Sanding Ball Diff Thrust Rings/Washers

[Origineelreclamebord 45]

I have a question about sanding the thrust washers/rings of the ball diff. Some people swear to using sandpapers to polish them up, other people say it works better to roughen them up a bit so the grip of the balls on the rings is better. And there's another group, probably quite large too, that don't actually sand the rings at all.

I've sanded a pair of rings try out if quite a rough sandpaper works. I used 240 grit, which I know should be way too rough - so I'll be sanding it finer in a minute - but I couldn't resist assembling the diff to check out how it feels - and actually the diff feels pretty good when you turn it

Anyway, I'll be buying several types of sandpaper in a minute, so I can choose how fine I want it... But I was still wondering: Is there a proven difference between the rougher and the finer sanding jobs on the diff rings? And to how rough a sandpaper can you go before you should be worrying about the diff balls?

[digitrc 0]

I have a question about sanding the thrust washers/rings of the ball diff. Some people swear to using sandpapers to polish them up, other people say it works better to roughen them up a bit so the grip of the balls on the rings is better. And there's another group, probably quite large too, that don't actually sand the rings at all.

I've sanded a pair of rings try out if quite a rough sandpaper works. I used 240 grit, which I know should be way too rough - so I'll be sanding it finer in a minute - but I couldn't resist assembling the diff to check out how it feels - and actually the diff feels pretty good when you turn it

Anyway, I'll be buying several types of sandpaper in a minute, so I can choose how fine I want it... But I was still wondering: Is there a proven difference between the rougher and the finer sanding jobs on the diff rings? And to how rough a sandpaper can you go before you should be worrying about the diff balls?

Any non-polished sanded finish will wear smooth in a very short space of time. I don't think the "rough" diff prep is worth it, and I have always had very good results with just leaving the parts as they are, degreasing them and assembling them. I think the design of the outdrives/pulleys and the lubrication of the thrust bearing has much more impact on the diff smoothness than the materials and preparation of the balls and plates.

[Origineelreclamebord 45]

Any non-polished sanded finish will wear smooth in a very short space of time. I don't think the "rough" diff prep is worth it, and I have always had very good results with just leaving the parts as they are, degreasing them and assembling them. I think the design of the outdrives/pulleys and the lubrication of the thrust bearing has much more impact on the diff smoothness than the materials and preparation of the balls and plates.

Yeah I heard that too. Pretty funny you mention it, as I already saw a line appearing where the balls run, and the diff has so far only been rotated by hand - quite a lot I have to admit: I was working on it the whole day yesterday as I'm switching to modern diff internals, but still.

The modern diff internals do confirm what you said though about the influence of the design. It's a Dyna Storm differential, and it used 9 conical washers (disk springs Tamiya call them) placed in opposite direction 3 by 3 to create a spring - and of course a 620 pre-assembled thrust bearing. Even with the rough sanded surface of the diff, it felt silky smooth unlike the stock diff which I had beside it to compare it with (also new and unused). The stock one feels ok, but feels grainy still. I don't know if it's the thrust bearing, the steel balls (instead of the silicon nitride ones) or the switch to a coil spring, but in terms of feel they are miles apart!

I heard another theory by the way about sanding the diffs. It was because the surfaces can get slightly uneven due to the stamping process that is used to make them.

No matter what's the best method is (if there is one), I'm sanding them anyway I decided to go up to 600 grit, and I also have 1000, that I may use after that

[Dombrasky 0]

Ive always used 600 wet and dry with a bit of wd40 on a flat surface,it helps make the surface of the ring completely flat

and also removes the slight groove you get after running for a while

I find the slight roughening you get helps the balls grip,so you get a nice smooth action without slipping

If you have two shiny surfaces ie;the rings and the balls, you will have to tighten it more to stop slip,which makes it not so light or smooth

Ive used this method on 1\12th 10th and 1\18th and it works well for me

HTH

[94eg! 834]

Ive always used 600 wet and dry with a bit of wd40 on a flat surface,it helps make the surface of the ring completely flat

and also removes the slight groove you get after running for a while

I find the slight roughening you get helps the balls grip,so you get a nice smooth action without slipping

If you have two shiny surfaces ie;the rings and the balls, you will have to tighten it more to stop slip,which makes it not so light or smooth

Ive used this method on 1\12th 10th and 1\18th and it works well for me

HTH

Yes, making the ring surface completely flat is the true purpose of sanding. And because the balls run the surface smooth in just a single run, there is really no single grit that used as an industry standard. No matter how you prep your diff, you will almost always have to re adjust it after the first break-in run.

I've found that using one of the oudrives as a holding tool for the ring really distributes the pressure evenly. Just a couple drops of bearing oil on the sand paper and your ready to get the job done. You will notice after making the first swirls of the ring around the sand paper, there are many many hi and low spots on the face. Once these are knocked down, the balls are then able to run extra smooth with nice even pressure as they roll.

Upon assembly, you may find that no matter what style of ball you use, the diff will have the same feeling as long as the balls are new. It's when reassembling a diff with used balls, that the various styles of balls comes into play. You will find that used steel balls will almost never run smooth. Ceramic, on the other hand, will run just as smooth after years of use as they did the first time they left the bag. This is where their added initial cost really pays off. I've been running the same set of used ceramic balls in my touring car for years now and that diff is smoother than any diff I've ever built.

BTW: I've never had a thrust bearing fail on me. I always soak them in motor spray repeatedly when rebuilding, and I always pack them with anti-wear grease when installing. Of course I don't race off-road, so I could see how that might make a difference with all the extra contamination. I personally don't think a ceramic thrust is necessary since the balls won't experience slippage like diff balls do.

[terry.sc 16]

The sanding has nothing to do with surface finish, highly polished or rough finish will make no difference to the smoothness or how much grip the balls have. it's entirely down to making sure the diff washers are flat so there's an even contact between all the balls and the washers. Use 600-800 grit sandpaper, fine enough to get a smooth surface but any finer will just take a lot longer to sand down the high spots.

[Dombrasky 0]