Went 4-wheel disc: do you remove factory proportioning valve

[omureebe]

I’ve had the Chevy front disc conversion for years and recently put on Wilwood rear discs. I added the Wilwood adjustable proportioning valve after the master, but I did not remove the factory disc drum proportion valve. Should this be removed? What I’m finding is when I bleed the brakes, the fronts barely any fluid comes out so I think the shuttle
moved.
Thanks
Omar


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[Oldtimer]

The Ford factory disc-drum combination valve shuttle is self centering.
The Ford factory drum-drum pressure differential switch is not self centering.
Can you post a picture of the valve you are talking about

 

[Oldtimer]

Disc drum (76-77) combo valve, thanks JamesR

Drum drum pressure differential valve (H-block), thanks Wild Horses

The Comb valve has a bleed port on the front that mus be pulled out when bleeding.

 

[ksagis]

The Hblock doesn’t do any pressure control. It’s simply a passthrough and shuttle valve to trigger switch to indicate a failure in on of the circuits.

 

[nvrstuk]

My recommendation is to ditch the stock proportioning valve since it was designed for disc/drum and you need the extra volume required for rear disc. Go with an adjustable one so you can dial it in.

The adj ones work great.

 

[omureebe]

So apparently I removed the factory block years ago…. Time to check for odd things (like a pinched line)

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[Oldtimer]

What do you have for pressure differential warning light?

 

[Broncobowsher]

What do you have for pressure differential warning light?

You mean the red warning light that has not worked since Carter was President?

 

[omureebe]

You mean the red warning light that has not worked since Carter was President?

Everyone likes a peanut farmer. Yeah it’s not connected.

I’ve tried two boosters, three master cylinders (1-1/8 and 1-1/4) and basically the Bronco barely slows down.

I’ll have ale a look at the lines to see if something is weird. Good pedal pressure fyi.


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[omureebe]

Still can't figure it out. I think I'll remove the bleeders and stomp on the pedal to see if something got lodged. So strange that I have solid pedal but little stopping.... Took it around the block and can't understand why it just "slows down".

 

[joebronco73]

So apparently I removed the factory block years ago…. Time to check for odd things (like a pinched line)

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When the previous owner's work looks familiar:

 

[DirtDonk]

Which rear discs did you go with? What size Kristen, and how many?
The master cylinders you’re trying are possibly too big. Although, with a booster things change.
The hard pedal does not mean it’s working properly. The bigger the master cylinder piston, the harder you have to push to get the vehicle to slow down.
If you went down to a 1 inch, it would probably slow down better, but your pedal would travel further.
I wouldn’t necessarily pull the adjustable proportioning valve off just yet. You can turn it all the way down, and leave it there for now. Until you get the power thing sorted.
Besides, it doesn’t affect the front brakes at all, and you should be seeing plenty of breaking power from the front all by themselves.
If your boosters are too small, or not working properly, a one an eighth or one and a quarter master cylinder would be held to push.

How much vacuum does your engine produce?
Before the swap to discs in the rear, how well did it stop?

 

[omureebe]

I have the GM fronts and Wilwood 140-13320 rear discs. Initially I had a 1" bore that just went to the floor with little resistence, and found the 1-1/8" firmed up the pedal. However, just no real brakes to speak of when I did my test drive. So swapped out with another 1-1/4" booster, same thing. Then bought a booster/master setup from one of the vendors that specified disc/disc setup, bench bled the master, adjusted the depth on the booster to make sure it's a smidge off of the bore, and.... same thing. I'm at a lose. I think next step is to have the fronts bypass the proportinging valve, bleed, and test drive again. There is extremely limited braking power from fronts or rears to speak of.

Everything worked well but I had the brilliant idea of "upgrading" to rear discs. Ugh.

Thanks for the ideas here - something will change!

 

[nvrstuk]

Are the lines connected to the mc correctly? Frt lines to the appropriate fitting on the mc?

 

[DirtDonk]

What do you mean by bypass the proportion valve? Your adjustable valve is only in the rear, and I thought you said you were not running front valve anymore at all. Is that not correct?
And presuming that this is a pre-76 bronco, it would not have had a proportioning valve from the factory so, if there was one at some point, you would’ve added it originally when you did the swap presumably.
But you stated that nothing is in the front lines anymore. So what exactly are you bypassing?
You can certainly block off a port of the master, or the lines to the rear or front for testing. Just didn’t sound like you had anything in the front to bypass.

So a 1 inch went to the floor, but 1 1/8 inch was firm? I know there’s a detectable difference between the two, but I wouldn’t have thought it would be that drastic.

It might come down to putting a pressure cage on the ports. See what fluid pressure you’re actually putting out.
Seems like it’s going to be a booster Issue (still very possible), a friction coefficient on the pad material (seems very unlikely), or something wrong with all four calipers (also seems very low on the list).
Getting a couple of bad masters in a row doesn’t seem far-fetched, but it doesn’t seem likely either. Considering that you got them from different sources, likely different brands, and different sizes.

Can you post up some pictures of your whole system? From master, down the lines, down to the calipers?
Maybe somebody can see something.