Just a heads up for anyone needing to modify their clutch pack. 9.75-9.85 is quoted so often i recently modded my 2018 clutch to around 9.80 then found this information the next day.

which says that 9.8 would be beneath spec for the newest bikes. I didnt think the clutch changed so much over the years. Take what you want from it, but just a word of warning that the often quoted 9.8 may be going too far especially if you decide to sand down your fibres.

Still don't know why they don't make 1.9, 1.8 1.7 mm thick plates

Edited July 14, 20215 yr by faussy

This has to be taken into account with the other parts that have changed though.

Mainly the Belville spring thickness, and the pre-load plate (with the 10 screws) that clamps down on the said spring.

Early bikes had a 1.7mm thick spring, MT280232015. Then in 2006 Gas Gas went to a 1.5mm spring MT2806320015, then in 2015 they went to a 1.2mm thick spring MT22020GG-CGI-1, all affecting the clutch action.

There is also different pre-load plates.

It is not just the combined stack height that affects clutch action. 

I've asked this before but how much pressure should be applied when measuring the thickness of the clutch plates ?

Should they be measured whilst clamped in the hub ?

Applying force to a vernier can make quite a difference,  more than the tolerance above.

My experience is... install new clutch within or close to specs, try... if you don't like it, adjust thickness, repeat.

Measure the pack with a good caliper, wet (not dry) and with a reasonable squeeze on the caliper.  If you have new fiber plate, let them soak in oil overnight (some fiber plates use to swell a bit, especially in tranny oil if you listen to the old man tales!).  Make sure you also measure each steel plate in multiple  place around the circumference to make sure they are even and then make sure the plates are flat (use a piece of glass and you should not be able to see light between the glass and the plate).  It doesn't hurt to check the fiber plates too.

Thicker clutch pack will make for a faster clutch engagement, but less progressive and a harder pull and possibly more drag (beware that Gas Gas TXT Pro clutches have a reputation for drag anyways).  This is the setup for advanced riders, good for zaps, etc...

Thinner clutch pack will make for slower clutch engagement, but more progressive and lighter pull and possibly less drag.  This is the setup for "not so advance riders".

When reassembling the case on the bike, make sure the put a dab of grease on the thrust bearing and washer on the slave clutch cylinder to keep them in place during assembly.  They can slip during assembly and drop in the engine (don't ask me how I learned that... the only thing I would say is that it was an expensive lesson).

In my experience (YMMV) oil viscosity also has an impact on clutch drag, but not much on engagement speed (I use Maxima 75W).  I never tried tranny oil, I know as many people who love it as people who hate it.  I've learned to live (and embrace) the clutch drag.

Clutch pull: it seems that going to Silicon based Brake Fluid (DOT 5) makes the pull a little lighter (it's less viscous than the mineral oil and is compatible with the mineral oil clutch master and slave cylinder).  But in the end, a good Hand Grip Strengthener device is your best friend against stiff clutch pull 😁