Curing Clutch Drag

What is meant by clutch 'drag'?  This is where the bike 'creeps' forward even with the clutch fully in or in really bad cases and when the bike is cold, it stalls when you put it into gear.  Some bikes are notorious for the clutch to 'stick' or be unwilling to disengage when cold (some Fantic models. some Beta etc.) as long as the clutch works properly when the engine is warm then there is no problem.  If you are still having trouble with a warm engine (crunching going into gears, jumping forward, not disengaging properly), then you have clutch drag.

In essence there are only 3 types of clutch you get on a trials bike, one is the multl-plate, multi-spring wet type which most bikes have, another is the 3 plate diaphragm wet clutch used on the GasGas Pro models from 2002 and finally the centrifugal dry clutch on the 'twist and go' kids bikes.

The difference between a wet clutch and a dry clutch is that the wet clutch runs in oil or ATF (Automatic Transmission Fluid), so first job is always to drain the gearbox of oil!

It is rare that the centrifugal clutch suffers drag and mostly suffers from work friction shoes or weak springs.

Both the multi-spring and the GasGas diaphragm clutch will suffer from drag if they are not adjusted properly or not bled properly in the case of a hydraulic clutch.  Cable clutches are easier to see if it is adjustment as you can see the actuation, a hydraulic clutch may not operate entirely correctly if the master cylinder has a slight leak, the slave cylinder had a slight leak or ther is a problem in the hydraulic pipe or any of it's unions.

This section assumes that you have adjusted your cable clutch properly so there is only a fraction of free play or that you have established that your hydraulic system is functioning correctly (fluid does get 'tired' and need changing at regular intervals).  You still have clutch drag and you don't have a GasGas (these are dealt with here) or a 'twist and go' bike.

For this explanation, I have been working on a cable clutch Yamana but the priciple is the same for a hydraulic Sherco or Fantic, there slight differences in all models and some of the clutch actuation is in different places but the likely cause of clutch drag is invariably the same.

Firstly, drain the oil from the bike, sometimes you have to remove the bash plate to do this and probably to get at the casing screws.  Most bikes hold up to a litre so be prepared!

Remove the kickstart and the side casing.

Below you can see the clutch 'basket' and the plates sat in it on the clutch 'hub'.  The pressure plate and the six springs have been removed, you can see where they screw into the clutch hub.  The push rod in the centre of the clutch nut is what pushes against the pressure plate and allows the clutch friction and steel plates to spin independently.

The plates are arranged in the basket with alternate friction and steel plates.  The steel plates drive the centre hub and the friction plates are rotated via the basket by the engine.  You can see the teeth on the inside of the steel plates engage with the hub and the tabs on the outside of the friction plates engage wit the gasket.  When the steel and friction plates are under pressure, the engine drives the gearbox (and so the drive chain) through the clutch.

Removing the clutch centre nut requites a clutch holding tool, there are more than one design of these on the market and the can be bought for about £12.

Once you have removed the hub and taken the basket off you can begin to see the problem.  The steel of the friction plates 'digs in' to the softer metal of the clutch basket creating 'grooves' as can be seen below.  These grooves hold the plates in position in the basket when the clutch is pulled in and this stops then disengaging properly and spinning freely.

The cure is free and painless!  It just takes a little care with a file to even out the grooves, don't file to much - just enough to remove the grooves.  Keep the file level and travelling through the centre axis of the basket as you file.  Remember the basket nas been running in oil so you may need to degrease it in order to file it.

Once you have done all the edges and removed any filings so the basket is clean, you can begin to re-assemble the clutch.

I have only ever had 2 trials bikes where this did not need to be done and anyone will tell you I have had a lot of trials bikes!  It is of course not the only reason for clutch drag but if you have explored all other possibilities without getting insidethe engine then you may find this is the culprit.  Taking photos as you go (or someone with clean hands doing it!) is a good idea and be methodical in your work so you don't lose bits!

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