OK, I'm at my wits end with this thing...1989 Ram Charger, 4x4, non-RWAL, front disk/rear drum. I have replaced all rubber lines, rear wheel cylinders, drums, shoes and hardware, front calipers and disks. I thought the original master cylinder was bad as I could not get all the air out of the system when bleeding. Bought a new MC, bench bled and installed on truck, same issue. Air coming out each corner every time I bleed. So I go back to the parts store and swap MC with another new one, bench bled and same issue as before. I have double checked all the line connections and made sure they were tight and could not find any leaks. No sign of leakage at the wheel cylinders or calipers. I have just about worn out the bleed screws because how many times I have bled this thing. Does anybody have any ideas for me to look into. It has to be an internal leak which would lead to the MC again?

Have you tried gravity bleeding?

Yes, I start my bleeding process that way, I get fluid running out of each bleeder. Also to note, I bleed with out the truck running (no vacuum assist) and the brake light is on and won't reset.

How the port valve?

As long as rear shoes are somewhat adjusted, and front calipers are on correct side etc, that should be it. I would close all bleeders, fill master cyl, then pump the heck out of brake pedal, and start over w/gravity method. Helps to leave cap off master while gravity bleeding. Just don't hit pedal while cap is off.

You have a leak somewhere. I'd start with the copper washers connecting the brake hose to the calipers or wheel cylinders. They're really thin and cheesy these days. It's a long shot but don't overlook multiple leaking master cylinders. 2¢

Robert

Ok, rear shoes are adjusted so I can slid the new drums on with a slight drag. As stated, no visible leaks or fluid on any of the lines that I touched or the new calipers and wheel cylinders. I also forgot to mention, after bleeding, the pedal is hard like it should be, but when I start the truck up, the pedal is very soft and goes down way too easy. I know I'm getting air from somewhere, I run a rubber hose from the bleeders into a bottle with fluid in it and get air bubbles the first time I break any of the bleeders loose. The 2nd and 3rd time no bubbles, I then refill the MC and bleed again and get air bubbles in the fluid.

The last truck I had to bleed the brakes on I had to use a vacuum pump to suck the fluid through the system. I tried every other way, and nothing else worked. I had to borrow a vacuum pump.

That process took about 20 minutes. You fill the master, hook the pump to the bleeder screw open it and pump the pump until the fluid flows without air. It took a couple minutes with the farthest bleeder from the master, but each one after took less. Be sure to refill the master after each bleed. One time at all 4 bleeders and I was done! Didn't trip the proportioning valve or anything. Guess how I'm going to bleed brakes from now on...Gene

I had an '85 W150, and the brakes kept getting air, finally figured out the exhaust was blowing on one of the rear brake lines on the diff. The PO had run a new line and had looped it above the housing, getting the heat from the exhaust. Ran a new line properly, and that solved that.
and second the the master cylinder being suspect...just becaue it's new doesn't mean it's good now a days.

As a note on those master cylinders when you bench bleed them you can damage the internal seal if you bottom out the piston. Check how far down the piston will go on the old master cylinder before getting the new one. Then when you bench bleed the new one stop short of bottoming it out by about a quarter inch.

OK, I'm about to burn this damn thing to the ground! So I started today with buying a mightyvac and bleeding the 2nd new MC, still no go. I re-installed the original MC for S&G and still no go. When to the parts store and got a 3rd new MC that is installed right now, still can't get any pedal after I start the truck and the brake warning light will not go out. As the bleeding the MC, The brass drift I have been using to bench bleed it, I marked a line at 1 inch as to not push the piston in foo far. Again, no external leaks, all new hydraulics, new pads, new shoes, disks and drums. I am thinking about removing the combo valve and trying to clean it, but I really don't see how that will help.

I mentioned the valve a while back. I would done this before changing the master 2, 3 or 4 times? I lost count.

Ok, but how would the valve have anything to with air getting in the system and the booster not having any pull when the truck is running?

is the master cylinder new...or re-manufactured/rebuilt?

New ones from O'Reilly's.

witch booster is on your truck may be over boosting the brake leading to not feeling like there is entry pedal and how much vacuum are you producing not enough and the booster wont work or the boosters bad this dose not help with the air in lines

As far as I know it's the stock booster. I did ck the vacuum and it is pulling 18 psi at idle with the gauge hooked up to the nipple for the cruise control. But the booster would have nothing to do with air getting in the system when I bleed while the truck is not running.

+1

Had problems with Fords at the shop mostly.We found out if you had all bleders closed and then had someone slam the pedalas you opend a frt they would reset the light.Never had problems with air constant in the lines once gravity and a few quick bleeds.Did you pull the drums and check to see that wheel cyls arent leakung.My Ram had problems and one was bad but not dripping so you could see fluid.Rocky

OK, update: I broke down and removed the combination valve even though I was pretty sure it was not the problem. Well, after I removed and dissembled it, I found one of the packings/o-rings was cut. When I was messing around with it before I broke it down, I couldn't get the slider for the brake light light switch to move very well, and that was the main problem. The valve was nasty inside, lots of crud and rust. After cleaning the crap out of it and using brass brushes in all the bores, replaced the bad o-ring and put it all back together. I got the brakes bled with the minivac, wasn't sure I got all the air out, but the valve reset and the light went out...progress! So I started it up and had peddle, but still not too stiff. I bled again, and everything was good. The brakes are all good now and will put you in the windshield if I not careful!

You had pretty much ruled everything else out and I have seen a gunked up valve cause problems. Glad you got it working.

good news