A few Qs about clutch adjustment
 

I'm trying to fix a slipping clutch issue by following the FM guide for clutch adjustment ( https://www.flyinmiata.com/support/i...structions.pdf ) but using 949 4 puck clutch setup. I assume should be the same but wanted to point that out just in case. I'm specifically referring to step 14-19 in this guide.

My question are:

1. FM says "The second bad thing is this: as you remove free-play and pass the bleed/fill hole, you are “reducing” clutch travel by moving a smaller volume of fluid than if the piston were properly adjusted with the piston resting just behind the fill hole. This is a common error. “If I tighten it more, I’ll get more travel, right?” This is correct up until the bleed hole is covered. At that point, not only are you ensuring that the clutch will disengage / slip as the fluid warms up, you’re also lessening the fluid displacement, i.e., slave cylinder travel".

Assuming disc is good and installed correctly. Is this the only condition that clutch hydraulics can cause a slipping clutch ?

2. The rod length is what controls clutch engagement point in pedal travel.
The pedal switch nut controls the resting height of the pedal.
Adjusting for a higher pedal moves the rod out away from the piston inside the master, but there's no clutch actuation until you press the pedal far enough to start pushing the piston in. "Far enough" depends on the rod length.

Is this a correct understanding ?

3. In step 16, FM say to test slave by pushing the rod back in. How much force should I be using when performing this test ?

4A. Currently with a brand new disc, clutch pedal switch adjusted as FM suggest in step 14 ( flush with metal nut ), free play set to minimum per step 15 ( turn clockwise until pressure then back off 1 full turn ), and being able to push the piston back into the slave with lots of pressure on 1 finger, my clutch pedal sits very high. Feels like it starts working at about 5% and clutch is fully disengaged at about 25%-30% of total pedal travel ( I can move shifter freely into next gear ). Is this normal ?

4B. FM advice "If you’re able to disengage the clutch properly with less than full pedal travel, back off on your adjustment until 100% pedal = 100% disengagement.". If I do that, with the same pedal height, wouldn't that be the same as adding a bunch of free play that does nothing during the first portion of the travel so I might as well take it out by adjusting the spedal switch nut in further ?

When is it slipping? RPM/throttle/speed? without reading all the steps, I would say you should adjust hydraulic system to favor full engagement. Later you can worry about getting it fine tuned

It slipped on dyno at around 180 wheel torque when disc rated for a lot more. Guessing around 5500rpm ? Hold fine all the way up to redline when we did low boost tune that goes to 163 w torque. As this is the second time it happened, both times with new discs, I'm looking into other possible causes in my setup before blaming the disc.

I have the same clutch and also had really high engagement following FM’s instructions. I added free play to bring the disengagement point closer to the floor, then I lowered the resting height to take up most of the slack.

The clutch that the instructions are for must must have an engagement window that is close to stock. The 949 clutch engages over a very narrow portion of pedal travel, so there is a lot of adjustment possible without having slipping problems on either end.

Now I just wish I could easily raise the pedal’s lower stop relative to the master cylinder. If it didn’t bottom out on the floor, I could move my seat back more.

Okay thanks. I'll shorten the rod to bring engagement point closer to the floor. Then lower the resting height to take out the slack as well which I think actually brings me back quite close to where I had it previously before following the FM adjustments.

I'm still not seeing a reason on why it could have slipped but am going to replace both my master / slave as well as putting with new fluid in the system. Is there anything else that could cause slipping clutch if the disc is good ?