I have dealt with this multiple times. As previously mentioned, master is best bled off the truck before installing. If either the mc or slave leaks and you don't keep fluid topped off, it will eventually get air pocket in high end of MC that is difficult to rectify. Shifting becomes more difficult until it just won't shift. Won't bleed like most vehicles because Ford put MC at opposite slant to do that. Air becomes trapped in that higher end which has no bleeding provision.

MC bleed on truck can be done by disconnecting rod from pedal under dash and pulling circlip which allows piston to come out far enough to leak the air out and you will know it has when brake fluid comes out. Don't pull piston completely out, just enough to leak fluid and have reservoir full and a helper to add fluid as it drops in reservoir. Immediately push piston back in and reinstall circlip. Have rags on toe board and floor to catch spilled fluid.

There are You Tube videos out there on this process and this topic is discussed at length on the Ranger Forum.

This Ranger forum..

Ford Ranger Forum - Forums for Ford Ranger enthusiasts! - Search Results

The link worked yesterday but doesn't now either, but you can probably do a search on clutch bleeding if you want to see more info. You tube video out there on this procedure still as of a couple years ago too.

There may be enough fluid in full reservoir to do alone, if you get the piston back in position quickly. I don't recall if I had a helper both of the two times I did this. On my 96 the slave had a slow leak and so even after installing a new master I had the same problem recur until the slave was replaced. But if a slow leak and you check fluid frequently you can get away with slow leak from the slave for a very long time.

Yes, that circlip/snap ring is the one, seen inside rod end of mc under dash.

Pumpng pedal and gravity bleed will only clear air from the slave, so don't pump until you refill the reservoir after process of MC bleed under dash. It should work on the first pump afterward, but if there is air in the slave (may not be...), then you will just reintroduce air into mc if you jump the gun by pumping before topping off reservoir again.

F150 has an external slave but Master is similar. However it doesn't mount to truck at such an extreme angle as the Ranger does. You may be able to get air out of it by raising the front of an F150, loosen the cap and let it sit a day or so with full reservoir and pedal up. If fluid drops, it may have resolved. If it doesn't, it still has air in it. Hand vacuum pump at the slave might work on F150 also, but prop pedal up to top with something first if you try that.

But, yes I thought you had a Ranger and I have not tried this bleeding under dash on an F150. Rangers are notoriously difficult to bleed on the truck. Looks like your posts are on the Ranger subsection of the Forum too, not the F150.