These big old trucks are harder to bleed clean. I never bench bleed. But, the little holes better be open for the fluid return in MC. That includes adjusting the pedal link to allow the push rod to come all the way back, or it won't get new fluid to refill. Adjust the link first. I then start at master, loosen rear main fitting till it drips, go to next spot, probly the Booster, which may have two bleeders on it. then go to closest, shortest front wheel, open till starts to be wet, then other front, then back ones. I feel I am allowing the fluid to "follow" me and system around till mostly full. THEN, use book procedure with rears first and so on to final bleed. If you're rears have dual cyls, it is sometimes harder to get all air out.
On "Gravity Bleeding" all that is meant is leaving ports open and fluid flows down eventually from gravity pulling. Won't work if it has to go uphill, as at wheels. Works pretty good with higher Master Cyl in modern vehicles.
Mighty Vac bleeder tool is sometimes workable. I never had luck with "One-man" bottles, peices of junk. The speed-bleeders seem like good idea, BUT, most stores don't have the 7/16" ones needed for many big trucks. If you have 3/8", you are in luck.
ONe more note on "helper" pumping pedal. Only go down to floor, not let up till you have bleeders closed again, or you will just draw air back in the bleeder. After fluid is at site, you can have helper pump with bleeders shut till he gets "pedal", then hold it. You open bleeders, pedal goes down, you close bleeder, pedal comes up, and pumps up again. Best if you can close bleeder Before he gets pedal to floor actually.
