RcTek : Information & Resources for the Model Car Racer

Model Car Differentials - The Ball Differential

This section of the RcTek site is devoted to differentials, what they are, what they do and the different types of that can be fitted to radio controlled model cars.

This particular article aims to inform the model car owner about how a ball type differential works.

Ball Differentials

Model Car Ball Differential

There are a many different variations of the ball differential, but all use the same basic principle described in this article.

The differential featured in the images in this article is not based on any particular differential and only serves to represent the functionality of a ball differential.

For information about why model cars have differentials and how they work please see the Differential Basics and How Differentials Work articles.

Parts Identification

Komatsu Zenoah G230RC Engine Retaining Screw Output Cup Adjusting Collar Belleville Washer Thrust Washer Ball Bearings Drive Gear Thrust Washer Belleville Washer Thrust Race Bearing Belleville Washer Output Cup


To serve as a reference for this article and others, we have an exploded diagram of a representation of a ball differential above.

If you place the mouse pointer over the various parts, the name and a description will appear of that particular part.

Parts Descriptions

Retaining Screw
The retaining screw holds the whole assembly together and can be used as a means to adjust the action of the differential.
Output Cups
The output cups are the part that connect the internal parts of the differential to the driveshafts.
Adjusting Collar
The adjusting collar allows for the adjustment in the amount of slip in the drive gear.
Belleville Washers
The Belleville washers provide pressure on the ball bearings fitted inside the drive gear and on the those in the thrust race.
Thrust Washers
The thrust washers, or as they are more commonly referred to, diff rings, provide a hard and smooth surface for the ball bearings to contact with.
Ball Bearings
The ball bearings allow the other parts of the differential assembly to rotate relative to each other.
Drive Gear
The drive gear transfers the rotational movement of the engine/motor to the differential.
Thrust Race Bearing
The thrust race bearing allows for rotational differences (differential action) between the output cups.

The Differential

Ball differential

The parts that provide the differential action are shown in the image and consist of a Thrust Race Bearing (yellow), Belleville Washers (green) and a retaining/adjusting screw.

The thrust race allows for the output cups to rotate at different speeds and the belleville washers provide a load to restrict the difference in rotational speed. If implemented, the adjusting nut allows the level of restriction to be altered.

A Ball Differential is More than a Differential

Slipper clutch cross section

The ball differential offers more than a normal differential as it also has an inbuilt slipper clutch to control wheel spin.

The slipper clutch, the working parts of which are shown in the image to the right, will be more fully explained in a future article but basically works by applying pressure to the ball bearings (grey) through the Belleville washers (green) via the thrust washers (yellow).

Related Information

Belleville Washers
Thrust Race Bearings

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© 2001, 2009 by Darren Burnhill