Hey guys, i went and replaced a rear brake line that rusted through and then went and bled all the brakes and abs valve in order. I still have air in the system and can't figure out what to do next other than take it in to a shop and have it pressure bled.

Anyone have any ideas on what else i can do?

 

Are the wheel cylinders in good non leaking condition? Are you getting air & fluid out of the rear? I ask because is the portioning valve tripped closed to the rear?

 

You may have another line that has a pinhole and is sucking air… sometimes they don't appear to be leaking but they will suck air.

Be certain you don't have a fitting cross threaded, too.

You may try this…. fill the fluid reservoir and crack open all four bleeders… then let it sit overnight. Leave the m/c loose. Check the m/c occasionally to be sure it hasn't run dry. This may work or may not… it's been a useful procedure for me on occasion.

 

I replaced both wheel cylinders and rear brakes at the same time so everything is in good shape.

At first I tried gravity bleeding everything but still had air trapped. Next I did the pump brakes and bleed routine... Still air there. I am so stumped by this I have gone through two quarts of fluid now!

 

One more thing is that the brakes were flawless before I had to change the line!

 

Did the master cylinder run dry while you where replacing all those parts at the rear?

If so you need to bleed the master cylinder first, then the lines and including front wheels.

 

Yes it did run dry driving home with a blown brake line!! Now I have no experience with a master cylinder... How do I bleed it? Take it off is step one... Then what do I do?

 

Instructions assume model year truck with plastic reservoir on M/C.

Don't have to take it off but its better if you do.

Remove and solid plug front and rear line ports, ports must not leak and must be able to hold given amount of pressure. The good quality plastic plugs that come in new one will work, the cheapies will not will just get blown out.

Fill about half way with fluid hold level forward end slightly up, cycle piston in and out of its bore slowly using suitable pin such as a large philips screw driver by hand, avoid exceeding an inch of piston travel into the cylinder bore (do not use full strokes). You already have while driving it no doubt but might not be too late.

Do so keeping it half full of fluid until piston is solid and you no longer see bubbles rising in the reservoir. Do so until piston will not move forward in its bore more than about an 1/8 of an inch and feels rock solid at that point. The process will take some time yea but not all day, a good one will pump up in say 10 minutes or so.

If it does not pump up solid and resulting in 1/8" travel or less, pumps up but is spongy? the cylinder is toast. Buy a new one follow its included instructions to a T.

If early model using all metal M/C, get a bench bleed kit. Screw in adapters run hoses from line ports into reservoir, Fill with fluid pump pedal full strokes until see no more air bubbles coming from hoses (keep end of hoses below fluid level) no need to remove M/C from truck.

 

So alternatively can I leave tha MC on and just plug the two line exits and then lightly pump the brakes? Thank you!!

 

Just wanted to update this thread... After bleeding the MC the brakes were a little better but still thought i had air in the system. Buddy came over to help and he adjusted the rear drums and that's all it was in the end