RcTek : Information & Resources for the Model Car Racer

Centax Type Clutches — Further Information

In response to the requests for information regarding Centax type clutches, we have put together the following article that explains the way they work and what parts are involved.

The name Centax is used by Serpent Model Cars and is used throughout this article as it has become synonymous with this type of clutch.


Centax type clutches are reasonably reliable assemblies and their performance far outweighs any other type of clutch available today.

The only weak point on many of the centax type clutches are the small diameter bearings that are used, this is especially true of the thrust races. The exception to this was the PB Racing PBTec clutch, which used a rather larger and better specified bearing.

Considering the forces involved the bearings last some time, but careful maintenance will extend their lives greatly. The thrust races especially require frequent lubrication with a good quality grease. Molybdenum Disulphide (MoS2) is considered to be the best all round lubricant to use, although more expensive alternatives are available.

Please see our article on Thrust Race Bearings for more information.

Why use PTFE for the Clutch Shoes?

As PTFE is used for such things as non-stick pans, it does seem illogical to use it a clutch system. The centax type clutch relies totally on the centrifugal force of the flyweights to wedge the shoe against the clutch bell. The use of PTFE stops the shoe from sticking to the clutch bell along with a great deal of heat-resistance and gives positive engagement and disengagement.

Thrust Race Substitute

Some time ago it was suggested that the thrust race could be replaced with a plain bearing. A few people tried this, but after a time they all reverted to the original thrust race.

Centax Clutch modification

Centax Clutch Adapter

Shown on the left is a diagram of the modification, which involved changing the thrust race for a standard plain bearing and using the adapter (right) from the PB Racing clutch. This also had the bonus effect of adding instant adjustment to the Serpent clutch.

Whilst this modification looks promising, you are using a bearing that is designed for having forces applied to it from another direction. If the bearing only contacts the clutch bell using its outer race and the adjusting nut on its inner race it would seem to work well, but if you study the diagrams below you will see the problem with this solution.

Bearing Cross Section

Thrust Race Cross Section

A cross sectional view of a plain bearing is shown on the left and if you compare this with the cross sectional view of a thrust race on the right, you will notice that the contact area between the bearing races and the balls is completely wrong. When the bearing comes under load the ball will be wedged between the races, which will bind up the assembly and create heat.

The more end float there is the worse the problem becomes. The bearing will probably destroy itself and or create sufficient heat to damage/melt the surrounding parts.

It is for this reason that performing this modification is not recommended, the cost savings and/or reliability it seemed to promise are false ones. The thrust race bearing is used for a reason, it is designed to take the forces that it gets subjected to in a model racing car.

End Float - Too Much Shortens Bearing Life

This problem is covered in a separate article about Thrust Race Bearings.

Related Information

Parts Descriptions & Diagrams of Centax Type Clutches

How the Centax Type Clutch Works

Thrust Race Bearings

How Gears Work

Centax Adjusting Tool

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© 2001, 2009 by Darren Burnhill