GasGas Pro - Clutch Drag

The GasGas Pro modeld from 2002 onwards foe the 125cc to 300cc all use the wet plate diaphragm hydraulically operated clutch.  These clutches are superb and give good gradual operation when they are properly set up.  Note: this type of clutch is particularly noisy in neutral with the cltuch out and had a 'clattering' sound which is quite normal.

When the clutch starts to 'drag' the lever often gets heavier than it used to be.  Drag is where the bike 'creep' forward when you put it into gear or stalls or jumps forward.  If you have drag you will find it ver difficult to find neutral.  First thing you have to remember is that nearly all clutches will drag from cold because the oil is much thicker.  If you have evidence of drag when the engine is warm then first check that the hydaulics are correctly adjusted and that you are using the correct oil (Dextron 3 ATF (Automatic Transmission Fluid) is best) and the correct volume of oil.  You can download a manual for your GasGas here.

If you ahve checked everything else is in working order and you still have a problem (especially if your clutch lever is heavier to operate than it used to be) then you need to take the clutch apart to fix it.

The diaphragm design of the clutch is excellent but relies of strict tolerances being maintained.  Basically the problem is that the 3 clutch friction plates soak up the oil and swell a little.  There are 2 ways to cure this, either fit new friction plates (but the problem will reoccur) or replace one of the 2 steel plates for one slightly thinner.

To complete this job you will need Allen Keys, a 12 point (not a 6 point) 7mm spanner or socket and a Vernier Gauge.

Step 1 - Drain the oil and remove the kickstart.  I also remove the bash plate and rear brake but you may get away with not having to.

Step 2 - Remove the 5 allen bolts from the clutch cover casing and the 3 from the water pump.  Gently tap the casing to free it and then pull it off.  There is no need to disconnect the water pump or drain the coolant, the water pump will stay firmly in the clutch casing.

Note 1 - Once the casing is removed, do not turn the engine over or rotate the water pump from inside the clutch casing - these are perfectly aligned as the came off and should go back without a prolem is undistrubed.

Note 2. - There  is a shim on the kickstart shaft that may be stuck to the inside of the clutch casing, there is also a thrust washer and bearing on the inside of the clutch casing on the slave cylinder.  If you take these off, make a note of how the go back on.

Step 3 - Remove the 10 small bolts that hond the clutch spring in place.  You will notice that unlike a conventional clutch, the GasGas only has one spring and that is a 6" ring of convex spring steel.  Once you have removed all bolts, the clutch can be disassembled and cleaned.  Look for debris under the spring as this will affect operation.

Note 3 - There are 10 'leaves' that make up the diaphragm actuation, make a not of how thses are fitted and which way aroung the came out as it is important to put them back the same way they came out.

Step 4 - Hold the 3 friction plates and 2 steel plates together and measure their combined thickness with a Vernier Gauge, be careful not to let the blade of the Vernier drop into the slots on the friction plates or it will give you a false reading.

The reading should be between 9.75mm and 9.85mm for the clutch to operate properly.  You can buy thinner steel plates from GasGas or BVM Moto, these are about 0.20mm thinner than standard and will give you the desired thickness.

You will have to measure one of your steel plates and then order a thinner one, remember to order a new cover gasket at the same time.

Step 5 - Once you have your clutch plates to the recommended thickness and cleaned all the components, you can re-assemble the clutch.  The plates go - friction, steel, friction, steel and friction.  It doesn't matter if the thinner steel goes second or fourth.

Replace all 10 leaves and then put on the outer pressure plate.

Then replace the spring and retaining ring.  The outside edge of the spring should be in contact with the outer pressure plate.  Replace the 10 screws finger tight to start with.  Then tighten them sequentially as below about 1/2 a turn at a time.  You should feel the pressure of the spring as you tighten them.  Do not over tighten the screws.

Once all the screws are done up securely, you should be able to move the leaves in and out a little, if any or all of them are firm, you have done something wrong and you will have to take the spring off and re-assemble the clutch.  All things being well, make sure you have the kickstart shim and the clutch thrust washer/bearing in place, fit the new gasket and push the casing back into position.

Step 6 - Replace the casing allen bolts and tighten the casing, if you have moved the engine or water pump pinion you will have to re-align these before the casing will fit properly.  Ensure you have replaced the drain plug and then refill the gearbox with oil to the specified level and the job is done! 

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