Clutch problems
 

I have a 98 Ranger with manual transmission. I keep getting air in the master cylinder to slave line. I have replaced master cylinder and bled well. I keep getting air in the line after all has been bled out, resulting in very hard shifting when the truck is stopped. Truck can sit awhile and seems as if the air bubbles out ( I am assuming) and shifts for a few minutes easily and then hard shifting again. It appears that the travel of the slave to clutch fins is about 5/16". Does anyone know what the travel distance should be? Or if possibly the oring in the quick connect to slave could be allowing air in? No fluid leaks at all. I have changed out clutch and all components about 5 years ago and am dreading it already. I want to exhaust all possibilities before doing that.

Did the clutch Master come with new reservoir?

Air can't just "come in", it needs to be "Sucked in"
That can only happen as clutch pedal comes up

When pedal is up all the way the reservoir is connected to master so any leaked fluid can be replaced
As soon as pedal is pushed down, even a little, the reservoir connection to master is closes so pressure/fluid flows down to slave

Try this to test for a leak
Make sure reservoir is topped up
You can leave cap off
Get a stick of the right length to hold clutch pedal down all the way, stick against seat
And wait
With continuous pressure the leak will show it self

Yes, new reservoir.

Changed rear main seal, pilot bearing, clutch, pressure plate, slave cylinder and master cylinder. Truck is performing as normal now. Clutch disc and pressure plate looked good as did pilot bearing. I suspect the slave was leaking air into and not delivering a sufficient stroke to disengage the clutch.