Kraton The famous shim in the 3-4s diffs

[Surchaufeur]

From the factory theres a little shim who goes to one side making the crown gear get a tighter fit against the sun gear when remplacing the diffs or servicing them they don't spin smoothly. Were they designe dlike that for their durability and normal operations? Razor rc has bring this up to switch the shim to the other side to make the diff spin more freely. But i think theres might be a reason to this knowing arrma they don't include stuff for nothing.

 

[Dulb_D]

I don't know if moving the shim to the other side really does anything but getting the diff to spin freely and without binding at all seems more difficult than it should be. I struggled with the front diff after taking it apart to change the bearings out. After I took it apart and put it back together 3-4 times it finally spun fairly freely though not perfectly after moving the shim to the other side. I decided I'd just run with it and if I strip something out I'd replace it with parts that would hopefully fit together better...

 

[jondilly1974]

If your diffs are binding, try loosening the yoke screws a tiny bit.

 

[Surchaufeur]

If your diffs are binding, try loosening the yoke screws a tiny bit.

I don't think its a good idea

 

[jondilly1974]

I don't think its a good idea

Ok ?? ??

 

[Surchaufeur]

Ok ?? ??

If someone diff explodes out of the yokes we will know why?

 

[jondilly1974]

If someone diff explodes out of the yokes we will know why?

Aren’t you the guy that shreds diffs? I thought so. ???

 

[Surchaufeur]

Or there is the hot racing bling bling yokes for 40$ but i don't trust really their alluminum anymore

Aren’t you the guy that shreds diffs? I thought so. ???

Im the diff slayer

 

[jondilly1974]

Or there is the hot racing bling bling yokes for 40$ but i don't trust really their alluminum anymore

Im the diff slayer

Look, the yokes get inserted into the tower, which won’t really give under these types of loads. I’m not saying leave the yokes unsnug, I’m saying you are tightening them too much. If they still fit in the tower and chassis, they aren’t a problem being too loose.

 

[Surchaufeur]

Look, the yokes get inserted into the tower, which won’t really give under these types of loads. I’m not saying leave the yokes unsnug, I’m saying you are tightening them too much. If they still fit in the tower and chassis, they aren’t a problem being too loose.

True

 

[jondilly1974]

I’ve had mine too tight before. Just backed the screw an 1/8 turn at a time until it didn’t bind anymore. Works fine. I’ve never had to replace a diff or input gear yet.

 

[Surchaufeur]

At first when i put them togueter the diffs they are always binding even if i back of the screws still binds but goes away after i run a few times now im questioning myself if i should keep how they came our from the factory
What side you have the shim on?

 

[Dulb_D]

I will say I did try not to "over tighten" them and kinda worked the gear around until it would spin freely... I think it's annoying that it's that sensitive and the screws were in there tight before I initially took it apart so not sure why I'd have to leave them looser than they were but maybe with aluminum yokes there wouldn't be this issue?

 

[jondilly1974]

At first when i put them togueter the diffs they are always binding even if i back of the screws still binds but goes away after i run a few times now im questioning myself if i should keep how they came our from the factory
What side you have the shim on?

I put mine back together the way the factory put them together. Shim stays put.

 

[Surchaufeur]

I put mine back together the way the factory put them together. Shim stays put.

Mhm might do that to get rid of the gear mesh i have atm on my diff and the noise its making
Nvm it still binds in a few spots how it is atm

 

[unclebrudy]

Something people need to watch out for is deformed diff gaskets.

I had a binding diff and did @jondilly1974 ’s troubleshooting by loosening the yokes a tiny bit. No problems. Try it. If you tighten it too much on purpose you may get binding issues I’ve had if you want to test.

However I did this on another diff and still had binding issues. After losing a lot of my hair it turns out I overtightened the diff and the gasket was “squishing” out, getting caught on the planetary gear. Was driving me mad til I figured it out.

Since I had a track day then I used my knife to trim the parts of the gasket sticking out, but after changing them and NOT cranking the diff closed I had no more issues.

I guess moral of the story is don’t overtighten anything in the diff assembly. I’ve since gone lightly finger tight and have had zero issues, and I swap fluid often.

Oh, and shim on the factory side. Lol.

 

[Surchaufeur]

Well i mean parts where the screws are are going to squish the gasket more than the other two blank spots my diff crown gear cover is never streight when i spin it

Something people need to watch out for is deformed diff gaskets.

I had a binding diff and did @jondilly1974 ’s troubleshooting by loosening the yokes a tiny bit. No problems. Try it. If you tighten it too much on purpose you may get binding issues I’ve had if you want to test.

However I did this on another diff and still had binding issues. After losing a lot of my hair it turns out I overtightened the diff and the gasket was “squishing” out, getting caught on the planetary gear. Was driving me mad til I figured it out.

Since I had a track day then I used my knife to trim the parts of the gasket sticking out, but after changing them and NOT cranking the diff closed I had no more issues.

I guess moral of the story is don’t overtighten anything in the diff assembly. I’ve since gone lightly finger tight and have had zero issues, and I swap fluid often.

Oh, and shim on the factory side. Lol.

I once screwed trought the diff case the screw almost ripped out trought the cover and fluid was leaking and it was done the diff was dead

 

[razorrc]

Sounds like I need to a video on diffs, diff assembly, and proper diff shimming.

Look, that shim is to make an adjustment to the shim for proper teeth mesh. The ring and pinion gears are plastic, and have variation in their tolerances, that's what the diff shim is for. To adjust as necessary to get proper mesh. Every properly designed diff has these shims, and you adjust on a per vehicle basis to get the right mesh.

 

[Branson_Basher]

Seems to me that the first step is learning the principals of diff gear mesh as it applies to any gear set. Then examine your particular gears and shim as necessary.

The person working on the assembly line may have gotten it right, maybe not. Double check their work and adjust if necessary.

Shim packs are inexpensive and a necessary part of any RC hobbyists tool kit.

The shim used by the factory may, or may not even be the ideal thickness for the diff you have in your RC. Trial fitting is the only way to find the perfect shim but that's just how it goes.

 

[MikeCheck1212]

I'm completely new to all this so thought it was just me being dense but I had similar trouble changing the bearings and oil in the granite 3S front diff (not done the back yet).

When I put it back together it felt notchy and isnt smooth to turn, I undone and redone it about 3 times and ended up not tightening the screws fully which has helped but not fully eliminated the problem.

I also had real trouble getting one of the new bearings on the outside of the diff housing, no matter how i tried it wouldnt go on flush like the other side did.

I have done diff's with a little FTX previously and had no problems at all.