Issue with the arrma alloy diff cup... seems too long.

[slick2500]

And... the rear diff is done. Not sure if it's from the impact that shattered the outdrive cup or what. I didn't notice it until I was replacing the hinge pin braces and was spinning the diff to check the bearings. It caught in a spot. Upon further inspection, the tip of one tooth is gone and the one next to it almost looks sheared. The shims behind the pinion are gone/ground up into almost nothing. I wasn't even really on the throttle when it broke.

Definitely tired of arrma diffs... I've gone through more diffs in this thing than I have my other 3 electric trucks combined. Almost glad there's snow on the ground as the outcast is going on the shelf until spring... unless it warms up and the snow goes away.

Going to order another diff and just go back to stock cup on the rear, shim it and just not think about how annoying these alloy cups have been.

Anyone tried another companies gears in these diffs to see if they fit? Tekno, mugen, losi? Just curious...

Word on the street is these work
https://www.amainhobbies.com/mugen-seiki-htd-differential-gear-4-10t-muge2238/p587568

https://www.amainhobbies.com/mugen-seiki-htd-differential-gear-2-20t-muge2239/p587569


The diffs in these are weird, I see people shredding them all the time, then I see people beating the snot out of their box stock trucks and not having any problems. My diffs have all been destroyed either by user error or something else failing. My first set of diffs I destroyed when I first bought it, self righting and constant standing backflips are killer on diffs, the second diff was taken out when the outer pinion bearing fell apart, the second set was taken out when my motor grenaded mid back flip and the last one failed because the diff cup came off..... I keep losing diffs in my Lc Racing vehicles for this reason, even with red loctite those damn pinion gears work themselves loose I don't get it.

 

[Notorious J]

Word on the street is these work
https://www.amainhobbies.com/mugen-seiki-htd-differential-gear-4-10t-muge2238/p587568

https://www.amainhobbies.com/mugen-seiki-htd-differential-gear-2-20t-muge2239/p587569

The internals aren't the issue as much as the ring and pinion. Like @olds97_lss, I've had teeth chip on the large pinions a little to often for my liking. I know it has to do with the intensity that I push my truck at now, but I'm also landing better, with very few on throttle ones. Still have yet to try the @Camaroboy383 dif pinion shimming, but I'm still wondering why those ring gears get chipped so easy now. This was never an issue in the first 6 months I owned the truck (November to May). Almost every one since then hasn't made it through more than 2 packs. Ordering online in bulk now so I don't end up without a running truck. Huge $$$ for that gear too.

 

[slick2500]

The internals aren't the issue as much as the ring and pinion. Like @olds97_lss, I've had teeth chip on the large pinions a little to often for my liking. I know it has to do with the intensity that I push my truck at now, but I'm also landing better, with very few on throttle ones. Still have yet to try the @Camaroboy383 dif pinion shimming, but I'm still wondering why those ring gears get chipped so easy now. This was never an issue in the first 6 months I owned the truck (November to May). Almost every one since then hasn't made it through more than 2 packs. Ordering online in bulk now so I don't end up without a running truck. Huge $$$ for that gear too.

Oh. I think it's because of the design of the gears themselves, the teeth are too small they need to be wider and deeper like other 8th scale diffs.

Just a side by side of the Hot Bodies D8T diff and the Arrma.

 

[olds97_lss]

Yeah, I was talking about the ring/pinion, not the internals. I haven't had any of those break on me yet in any of the diffs. This is my 6th diff in 15 months. That's $250 worth of diffs... the first three were when I ran 4S and took about a year! The last 3 have happened in 3-4 months. 2 of which were after installing the arrma alloy cups.

To me, that's excessive. Even in the first year of bashing my savage flux on 4s, I broke 2 or 3 pinions. The ring gears were fine. They were the BP ones. Even my ERBEv1 on 4S never had a diff go out in 3 years! I replaced bearings on them every year, but otherwise, never messed with them.

All I can think is it's partly the depth/size of tooth and partly the material. I bumped the tooth that was rolled over with a dremel on low rpm and it took a decent amount of material away. It should have taken way more effort than that. My other ring gears for pretty much every truck I got are super hard metal.

If there was a ring/pinion that would work, or even a ring gear that worked with arrma's pinion that was made of better stuff, I'd snatch a couple in a heart beat.

 

[slick2500]

Yeah, I was talking about the ring/pinion, not the internals. I haven't had any of those break on me yet in any of the diffs. This is my 6th diff in 15 months. That's $250 worth of diffs... the first three were when I ran 4S and took about a year! The last 3 have happened in 3-4 months. 2 of which were after installing the arrma alloy cups.

To me, that's excessive. Even in the first year of bashing my savage flux on 4s, I broke 2 or 3 pinions. The ring gears were fine. They were the BP ones. Even my ERBEv1 on 4S never had a diff go out in 3 years! I replaced bearings on them every year, but otherwise, never messed with them.

All I can think is it's partly the depth/size of tooth and partly the material. I bumped the tooth that was rolled over with a dremel on low rpm and it took a decent amount of material away. It should have taken way more effort than that. My other ring gears for pretty much every truck I got are super hard metal.

If there was a ring/pinion that would work, or even a ring gear that worked with arrma's pinion that was made of better stuff, I'd snatch a couple in a heart beat.

And the angle of the spiral needs to be increased as well.

 

[Lride Chart]

And... the rear diff is done. Not sure if it's from the impact that shattered the outdrive cup or what. I didn't notice it until I was replacing the hinge pin braces and was spinning the diff to check the bearings. It caught in a spot. Upon further inspection, the tip of one tooth is gone and the one next to it almost looks sheared. The shims behind the pinion are gone/ground up into almost nothing. I wasn't even really on the throttle when it broke.

Definitely tired of arrma diffs... I've gone through more diffs in this thing than I have my other 3 electric trucks combined. Almost glad there's snow on the ground as the outcast is going on the shelf until spring... unless it warms up and the snow goes away.

Going to order another diff and just go back to stock cup on the rear, shim it and just not think about how annoying these alloy cups have been.

Anyone tried another companies gears in these diffs to see if they fit? Tekno, mugen, losi? Just curious...

Yeah running these on 6s seem to kill diffs pretty easy. I’ve seen some people trying the gpm harden diff parts. But seems like mixed luck. Yeah I haven’t heard of anyone trying other brand diff parts. With all the brain power on this forum I’m sure someone has.

But yeah if I can get away from rebuilding diffs that would make my life better. ?

 

[slick2500]

I am having the same problem with the Hot Racing 2 piece diff cups. I can only fit 2 shims in it and there is way too much slop in the crown and pinion. I need a lathe......
Stock Arrma diff measured from outside edge of bearing to outside edge of bearing I came up with 31.8mm just like you did, the Hot Racing one is 32mm. With the stock diff cup I had to use 3 shims on the crown gear side with the HR cup I can only fit 2 shims.
Strange thing is that it fits fine in the rear

 

[slick2500]

Now I think its too tight....

 

[olds97_lss]

Well, against my better judgment, I stuck with the arrma alloy/steel cup. When putting the bulkhead/diff cap back on, one of the screws was stripped, so I replaced it with the new bulk that came with the diff. With the alloy/steel cup having one gasket still removed (RTV sealing the cap end), I was able to fit 2 or 3 (I think 3) shims in and mesh was too tight! So it seems the new case allowed more room. I removed one of the shims and the mesh feels perfect. Finally. I don't have any shims behind the pinion as I thought I bought some that fit, but I didn't... not sure what the ones I bought are for now... but I have 30 of them! LOL!

So, it's all back together, new bulk, new ring/pinion and new outdrives. Didn't bother with the internal gears/shims as they were all fine. Now it will wait for warmer weather before I run it again.

 

[SrC]

Well, against my better judgment, I stuck with the arrma alloy/steel cup. When putting the bulkhead/diff cap back on, one of the screws was stripped, so I replaced it with the new bulk that came with the diff. With the alloy/steel cup having one gasket still removed (RTV sealing the cap end), I was able to fit 2 or 3 (I think 3) shims in and mesh was too tight! So it seems the new case allowed more room. I removed one of the shims and the mesh feels perfect. Finally. I don't have any shims behind the pinion as I thought I bought some that fit, but I didn't... not sure what the ones I bought are for now... but I have 30 of them! LOL!

So, it's all back together, new bulk, new ring/pinion and new outdrives. Didn't bother with the internal gears/shims as they were all fine. Now it will wait for warmer weather before I run it again.

 

[slick2500]

Well, against my better judgment, I stuck with the arrma alloy/steel cup. When putting the bulkhead/diff cap back on, one of the screws was stripped, so I replaced it with the new bulk that came with the diff. With the alloy/steel cup having one gasket still removed (RTV sealing the cap end), I was able to fit 2 or 3 (I think 3) shims in and mesh was too tight! So it seems the new case allowed more room. I removed one of the shims and the mesh feels perfect. Finally. I don't have any shims behind the pinion as I thought I bought some that fit, but I didn't... not sure what the ones I bought are for now... but I have 30 of them! LOL!

So, it's all back together, new bulk, new ring/pinion and new outdrives. Didn't bother with the internal gears/shims as they were all fine. Now it will wait for warmer weather before I run it again.

I've noticed discrepancies between the clearance inside the stock gearboxes, I've had one where I had to put a shim on the other side of the diff cup, I needed 3 shims to keep the diff from loving side to side but with 3 on the crown gear side the gears would bind up so I stuck 2 on the crown gear side and 1 on the other. ?‍

 

[SrC]

Are you shimming the outdrive dogbone cups?(outside bearing sides) This will affect the internal diff gear mesh(satellite and sun gears) as well as the fit within the bulkhead case. It will also affect the total width of the complete metal diff assy when shimming as it is fitted within the bulkhead case. The Metal diff builds slightly different than the plastic ones. There are slight variations between the plastic and the metal ones
I am only using the Arrma metal diff cup for my center diff. I did use one external Tekno shim at the forward side(.15mm) to reduce endplay at the center when lining up motor pinion gear to the spur. The only benefit I can see with metal is heat dissipation. And it works well. But Front and Rear diffs don't get hot or even warm. And the added weight of this metal diff at the front and rear is considerable and thus affects rotational weight bias adding resistance to spool up. Basically not what is desired for drivetrain efficiency. I feel the metal diff is only beneficial at the center. I notice that unlike my Tekno Diffs, that the Arrma diff setups and builds never assemble like the next one. No two assemble with the same results. Much inconsistency in Mfr. precision is the cause. That's why diff building can be very time consuming to get close enough to good enough. New diff builds should be broken in after about 10 packs give or take based on your driving style and then rebuilt with fresh oil and without changing location of the sat. and sun gears or changing out the shims as originally setup. I find if you do this the diffs last much longer. Tight figure eight driving for most of the first lipo pack after F/R diff rebuilds helps seat the gears before you put heavy loads and bash hard. IMO. That's what I do.
Good luck

 

[olds97_lss]

Are you shimming the outdrive dogbone cups?(outside bearing sides) This will affect the internal diff gear mesh(satellite and sun gears) as well as the fit within the bulkhead case. It will also affect the total width of the complete metal diff assy when shimming as it is fitted within the bulkhead case.

I missed this posting. I'm not sure what you mean here. Are you talking about the smaller shims to remove slop from the output cups themselves? Adding shims there will change nothing in relation to the width of the diff from bearing to bearing. It would only change it from cup to cup.

The ones where it says "Use 2xSHIM behind each planetary gear":

I didn't use their shims, I used the larger mugen shims there.

I then put enough of those shims they inlcuded outside the diff before inserting the output cup to remove almost all the in/out slop for the diff cup.

 

[SrC]

The 2 diff cups being shimmed outboard affects the overall spacing of the of the 2 bearings which affects spacing between the ring and pinion gear. It also affects the position of the sun gears placing them close or farther from the sat. Gears. Perhaps my terminology used in describing these parts are confusing my point.?

 

[olds97_lss]

The 2 diff cups being shimmed outboard affects the overall spacing of the of the 2 bearings which affects spacing between the ring and pinion gear. It also affects the position of the sun gears placing them close or farther from the sat. Gears. Perhaps my terminology used in describing these parts are confusing my point.?

Yeah, without a diagram, hard to get the point across as there are multiple ways to shim a diff.

To shim the bearings, I use larger od shims like the stock diffs use between the outer race and diff case. With the gaskets on both of the cup ends (one under the ring gear, one under the diff cap), I wasn't able to add any shims outside the ring gear bearing to move the ring gear closer to the pinion.

Some people put the shims on the ring gear first, then the bearing, but that's too tedious for my taste.

I was pretty sure the instructions I received with the arrma diffs had shown that smaller 5mm or 6mm shims were to be used before inserting the output cup shaft into the diff, but I wasn't clear why as I never really cared about the slop of an output cup, but I added some anyway.

 

[SrC]

I think Mugen has been used by someone else.

 

[PaPa Thorn]

I'm avoiding the issues all together, I'm sending my Arrma Alum. to another forum member.

 

[SrC]

Yeah, without a diagram, hard to get the point across as there are multiple ways to shim a diff.

To shim the bearings, I use larger od shims like the stock diffs use between the outer race and diff case. With the gaskets on both of the cup ends (one under the ring gear, one under the diff cap), I wasn't able to add any shims outside the ring gear bearing to move the ring gear closer to the pinion.

Some people put the shims on the ring gear first, then the bearing, but that's too tedious for my taste.

I was pretty sure the instructions I received with the arrma diffs had shown that smaller 5mm or 6mm shims were to be used before inserting the output cup shaft into the diff, but I wasn't clear why as I never really cared about the slop of an output cup, but I added some anyway.

I find that if you have significant slop of the output cup, it creates a poor and inconsistent mesh between the sat and sun gears. The sun gears will rock back and forth under load. This also leads to damaged O-rings and diff fluid leaks and ultimately undue wear of the two outboard bearings. I, like most others here have built these diffs 20-30 times and I see a common denominator here. The stock plastic diff cases will twist under load causing ring and pinion mis-alignment and broken teeth under excessive load. Every diff for me has assembled and fit different than the next. The 3 different types of shims used in 3 different areas are pretty much subjective to each specific build.

 

[SrC]

I'm avoiding the issues all together, I'm sending my Arrma Alum. to another forum member.

Like I stated prior, the Alu. Arrma diff cup is great for the Center diff only. IMO. I've had zero issues with it. I would gladly take it from you.

Yeah, without a diagram, hard to get the point across as there are multiple ways to shim a diff.

To shim the bearings, I use larger od shims like the stock diffs use between the outer race and diff case. With the gaskets on both of the cup ends (one under the ring gear, one under the diff cap), I wasn't able to add any shims outside the ring gear bearing to move the ring gear closer to the pinion.

Some people put the shims on the ring gear first, then the bearing, but that's too tedious for my taste.

I was pretty sure the instructions I received with the arrma diffs had shown that smaller 5mm or 6mm shims were to be used before inserting the output cup shaft into the diff, but I wasn't clear why as I never really cared about the slop of an output cup, but I added some anyway.

Yes I agree that the trial and error of using bearing spacers outboard versus at the diff cup shaft is daunting for sure. Ive spent numerous hours even days doing one diff assy. dry. Then several hours filling and bleeding the fluid correctly using a shock vac. pump.to bleed air out of the diff cup using 500k cst. But I am anal about that. Maybe ludicrous for most to do. But I feel that is 1/2 of the equation for durability and consistency. I would love to do a video for everyone.....the best way to show how I do it. Not that my way is best.

 

[PaPa Thorn]

Like I stated prior, the Alu. Arrma diff cup is great for the Center diff only. IMO. I've had zero issues with it. I would gladly take it from you.

Yes I agree that the trial and error of using bearing spacers outboard versus at the diff cup shaft is daunting for sure. Ive spent numerous hours even days doing one diff assy. dry. Then several hours filling and bleeding the fluid correctly using a shock vac. pump.to bleed air out of the diff cup using 500k cst. But I am anal about that. Maybe ludicrous for most to do. But I feel that is 1/2 of the equation for durability and consistency. I would love to do a video for everyone.....the best way to show how I do it. Not that my way is best.

It's not so good for a center diff cup either unless you're using the stock mounts maybe.