Air in brake line drivers side

I hooked up a pneumatic brake bleeder to my truck to try and find why the brakes are weak, the passenger side front and back brakes ran solid liquid, no air bubbles, and i ran it untill clear cause i also had a master cylinder that had gone out, and i just changed it.

however on the drivers side, both the front and back brake bleed valves had visible air bubbles, and a lot of them, in fact both were pretty much the same with the way the bubbles looked, closest thing i can describe it to is, the way a straw looks when you are at the end of your drink.

I checked all the fittings on the master i just changed, nothing was loose, and everything was dry, all the brake lines around the wheels are also dry and i moved around the lines to check for leaks. nothing showed.

With it being both and them looking the same, i am inclined to think that somewhere upstream the front and back brakes are one line and that is where it is leaking?

any ideas what might be going on?

Also i will be fully replacing the brakes front and back, i did remove the drum and saw nothing that indicated a leak

 

Sure your not sucking in air when bleeding the brakes at the master cylinder when fluid is low in the reservoir ?

 

Nope, fluid at reservoir is full, my pneumatic kit came with a bottle that sets in the reservoir and fills it as the other end pulls the fluid out the bleed valve, my first thoughts were actually that the boot for the bleed kit was loose, so i moved it around to see if it made a difference and it didnt, i also thought that the nipple might have been letting in air with the way the bleed kit worked but even running it in all the way to where the fluid stopped and just cracking it, the bubbles were still there. I dont have a 2nd person who can pump the brakes while i run the valves to make sure, so i had to use the kit.

the passenger side worked fantastic with this kit by the way, so i really doubt it is the kit, and even went as far as taking it back to one of the passenger side wheels and connecting it to rebleed it, it had no issues, no bubbles nothing.

 

Brake fluid pressure is very high air pressure is not if it's going to leak it's going to be brake fluid. When the brake pads ware the fluid level drops if it drops low enough it is possible it got air in the system but not real likely.

 

fit a small clear hose on the brake bleed screw and loosen it like your bleeding it, then stick the hose in a soda bottle with just enough brake fluid in it to cover it an inch deep, set it on the ground or something so it stays upright and then go pump the brakes and top off the master cylinder as needed. this method eliminates the air getting sucked back into the line and allows you to quickly and effectively bleed your brakes by yourself. when you see no more bubbles and the hose is solid clear fluid its completely bled out of all air.

this video shows how to do it: https://www.youtube.com/watch?v=MfTmlOZbXgs

 

It's possible that you're sucking in air from the bleeder valve threads not from somewhere in the system. If that's the case, then using the method above that keakar posted would suck air back in when you let off the brake pedal when the bleeder valve isn't closed. Ideally, you have a second person to bleed the system with you.

 

very nice thank you, i'll give that a try.