Has anyone ever measured the preload (either gap or amount of engagement) that is on their ZF5 swap?

I’m getting ready to re-install my rebuilt ZF-5 into BSD and while it’s all torn apart I’m doing some much needed maintenance and troubleshooting. One of my ongoing problems has been slave cylinder failure and I’m trying to reduce the incidence of it happening. Right now I have ~ 1/2” of preload on the “throw out” / engagement bearing. I’m using the trans bell housing & motor mating surface as my measurement reference points. At first thought that seems excessive, since the bearing would always be spinning. But after a little reading it seems that hydraulic clutch systems run some preload (that’s what the spring on the Concentric Slave Cylinder is for, unlike older mechanical linkage systems, which have no preload.

Of course I my system isn’t factory, the 4BT adapter setup is a Cummins product built to put the motor into bread vans which had inline 6 300s w/ a T-18/19 trans and mechanical clutch engagement systems.

Update: I went up to NAPA and checked out a couple of different clutches they had in stock and compared them to what I just pulled out of the Bronco plus a spare I had on the shelf. They all seem to put the diaphragm fingers at the same depth to the motor mounting surface once they are torqued down. I purchased a new OEM/LUK kit with a diameter of 11 9/16” for the clutch itself. This is larger than what was in there and larger than most replacements, I’m looking for all the engagement I can get.

I don't have that info, but have read that if the pedal travels too far it can damage the slave cylinder. The suggestion is to limit the pedal travel to a minimum after engagement. I added an adjustable pedal stop to prevent over-travel. I only read about this after I had everything installed and was testing the clutch and pressing the pedal to the floor. Hopefully I didn't damage anything with my testing. Of course nothing has actually been run yet.

I’ve read that as well, at the moment it doesn’t over travel. I think I may have a mismatched master / slave cylinder problem, early style master w/ later style slave. Like usual I used JY parts and I can remember what year I pulled the master from. I’ll likely order a new later style master and compare them.