Soft Brakes, Pedal Goes To Floor

[Cruzmoan]

I have a '67 Bronco. New brake booster, master cylinder, and new brake lines. Brakes worked great for a while, but are now soft. The brake pedal goes all the way to the floor. There was brake fluid in the rear brake fluid reservoir, but not the front. Where do you suggest I start troubleshooting?

 

[Beau Nugget]

Assuming the front reservoir was full to start with, that fluid had to go somewhere. I would start looking for leaks downstream of the master cylinder. You don’t say if the front reservoir controls the front or the rear brakes, but I would look around whichever the front reservoir does supply. If you don’t find any leaks, I would refill the reservoir, bleed it and drive it again, and keep an eye on it for leaks. If there’s a problem, it will show itself at some point.

 

[CopperBronco]

Finding brake fluid should be easy as it eats paint… you can also refill, make sure pedal is firm, and while parked and with engine / booster on, slam on the pedal as hard as you can. If you don’t have a leak or can’t find one, then you might had air in the brakes and did not bleed properly. A pressure bleeder can help with this, it straps to master cylinder.

Another potential problem is that your brake lines are running too close to headers/exhaust or anything hot really and you are evaporating your brake fluid inside the lines. The you need to re-route possibly, or less troublesome, put heat shield on brake lines or on part that’s causing the excessive heat.

Lastly I don’t recommend this unless you are a brake guru or an experienced mechanic on brakes, but you can do a brake stop test, which any good pro mechanic IMO will do after a full brake swap. James Duff has videos on this as a protocol to test a new install. It can hunt down leaks, and also make sure your prop valve locks up your rear brakes first in the case of an emergency at high speed and having to slam on your brakes. Without being present and knowing your issues I don’t recommend this as a first resort solution at the risk of you harming your Bronco or yourself. It sounds like this brake stuff might be new to you, maybe just take to a mechanic for something like this and let them suss out problem. For all we know you are leaking brake fluid from a faulty master cylinder back into the booster and can’t see the leak , online diagnosis isn’t exactly a good measure for accuracy on something as important as brakes. Best of luck! Others more experienced than me please correct if any of the above is wrong or bad advice. I replaced my brakes top to bottom for first time last year and did a crap ton of research, and went through Wilwood and James Duff protocols for testing my brakes and dialing in master cylinder and it all worked great. Found small leaks with my stop tests once the test got up to higher speeds and got the whole thing sealed up. So I’ve done it, even flared my own lines, but still not a guru here. So I reluctantly give out advice in the spirit of helping, but some of these other guys know SO MUCH MORE!

 

[Johnnyb]

Two things I can think of:

The factory distribution block on the frame (with switch for warning light, often mistaken for a proportioning valve) often leaks internally between front and rear systems, effectively turning your Bronco into single-system. Mine was this way until I put WH actual proportioning valve and bracket in place. In January, I was doing some pretty decent wheeling in Borrego and I tore off the rear brake flex line completely, but lo and behold I still had front brakes! The WH valve was functioning perfectly.

Also, I agree with @CopperBronco. I installed a simple heat shield between the headers and the WH proportioning valve, just because I could see that the increased height of the valve on bracket put it closer to my headers than I was comfortable with. I will try to get a picture of the installed heat shield - if I could make them in quantity, I would sell them!

-JB

 

[ksagis]

and also make sure your prop valve locks up your rear brakes first in the case of an emergency at high speed and having to slam on your brakes.

My practice is to have front brakes lock up first to avoid swapping ends under heavy braking. Has a EB vendor or your research indicated EBs should be set up to have the back brakes lock up first?

I will try to get a picture of the installed heat shield - if I could make them in quantity, I would sell them!

Would be interested in pic for sure.

Does anybody know any rules of thumb for how close to headers is too close for brakes lines?


OP, sounds like you have a fairly bad leak, should be fairly obvious as it sounds like the brake job was fairly recent. Look for wetness and let us know what you find.

 

[CopperBronco]

@ksagis i stand corrected… https://shop.wilwood.com/blogs/news...ever,brakes before proportioning is triggered.

You are right, fronts should lock up first… I went back to Wilwood article above, memory didn’t work right…. But the description of it having your tires “jumping” is correct, if they lock up at right rate they won’t do that and you want to avoid that. I’ll amend my earlier post.

 

[DirtDonk]

My first thought was that if this is a disc brake conversion, check for clearance between the calipers and the knuckles where they were ground.
If you can't see good daylight between them, maybe they're catching and forcing the pistons to extend too far each time.
But missing brake fluid, if it's not filling up the calipers, has to go somewhere. Like was said...

Proportioning valves are designed to keep the REAR from locking up prematurely. And they don't necessarily limit pressure during normal braking. They limit the sudden onset of high pressure such as under a panic stop.
Personally, I still prefer my rears to lock up first. Just barely, but first so I know that I'm about to lose all control if the fronts lock up!
I've locked up the rears on many different cars, and have not once had the rear end try to come around. Now, I've never locked them up going around a sharp corner, but have done it going around mild corners and while moving over to a different lane position to avoid someone else's sheet metal. Never once found it disconcerting to lock up a rear first.
Now, a front? I seriously dread the thought of locking up a front brake under any condition except straight ahead on a hard surface. Only a few places would locking up a front not bother me.

But I get the overall logic of not locking the rears. So the whole idea of a "combination valve" with all the bells and whistles, is to first delay the fronts (metering or delay valve), flip the switch in the case of a pressure differential, and block the sudden onset of high pressure in the rear. Multiple jobs, which is why it's called a combination valve.
Fords up until the late sixties used three separate components for these jobs with disc brakes. Or four, if you include the residual pressure check valves.

Paul

 

[Apogee]

The brakes worked well initially, so find your missing brake fluid, and you found your problem.

 

[DirtDonk]

And when searching for that leak, don’t neglect to pull the master away from the booster to see if it’s leaking out the back of the piston.