How to shim your Arrma diff

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I'm finally going to shim all my diffs & started with my front diff on my V3 Kraton. I've built diffs before, but not Arrma diffs. I have the diff all clean and also fully understand how to shim them, so no problems there. However, I cannot remove the internal sun gear on the diff cup side. The other side (which has the large external crown gear) was easy to remove the sun gear. However, the sun gear is quite deep down in the diff cup side, and hard to get at, so very difficult to pull it off the pin/outdrive compared to the other side. I've even tried using needle nose vise grips (which should work), so not sure why I cannot remove the sun gear on the diff case side? I want to add a new bearing on this side, plus remove the o ring to lube with some green slime & most importantly, I need to add a 5x18 shim on the diff cup side. Also, what is the small set screw for on the side of the diff, as not one video addresses this?
That small screw can be used to bleed excess diff fluid after assembly and if removed, you can use a small screwdriver as a lever to loosen that stuck sun gear.
 
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For the one inside the cup, you can't use a screwdriver. I was rebuilding a diff just last night and had this same issue. Good Needle nose pliers and some patients, (and a few curse words) and it came out - but it took several minutes of working on it.. This was a new diff from Lumidav35 (ebay kit breaker). I have had all four of my old diffs apart several times, and never had a sun gear fit that tight on the outdrive. Maybe the new diffs are built tighter?

Also, post shimming, it was very notchy, more so than my past diffs. I am gonna run it and see if it smooths out, but will need to watch it.
 
Thanks blindy & jerry-rigged for your quick reply. I made up some special needle nose pliers I curved at the end to get underneath the gear, but still could not get it out. Man, I finally did get it out by using a very tiny precision flat head screw driver through the side hole in the diff cup & the sun gear finally broke free. Definitely have to be careful using a screw driver through the hole if anyone does try this method, but it was the only method that worked for this diff. Good news about Arrma diffs, as my V3 Kraton diff had about 8 runs on it (using 6S) and all gears, etc, looked "brand new". I sure hope my other 5 diffs I still need to shim, don't have this same problem with a stuck sun gear on the diff cup side...
 
I know it can possibly vary how many shims to use, but generally speaking, what works for one diff, should work for the others. Anyways, I thought I would mention what I found. As per the Arrma diff videos, I used a total of 2 (3.5x12x.2mm) shims for the Planetary (small) gears, otherwards, only 1 shim on each of the two metal cross shafts. I also added a total of 2 (5x18x.2mm) shims, one behind each of the two larger Satellite/Sun gears. I then dry fitted it (with no oil), to check for smoothness (Note when dry fitting, I did use some "Green Slime" on the o-rings & a bit of oil on the pins before installing the sun gears). Once I installed the large Crown gear end to the diff, the diff immediately felt wrong (tight, notchy) and after I tightened up the 4 screws, it was even worst, and now way too tight. Since the diff seemed ok w/o the crown gear end on, I gathered the problem maybe with the larger 5x18 shims behind the satellite gears. I decided to remove the satellite shim on the crown gear side 1st, as this was much easier. After this, the diff was definitely better, but I was still not fully happy with how it felt. I decided to put the shim back on the crown gear side again, then struggled again for a bit to remove that damn satellite gear from the diff cup side. After removing this shim, the diff now feels "buttery smooth." I will fill the diff with some new oil tomorrow, then start on my other diffs (which should be the same to shim...)

Any side to side play after shimming should not be mistaken for internal, as this is the outdrives which you will use the 13x16 shims for when the diff is re-installed back into the gearbox/vehicle.

I believe by putting a shim under the satellite gear on the diff cup side pushes all the internal gears up the diff cup too much. Also when you use 2 satellite shims (one on each end) may cause both the satellite gears to press too hard into the smaller planetary gears (where gears are almost binding and gritting against each other). If this happens, it could be as bad or worst than having the motor pinion way too tight.

I've heard a few members mention after shimming their V3 diffs, that maybe their diff is too tight afterwards. I just wanted to immediately point out what I just found after shimming my 1st Arrma diff. Furthermore, I will also provide some feedback on the condition of my other 2 diffs, as hopefully they also look brand new. Since I have about 8 runs on 6S, this would be great news if my other diffs looks just as good.
 
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So the sun gear is just held on by a vacuum caused by the diff fluids itself. I had to hold mine upside down and tap on it, then go at it with needle nose. Keep trying it will eventually move. Do not turn it back right side up till the gear is out or it will just slide right back where it was.

The small set screw is there to relieve the pressure inside of the diff cup as you tighten down the ring gear to the diff cup. Having the set screw out for the last 3 turns of each ring gear screw will cause a bit of diff fluid to ooze out of the weep hole. This will prevent overfilling, which will cause the gears to overheat and the diff cup to possib begin leaking.
 
So the sun gear is just held on by a vacuum caused by the diff fluids itself. I had to hold mine upside down and tap on it, then go at it with needle nose. Keep trying it will eventually move. Do not turn it back right side up till the gear is out or it will just slide right back where it was.

The small set screw is there to relieve the pressure inside of the diff cup as you tighten down the ring gear to the diff cup. Having the set screw out for the last 3 turns of each ring gear screw will cause a bit of diff fluid to ooze out of the weep hole. This will prevent overfilling, which will cause the gears to overheat and the diff cup to possib begin leaking.
Motorider. Thanks, but I even tried 3 different needle nose pliers + I even tried making some needle nose pliers with curved ends, but to no avail. No luck, as I even kept the diff turned upside down while tapping on it & pulling with the needle nose. However, the method recommended by blindy did finally work, and had to do this 2x when I was shimming (see my comments above).
 
My old V1 diffs, yes it was vacuum holding it on. For my V3 diff, it just fits the outdrive tight. A very different feel trying to get the sun gear off. Plus it seems now several have reported you build the V3 diffs with 6 shims, and they are too tight. The V1 diffs, 6 shims got them just right.

didn't Arrma change factories last year? New shop apparently has tighter tolerances.
 
My old V1 diffs, yes it was vacuum holding it on. For my V3 diff, it just fits the outdrive tight. A very different feel trying to get the sun gear off. Plus it seems now several have reported you build the V3 diffs with 6 shims, and they are too tight. The V1 diffs, 6 shims got them just right.

didn't Arrma change factories last year? New shop apparently has tighter tolerances.
Yes, maybe that's what happened. Actually I used "only" 3 shims total internally for the diff (not including the 13x16 shims for the outdrives). I used "only" (2) 3.5x12x.2mm shims on the planetary gears (Arrma already has 4 planet gear shims in the diff) & I ended up using "only" (1) 5x18x.2mm shim on the satellite gears (just on the crown gear side). Not sure about earlier models, but on the V3 diffs, you definitely don't want to have to take the satellite gear off the diff cup end, especially if you don't have to. It is extremely tight to get off the outdrive. However, the good news is, I found the diff does not like a 5x18 shim behind the satellite gear on the diff cup end (too tight & notchy), so should not have to remove this to shim?

I would like to hear what other members have found when shimming the new V3 diffs.

What is everyone using for "GREASE" between the external diff gears (between the 43T Spiral Diff Crown Gear & 10T Main Input Gear?) I have lots of Mobil (automotive/industrial) high performance 100% synthetic grease. It is white color, but looks like it would be good to use for this purpose? What do you think?
 
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My old V1 diffs, yes it was vacuum holding it on. For my V3 diff, it just fits the outdrive tight. A very different feel trying to get the sun gear off. Plus it seems now several have reported you build the V3 diffs with 6 shims, and they are too tight. The V1 diffs, 6 shims got them just right.

didn't Arrma change factories last year? New shop apparently has tighter tolerances.

Further to my last post, are you sure members are adding 6 shims to the new V3 diffs? How many shims did you use? The Arrma diffs already come stock with 4 planetary shims installed, so if (4) more 3.5x12x.2mm shims are added to the planetary gears, that's 8 shims for just the planet gears? I only added (2) of these 0.2mm shims & diff seems good and smooth now. I also have (8) 3.5x12x.12mm shims that I may try using when shimming my Talion diffs. Since these are "only" .12mm thick compared to the Mugen .2mm shims, in this case, I may be able add (1) more shim behind each planet gear (otherwards, adding 4 more plate gear shims to the diff)? Two (2) of these 3.5x12x.12mm shims would add up to .24mm thickness, compared to only one (1) of the Mugen .2mm shims, so very close. This option may work + possibly be better with equal shims on each side?
 
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Further to my last post, are you sure members are adding 6 shims to the new V3 diffs? How many shims did you use? The Arrma diffs already come stock with 4 planetary shims, so if (4) more 3.5x12x.2mm shims are added to the planetary gears, that's 8 shims alone for just the planet gears. Also with 4 more shims, this adds 0.8mm more thickness, and that's a lot, and probably reason maybe diffs are too tight? I only added (2) of these 0.2mm shims & diff seems good now. I also have (8) 3.5x12x.12mm shims that I may try using when shimming my Talion diffs. Since these are only .12mm thick compared to the Mugen .2mm shims, I may be able add (4) of these (1 more shim behind each planet gear)? Four (4) of these 3.5x12x.12mm shims would add up to .48mm thickness, compared to .4mm for only 2 Mugen 3.5x12x.2mm shims.

When rebuilding my Talion/Kraton diffs, I'd only needed to add a single shim on each of the cross pins, and one on the cup side of the diff. The total was 3 additional shims in each diff, and it gave them a nice feel. This was the same across all six diffs.

Note: Both my Kraton and Talion are 2018 variants, and I was using the E0206 Mugen shim set. I kept all original shims in place.
 
When rebuilding my Talion/Kraton diffs, I'd only needed to add a single shim on each of the cross pins, and one on the cup side of the diff. The total was 3 additional shims in each diff, and it gave them a nice feel. This was the same across all six diffs.

Note: Both my Kraton and Talion are 2018 variants, and I was using the E0206 Mugen shim set. I kept all original shims in place.
Dingo. My Talion & Kraton are both V3's also. I also only used 3 shims, and think this is the way to go. The only difference is it sounds like you put the (1) 5x18 shim on the diff cup side, and I put this shim on the crown gear side. You must have had to pry off the satellite gear on the difficult diff cup side for all 6 diffs?

I'm also using the E0206 Mugen shim kit. Since the V3 diffs only need (1) 5x18 shim per diff, one Mugen diff kit now has nough shims to do all 6 of my diffs, except kit is short (2) 3.5x12 shims. I need 12 of these to shim all 6 diffs, and only 10 shims in kit. I had some Serpent 3.5x12x.2mm shims which I used on my Kraton, as these are exactly the same as the Mugen shims (Note: Mugen shims are incorrectly listed as 3.5x12x.02mm, but are actually .2mm thick.) I also have (8) 3.5x12x1.2mm Team Associated shims that I may try on my Talion (using 4 of these shims per diff). See my last post comments...
 
Dingo. My Talion & Kraton are both V3's also. I also only used 3 shims, and think this is the way to go. The only difference is it sounds like you put the (1) 5x18 shim on the diff cup side, and I put this shim on the crown gear side. You must have had to pry off the satellite gear on the difficult diff cup side for all 6 diffs?

Correct on the diff cup side. We had a hell of a time getting the gears out, but we were also replacing bearings, so they needed to be removed to properly rebuild.

I noticed the same thing regarding the thickness of the Mugen shims, but continued on. Good to know about the Associated shims. Keep us in the loop of how they work out if you go that way?
 
Correct on the diff cup side. We had a hell of a time getting the gears out, but we were also replacing bearings, so they needed to be removed to properly rebuild.

I noticed the same thing regarding the thickness of the Mugen shims, but continued on. Good to know about the Associated shims. Keep us in the loop of how they work out if you go that way?

Before I checked with my digital calipers, I knew the Mugen shim thickness must be .2mm, as .02mm had to be a misprint for their shim specs. At 0.02mm, shims would probably be see through and bend in the wind, & you'd be lucky if they lasted more than 1 second, especially on 6S, LOL. I remember long ago, my 1st vehicle (full size) at 16, was a dune buggy that pulled the front wheels of the ground. The best warranty I could get on this rebuilt motor was 3 seconds, or 3 feet, which ever comes 1st, they said...

I'm also changing the diff bearings while I shim them (may as well), as I have about (8) packs running 6S on my Kraton. I found that my diff liked the 5x18x.2mm shim on the crown gear side more than the diff cup side (I tested it both ways, but my test was not totally accurate, as I used a different shim on diff cup side. Instead of the Mugen shim, I used a Serpent 5x15x.3mm. This extra .1mm thickness could have been the reason why my diff was smother with the shim on the crown gear side? I'm now wondering if it makes any difference, what side of the diff (crown gear or diff cup side) the 5x18 shim goes on? Would be nice to know, as I'm not sure if I will change my Talion bearings while I shim the diffs (as it's only got 1/2 battery run through it). Don't want to have to remove the satellite gears on all the diff cup sides, especially if I don't have to...
 
After shimming my Kraton rear diff (using 3 shims total) & just before filling up with new fluid, I decided to try one more "dry fit". There is no doubt, after "tightening" down the 4 screws again (crown gear side), the diff "tightens up", and feels a bit notchy. Before tightening the 4 screws, the diff feels great (buttery smooth, yet no play), but once tightened down, it does not feel right. This tells me the diff does not need a 5x18 shim. I originally tried (2) of these 5x18 shims, and diff would barely turn. With 1 shim, it's better, but still not as smooth as it should be. When I removed this 5x18 shim, the diff now feels great (buttery smooth), even after all 4 screws tightened down. After many different dry fit tests, the new V3 diffs look like they need "only" (2) 3x12x.2mm shims, and no 5x8 shims? If this is the case, the (sometimes hard to find & expensive) Mugen diff shim kit may not be needed now for the 5x18 shims, as it's much easier to find the 3.5x12 shims (Serpent 110427, Team Associated ASC81381/89108, & Arrma AR709024).

The Arrma AR709024 shims are 3.5x12x.15mm. These shims are the same as the 4 shims already in the diffs, behind each of the small planetary gears. Would be interesting to also see if 2 or even 4 of these would work shimming the new V3 diffs, as Arrma shims are .15mm thick compared to the .2mm Mugen shims, & Serpent shims which are only .12mm thick. Anyone else try the thinner Serpent or Arrma shims?

I know a diff that is built a bit tight, will loosen up, but with any 5x18 shims installed in the diff, it seemed too tight to me. Furthermore, my diff looked brand new after 8 battery packs using 6S. This tells me the V3 diffs do not need shimming that badly? We would all appreciate any comments any other members may have when shimming the new V3 diffs?

Can I use "white" Mobil high performance GREASE on the large external crown gear?
 
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The tolerance on these RTR diffs have gotten much better than the V2. For my V2s, I was all over the place with the amount of shims worked for what diffs. However, for my V3 Kraton, Talion, & Typhon I did nothing. The gears are way too tight to try to wedge any shims. As the gears wear in I'll revisit them to see if they need shimming. I have already opened them for their 3 month checkup & they need nothing. I have to open the Talion & Typhon next month for the 6 mo review.

As for the grease, any white lithium grease will do so the mobile will work great.
 
The tolerance on these RTR diffs have gotten much better than the V2. For my V2s, I was all over the place with the amount of shims worked for what diffs. However, for my V3 Kraton, Talion, & Typhon I did nothing. The gears are way too tight to try to wedge any shims. As the gears wear in I'll revisit them to see if they need shimming. I have already opened them for their 3 month checkup & they need nothing. I have to open the Talion & Typhon next month for the 6 mo review.

As for the grease, any white lithium grease will do so the mobile will work great.

Megasty. Thanks for your comments. Much appreciated & very interesting. Everyone was recommending "YOU MUST" shim the Arrma diffs if running 6S. I spent a lot of time worrying about this, so I'm really glad to see you found the same as me. The new V3 diffs are fine & do not need shimming. The diffs definitely do "not" like any 5x18 shims, as diff becomes too tight. However, it does look like the V3 diffs could maybe use two (2) of the small 3.5x12 shims, as the diff still seemed smooth to me when I installed 2 more of these shims? I will try one more dry fit with and without the 2 extra 3.5x12 shims. Did you use any more 13x16 shims on the outdrives (Arrma includes just one on the left side)
 
The outdrives of all three seemed to be fine but I put a shin behind the large input bearing just to be safe as the mesh between the input & ring tends to wear the fastest.
 
The outdrives of all three seemed to be fine but I put a shin behind the large input bearing just to be safe as the mesh between the input & ring tends to wear the fastest.

Megasty. I will check my outdrives to see if they also don't need shimming (13x16), as I'm finally about to reinstall my rear diff. Do you mean you shimmed the bearing on the Main Input Gear 10T Spiral (AR310498), that's only on the front/rear diffs? If yes, curious, if all your V3 diffs needed this, as I checked my Main Input gear on my rear diff & it's fine, no play at all? I will check the front on m Kraton & Talion when I do it later.

For the 3.5x12 shims, I'm going to try "one more dry fit". I'm very picky, and since I have 6 diffs to do, may as well try one more thing. My plan is to "remove" the four (4) Arrma 3.5x12x.15mm shims that come preinstalled in the diff and "replace" with four (4) 3.5x12x.2mm shims. This will be the same amount of shims in the diff, but should tighten the diff up just a bit more from stock (.05mm more behind each planetary gear). This should also be better and more evenly shimmed than adding just one .2mm Mugen shim per side. I also think the thicker .2mm shims may last longer than the .15mm Arrma shims? Since I have twenty (20) 3.5x12x.2mm shims (10 Mugen & 10 Serpent ), I'm hoping this maybe the BEST PLAN for perfectly shimmed V3 diffs. If this works, I would be short one diff for using .2mm shims.

For my last diff, my plan is to leave just (2) of the (4) Arrma .15mm shims installed in the diff, and add a total of (4) of my .12mm shims (from ASC81381 kit). I will use two (2) of these shims on just 2 sides only. So really, all that I'm adding is just .09mm shim thickness to the last diff, compared to my other 5 diffs that I will be increasing the total shim thickness by .1mm for the planetary gears.

I WILL REPORT BACK!
 
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The input will have no play if it is tightened properly. The way I tell if there's any play between the input & ring is to hold the entire assembled diff in your hand, put a finger on the input drive cup so it doesn't move, & wiggle the ring from below. Listen for clicking as if you are doing it for a spur/pinion mesh. I don't like to hear any clicking when I do this.
 
Just to clarify, when I said 6 shims in the diff, I did NOT mean, add 6 shims to the 4 pre-installed. I meant add 2 (sun gear shims) to the 4 in the diff = 6 shims.

And yeah, for the ring & pinion, I use white lithium grease.
 
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