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Old 2008.08.17, 01:33 PM   #1
Tjay
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how smooth is smooth... ball diff

Ok, I have been rebuilding kyosho diffs for quite some time now and I thought I got it all figured out... "smooth is better", "smooth like butter" is what you'd always here at the track when they talk about their diffs but how smooth is smooth?

When I sand down the diff plates, I use circle motion until the lines/marks from the diffs plates are completely gone. After the rebuild, when I feel the diff by moving the wheel back and forth, it feels like I'm moving the front wheel back and forth. It's that smooth. Lately, I decided to use "figure 8" instead of just "circle" on the plates when sanding them and noticed that when I move the wheel back and forth, the diff feels gritty... Does this means that the balls are actually "rolling" on the plates? How about the circle motion? The plate has gotten so smooth that it's probably polished instead of having a scratch mark on it for the balls to have a grip on?

On the track the results feels the same for both smooth and gritty diffs but the question is, how smooth is smooth?

Thanks!
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Old 2008.08.17, 03:37 PM   #2
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Good question. I'd like to know how smooth to polish diff rings also. In an old tutorial on AM that CT wrote on "How to build an Ultimate diff" they used 3000-grit sandpaper. I went and bought some Meguiars 3000-grit paper (The only 3000-grit I could find, actually) and used that for polishing my rings for a while. Then I read on here that it is better to use 800-1200 grit paper so that the balls have something to "grip". Now I use 1000 grit - But the smoothness is lessened slightly. Is super smooth best? Or is a little "bite" good for both MR02 and MA010 ball diffs?
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Old 2008.08.17, 08:37 PM   #3
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I don't take it to that level but I've found that taking a lumpy diff and putting into my dremel smooths it out real fast. I set it up so that there is a "racing" of tension on it first then I just use a little 3 in one oil on it, drop the drivers side end into the dremel and before I turn the thing on I hold the spur gear between my fingers (critical thing to do here). Just run it for a few seconds. It's not a pretty way to do it but the last one I did went from incredibly crappy to smooth as glass within 30 seconds. It's a brutal way to get it done, I admit... but it did work, and it still works.
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Old 2008.08.18, 08:25 PM   #4
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TJ
To me smooth is when you turn the wheels and you feel like the front on TWD, completely free movement.
After I file down the diff disc with figure 8 on 800 water file paper on top of a table glass top, then I mirror polish the discs with Brasso metal polisher on a cloth, same table glass top, and when assembling back I only use of the diff ceramic balls, that would be 4 diff balls on the AWD and 3 diff balls on the TWD.
Before I place in the ceramic balls, I run them on top of the clean glass tabletop, they have to go straight, if a ball goes to a side or wiggles, I depose it.
I wish some one comes-up soon with ceramic diff discs!!!!!
Cheers

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Old 2008.08.18, 09:15 PM   #5
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ive only had one kyosho diff in all of my miniz.....it was really smooth after i built it like the atomic mods tutorial that ct did....
since then i have had only pn diffs
the new ceramic diff with the rebuild is so smooth....i ues a 800 grit waterstone
the same stone that i use for finishing surfaces im my race motors
so smooth.....feels like a freshly polished new car as you slid a clean cloth across the smooth surface......
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Old 2008.08.18, 10:01 PM   #6
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yasuji - What did you use between the blue hub and the rings to keep the rings from slipping on your old Kyosho diff? I am just about re-rebuild my Kyosho MR02 diff because the rings are slipping bad. I'm thinking about using white glue instead of CA, but your thoughts on this would help also.
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Old 2008.08.18, 10:30 PM   #7
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Quote:
Originally Posted by imxlr8ed View Post
I don't take it to that level but I've found that taking a lumpy diff and putting into my dremel smooths it out real fast. I set it up so that there is a "racing" of tension on it first then I just use a little 3 in one oil on it, drop the drivers side end into the dremel and before I turn the thing on I hold the spur gear between my fingers (critical thing to do here). Just run it for a few seconds. It's not a pretty way to do it but the last one I did went from incredibly crappy to smooth as glass within 30 seconds. It's a brutal way to get it done, I admit... but it did work, and it still works.
As long as the plates were flat to begin with this should be an equivalent method. The balls will eventually wear their own groove into the rings, which negates the effect of sanding or polishing over time. I just hold one wheel still and gun the trigger to break in a rebuilt diff, it's quick and it's a 95% fix solution. I really don't think the last 5% of smoothness makes much of a difference since you're going to get grit in the diff as you drive anyways. If the diff is still 95% smooth (at most a tiny bit of "grit" feeling at one or two points per rotation) after you come off the track, I'd call it a success.
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Old 2008.08.18, 10:37 PM   #8
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Yasuji,
Do you use the stainless steel shaft on the pn diff, or did you swap it?
I was reading the reviews and one said the diff was heavy, I take the shaft would cause some of that issue. Thanks in advance
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Old 2008.08.19, 06:08 AM   #9
hpgod
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On any ball diff put diff lube on the back side of the rings. The Large surface with surface tension from the lube will prevent the ring from spinning on the back plate. put 3-4 drop on the back side then spin slightly to spread. I use AE diff lube from my 1/10 days.
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Old 2008.08.19, 09:31 AM   #10
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Quote:
Originally Posted by Felix2010 View Post
yasuji - What did you use between the blue hub and the rings to keep the rings from slipping on your old Kyosho diff? I am just about re-rebuild my Kyosho MR02 diff because the rings are slipping bad. I'm thinking about using white glue instead of CA, but your thoughts on this would help also.
i always assembled it dry.....it is a hassle
another thing i did was sand both sides of the diff rings.....think about it...
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Old 2008.08.19, 09:35 AM   #11
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Quote:
Originally Posted by blt456 View Post
Yasuji,
Do you use the stainless steel shaft on the pn diff, or did you swap it?
I was reading the reviews and one said the diff was heavy, I take the shaft would cause some of that issue. Thanks in advance
i use the pn diff shaft.....funny thing is that i raced the pn regional with a brand new pn diff with the 64 pitch convert and kyosho diff lube
i didnt even prep it.....lol i had huge problems the day before
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