Kraton EXB diff input shim required?

[Hector_Fisher]

I've assembled my diff multi different times in different configurations trying to diagnose some binding. The one way I can definitely stop the binding is to remove the input washer/shim. In fact, i can add two shims on the ring gear and get basically perfect mesh, but only when the input is not shimmed. Not sure whether its the gear teeth binding or the input gear binding on the plastic diff case. So is the input shim required?

Came from the factory with one. So i was wondering if they perhaps help distribute load amongst the gear teeth onto the bearing racing or something. But exploded view doesn't show one.

 

[Dan B.]

I try to run the input shims as it protects the bearing face to a certain extent. But all of these diffs are different (manufacturing tolerance variance) so shim as needed, or don’t, to get A smooth diff with no binding anywhere in a full rotation. I have diffs that run a couple shims on the input and some that run none.

 

[Surchaufeur]

I run wihout the input shims behind the small bearing against the outdrive but thats a me thing to take out the slop. But the little slop i wanted gone comes back after the first run¯\_(ツ)_/¯ . Running a shim behind the sun gear is going to ruin it over time

 

[Dan B.]

Running a shim behind the sun gear is going to ruin it over time

I have to disagree. If properly set up (pinion and input shaft assembled having the drive cup nice and snug before the diff is installed) then the face of the shim serves to protect both the inner bearing face as well as the pinion gear while offering very smooth operation. The number and placement of shims, both internal and external, depends on each diff.

 

[Surchaufeur]

I have to disagree. If properly set up (pinion and input shaft assembled having the drive cup nice and snug before the diff is installed) then the face of the shim serves to protect both the inner bearing face as well as the pinion gear while offering very smooth operation. The number and placement of shims, both internal and external, depends on each diff.

Arrma uses a specific shim that comes with the new trucks. Those one will get destroyed. If you use smaller one it should be fine

 

[Dan B.]

Arrma uses a specific shim that comes with the new trucks. Those one will get destroyed. If you use smaller one it should be fine

IIRC, I’m using the .02’s.

 

[PeighDay]

I noticed in the exploded diagrams the Outcast EXB and Talion EXB all have a shim behind the input gear (ARA709064) but for some reason the Kraton does not. Not sure why. Both my Outcast and Talion came with that washer / shim.

Edit: Looks like the fireteam does as well.

 

[Dan B.]

I would always want to run one as long as it didn’t make the mesh too tight. It usually has been necessary and improved it in my experience, most of my diffs like at least one and I have one that took 2 to mesh right.

 

[KnowAir]

I can see in your pics that the input gear has been chewing on the diff cup.. that shim looks too thick to me.
I wonder if they installed the wrong shim at the factory?
I would run it without the input shim.

 

[KnowAir]

Perhaps a thinner shim? I've noticed on most of my rigs that there is always a bit of play at the input shaft (in/out). I think it's necessary. To allow the gears to have a bit of lash between them. Just my experience. I also don't take apart diffs until there's a problem so, I may be off base here..

 

[Double Apex]

Some of my Diffs needed shims behind the input gear. If they are necessary I always put them behind the bearing and use 13x19x.2 shims

 

[fozzy71]

13x19x.2 shims

Do you happen to know the part number?

 

[Double Apex]

It’s not an Arrma part and they where quite hard to find I must admit.

 

[Hector_Fisher]

Some of my Diffs needed shims behind the input gear. If they are necessary I always put them behind the bearing and use 13x19x.2 shims

Why would you shim the bearing out of its seat in the housing instead of just shimming the input gear?

I feel like I'd much prefer full bearing engagement into the housing and then slightly shim the input gear out if needed, rather than the other way around. Mostly because I feel like the shim for the input gear would help inputs last longer and distribute pressure onto the teeth/bearing race equally.

Perhaps a thinner shim? I've noticed on most of my rigs that there is always a bit of play at the input shaft (in/out). I think it's necessary. To allow the gears to have a bit of lash between them. Just my experience. I also don't take apart diffs until there's a problem so, I may be off base here..

Idk, the shim was pretty thin. Maybe 0.2mm? I only tore apart the diff because the bearings seized. I guess that's bound to happen after over a year of ownership and living in the rainy pacific northwest. Discovered the issues on the rebuild. The shim wasn't flat weirdly enough, like it was a special cupped shim. Didn't like it since it was cupped down and was rubbing on the bearing shield anyway. That's when i found the interference. Might try ARA709064 in the future (the ones that come on the OEXB and TEXB), but for now, i'll press my luck without the shim since the mesh seemed so nice without it.

The only risk is that the input gear doesn't like being seated on the bearing race without a shim.

 

[Double Apex]

I basically followed this guys example and its only .2 max .4 of a mm. The bearing won’t notice the difference in support and the function of the bearing is to facilitate rotation not manage up or down forces.

Besides that I personally don’t want a shim directly behind the spinning head of the pinion. I am not convinced it distributes the pressure since those shims are not ment to handle pressure, they’re too thin. They also rest on the inner metal part of the bearing only. So the surface that can handle pressure doesn’t really increase.

Oh and the risk of the crown gear grabbing the edge of the shim…

 

[KnowAir]

Why would you shim the bearing out of its seat in the housing instead of just shimming the input gear?

I feel like I'd much prefer full bearing engagement into the housing and then slightly shim the input gear out if needed, rather than the other way around. Mostly because I feel like the shim for the input gear would help inputs last longer and distribute pressure onto the teeth/bearing race equally.

Idk, the shim was pretty thin. Maybe 0.2mm? I only tore apart the diff because the bearings seized. I guess that's bound to happen after over a year of ownership and living in the rainy pacific northwest. Discovered the issues on the rebuild. The shim wasn't flat weirdly enough, like it was a special cupped shim. Didn't like it since it was cupped down and was rubbing on the bearing shield anyway. That's when i found the interference. Might try ARA709064 in the future (the ones that come on the OEXB and TEXB), but for now, i'll press my luck without the shim since the mesh seemed so nice without it.

The only risk is that the input gear doesn't like being seated on the bearing race without a shim.

Maybe it's the bearing sticking out of the housing I'm seeing and not the shim? Either way, I would run without the shim if that's where it spins smoothly.
I also see that it appears your gearbox may have been a bit loose from the chassis from the wear around the mating surface and evidence of debris in the gears. They (gearboxes) do loosen up with use for sure. I bet it'll be fine without the shim.
I have to say, for the money, I'd just run it till failure and then buy a complete assembly off JRC when the time comes..

 

[Double Apex]

I always aim for about 2 mm space between the pinion and the diff cup. ( also copied from the video). And of course the diff has to spin smoothly.

 

[Hector_Fisher]

I basically followed this guys example and its only .2 max .4 of a mm. The bearing won’t notice the difference in support and the function of the bearing is to facilitate rotation not manage up or down forces.

Besides that I personally don’t want a shim directly behind the spinning head of the pinion. I am not convinced it distributes the pressure since those shims are not ment to handle pressure, they’re too thin. They also rest on the inner metal part of the bearing only. So the surface that can handle pressure doesn’t increase.

I see where you're coming from. I disagree on a few points.

I think the first question to answer is: gear mesh reasons aside, should I have a shim/washer between the input and bearing race?

I find it curious that the Kraton and mojave EXB, the first "EXBs" released, don't have one in the exploded view diagrams, but the outcast, mojave, and talion which were released a year or two later, do have the shim/washer. So why did Arrma change that?

I don't have any concern with a shim/washer behind the input gear. The input SHOULD be spinning the same RPM as the inner race. If a shim is installed, it should also be spinning the same speed. If not, then your bearing is seized - but that's a different problem. Since my input gear and shim aren't brand new, i don't know that they are good examples to take about whether the gear and shim normally sit flush or not.

I agree, thinking deeper about it, a fraction of a mm probably wouldn't make a big difference for the bearing in the housing. But leading back to the question above, if the shim behind the input gear IS required, then it makes no sense to shim the bearing. Just shim behind the input gear.

Maybe it's the bearing sticking out of the housing I'm seeing and not the shim? Either way, I would run without the shim if that's where it spins smoothly.
I also see that it appears your gearbox may have been a bit loose from the chassis from the wear around the mating surface and evidence of debris in the gears. They (gearboxes) do loosen up with use for sure. I bet it'll be fine without the shim.
I have to say, for the money, I'd just run it till failure and then buy a complete assembly off JRC when the time comes..

Could be. Perhaps I needed to use a socket and hammer to tap the bearing in further...

Idk, it's in the truck and rebuilt now. And i have no intention of spending another few hours to remove everything to tap it in a little further. Unless somebody says something eye-opening here. So we'll just drive it till it breaks

It wasn't hard to want to leave it like it is. Without the input shim, the mesh was near perfect and the gears spun soooo smooth. Like almost as smooth as my MT410

 

[Double Apex]

Fair points. I’m no engineer so everything I tell you is no more than my opinion. And I’m allays prepared to learn something new and change my opinion.

One last thing that probably deters me from putting a shim behind the pinion is the fact that I bought my outcast used and that particular shim was bent and partially chewed up. Not sure though if it was a factory installed shim or a diy job.

 

[Hector_Fisher]

Fair points. I’m no engineer so everything I tell you is no more than my opinion. And I’m allays prepared to learn something new and change my opinion.

One last thing that probably deters me from putting a shim behind the pinion is the fact that I bought my outcast used and that particular shim was bent and partially chewed up. Not sure though if it was a factory installed shim or a diy job.

I suspect yours was probably similar to mine for whoever did work on it previously. The shim was near impossible to slide off the input. Had to kind of pry at it. Ended up bending the corner a bit during removal. All good since I didn't reinstall it.

Perhaps a new shim might make the difference here. That much more "flat" so it doesn't cause the input to rub on the diff case.