What weight oil should I use in 3s big rock front and rear diff?

[SwampYeti]

been lurking here for a few weeks and this forum has helped me with so much already, so first of all, thank you!

I recently shredded my diffs at the local rc track, so now I'm upgrading to the metal parts but while I'm there I wanted to address some handling issues I have. First the rear diff id like to tighten it up and get more bite before slipping. If I understand correctly stock is 10k cst? would going to 20k be alot? I don't really want the rear slipping much at all.
for the front diff id like to get a little less wheelspin out of it when I lift a tire but I still want to be able to turn at the track which is pretty slick on stock tires. I was thinking maybe 15k?
any input or experience is very much appreciated! Thank you!

 

[SrC]

I believe 10k is stock oil, Fr and Rr. Try upping the front diff first, perhaps to 20 or 30k. Leaving 10k in the rear for now. One change at a time. Too thick in the rear may cause steering stability issues. If anything no more than double the front oil thickness, give or take, of the rear diff as a rule. To keep steering and traction stability more balanced. How I run my 6s platforms. Much is trial and error and based on how you like to drive.
I'll let other 4x4 guys chime in with actual experience.

 

[SwampYeti]

I believe 10k is stock oil, Fr and Rr. Try upping the front diff first, perhaps to 20 or 30k. Leaving 10k in the rear for now. One change at a time. Too thick in the rear may cause steering stability issues. If anything no more than double the front oil thickness, give or take, of the rear diff as a rule. To keep steering and traction stability more balanced. How I run my 6s platforms. Much is trial and error and based on how you like to drive.
I'll let other 4x4 guys chime in with actual experience.

A little oversteer is fine, but I wanna avoid understeer which is what I'm concerned about with the front diff. This is mostly a basher, I just took it to the track cause it's hard to find places to bash with decent jumps.

 

[Neelis]

30k in the front and 10k in the rear works for me.

 

[Bustedaw11]

I'm running 20k front and 15k rear in my big rock. Handling is solid. Dirt/rock/onroad. Don't have any issues with understeer or oversteer on any surface. Much better overall. Not ballooning 1 inside tire like when on stock 10k.

 

[SwampYeti]

I'm running 20k front and 15k rear in my big rock. Handling is solid. Dirt/rock/onroad. Don't have any issues with understeer or oversteer on any surface. Much better overall. Not ballooning 1 inside tire like when on stock 10k.

Intresting I thought you'd want it the other way around. I want my rear to feel like its locked, and if your saying 20k in the front isn't causing understeer I'm thinking maybe I should just go 20f/20r or maybe even 20f/25r

 

[Bustedaw11]

Intresting I thought you'd want it the other way around. I want my rear to feel like its locked, and if your saying 20k in the front isn't causing understeer I'm thinking maybe I should just go 20f/20r or maybe even 20f/25r

The reason I went for that was I had more issues picking up a front inside tire and ballooning it. It was clearly overdriving 1 front on me. I went to the 20k and I don't have nearly the issue if at all now. I wouldn't want to go higher as I have the feeling I'd start to get understeer. 15k works well out back for me. I can drift on blacktop no issues. In wheelies it keeps the rears spinning the same speed consistently.

You could bump it up out back but a locked rear can also produce understeer on throttle When the front ends lighter.

 

[SwampYeti]

The reason I went for that was I had more issues picking up a front inside tire and ballooning it. It was clearly overdriving 1 front on me. I went to the 20k and I don't have nearly the issue if at all now. I wouldn't want to go higher as I have the feeling I'd start to get understeer. 15k works well out back for me. I can drift on blacktop no issues. In wheelies it keeps the rears spinning the same speed consistently.

You could bump it up out back but a locked rear can also produce understeer on throttle When the front ends lighter.

Good to know, Ive been running a little preload on the rear springs to help pop wheelies. So I might experience what your talking about. Although I'm less worried about understeer under throttle than I am while braking.

Your insight has been helpful, I think I'll order 20k, 25k, and 15k and play around with it to see what I like best.

 

[MrTitanium]

I recently installed the steel diff gears and did a lot of research on oil viscosity for the front and rear diffs. In the end, I decided to go with 20k rear and 15k up front.

Keep in mind that the small satelite gears are made of cheap material and of poor design. They chip easily. Going too thick an oil viscosity will put a lot of strain on those little fellas.