Brake Bleeding issue

[ep67bro]

I am working on my 67 bronco. It has vacuum boost brakes from a 77 on it dana 44 with factory ford discs, drum rears. standard H distribution block no proportioning valve.
I recently put a new suspension on it did a brake breading and everything was good. When I was working on the truck I notice my master cylinder was leaking from the piston. So I got a new master cylinder from JBG. I did the basic bench bleeding procedure that was recommended, filled with fluid put it on the truck blead the rears no problem, bled the front no fluid? I get very little fluid through my vacuum pump when I bled the fronts. Took it for a ride and don't have any real front brakes until the peddle is about half way down. If I floor the brakes I can get the back to lock up but the front just barely lock.

So any ideas? I have vacuum bled the brakes at least 4 times now gone through over a pint of brake fluid I almost feel like I got a bad master cylinder because the old one worked fine.

 

[savage]

Bleed it at the master cylinder ,put a rag under or around the line that goes to the front breaks at the master cylinder, have someone push and hold the brake pedal, and crack the line,when pedal bottoms close line repeat if needed then, you can try your vacuum bleeder to see if you get more fluid.It sounds like you have a air bubble up by the master cylinder.

 

[75MIKE]

Did you make sure the plunger out of your vacuum booster is still adjusted correctly with the new master cylinder?

 

[ep67bro]

I will try to bleed it at the master again.

As for the plunger, it seemed like the two masters were identical and there is really no play in the peddle before it contacts the plunger. I didn't want to adjust it and have the brakes drag.

 

[75MIKE]

Well......... bleed plugs are clear no mud or rust? Fluid gushes out with the bleeders completely removed?

That's about all I can think of.

 

[ep67bro]

So I bled the master right at it and fluid came out clear and easy. It seem as if there is some issue with the bleeder or some thing else in the lines. I will try to bleed it down from each connection ending at the wheels. The bleeders are clean(calipers are not that old and have never been in the dirt) But the passenger side bleeder is kind of stripped and a real Pain in the ass to work with. I have been doing brakes my self for a long time and never had this issue! Oh well life with an old bronco!

 

[Seventee]

Have you checked to see if your H-block piston is shifted?

 

[ep67bro]

Ok fill me in on this? I didn't think there was anything in the H block? This is not a proportioning valve. This is the stock 1967 bronco H block.

 

[MonsterBIlly]

The stock h block actually has a small residual valve inside it to keep a small amount of pressure in the rear drums. If you have disc up front, you should not have the stock h block. You should have an updated one for disc/drum.
There is a small stopper you need when bleeding, that screws into the top port which holds open the rear line for bleeding. You screw it in just for bleeding only, then remove and plug for driving. I had this same issue. When the disc brakers were added this block most likely should have been swapped out as well.

 

[MonsterBIlly]

Look here and see diagram at bottom of page

https://www.speedwaymotors.com/Spee...MI1cStoer84AIVOB6tBh3ClgrUEAQYBCABEgJQmfD_BwE

 

[MonsterBIlly]

That is also the prop valve you should be using with the disc drum brakes.
It is an h block with the prop valve build into it.

 

[ep67bro]

It is the stock H block NO proportioning valve. It is the same H block that has been in place since the truck was new in 1967. I swapped the Dana 44 6 years ago and never changed it never needed to the brakes worked great before I swapped master cylinders a week ago.

See attached.

 

[Seventee]

Ok fill me in on this? I didn't think there was anything in the H block? This is not a proportioning valve. This is the stock 1967 bronco H block.

Correct, it is not a proportioning valve. But it contains a plunger that shifts one way or the other to trigger the imbalance switch (and dash light) when either the front or rear brakes lose pressure. When it is shifted, it will reduce fluid flow to the side that loses pressure.

It is supposed to reset once the problem is fixed and pressure is re-established. However I discovered on mine that it was so stuck that I had to disassemble it to clean and reset.

 

[Rustytruck]

Make sure the rod operating the master cylinder goes all the way back so the piston inside the master cylinder goes all the way back and gets refill brake fluid inside the master cylinder port.

 

[DirtDonk]

The residual pressure check valves were always in the master cylinders on our Broncos. Not in the H-block.

BTI (before the internet) I always thought that when the shuttle piston thingy moved towards the side with the leak, it reduced or blocked flow to keep your brakes firm and working on the good circuit. But I was corrected by many that said that there is no flow reduction at all and the piston is simply to trigger the light.
Seemed a waste of a good chance to stop a leak to my mind, but I never actually tested one to see just how much flow would, or could be reduced. If any.

And that actually did make sense if you look closely. Going by the diagram Seventee posted, you can see how the end of the shuttle has a reduced diameter that reaches the notched end of the block. According to the factory diagram, none of the full diameter of the shuttle enters the fluid flow stream.
This reduced diameter should let full flow past it and to the brakes.

So for years now I've gone under the impression that no effect on fluid flow is achieved and only the light comes on.

Paul

 

[ep67bro]

Thanks for all the info. I hope to have a few minutes today or tomorrow to mess with this again. Think I will try and vacuum blead the front brakes at the H block. That will determine if the H block is blocked somehow. If flow is low then I will take it off and clean it. Then if that doesn't work I will just burn the bronco! LOL

 

[Seventee]

And that actually did make sense if you look closely. Going by the diagram Seventee posted, you can see how the end of the shuttle has a reduced diameter that reaches the notched end of the block. According to the factory diagram, none of the full diameter of the shuttle enters the fluid flow stream.
This reduced diameter should let full flow past it and to the brakes.



Paul

Paul, while I agree it does not seal off completely, it does reduce the cross sectional area available for flow. And depending on how much crud has built up on the end of the plunger over the years, could have a dramatic effect on the braking circuit.

Not certain this is even a problem in this instance, but just one more thing to check for a braking mystery when you have flow to one end but not the other.

 

[Seventee]

Thanks for all the info. I hope to have a few minutes today or tomorrow to mess with this again. Think I will try and vacuum blead the front brakes at the H block. That will determine if the H block is blocked somehow. If flow is low then I will take it off and clean it. Then if that doesn't work I will just burn the bronco! LOL

You may still get some flow for the reasons stated previously. After you disconnect the line, you could use something like a drill bit just small enough to fit through the H-Block fitting to check to see if the plunger is shifted. If the bit bottoms out about halfway through the block then you will know it is hitting the end of the plunger.

Edit: I also meant to say that having a functioning brake warning lamp takes out the guesswork in this, obviously. I learned that the hard way.

 

[ep67bro]

So I did a lot more bleeding from points down stream of the H block and got good fluid so I don't think that was the problem. I really think the problem was the bleeders at the wheels especially the passenger side was loose in the threads and was pulling air along with fluid when I vacuum blead them. So I went old school and had my brother in law push the brakes and bled them that way. No more air good fluid flow replaced the bleeder that was messed up and brakes work good but boy they are touchy, seem to be much better than before but still have about 1/4 travel in the peddle before the brakes do much of any thing. I adjusted the plunger out of the booster out about a 1/4" and it seems better just not like it was before the master cylinder swap. Think I am going to drive it for a while and get a feel for it again. to be honest I have barely driven this truck for the last 9 months.

 

[DirtDonk]

...No more air good fluid flow replaced the bleeder that was messed up and brakes work good but boy they are touchy, seem to be much better than before but still have about 1/4 travel in the peddle before the brakes do much of any thing.
I adjusted the plunger out of the booster out about a 1/4" and it seems better just not like it was before the master cylinder swap.

That adjustment is not guesswork. You must either measure the depth of the piston vs the extension of the rod, or adjust them until it hits then back off until it does not.
The amount of air-gap between the rod and piston is miniscule. Like measured in the thousandths.
If it's more than 1/64" it's too much.

Easy to do though, as you found. Leave the lines connected and just pull the master forward to gain access to the rod. Adjust it out a bit, slide the master up until it either bottoms out on the flange or bottoms out on the rod.
If the rod hits first, it's too long and you can adjust it back in until there is no contact of the rod to the piston before the master mates up to the booster.

Remember that with about a 6:1 pedal ratio (or whatever ours happen to be) a 1/4" gap is 1 1/2 inches of pedal travel.

Hope it's as simple as that. But don't ignore the rear brakes still either.
When mine gradually would get a longer pedal throw, it was the rear brakes wearing down and not self-adjusting (as if!) enough.
I could tell easily by pushing the parking brake pedal down one or two notches. When I did that the main brake pedal reacted quicker and remained very high.
So if you click the parking brake and the brake pedal gets a little higher, your rear brakes could still be adjusted a little tighter.

Paul