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Ball Diff vs Gear Diff

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Old 04-07-2017, 07:46 AM
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Default Ball Diff vs Gear Diff

Ok, i searched and found nothing conclusive.

Gear vs Ball diffs in 2wd, why would a ball diff drive better on dirt? They both allow the 'differential ' in speed to allow cornering, ball diffs shouldn't be slipping-that's what the slipper is for. Gear diffs have resistance to rotation (like a ball diff) by adjusting fluid. So what is the actual 'diff'erence?

Not just 'more side bite' or 'more forward traction'-there must be a reason for the feel differences, so does anyone know?

Back in the day, a gear diff would diff out onto the unloaded wheel in a corner-this has been countered with sealed fluid filled diffs, this is why everyone preferred ball diffs.

What i don't understand is why a ball diff should be preferred on dirt nowadays?

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Old 04-07-2017, 08:49 AM
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One difference is the way resistance builds as torque is passed through the diff. A ball diff won't see a very extreme increase in resistance, because it is running on balls, which we all know are quite low rolling resistance. (Haha) a gear diff however with oil will see a much more drastic increase in resistance since the oil functions by moving around between the gears and as speeds increase in the gears the oil has a greater resistance.

I found ball diffs to feel more planted and solid on dirt and gear diffs to be a little more skiddish.
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Old 04-07-2017, 10:12 AM
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Ball VS Gear Differentials Kriostasis Racing Works
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Old 04-07-2017, 10:57 AM
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^good little bit of literature right there
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Old 04-07-2017, 11:26 AM
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Perfect-exactly the kind of explanation i was after! I wonder if a friction reducer in the silicone would prevent a gear diff binding as much under load?
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Old 04-07-2017, 12:10 PM
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Originally Posted by oldernoob View Post
Perfect-exactly the kind of explanation i was after! I wonder if a friction reducer in the silicone would prevent a gear diff binding as much under load?
There are a few things you can do to reduce the friction, but I haven't found a way to get it as free as a ball diff. There's a whole list of binding that happens under load in a gear diff that adds up:

- >Friction between the teeth of the gears trying to move against each other under load.

->Friction between the backs of the gears and the wall of the differential (as more torque is applied, the gears want to separate more and that force has to have an equal and opposite counterpart).

->Friction in the seals.

->Friction of the spider/planetary gears on their pins.

Yeah, most of those forces are small, but they add up relatively quickly compared to a ball diff. Some tricks to reduce friction include:

->Brass washers instead of steel (brass on steel has less friction that steel on steel). However, brass isn't as durable as steel and probably won't hold up behind the output gears on most diffs.

->Mixing plastic and metal gears in the diff. Some companies offer both types of gears, but they might be designed with different teeth, so double check. This again reduces durability, but wouldn't be an issue in spec classes.

->Polishing all surfaces that come in contact with another part.

I ran a gear diff in a 2wd sct for a while when I had very little time to maintain my cars. I ended up using just black grease or 35 wt shock oil to get the best feel on a low/medium grip track. Still not as good as a well built ball diff, but was better than a crunchy one.

Food for thought.
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Old 04-07-2017, 10:20 PM
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Last I tried a gear diff in the dirt it was undriveable, would diff out and jump power from side to side the whole way down the straight making it almost impossible to keep it straight
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Old 04-07-2017, 11:57 PM
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I had a similar experience to the one above with my Schumacher KF2 on dry astro. It was a new car, and I had the ball diff in as it had been damp earlier. I thought I would try the gear diff for the last round. On the straight It was swerving from side to side under power, and almost undriveable. Was the diff oil too thin, or too thick?
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Old 04-08-2017, 12:07 AM
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Originally Posted by stueys View Post
I had a similar experience to the one above with my Schumacher KF2 on dry astro. It was a new car, and I had the ball diff in as it had been damp earlier. I thought I would try the gear diff for the last round. On the straight It was swerving from side to side under power, and almost undriveable. Was the diff oil too thin, or too thick?
Too thin.
However I can have mine as thin as I like but have to be wary of rear end roll. If the end is flat, it cant diff out.
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Old 04-08-2017, 01:01 AM
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Originally Posted by Krio View Post
There are a few things you can do to reduce the friction, but I haven't found a way to get it as free as a ball diff. There's a whole list of binding that happens under load in a gear diff that adds up:

- >Friction between the teeth of the gears trying to move against each other under load.

->Friction between the backs of the gears and the wall of the differential (as more torque is applied, the gears want to separate more and that force has to have an equal and opposite counterpart).

->Friction in the seals.

->Friction of the spider/planetary gears on their pins.

Yeah, most of those forces are small, but they add up relatively quickly compared to a ball diff. Some tricks to reduce friction include:

->Brass washers instead of steel (brass on steel has less friction that steel on steel). However, brass isn't as durable as steel and probably won't hold up behind the output gears on most diffs.

->Mixing plastic and metal gears in the diff. Some companies offer both types of gears, but they might be designed with different teeth, so double check. This again reduces durability, but wouldn't be an issue in spec classes.

->Polishing all surfaces that come in contact with another part.

I ran a gear diff in a 2wd sct for a while when I had very little time to maintain my cars. I ended up using just black grease or 35 wt shock oil to get the best feel on a low/medium grip track. Still not as good as a well built ball diff, but was better than a crunchy one.

Food for thought.
I agree, my experiences have been pretty similar. I've been switching back & forth in my Tamiya buggy(my TRF211XM came with both a ball diff & gear diff, so I built both), & I also found that when there's plenty of grip & I want to make the car feel more aggressive on power, then I like the gear diff, but if grip is lower or the surface is rough, I prefer the ball diff(which also gives you the ability to make very small adjustments very quickly). But that being said, on carpet tracks, I think I'll prefer the gear diff, once it's set up right, it'll be easier to keep that way for longer(I can never keep a ball diff working smoothly on carpet for very long, within a month or so, they start to get gritty & start slipping & barking under hard acceleration). So both have their uses....
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Old 04-24-2019, 10:48 AM
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Originally Posted by oldernoob View Post
Ok, i searched and found nothing conclusive.

Gear vs Ball diffs in 2wd, why would a ball diff drive better on dirt? They both allow the 'differential ' in speed to allow cornering, ball diffs shouldn't be slipping-that's what the slipper is for. Gear diffs have resistance to rotation (like a ball diff) by adjusting fluid. So what is the actual 'diff'erence?

Not just 'more side bite' or 'more forward traction'-there must be a reason for the feel differences, so does anyone know?

Back in the day, a gear diff would diff out onto the unloaded wheel in a corner-this has been countered with sealed fluid filled diffs, this is why everyone preferred ball diffs.

What i don't understand is why a ball diff should be preferred on dirt nowadays?

Asking for a friend ;-)
I started RC cars right back when Tamiya released their Sandscorcher. It didn't even have a diff! Cecil Schumacher's ball diff was the solution for high-end model racing cars back in the day, especially in 1/12th and 1/10th scales.

The ball diff worked, it was light, adjustable and cars were winning with them.

Tamiya's hugely successful cars, throughout their range, sported gear diffs. In electric classes, I think this sealed the mind-set:

Competition oriented cars use ball diffs.
Hobby grade cars used gear diffs.

And thus it was - just because.

My feelings were that ball diffs were very light and when properly assembled and maintained, produced a really smooth diff action. Ideally, the diffs needed to be sealed from the elements, which was generally harder to do on 4wd cars. Dirt ingress resulted in crunchy, rough/poor diff operation. Likewise, incorrect adjustment would result in loss of drive (if set to loose) or binding/broken diff screws (if set too tight).

The adjustability range of the ball diff is very small. Being able to adjust the diff without disassembly was more a case of finding where the diff worked without slipping or breaking rather than a tuning aid.

The ball diffs in my CAT 3000, Axis, Associated TC3, Yokomo SD Rayspeed all performed very well with a silky smooth action. I was familiar with them and knew how to get the best out of them. It wasn't always plain sailing with my older CAT XLS, Pro CAT and Boss CAT. The diffs were finnicky and became contaminated easily.

All my 1/8th cars used gear diffs. Tuning these sealed, fluid filled diffs gave a viable tuning option and were lower maintenance.

I liked both types of diff. With the more limited power that we had in the electric classes, ball diffs were a solution to a problem that minimised the rotating mass of the driveline yet still gave us great handling - on or off road.

Now that brushless and lipos fill the electric classes, 1/10th scale cars are dealing with waaay more HP than what Cecil had in mind. Gear diffs make much more sense in 2019.

Ball diffs may have a hardcore following. But they fill a (very small) niche in RC 1/12th, 1/10th scale racing and lawn mowers. Gear diffs may well just become the norm as ball diffs become antiques. Possibly

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Old 04-24-2019, 11:19 AM
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I'm such a noob when it comes to ball-diffs and 2wd. I feel like my car runs pretty good but I'm getting a squeal now from my 22 4.0SR when I am in the upper rpms. So I assume that means that the ball diff is out of adjustment or going bad? It took me a bit to feel like I had it set in the first place. I'm half tempted to rebuild with a gear diff, even though the car primarily runs on low-bite dirt track. It can be frustrating.
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Old 04-24-2019, 12:15 PM
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Originally Posted by AJH387 View Post
I'm such a noob when it comes to ball-diffs and 2wd. I feel like my car runs pretty good but I'm getting a squeal now from my 22 4.0SR when I am in the upper rpms. So I assume that means that the ball diff is out of adjustment or going bad? It took me a bit to feel like I had it set in the first place. I'm half tempted to rebuild with a gear diff, even though the car primarily runs on low-bite dirt track. It can be frustrating.
While I can't imagine racing 2WD cars and trucks on astro or carpet without a gear diff and would not put ball diffs in a 4WD in any condition anymore, low bite and 2WD continues to be the domain of ball diffs. Yes, they can be frustrating at first, but once you get them on point, they will reward you with a smooth and consistent ride. Follow the sticky thread on the top of the forum page and you are on the right track. I found that using ceramic diff balls and either AE or even better Yokomo silicone diff grease help a lot, Tungsten thrust balls are ok. IIRC TLR already grinds the diff rings for you, so that should not be a problem.
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Old 04-25-2019, 06:02 AM
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I race on carpet and high bite clay with a gear diff (usually 20k on carpet and 1k-5k on clay). I'm certainly not the fastest guy but I can hold my own. I've never really experimented with ball diffs because ....... well to be honest, I was sort of afraid of them. I did race a B4.2 back in the day but I was still a noob and had my buddies set everything up for me.

Anyway, I just recently purchased a dirt edition buggy (with a ball diff) and plan on forcing myself to learn. There is a great thread at the top of this section ("How To Properly Build And Break In a Ball Differential and Slipper Clutch") that shows you how to build and break in a ball diff. I followed this process on Monday and my diff feels buttery smooth.

I'm excited to compare the carpet buggy vs. the dirt buggy sometime.
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Old 04-25-2019, 06:56 AM
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Does anyone have experience with TLR's planetary gear diff on dirt? It seems like that design would have less bind under load (which may be why they've gone away from it on their carpet spec car..), lending itself to better dirt performance. I think the tuneability of different fluid weights would be valuable on dirt.
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