so a .18 to a .26 step? alright
Well actually the 0.026" is the actual difference between the two surfaces. The person who is surfacing the flywheel only has one measurement to decided on. The two surfaces are the clutch's frictional surface and the surface that the pressure plate bolts down on. Therefore, if these two surfaces have a greater difference, ie the clutch friction surface is higher than the pressure plate bolting surface, then the area between the pressure plate and the flywheel is decreased, so the clutch is in effect
tighter.
The effect of this will be that the actual friction "point" on the down travel of the clutch will be moved
higher. That's how you can tell if your clutch is worn out. A new clutch should have a friction "point" of somewhere near the end of the clutch pedal movement, and a badly worn out clutch will have a friction "point" almost at the very beginning of the clutch pedal movement.
As the clutch disk wears, it gets thinner, and less expansion between the flywheel and the pressure plate is needed in order to release the clutch; in this case your foot doesn't have to really press the pedal down so far and the clutch is already disengaged.
So by surfacing the flywheel beyond what Toyota recommends, you are placing the pressure plate closer to the clutch disk, so more clutch pedal movement is required to disengage the clutch.
Now this is good for the following reasons:
- The clutch will last longer because these is less space for it to work with, so it will still be working even when it is badly worn and very thin, it will still work.
- Since the space is decreased yet the clutch is still the same thickness, the pressure plate will actually "grip" the clutch at a higher level of force because the springs in the press. plate will be displaced at a greater distance. Spring rate is equal to the spring constant x distance. So the more the pressure plate is "opened" the greater the spring force. So with the flywheel surfaced at a greater difference than what Toyota recommends, now the pressure plate has to open up more to "let go" of the clutch.
- The above reason amounts to better gripping force from the pressure plate, so the clutch Performance is increased due to more friction, as Marlin said in his post above.
The only bad thing about doing this is that when you first do it and your clutch is fresh and thick, the clutch pedal will have to be pressed almost all of the way to the floor just to release the clutch. This is great because the clutch frictional pressures are greater, BUT, this means that it will be more difficult to speed-shift (hehe if you even do that with a truck
) and if you have a bad habit of not pressing the clutch pedal all the way down before shifting, then there will still be some friction on the clutch disk, and when ever you shift, the synchros need to change the speed of the input of the trans - which is connected to the clutch disk right? So if you only press the clutch pedal down about 60% when it really needs ohh say 80% to really completely release the clutch disk, then the clutch isn't completely released, and when you shift, the synchros will be trying to change the speed of the clutch disk and of course the frictional forces still acting on the clutch disk are pretty high for a little synchro to act against, so this can be very detrimental to your transmission shifting performance if you do not use the clutch correctly.
And through all of the many years of experience, Marlin has found out that the flywheel surface difference of 0.026" offers the best clutch performance while still being able to disengage the clutch disk from the drivers seat. For instance, if you were to try, or say 0.030" or something, when you put it all back together, it's likely that even with the clutch pedal all the way down to the floor, the clutch could still be engaged and you would never ever be able to shift at all if the engine is on or if you are traveling at speeds greater than 5mph or so.
So surface your flywheel to 0.026" and be happy with the results!
BigMike
