When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Are you for sure the master cylinder and power brake booster are working properly? NO vacuum leaks? Do you hear a vacuum leak (air woosh sound from under the dash) when pushing on the pedal?
Do you have a good amount of vacume? Did you pull the tube and ck it? If you try to pull the ck valve and break it you will probably have to get a new power booster....
If it is all properly bleed and you still have a pedal bleed off, I would say bad power brake booster.
We've bleed the brakes , rear to front , a few times and the rear brakes had no air in them.
Bleed the front back (R) & forth (F) and the air is still in the lines and then checked the rear and no problem.
Rear drum , front disc.
Was thinking of just the check valve but will have chats with some of my local buddies along with advice from here before getting a new boo$ter & ma$ter cylinder.
I'm not sure what you're referencing by "check valve"?
The only thing between the MC and the brakes themselves is the brake valve. On your truck, the brake valve probably looks like this.
Cutaway view of the internals of this cast iron Kelsey-Hayes valve showing the Metering (hold-off) valve going to the front disc brake circuit, the Pressure Differential Valve in between the front and rear disc brake circuits and the Proportioning Valve going to the rear drum brake circuit.
The Metering Valve pin sticking out of the valve body, on this style of valve on a truck under 6,800 GVW, is supposed to be pulled outward when bleeding the brakes.
If the brake warning light on your dash is lit up, the Pressure Differential Valve spool inside the valve body assembly needs to be recentered.
Is there any correlation between how much you bleed/pump the rears and how much air in the lines? Meaning is there more air the more you pump?
And I know while you are bleeding you are probably looking at the lines/cylinders but have you looked at them carefully when you are not bleeding them and pumping them to see what they look like under pressure?
The lack of pressure would lend itself to recommending carefully bench-bleeding the master cylinder and the valve... but if you are constantly getting new air in the lines, that's a question.
If the vacuum check valve on the booster is bad, that'll be a separate problem from air infiltrating the brake system. The booster and MC are items that work in conjuction with each other but, at the same time, are separate items independent of each other. The booster is just a force multiplier that acts on the MC to multiply the amount of force being applied to it, through the leverage of the brake pedal.
I don't know what bleeding method is being used --forcing fluid out of the system via pressing on the brake pedal and opening/closing the bleeders or, if a vacuum source is being used like a Mighty Vac (?). If it's a case of the latter, a false impression of air coming out of the system can be given by the vacuum method. The air seen coming out could actually be the vacuum pump is just pulling the air in from around the threads on the bleed screws or from around the nipple where the vacuum hose is attached and may not actually be coming out of the brake circuit itself.
07-03-2016, 03:29 PM
