Kraton Two brand new differentials, one is grinding

[gnobes]

I am still pretty new to the RC world. I was not ready to crack open the diff cups when I was building my Kraton. Rather, I ordered replacement bulkheads from Jenny's so I could disassemble them at my leisure and have the originals as spares. Reason for disassembly is to inspect fluid levels and replace the cup's with HR diff cups.

These are the two bulkheads that I received. I am about to crack them open and see if I can figure out why one is not as smooth.

The differentials are snug inside the bulkheads. There is ZERO side to side play. There is no play in the input shaft cup.
It does not feel crunchy all the way around. While you are spinning the diff, it only happens on half/part of the spin.
It is much smoother when you are spinning via the input shaft.
The smooth diff also feels smooth when only one output cup is twisted. The crunchier diff feels... well, you can feel the binding when you twist one side.

Is it possible the grease used on the gears is just causing it to bind and heat/use would resolve it?

 

[morrjr71]

I would check the gears inside of the diff.

 

[Harriot10]

I am still pretty new to the RC world. I was not ready to crack open the diff cups when I was building my Kraton. Rather, I ordered replacement bulkheads from Jenny's so I could disassemble them at my leisure and have the originals as spares. Reason for disassembly is to inspect fluid levels and replace the cup's with HR diff cups.

These are the two bulkheads that I received. I am about to crack them open and see if I can figure out why one is not as smooth.

The differentials are snug inside the bulkheads. There is ZERO side to side play. There is no play in the input shaft cup.
It does not feel crunchy all the way around. While you are spinning the diff, it only happens on half/part of the spin.
It is much smoother when you are spinning via the input shaft.
The smooth diff also feels smooth when only one output cup is twisted. The crunchier diff feels... well, you can feel the binding when you twist one side.

Is it possible the grease used on the gears is just causing it to bind and heat/use would resolve it?

They could be grinding for many reasons. Check all the internals, and the tolerances from input to main gear. Could just need shimmed. Diffs are funny, none fit exactly the same.

 

[slick2500]

I bought 2 new diffs from Jenny's once one of them would not spin smoothly it would catch at a certain point I tore that gearbox apart and put it back together like 6 times and always the same result, so I tried a different gearbox case and then the diff started to spin smoothly. The gearboxes on these aren't molded that well and the diffs have a tendency to get snagged on them.

 

[K-BASH]

I'd back the 4 screws off slowly an se. If it frees up.after I rebuild them they are tight an will loosen up.i will leave the 4 screws somewhat loose an tighten more after a few runs.works for me

 

[Adiabatic]

My rear diff did the same. Moved the shim from the ring gear side to the diff cup side and it was resolved, although the mesh is now a bit loose on the previously smooth half of the rotation.

 

[N.Mango]

All else fails, run it like you stole it and let the gears break in. Worth a shot if all else fails imo.
(if it works then you'll have to rebuild to get the crap out of the diff after)

 

[gnobes]

I'd back the 4 screws off slowly an se. If it frees up.after I rebuild them they are tight an will loosen up.i will leave the 4 screws somewhat loose an tighten more after a few runs.works for me

The moment I took the screws out and popped that cover off it spun smoothly. I re-packed everything - fluid was a little low. One is as it was but the grindy one is now smoother. It's not perfect but it's much better than it was.

 

[K-BASH]

The moment I took the screws out and popped that cover off it spun smoothly. I re-packed everything - fluid was a little low. One is as it was but the grindy one is now smoother. It's not perfect but it's much better than it was.

When ya tighten it back up ,turn each screw a little bit at a time checking for smoothness as ya go....like I said,I always leave it alittle loose an tighten alittle more after each pack till screws are tight an everything is smooooth