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BuggyDad

Tightening ball diffs

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I assembled my first ball diff yesterday. 

The instructions in the manual I have are simply this:

Screenshot_20230131_043902_OneDrive

So mine is tightened just to the point that with something in the diff cups as shown, I can't make it slip when pushing it down and away from me (on a carpet for grip). I did it up a quarter turn at a time to reach this point so I could make it slip without too much difficulty 1/4 turn looser. It feels a little rough though. Is this OK? Did I push too hard in testing it? It's still runs quite freely (not like an open one, but freer than one with anything more than fairly light oil I'd say). 

I have a feeling this was mentioned in another thread not long ago, but I can't find it. Please feel free just to point me in that direction if so. 

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It's something you will get a feel for with experience. It's easier to set them up in the car, you'll get a better sense of how tight the action is, and whether they are slipping (you never want them to slip).

For first build I always do them hand tight and then back off 1/8th of a turn.

If they are gritty there is either wear on the balls already, or just not enough cleanliness/lubrication. The thrust washer bearing needs lots of black grease, the main balls need a coating of silicone grease.

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10 hours ago, sosidge said:

It's something you will get a feel for with experience. It's easier to set them up in the car, you'll get a better sense of how tight the action is, and whether they are slipping (you never want them to slip).

For first build I always do them hand tight and then back off 1/8th of a turn.

If they are gritty there is either wear on the balls already, or just not enough cleanliness/lubrication. The thrust washer bearing needs lots of black grease, the main balls need a coating of silicone grease.

Thank you. I opened it back up to have a look. I did wonder a bit about the thrust bearing, so added more grease there. 

And I checked that a quarter turn looser and I could make it slip without much difficulty, so I went back to the same tightness. In any case, the feeling is the same with it looser. It's more of a light buzz than a grittiness. A very uniform vibration, so it's not dirt. Most likely I guess it's slight out of roundness of balls from tightening it straight up rather than running it in. Unless anyone advises otherwise I think I will run the car lightly for a while and keep an eye on how it develops. I may also stock up on a new set of balls. 

The differential action is in the same ballpark as my XV-01 with 20k oil in, perhaps a little lighter. 

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I usually assemble them to the point I can't easily make them to slip.. and adjust tightness later as I see fit with traction levels in mind.  I will note the thread lock weakens after so many adjustments so might want to consider reapplying as needed.  

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45 minutes ago, BuggyDad said:

It's more of a light buzz than a grittiness. A very uniform vibration

I only had few ball diffs, they all feel like they have that grittiness/buzz.  My guess is that the balls make very small contact points and the metal surface they run on cannot be all that uniform.  For whatever it's worth, I don't think it's the balls. 

I use silicone faucet grease instead of Tamiya ball diff grease.  It's a bit thicker, and that widens the adjusting points.  If workable angle was a certain quarter turn, faucet grease will widen that a bit, so you'd have more to work with.  It could be in my head, but it feels like it needs less re-adjusting too.  

 

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6 hours ago, Willy iine said:

thread lock weakens

Mine won't. I didn't apply any 😬

Oops. 

Actually, it didn't call for it in the manual? I think I will use this as part of the "running in" / "keeping an eye on it" opportunity. I anticipate I'll fiddle with it a bit so maybe there'll come a better point to take it out and thread lock once I think I have a position settled. 

6 hours ago, Juggular said:

I only had few ball diffs, they all feel like they have that grittiness/buzz.  My guess is that the balls make very small contact points and the metal surface they run on cannot be all that uniform.  For whatever it's worth, I don't think it's the balls. 

I use silicone faucet grease instead of Tamiya ball diff grease.  It's a bit thicker, and that widens the adjusting points.  If workable angle was a certain quarter turn, faucet grease will widen that a bit, so you'd have more to work with.  It could be in my head, but it feels like it needs less re-adjusting too.  

 

Ah ha. This is very good to know. So it might be I'm just fussing over something which is actually normal? I did wonder. 

I shall keep an eye on it and run it in gently. It has a lesser motor (SP 17.5T, 0° timing) than many, plus its application should be relatively low stress (reduction in wheel size from touring/rally to M chassis directly proportional to torque demand at diff, all else being equal). 

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In my experience all ball diffs will feel rough when tightened properly, unless you spend time polishing the plates (all the way to 3000 grit at least) and use very high quality balls. To polish I lay a piece of sand paper, wet of course, on a quartz countertop or a glass coffee table. Turn the music on and take your time... it takes a lot of time on brand new plates. After that I give it a quick sand once in a while to maintain the finish.

To adjust the tightness, everybody has their own tricks. Mine: I make a small sharpy mark on the inside of one wheel. Then I spin the opposite wheel by snapping my fingers. I try to look for/count how many turn it will spin. Then you eventually know such car will drive well with 1 full turn, the other one with heavier wheels needs 1 and a half turn etc.

Good luck!

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7 hours ago, Pylon80 said:

In my experience all ball diffs will feel rough when tightened properly, unless you spend time polishing the plates (all the way to 3000 grit at least) and use very high quality balls. To polish I lay a piece of sand paper, wet of course, on a quartz countertop or a glass coffee table. Turn the music on and take your time... it takes a lot of time on brand new plates. After that I give it a quick sand once in a while to maintain the finish.

To adjust the tightness, everybody has their own tricks. Mine: I make a small sharpy mark on the inside of one wheel. Then I spin the opposite wheel by snapping my fingers. I try to look for/count how many turn it will spin. Then you eventually know such car will drive well with 1 full turn, the other one with heavier wheels needs 1 and a half turn etc.

Good luck!

Thank you. This is good to know. I just assembled mine out of the pack. No polishing. Does polishing the plates have a significant impact on longevity or is it more about the nth degree of performance? 

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@BuggyDad I think it is as you said, the nth degree of performance. For more casual use it is ok to assemble straight from the pack and the balls will cut a circular "race" in the plates after the diff has broken in.

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@BuggyDad, yeah we discussed this on a thread the other day, I don't know where it is either😂 I was querying similar when building my EVO diffs. I interpret that Tamiya diagram to mean that you tighten it up bit by bit, like you did, until when holding something in each drive cup and holding them still with your hands, you're finally unable to spin the gear with your thumbs.

I agree when it's done like that it does feel a little gritty when you spin the cups. In the finished car though it feels fine. Perhaps a tiny bit tight, as I get 3/4 of a wheel spin every time on the opposite wheel when I flick the wheels round with my fingers, and that's on both front and rear diffs, they are exactly the same. I reckon they would loosen up and wear in nicely within a run or two and be spot on.

Whilst we're on the subject, when people say ball diffs require more maintenance than say a gear diff, what does that mean?

I've contemplated fitting a ball diff to my DT-02, but what am I looking at, checking for tightness regularly? Taking it apart and re-greasing regularly? Replacing the balls regularly? And if any of those are the case how often is regularly?😂

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8 hours ago, Pylon80 said:

@BuggyDad I think it is as you said, the nth degree of performance. For more casual use it is ok to assemble straight from the pack and the balls will cut a circular "race" in the plates after the diff has broken in.

In that case, my methods suit my use case! 

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34 minutes ago, Kol__ said:

@BuggyDad

Whilst we're on the subject, when people say ball diffs require more maintenance than say a gear diff, what does that mean?

I've contemplated fitting a ball diff to my DT-02, but what am I looking at, checking for tightness regularly? Taking it apart and re-greasing regularly? Replacing the balls regularly? And if any of those are the case how often is regularly?😂

These are questions I could probably do with knowing the answers to too! 

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Agree with @sosidge but also consider the grease you use 

Tamiya / Associated offer various that imbed then break down under wear 

Each therefore loads the drive differently - with Tamiya TRF grades working best for me 👍

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