Brake bleed problem

Hello,

So, there isn't a whole lot of information due to the vehicles age, but it looks like the Metering Valve, which is part of the Combination Valve, must be held open while pressure bleeding this system.
So, the Combination Valve is going to be on the brake line, I believe the front lines run through it, but there are no diagrams for this. It applies to disc brakes so I would think its balancing out the front brakes. It does not say how to open the metering valve, just that it needs to be open to bleed them.
Have you tried bleeding the Master Cylinder? It's possible that the Master is clogged up in a couple of passages. Of maybe the Combination Valve is bad all together. You should be able to find it by just following the brakes lines. This is all the info I could find. If I come across some more ill update it here.
There's also the Height Sensing Valves in the rear, these might have old brake fluid in them and be clogged up as well. Just trying to list possibilities here.
You may want to replace the Master Cylinder too if the fluid had a dark color to it, that's the seals in the Master going bad.

I had an old Ford that had the metering valve. I'll locate that and give it a try. Master cylinder has been replaced by previous owner; old fluid looked okay. Thanks

Hi,

I noticed it has been a few days since we heard from you. Have you been able to make any progress? Also, what exactly is happening? Does the brake pedal go to the floor? If that is what is happening, there are no leaks, and the fluid is full and the master cylinder never drained, chances are the master cylinder has failed.

Oftentimes, when the brake pedal is pressed to the floor, dirt, and corrosion in the unused portion of the plungers cause damage to the plungers and allow fluid to bypass them when under pressure. Take a look through this link and let me know if it helps:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

If something different is happening, let me know.

Take care,

Joe

Ran into a problem with a flex line and waiting on parts. Should be here Monday or Tuesday, I'll follow up. Thanks

Hi,

Was it expanding when the brakes were applied, or did you find a leak?

Joe

Leak at the metal end at the caliper. Missed it the first time because I had used weasel juice on the banjo bolt. Just enough to drip after pumping, but probably pulling some air with the vacuum bleeder tool. We'll see when the parts come in. Thanks

100% leak free, bled with combo valve held open. Some improvement but pedal still soft. Pedal returns to full height after use but doesn't firm up when pumped. Going to look at cost of shop versus master cylinder and combo valve. The height sensing valve appears to be seized and wouldn't work anyway since the lever that attaches to the frame is gone.

you can try bleeding the master cylinder into itself, like a bench bleed. Two hoses on the outlets fed back into the reservoir. I do it right on the car. If you get bubbles while slowly pushing on the pedal, you know the master is no good. I had one pulling air from the seal in the back, where it goes into the booster. Couldn't find a leak anywhere until i did that, saw bubbles pumping right into the master cylinder. And if you keep the lines you took off the master facing up as much as possible, they won't get air in them. I did exactly as in the diagram below and it wouldn't stop bubbling. it was a brand-new master cylinder too. Grabbed another new one, did the same thing, car was all set to go. Hasn't had an issue since. I plugged the lines that I took off so I wouldn't have to bleed the whole system again.
It's worth a try if you do it right, then you'll know if it's the master or not.

I'll round up some fittings and give that a try. It would make sense for the soft pedal and pulling air while using a vacuum bleeder. Thanks

I just used a couple of old fittings that I could screw into the master that had a small piece of brake line on them and slipped a rubber hose over the end of those and put the end right in the master. It worked great. Best way to confirm a bad master cylinder. I will use that method from now on, it worked so good. Instead of chasing my tail all day looking for leaks etc.

Bled the master cylinder in the vehicle. Back port bled fine (just like the back brakes); front one ran bubbles in a circle (endless bubbles when I previously tried bleeding the front brakes). Sounds like the master cylinder is shot. Thanks

What's really awesome is the replacement part I found at one online source has a 9/16" -20 primary port, but the one on the vehicle is 9/16" -18. Ran into a similar situation with the alternator, the one in the truck is from a Ram, not a Dakota. Everything looks factory, though.

Yes, if you have endless bubbles the master has a failed seal inside. Cool test huh, it's nice and quick, and you don't have to through parts at it.

Problem I found out, though, is this one can't be bled in the vehicle because it's mounted at an incline. Air gets trapped in the high end. I took it out and it bench bled fine. Put it back in and now the fronts bleed fine, and everything works. I must have got air in it due to low fluid level when I was first bleeding at the wheels. Thanks for the master cylinder bleed tip.

No problem, glad you got it all set.. We're here if you need any more help.