3s Diff Issues

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Donovan

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Arrma RC's
  1. Granite
I have been having some issues when trying to install the metal diff I just bought for my Granite BLX. It seems like the metal diff is slightly bigger than the plastic diff. The yokes are pinching the diff just enough so the diff can barely move. Not sure what the deal is.
 
Are shims present?. And what side are they installed?

Bearings seated completely in the yokes after assembly?
 
I use those hot racing yokes combined with the kraton 4s metal diffs off Jenny's. I do remember however test fitting my stock plastic yokes over the metal diff and there was no problem. That's why I'm asking where he got the metal diff from.

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Where did you get the metal diff from?
I got the diff from eBay, but PhillyB_RC had the same issue with metal diffs from Arrma. He solved the issue by adding washers between the yoke. I don't want to add washers because it causes the imputed gear to wiggle slightly.
 
Shims are on the gear side and bearings are seated.
How well does it spin when you remove all the shims? Are the gears rubbing on something, or are the gears too tightly meshed to spin freely?

Think of shimming as slightly moving the spur gear around from side to side to get the gear in the right place. You need to add and remove shims on either side until the mesh is perfect. It's a trial and error process. On one rare occasion, i had to put shims on the non gear side to move the spur farther away from the input gear just with how the manufacturing tolerances were.
 
Yes..I will say that I added 1 shim on the gear side and on the other diff ( I bought 2, one for each rig in the rear) I added 2 on the gear side to get that perfect ring and pinion mesh. Like Hector says, no one size fits all.
 
How well does it spin when you remove all the shims? Are the gears rubbing on something, or are the gears too tightly meshed to spin freely?

Think of shimming as slightly moving the spur gear around from side to side to get the gear in the right place. You need to add and remove shims on either side until the mesh is perfect. It's a trial and error process. On one rare occasion, i had to put shims on the non gear side to move the spur farther away from the input gear just with how the manufacturing tolerances were.
The gears are just way too close together. I tried removing shims but that didn't work.
 
What if you put a shim on the opposite side that they were on initially? Try one, then two, etc.
I'll give it a shot, but I don't think any amount of shims will be enough. The gears won't move.
 
I'll give it a shot, but I don't think any amount of shims will be enough. The gears won't move.
In my line of work, problem resolution starts with identifying what isn't work and finding out specifically why it isn't working. If you know the"what" and the "why" behind why something isn't working right, then you can figure out resolution to the problem. Gears not spinning are either because of 1) bad mesh which is forcing the gears together too much, 2) an issue with the bearings not letting the gears spin, or 3) the gears are rubbing on yoke/housing.

One of those will be the issue, and once you find out which one, you can determine the fix.
 
I use those hot racing yokes combined with the kraton 4s metal diffs off Jenny's. I do remember however test fitting my stock plastic yokes over the metal diff and there was no problem. That's why I'm asking where he got the metal diff from.

View attachment 296927

View attachment 296928
I have the Arrma CNC diffs in two vehicles. One was OK with the stock yokes, the other was tight. I replace the yokes with the HR ones and the diffs are smooth as glass without shims.
 
I just added shims to the non gear side of the diff, it was definitely better than it was. However, when I tried to put it all back together I just couldn't get the motor to slide into place. I messed around with it for a while, but then I realized the input gear was too long. I'm just going to return it and get a better quality one.

PXL_20230502_221225312.jpg
 
I just added shims to the non gear side of the diff, it was definitely better than it was. However, when I tried to put it all back together I just couldn't get the motor to slide into place. I messed around with it for a while, but then I realized the input gear was too long. I'm just going to return it and get a better quality one.

View attachment 296969
Easy fix, inside the slipper hub is a little black plastic nut, remove that nut and it will fit right in. Make sure you use thread lock on the screw that goes through the slipper assembly. That part was designed for the first gen Arrma 4x4 cars that did not come with that nut inside the slipper hub.
 
I took the plastic nut out of the slipper clutch, but the screw is still in the way. Should I cut it or is there a better way?

PXL_20230503_011719306~2.jpg
 
Is there not a hole in the end of the diff gear? Oh those dumb dumbs............
 
No, there is no hole in the input gear.
 
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