Help me bleed my brakes.
 

Just what the topic says'. My truck is a 72 with power brakes, and I am having a bit of trouble. I just put new calipers on my truck and I can't get my brakes bled. I have tried everything. I tried to gravity bleed them, I got one of those vaccum pumps, I had my wife pump the snot out of them, and still no luck. The master cylinder never ran dry, so I know that is not the issue. I get a lillte bit of air out of the system, but it never stops. I can't get it to run solid fluid. I have not bled the rears though since I thought that since the master is seperated, then I did'n have to. What am I doing wrong, and where could this air be coming from??

did you have the top off the master cylinder when you where gravity feeding it? Is there anywhere that has sprung a leak since you did the calipers?? It should gravity feed if you have the top off... but as you said it isn't. I would try to have her pump it again and see if it will work one more time. I am not sure as to the process that you are using to pump it but make sure that the top is on the master cylinder and have her pump it up then open the bleed valve and have her keep pressure on it till you completely close the valve then repeat over and over. Hope this helps :bowtie: :bowtie: :bowtie: :bowtie:

The top was off when I tried to gravity feed them, but nothing was happening. I let them stay open for 3 or 4 hours with no change. I know how to bleed brakes I have done it many times before, this time has got me stumped though. I have never had trouble before.

sorry about that.... sometimes people don't know. good luck

Had a similar problem bleeding my brakes. I replaced the back slave cylinders and could not get anythingg to them. The pedal was still stiff and pushing and holding the button on the proportioning valve did not help either. I had to crack open the fronts and then was able to bleed the system. I would imaggine you will need to cack open the backs and pump away on the pedal to recenter the proportioning valve in order to bleed the fronts.

Sometimes bleeding the truck brakes can be exaspirating and it
seems to take way more time than it should. I still don't have all of the air out of my latest truck and I have bled over a quart of fluid through it. Two suggestions. 1) bleed the master cylinder after the prop valve, one line at a time. With the right hose you can return the fluid to the reservoir. Bleeding this way you can know that the prop valve is open and remove any air that could have worked its way in. If you submerge the hose you can be assured of not getting air back into the master cylinder.

2) Use a hose and container to bleed the calipers submerging the
the hose in brake fluid. This allows you to pump with the bleeder open.

Not all prop valves have a way to push the slide valve back to the center, but you will need to look at yours to determine that.

If all else fails, power brake bleeders work well.

Good luck!

Jim

The way I always do my breaks is take a glass jar and fill it 1/2 way with break fluid run a piece of vacuum hose that fits tight on the bleeder valve to the jar and SLOWLY pump the breaks until the bubbles stop. The vacuum will suck up break fluid instead of air back up the tube then tighten the bleeder back up and the that wheel is done. I have done all four wheels at the same time but you really need someone to add the fluid to the master cylinder at the same time to do it this way.

OH keep the vacuum line off the bottom of the jar to keep from sucking up the junk that comes out. Of course if junk dose come out you should have flushed the system first.

I think I may have found the problem, but what do you guys think? I took the line between the master, and the P valve and plugged the master line with a clear hose with a tapered fitting on the end of it to make a seal. I then pumped the brakes as I watched the clear line. When I pressed the peddle down I could see bubbles coming out of the master, but when I hooked up the bleeber vaccum I didn't get bubbles. Has my master cylinder gone bad or what.

ttt

Sounds like your master cylinder is shot. A common thing that happens when you bleed the brakes is that you end up pushing the pedal all the way to the floor, where it hasn't been in years. This puts the cups of the piston in all the rust and crap that has built up, cutting the lips of the cup. I've read somewhere (GMCPaul's site maybe) to use a 2x4 under the pedal and bleed normally. This limits the travel.
Throw a new master cylinder on her, or rebuild your old one if the rust pits aren't too bad. Bubbles means it's getting air on the return stroke, probably past the seals. If you don't change it out now, you should wear your old shoes for a while - unless you like brake fluid stained shoes.

Another good reason to use my vacuum bleeder! The original reason was not having to listen to my wife ask me when she can stop pumping the pedal and go back in the house! Best $30 I ever spent.