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68c10airstream · 10-30-2017, 10:02 PM

A couple suggestions that almost always help is this;
Jack the front or rear of the truck to level out the master cylinder. as an example gm cars in the 80's had a master cylinder that was pointed uphill in the front and would get air bound up in the front chamber and was impossible to bleed. i did many for friends that couldn't get fluid to move through the lines. I would remove the master cylinder lid and watch the fluid as someone else jacked up the rear to level the master out. About when level air bubbles would come up through the brake fluid, and then you could proceed to bleed.

The last suggestion is to NOT pump the brakes up frantically in between each bleeding cycle. What happens is air will be introduced from the back side of the master cylinder. The plunger that moves back and forth with your pedal effort has lip seals that are pointed forward (towards the fluid) and when you repeatedly pump the pedal the return motion can only seal against the bore by the residual tension of the lip. When you push down on the brake pedal the lip is forced against the bore and seals tight, but the return motion isn't forcing the lip to the bore, it's just dragging along for the ride. So pump slowly and also don't bottom the pedal out because you are going into a portion of the bore that typically isn't used. I've seen them stick to the floor a couple of times.

10-30-2017, 10:02 PM	#3
68c10airstream Registered User Join Date: Mar 2013 Location: Marquette michigan Posts: 828	Re: Hydro boost swap A couple suggestions that almost always help is this; Jack the front or rear of the truck to level out the master cylinder. as an example gm cars in the 80's had a master cylinder that was pointed uphill in the front and would get air bound up in the front chamber and was impossible to bleed. i did many for friends that couldn't get fluid to move through the lines. I would remove the master cylinder lid and watch the fluid as someone else jacked up the rear to level the master out. About when level air bubbles would come up through the brake fluid, and then you could proceed to bleed. The last suggestion is to NOT pump the brakes up frantically in between each bleeding cycle. What happens is air will be introduced from the back side of the master cylinder. The plunger that moves back and forth with your pedal effort has lip seals that are pointed forward (towards the fluid) and when you repeatedly pump the pedal the return motion can only seal against the bore by the residual tension of the lip. When you push down on the brake pedal the lip is forced against the bore and seals tight, but the return motion isn't forcing the lip to the bore, it's just dragging along for the ride. So pump slowly and also don't bottom the pedal out because you are going into a portion of the bore that typically isn't used. I've seen them stick to the floor a couple of times.