Kraton Shimming the Rear EXB Open Differential

[bicketybam]

I have written this elsewhere but I wanted to break it out on its own for people to find easily. This is how you should approach the rear differential of your new Kraton EXB:

Open up your brand new rear diff on your new EXB. Pull it apart and clean whatever fluid is in there. You will need the two types of shims that are used in the diff from the factory: ARA709059 and ARA709060. When you reassemble the rear diff you want to start with the larger (in diameter) of the two types of shims and put that over the o-ring. Then you want to add a combination of the two shims so that you can get the pin through end of the outdrive and not have the outdrive move in and out. You want it tight but not so tight that it's difficult to turn the outdrive. You then do the same with the other side. Dry fit the rest of the diff together and check for smoothness. It should not feel crunchy/notchy. You should feel the gear teeth as you turn the outdrives in opposite directions but nothing more that that. If it's too tight, open it up and remove a shim. Reassemble and test again. Rinse and repeat until it feel right. Then you can add your desired weigh of fluid and run the diff in your truck.

Hope this helps.

 

[SrC]

^^^ follow the above to the T.
It doesn't get more explicit than @bicketybam states here.
There should be no confusion.
This is a Sticky for sure.

Ed, nice job.

 

[suchtragedy]

I did this by feel like you described, for me I added another *059 part number shim to the other 3 already had in it. That's 4 on each side instead of 3, but fitment felt good as did dry test. I didn't have any of the *060 part number ones to do it the "right" way of only using 3 shims per side to total 0.8mm shim spacing. We'll see how she runs I suppose ?

 

[SrC]

Shimming is all about trial and error and getting the end result. No two diffs assemble identical. Assembly line Mfr'ing doesn't always get it right. No matter the brand.
It's up to you.

 

[Lingerfelter6]

We need 0.01mm shims for the sun gear for refinement, I also think moving in the planetary gears help

EDIT : 0.1 mm

 

[SrC]

^^^Again, depends on the specific diff you have in front of you. Others will have differing scenarios with their diff. I even found myself shaving /grinding my shims thinner to accommodate certain diffs. Sometimes you just need that one extra razor thin shim.
Time, patience and experience makes for a good setup. If you're new to this and rush it, the diff will fail. Then you will come here to complain about bad parts.... an everyday ocurrance here.

 

[Lingerfelter6]

^^^Again, depends on the specific diff you have in front of you. Others will have differing scenarios with their diff. I even found myself shaving /grinding my shims thinner to accommodate certain diffs. Sometimes you just need that one extra razor thin shim.
Time, patience and experience makes for a good setup. If you're new to this and rush it, the diff will fail. Then you will come here to complain about bad parts.... an everyday ocurrance here.

basically, the idea here is to get all the teeth to be as close as possible without any binding. sake principle applies for spur and pinion. closer = more contact

 

[suchtragedy]

I measured all my shims as I took them out and I had variances up to 0.05mm between the *059s shims, so shimming definitely isn't an exact science due to the slight tolerance differences in mass produced parts.

Anyways! Thanks @bicketybam and @SrC for the K.I.S.S. (keep it SHIMple stupid) how-to breakdown ?.

 

[Engineer]

Thanks for the writeup. Not sure where to add this comment, but this thread seemed appropriate. Check the diff fluid levels on your other differentials. My center differential was pretty low on fluid and so I added a good quantity of 100K.

I didn't detect any wiggle/movement in the outdrive shafts so I didn't disassemble it further to check the number of shims.

 

[Jake4k]

Great video is here:

Thank you guys! Now I just need the actual truck ?‍?

 

[Jamart85]

Would using a washer as opposed to a shim like ARA709037 6x10x0.5mm Washer be ok to use in the diff?

 

[SrC]

Great video is here:

Thank you guys! Now I just need the actual truck ?‍?

I knew @razorrc had a video up his sleeve for this one....

Would using a washer as opposed to a shim like ARA709037 6x10x0.5mm Washer be ok to use in the diff?

^^^Technically speaking, Yes it would work. But again will vary from diff to diff. You would have to machine it to fit diameter and thickness as required.

Has anyone considered what the LSD spacing measurement is using the measurements of the LSD plates? That may just be a good starting reference point. Both LSD and Open diffs are the same. Just that the LSD plates are removed and replaced by shims for the open diff. design. Correct me if I am wrong here.

 

[JansonJanson]

Dumb question.... I read a lot about shimming...shimming and filling it up again with fluid ... But what is filling it up again? As much fluid as you can pack in it ...half way up, 3/4 ??? ????

 

[bicketybam]

Dumb question.... I read a lot about shimming...shimming and filling it up again with fluid ... But what is filling it up again? As much fluid as you can pack in it ...half way up, 3/4 ??? ????

There are a couple of schools of thought. Some believe that addi g fluid so that it covers the cross pins of the planetary gears is fine and others like to fill it completely. I go somewhere in between....over the cross pins but not all the way up.

 

[SrC]

Manual for both RTR and EXB diffs show the same fill line. Which appears to be a few MM. below the top edge of the Diff cup. Appears to be just at the cross pins as @bicketybam states.
Ideally, this would allow for displacement of fluid without overflow, when the ring gear/spur is assembled to the diff.
Filling completely to the top will cause initial overflow to come out as you screw the gear onto the cup. I find that overflow gets into the 4 screw holes and that can cause loosening of those screws over time... from my experience. But sometimes just cant be avoided. It happens. I also try not to waste much fluid needlessly. But not a priority IMHO.
Once screws are tightened, I check the diff action and may release oil with the grub screw. excess oil and air will come out( usually not much), then stop. I then close it up at this point.
I use a shock pump to remove air as I fill the diff. As air is removed, the level of oil drops , then I add more oil as needed. Using a shock vacuum pump is not necessary for most if you fill slowly and let the oil sit, between adding small amounts of oil. I only mention the shock pump because I noticed much air remains in the diff oil as you fill. And thick oil holds the air in it for very long.. Much of it is noticed when using a shock pump. Otherwise you would not truly see any air at all, but its there. A shock pump speeds things up for me.
And the air that remains and you don't see displaces any room for the proper volume of oil. Aerated diff oil runs hotter IMHO. That's why I like my diffs full, just not to point that it can cause hydro locking/ high internal pressure. Leaking oil is a sign of this. Releasing any excess oil/air once assembled tight using the Grub screw method helps in this regard. Most feel that grub screw is for access to the cup side cross pin. And It is. Its also great for releasing excess oil.
Everyone has different methods of filling. But however its done, the diff should be full IMHO. Its not a perfect science.
Some diffs like Mugen's fill by weight in grams using a scale. And the Track guys use shock pumps on their diffs. They want it that precise. I imagine being as precise as you can translates to any diff including Arrma's.

 

[JohnukRead]

Thanks for the writeup. Not sure where to add this comment, but this thread seemed appropriate. Check the diff fluid levels on your other differentials. My center differential was pretty low on fluid and so I added a good quantity of 100K.

I didn't detect any wiggle/movement in the outdrive shafts so I didn't disassemble it further to check the number of shims.

Have you had any troubles since writing this?

 

[Engineer]

Have you had any troubles since writing this?

So far, knock on wood, no troubles, but it's been really busy with work and I picked up some new cars, so I haven't really run my Kraton EXB a lot.

 

[B Diddy]

Manual for both RTR and EXB diffs show the same fill line. Which appears to be a few MM. below the top edge of the Diff cup. Appears to be just at the cross pins as @bicketybam states.
Ideally, this would allow for displacement of fluid without overflow, when the ring gear/spur is assembled to the diff.
Filling completely to the top will cause initial overflow to come out as you screw the gear onto the cup. I find that overflow gets into the 4 screw holes and that can cause loosening of those screws over time... from my experience. But sometimes just cant be avoided. It happens. I also try not to waste much fluid needlessly. But not a priority IMHO.
Once screws are tightened, I check the diff action and may release oil with the grub screw. excess oil and air will come out( usually not much), then stop. I then close it up at this point.
I use a shock pump to remove air as I fill the diff. As air is removed, the level of oil drops , then I add more oil as needed. Using a shock vacuum pump is not necessary for most if you fill slowly and let the oil sit, between adding small amounts of oil. I only mention the shock pump because I noticed much air remains in the diff oil as you fill. And thick oil holds the air in it for very long.. Much of it is noticed when using a shock pump. Otherwise you would not truly see any air at all, but its there. A shock pump speeds things up for me.
And the air that remains and you don't see displaces any room for the proper volume of oil. Aerated diff oil runs hotter IMHO. That's why I like my diffs full, just not to point that it can cause hydro locking/ high internal pressure. Leaking oil is a sign of this. Releasing any excess oil/air once assembled tight using the Grub screw method helps in this regard. Most feel that grub screw is for access to the cup side cross pin. And It is. Its also great for releasing excess oil.
Everyone has different methods of filling. But however its done, the diff should be full IMHO. Its not a perfect science.
Some diffs like Mugen's fill by weight in grams using a scale. And the Track guys use shock pumps on their diffs. They want it that precise. I imagine being as precise as you can translates to any diff including Arrma's.

What happens when the differential and case heat up? Expansion?