Soft brake pedal

[Concrete]

Hello, I trying to finish my 77. All new brake booster, master cylinder lines etc. from front to back all new. Bench bled master cylinder. Bled lines 3x. Still soft pedal. rears will lock up but not road worthy. Fronts are not helping at all. when bronco is running and apply brakes the pedal is soft and pedal travels far. Checked for leaks. dont see any. What am I missing? Thanks

 

[ol gray mare]

Is the brake light on, on the dash? if so, your dual master cylinder is only giving pressure to your back brakes. You can balance the pressure by alternately bleeding front and back brakes till the light goes out.

 

[Concrete]

Is the brake light on, on the dash? if so, your dual master cylinder is only giving pressure to your back brakes. You can balance the pressure by alternately bleeding front and back brakes till the light goes out.

No brake light comes on. Only when I push pedal

 

[DirtDonk]

New calipers have the bleeder valves at the top? Not necessarily facing up, but at the top.

Original proportioning valve? It’s possible that the valve is not doing its job anymore. Member bluebuckaroo had a good write up on rebuilding his.
Or did you replace it with a different one?

You said new master. Booster too?
One of the more common issues we come across is matching the booster rod to the master. All it takes is a tiny fraction of a variation to give you a long pedal travel. When you installed the new master did you adjust the booster rod appropriately?

 

[DirtDonk]

When you bled the brakes did you pull out on the little spring loaded needle in the proportioning valve?

 

[hummerdan]

When you bled the brakes did you pull out on the little spring loaded needle in the proportioning valve?

I am interested in this process since this is the first time I hear about removing the needle in the PV. What does this allow? I had a heck of a time bleeding my brakes a few months ago, I wonder if this would have helped. Easily bled them over 10 times because of soft pedal. At the end of the day a small adjustment on the pedal rod got me right to where I need to be.

 

[Broncobowsher]

I'm going to repeat the above. Start with the calipers. So common to put them on wrong. As in the left caliper on the right side wrong. That puts the bleeders where they won't bleed air and you will never have brakes with air in them.

 

[DirtDonk]

There can be a difference between a “soft” pedal and a “long travel” pedal.
Where soft is usually air in the system and long travel is usually a rod adjustment.
You found yours to be the adjustment.

But that one component of a combination valve is called a “delay” or “hold off” or “metering” valve. I hope I have the names right. Some variation. It’s purpose is to delay the application of the front disc brakes until the rear drum brakes have taken up there extra play and caught up. This stabilizes the vehicle during the initial application of the brakes.

But it also means that it reduces or completely illuminates fluid flow to the front brakes under low pressure. Which makes bleeding very problematic sometimes.
Most people never run afoul of it. But it crops up often enough to where we have to mention it every time.

It’s discussed in the shop manuals of these types of vehicles. Including the special tools that were available back in the day to hold the valve open during bleeding of the front brakes.

 

[Concrete]

No I had no idea on pulling on a spring on the proportioning valve. I will look into this. Would this mean that that’s restricting fluid transfer to the front? Thanks! Does this mean I need to get a special tool?

 

[DirtDonk]

That’s exactly what it does.
If the spring is soft and compliant then you still get fluid flow easily through the valve. If it’s a little stiff or sticky, then you would need to build up more pressure for it to move. Making it harder to bleed without pulling the pin.

If you have a helper you could have them push the brake pedal while you watch the valve. If it moves out when they press the brake pad it’s at least working visually.
Without a helper you could put your phone on video video mode and let it watch for you

 

[73azbronco]

Don't get discouraged, took me two weeks to get a firm pedal and I've done brakes, a lot. Same for power steering. Might be to old for this

I used to love speed bleeders, but now find them more of a pain than a help. Besides, what else does the wife have to do than be the brake pedal pusher on call? Shhh, don't repost that please

 

[El Kabong]

New calipers have the bleeder valves at the top?

I'm going to repeat the above. Start with the calipers. So common to put them on wrong. As in the left caliper on the right side wrong. That puts the bleeders where they won't bleed air and you will never have brakes with air in them.

I didn't see the answer to this ^ question. If the calipers are on the wrong sides the bleeders will be below the air pocket, & it is impossible to bleed them. It's a quick thing to check, & nothing else will help if that's the problem. Post up a pic if you're not sure.

 

[Concrete]

I forgot answer, but yes the calipers are on the correct sides. Good point I had to double check! Thanks for the insight! I will make my way to the barn in a bit and check the valve. Thanks for the help!

 

[Broncobowsher]

Did you plumb them correctly. Most people think front resivior, front brakes. When really it is backwards 99% of the time, the front port does the rear brakes, the rear port does the front brakes. Not usually an issue when just doing a master cylinder swap, when when everything is new the lines can get swapped. Not supposed to matter, but I have seen it matter.

 

[Concrete]

As for me plumbing it correctly, the front part of the master cylinder runs to the port in front of the brake warning sensor than running to the calipers. The bleeders are at 3 o’clock and 9 o’clock on the calipers. But no I did not pull the pin on proportioning valve while bleeding brakes.

 

[El Kabong]

Did you plumb them correctly. Most people think front resivior, front brakes. When really it is backwards 99% of the time, the front port does the rear brakes, the rear port does the front brakes. Not usually an issue when just doing a master cylinder swap, when when everything is new the lines can get swapped. Not supposed to matter, but I have seen it matter.

Nice catch.

As for me plumbing it correctly, the front part of the master cylinder runs to the port in front of the brake warning sensor than running to the calipers. The bleeders are at 3 o’clock and 9 o’clock on the calipers. But no I did not pull the pin on proportioning valve while bleeding brakes.

Yeah, the front half (closest to the radiator) of the master cylinder is for the rear brakes & vice versa. When reversed on some systems there isn't enough volume to the fronts & too much to the rears. Sounds like Broncobowsher might have nailed it.

 

[Concrete]

Ok well I’m gonna have to look into that. Thank you for the insight.

 

[DirtDonk]

Will usually depend on the master cylinder itself. If it’s a universal aftermarket unit, it might go contrary to factory original. But all factory original ford bronco dual master cylinders were back-to-front and front-to-back.

The fact that you could even hook yours up differently in the first place means that either the lines, the master, or both are non-reproduction replacements.

 

[mpboxer]

Don't get discouraged, took me two weeks to get a firm pedal and I've done brakes, a lot. Same for power steering. Might be to old for this

I used to love speed bleeders, but now find them more of a pain than a help. Besides, what else does the wife have to do than be the brake pedal pusher on call? Shhh, don't repost that please

Bahaha my wife will NEVER help my bleed mine again!

 

[Yeller]

Bahaha my wife will NEVER help my bleed mine again!

Stop YELLING AT ME