OK another brake question

[SLOWnEASY]

Are you making sure that the front brakes are plumbed to the larger reservoir in the master cylinder?

 

[ngsd]

Are you making sure that the front brakes are plumbed to the larger reservoir in the master cylinder?

Yes first thing I checked but even the new one is both the same fsize ront and rear without a change.

 

[DirtDonk]

I’m still thinking that it can’t be the combination valve.
If you were able to make it work as expected by simply changing to the old master and booster combo, then how can it be a combination/proportioning valve issue?

Now, it’s not like they are super reliable, and have never failed before. And this is often one of the symptoms.
But that symptom doesn’t jus usually go away when you change the master and booster.

I still think when you did that, you proved that it was a master/booster Issue.

 

[DirtDonk]

In fact, if you wanna drive it sometime soon, just put the old ones back on and be done with it.
Unless there was something wrong with them, other than being old, why can’t you run them?

 

[ngsd]

In fact, if you wanna drive it sometime soon, just put the old ones back on and be done with it.
Unless there was something wrong with them, other than being old, why can’t you run them?

They were full of sludge and dont want to introduce more of that back into it. It may be the last resort though if I fail!

 

[DirtDonk]

When I find sludge in used master cylinders, I’ve always been able to clean it out.
I got lucky I guess, and it was never inside the piston cylinder. Just the reservoirs.
So I would carefully wipe it out of the bottom of the reservoir, and introduced new fluid.
In theory you should be able to see whether there’s any inside the cylinder or not.

And in an emergency, such as when you can’t find a new master for a particular application, you can even disassemble them and clean them out.
We used to rebuild master cylinders back in the day. You may have done it in the past as well.
Pull clips, pull pistons, pull springs, flush it out with brake fluid, clean it up with a cylinder hone if needed, new parts back in, again if needed, and there you go!

Just a suggestion anyway. You know, for the “just in case“ scenario.

 

[ngsd]

Here is teh MC that was in it. 1.15 bore and alrge reservoirs with right side line inputs. do you recognize it? The part numbers dont come up with anything.

 

[DirtDonk]

I've never bothered to look at casting information on any part I've installed. Just the fact that something fits, or doesn't fit, works or doesn't work, was all that concerned me in the past.
So I can't tell what the numbers on yours mean, but I can tell you two things.
One is that it looks just like a standard Ford later model (such as '76 and '77 power setup) unit. The 4-wheel drum setups looked the same, but without the angle of the booster, the ports were on the left side. Yours with the ports on the right side would have been for a booster setup. At least on a Bronco. The larger piston size makes me think it's for a different vehicle. Unless some Broncos got the larger piston, I thought (but don't know) that all EB's got the 1" bore, whether manual drums or power disc setups.
And two, is that since it was made in the USA, it's a keeper!

Whether in as-is condition, or after a simple rebuild, I'd at least be considering keeping it, cleaning it up, maybe give it a quickie hone job (but only if needed) and re-use it.
Only if some damage makes using it problematic would I toss it out or use it as a core.

The earliest masters were single reservoir of course. Starting in about '66 or so, the disc brake cars got a slightly elongated dual-reservoir master, with two equal size reservoirs and rounded ends. Those were found on dual/tandem masters on '68 and maybe '69 Broncos with 4-wheel drums, making me think that, even though they revolved around disc/drum setups originally, Ford found the economy in using them for both drum and disc equipped vehicles. Sometime in either '69 or '70, Ford changed to the style like yours, with the two distinctly different sized reservoirs, with one square end and one rounded end. I've seen them with the large reservoir to the rear (most of them by far) and some to the front. No idea what dictated the different orientation.
My '71 came with the style like yours, but with the ports on the driver's side.

Paul

 

[robsim111]

I have built quite a few Broncos but these brakes are stumping me. Everything is new and I evern swapped out another new master cylinder but the brakes just keep going to the floor. 77 Brake booster and MC, Chevy front disc conversion with new calipers, rears are stock with new wheel cylinders, all new lines, brake proportioning valve. I have bled them to death, no air comes out. Bench bled the MC twice. I use a power booster and kept constant pressure on with no leaks. I am just asking to see if I am missin something. I had the same setup on it before but all the wear parts now are new.

Did you bench bleed the master cylinder good enough? Any air in a new master cylinder will cause your issue.

 

[ngsd]

Did you bench bleed the master cylinder good enough? Any air in a new master cylinder will cause your issue.

Yes for sure. Also tried three different ones all bench bled quite a bit. I did try and resue the original one again and it is the only one that feels good so now I am on a hunt for a rebuild kit or a new one but I have no idea what it came off of.

 

[robsim111]

Yes for sure. Also tried three different ones all bench bled quite a bit. I did try and resue the original one again and it is the only one that feels good so now I am on a hunt for a rebuild kit or a new one but I have no idea what it came off of.

If you want a quick way to test that they are fully engaging, put a quarter or a nickel or two inside of the back of the master cylinder and remount it. If the brakes build pressure, that means the power brake booster isn't fully engaging the master cylinder. Basically, just reduce the engagement space between master cylinder and brake booster.