There is a rubber grommet on the drivers side of the bell housing on my 92 F150 with the M5R2 transmission. It is about 3 x 2 inches or so . And when removed--it gives a good view of the clutch disc,pressure plate,slave cylinder and the the fly wheel.

What is the clutch disc thickness when new for this M5R2 transmission??

 

I'm putting a new clutch in my F150 right now so I looked at the new and old dics for you. Its probably going to be hard to tell how good your clutch is, because my brand new clutch is about 3/8" thick, and my clutch with 200,000 miles on it is about 1/4" thick......aint that much of a difference

 

Yeah, there is very little difference at all. I was surprised when I saw that, too. I was expecting the old clutch to be as thin as paper. The rivets really take up a lot of material.