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Old 11-29-2011, 01:45 AM   #1
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Default Could anyone tell me why ball diff uses thrust bearing?

From what I have searched from the internet, thrust bearing is mainly used to support axial load and the capability to support radial load is nearly 0. As the ball diff is completely tightened by the retaining screw, there would not be any axial movement, isn't it? Then why would ball diff uses thrust ball bearing instead of radial bearing.

The stock F103/104 ball diff is using thrust bearing + pressure spring installed inside the rear wheel. However, recently I found out that the Tamiya F104 option 54158 alu. diff housing is using radial bearing instead of thrust bearing. Why would that be the case???????

Please help me. I am very curious. Thank you very much.
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Old 11-29-2011, 02:34 AM   #2
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The thrust bearing is to take the axial loads from the retaining screw.
The radial loads of the whole diff is taken from normal radial bearings.
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Old 11-29-2011, 02:56 AM   #3
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Originally Posted by keithlaw View Post
From what I have searched from the internet, thrust bearing is mainly used to support axial load and the capability to support radial load is nearly 0. As the ball diff is completely tightened by the retaining screw, there would not be any axial movement, isn't it? Then why would ball diff uses thrust ball bearing instead of radial bearing.

The stock F103/104 ball diff is using thrust bearing + pressure spring installed inside the rear wheel. However, recently I found out that the Tamiya F104 option 54158 alu. diff housing is using radial bearing instead of thrust bearing. Why would that be the case???????

Please help me. I am very curious. Thank you very much.
A ball diff should never be completely tightened, the spring should always be applying the pressure to the thrust. And that is the axial load that the thrust is required to support.

As far as using a conventional ball bearing to support the thrust, I have seen designs where the inner race is used to support the spring while the outer race is supported in the diff half. It is an improper use of the bearing, but one which seems to have a following in some classes.
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Old 11-29-2011, 03:26 AM   #4
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Thank you for the input guys.
One thing I would like to know is, will the thrust bearing take any radial load when the ball diff is working. In other words, if 1 wheel is locked and the other wheel is spinning while the motor is running, is there any radial load? will the load transferred to the thrust bearing ?
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Old 11-29-2011, 03:36 AM   #5
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Last edited by Sydewynder; 11-30-2011 at 04:16 AM.
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Old 11-29-2011, 03:38 AM   #6
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In a touring car no.
I am not familiar with the Tamiya F103/104 so I can't say for sure.
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Old 11-29-2011, 03:42 AM   #7
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Last edited by Sydewynder; 11-30-2011 at 04:15 AM.
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Old 11-29-2011, 03:45 AM   #8
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The Tamiya F103/104 is also supported by "regular" bearings. They are inside the diff halves since the rear axle runs through the diff.
But F103/104 Option Gear Diff housing does not require a thrust bearing..Why???
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Old 11-29-2011, 04:01 AM   #9
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Last edited by Sydewynder; 11-30-2011 at 04:11 AM.
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Old 11-29-2011, 08:53 AM   #10
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Originally Posted by keithlaw View Post
But F103/104 Option Gear Diff housing does not require a thrust bearing..Why???
Because they put the side load through the inner race of the radial bearing instead of adding a thrust bearing. Compare the two types of diff assemblies in the Tamiya manuals
http://www.tamiya.com/japan/download...al/f104pro.pdf
http://www.tamiya.com/japan/download/rcmanual/f104.pdf

Pros:
Less weight
Less parts
Assembly small enough to fit inside the wheel hex mount.
Cons:
Bearing needs replacing regularly due to thrust loads it isn't designed for.
Loaded up bearing can easily be destroyed in side impacts as the impact load goes through the bearing.

Putting the side load through the outer radial bearing has been the way 1/12th scale diffs have been designed for years, and people say they do give a different diff action to using a thrust bearing. Personally having run both types of f1 diff I prefer the F103/thrust bearing style as I can get it much smoother.
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Old 11-29-2011, 02:29 PM   #11
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There's another reason why it is better to use the outer radial bearing to transfer the end load - the balls are smaller so the end load required to ensure the diff doesn't slip is lower. Always use a steel bearing and not a ceramic, as the ceramic is more inclined to slip.

For cars with more grip - F1 and GT10 - the difference is minimal between the thrust race and the radial bearing. For a 12th car, you can feel the difference between the two, and the radial bearing wins the handling test hands down.

In order to get a good life out of the radial bearing, always use at least two cone washers, and preferably three. They all go on the same way, and then you have a lot more adjustment and great protection for the radial bearing from side hits. HTH
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Old 11-29-2011, 07:29 PM   #12
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Originally Posted by terry.sc View Post
Because they put the side load through the inner race of the radial bearing instead of adding a thrust bearing. Compare the two types of diff assemblies in the Tamiya manuals

Putting the side load through the outer radial bearing has been the way 1/12th scale diffs have been designed for years, and people say they do give a different diff action to using a thrust bearing. Personally having run both types of f1 diff I prefer the F103/thrust bearing style as I can get it much smoother.
people say they do give a different diff action to using a thrust bearing?? That's interesting. How different the diff action will be??
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Old 11-29-2011, 07:34 PM   #13
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There's another reason why it is better to use the outer radial bearing to transfer the end load - the balls are smaller so the end load required to ensure the diff doesn't slip is lower. Always use a steel bearing and not a ceramic, as the ceramic is more inclined to slip.

In order to get a good life out of the radial bearing, always use at least two cone washers, and preferably three. They all go on the same way, and then you have a lot more adjustment and great protection for the radial bearing from side hits. HTH
1) What is the "end load"?
2) When end load required to ensure the diff doesn't slip is lower, what is the advantage of that??
3) What is a cone washers? Is that the one came with the F104 assembly kit??

Sorry, I have too many questions. I a not very familiar with ball diff.
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Old 11-29-2011, 09:07 PM   #14
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Tamiya has a gear diff? Are you guys talking like road wizard or duratrax?Maybe I just missed something here.
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Old 11-30-2011, 02:12 AM   #15
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Tamiya has a gear diff? Are you guys talking like road wizard or duratrax?Maybe I just missed something here.
Oh Sorry, that was a typo. I mean ball diff.
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