces this flex because it holds both the differential and input gear together with less flex than the plastic yoke. I have the Hot Racing metal yoke in the rear and I do think it helped reduce rear input gear/diff damage.

However, I jump pretty high, so I still managed to strip rear diffs on hard landings. I got the 4s tower to tower center brace. It most definitely reduces rear end flex. So far so good, I have not stripped the rear diff since.

The final solution would be to get the metal diff gear and metal input gear upgrade. But it's expensive, often out of stock, and I'd like to avoid the extra weight. So far the metal yoke and center brace are enough. If I strip another rear diff, I'll try the metal diff/input gear upgrade.

Ah ok it's the grease. Yeah I did use some Lithium Grease the time I had to open the Rear diff section on the truck. I've only used it the one time. Jumping could be my problem. It's something I started doing fairly recently and even built myself a 1.5 feet x 3 feet ramp. Even not going fast, the truck gets rather high. I need to be more careful with my landings.

Appreciate the input and thoughts on breaking diffs and the options I'd have going forward.

red&tacky is grease.

Diff oil is better

I have a box full of stripped diffs and input gears. I have the CNC steel diff set in one of my 3s rigs and it's solid. Hasn't stripped yet and I like to send em! But the composite one, well rebuild one just yesterday. Steel diff sets are expensive but back in stock.

I'm honestly avoiding getting into changing diff oil if I can help it. That's a bit too in the weeds for me. I'll replace it if I need to, but I don't see myself messing with other weights or anything like that. Truth is, I do not know if I would notice the difference even if I did try didn't diff oils.

I may get that metal diff parts after I've broken enough. But since was my first one after 4 months...I think I've been pretty lucky!


Thanks again everyone. New parts should be here soon. Maybe today.

 

[travykat]

Ah ok it's the grease. Yeah I did use some Lithium Grease the time I had to open the Rear diff section on the truck. I've only used it the one time. Jumping could be my problem. It's something I started doing fairly recently and even built myself a 1.5 feet x 3 feet ramp. Even not going fast, the truck gets rather high. I need to be more careful with my landings.

Appreciate the input and thoughts on breaking diffs and the options I'd have going forward.


I'm honestly avoiding getting into changing diff oil if I can help it. That's a bit too in the weeds for me. I'll replace it if I need to, but I don't see myself messing with other weights or anything like that. Truth is, I do not know if I would notice the difference even if I did try didn't diff oils.

I may get that metal diff parts after I've broken enough. But since was my first one after 4 months...I think I've been pretty lucky!


Thanks again everyone. New parts should be here soon. Maybe today.

Honestly ive been scared to change the diff oil but its really easy if you can take apart everything & actually change the input gear your capable of changing the diff oil trust you wont have to take the gears out just open put in oil thats it & I changed mine to 20k diff oil & you will see a huge difference & the yoke will just keep the rear solid I haven't stripped any gears since I installed it & I stripped 2 before

 

[Velodromed]

Ah ok it's the grease. Yeah I did use some Lithium Grease the time I had to open the Rear diff section on the truck. I've only used it the one time. Jumping could be my problem. It's something I started doing fairly recently and even built myself a 1.5 feet x 3 feet ramp. Even not going fast, the truck gets rather high. I need to be more careful with my landings.

Appreciate the input and thoughts on breaking diffs and the options I'd have going forward.


I'm honestly avoiding getting into changing diff oil if I can help it. That's a bit too in the weeds for me. I'll replace it if I need to, but I don't see myself messing with other weights or anything like that. Truth is, I do not know if I would notice the difference even if I did try didn't diff oils.

I may get that metal diff parts after I've broken enough. But since was my first one after 4 months...I think I've been pretty lucky!


Thanks again everyone. New parts should be here soon. Maybe today.

Diff oil is easy to change. Plus they only come 1/3 to 1/2 full from the factory, so typically I open them new to top off with a higher weight in front (50) and lower in back (30). Stock weight is 10 so mixing the two give approx 25-30 up front and 15-20 in back. You don’t have to remove the axles or bearings to open it, just the 4 small screws.

Just make sure to be careful when opening so you don’t mess up the gasket. I slide a razor underneath to careful pull the gasket free if it’s sticking. Next, do not get oil in the pin holes or screw holes. This will muck things up when you try to reassemble.

Simply fill the case about an 8th of an inch from the top. I don’t remove the inside gears when doing this. I only do that if the diff oil is dirty in a used diff. When re tightening the screws do so criss cross so it tightens down evenly.