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Discussion Starter #1
Hey guys, long time no log-in. Been lurking and occasionally sending new MN12 owners your way, but it's been a while since I actually posted anything.

Anywho, my sister has been the new owner of the '96 Thunderbird in my avatar for the past couple of years now, and she's got a problem with the car's brake pedal going to the floor. It's a V8, non-ABS model, rear disc, with 2 lines coming off of the master cylinder. Here's a full list of symptoms:


  • Pedal falls completely to floor with little-to-no effect on braking pressure.
  • Pedal momentarily hangs up a bit, about 2/3 of its way to the floor, but easily "pushes through".
  • LR rotor shows surface rust, while all other corners are clean.
  • Brake fluid reservoir was empty, indicating a loss of fluid somewhere.
  • All calipers, hoses, lines, and even the master cylinder itself show no external leaks EXCEPT for:
  • Valve blocks behind L headlamp and some of the surrounding lines are wet.
She'll be cleaning up that area soon to try to narrow down the leak, but she's also reporting that pressing the pedal is not helping to pinpoint the leak. It doesn't seem to squirt out anywhere when she hits the pedal. So I'll be helping her look at it more closely this weekend.

Now I remember seeing some threads around here about these valve blocks going "bad" and being unavailable except from a junkyard. If that ends up being the issue here, then I'd like to try and rebuild them. There used to be some pictures in this thread, but they seem to have fallen victim to the infamous Photobucketometer crap. Is there another write-up somewhere that I've overlooked?
 

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The Parts Guy
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Download and install a "photobucket fix" for whatever browser you use. You'll be able to see the photos then.
 

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Discussion Starter #3
Update:

So it turns out that there was air in the system stopping us from finding a leak. Whatever fluid had leaked out previously had already drained away, leaving only a light residue on the valve blocks by the battery. And because air had gotten into the system, the pedal was now compressing that air instead of squirting fluid out to reveal the leak point.

Still not sure exactly where it's leaking from, but the bottom of both valve blocks are wet where they contact the mounting bracket, and there appears to be a significant amount of corrosion in that area. It sounds like these blocks are unobtanium, so before I spend a lot of time searching for used ones, I'd like to take a closer look at these and see if they can be rebuilt. It would be nice if the culprit ended up being nothing more than a 20-yr old O-ring.

I managed to find a browser extension to unlock the pictures in that thread. Unfortunately, the disassembly pics are showing a different kind of valve than what we've got here. I came across another website that might have some more information, but it's "temporarily off-line" until Saturday. I don't know if I can wait that long, so I might just slowly and carefully disassemble one of the blocks and keep track of where all the little parts go until I have a better sense of what I'm dealing with.
 

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Super Moderator
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Most likely, the leak is where the metal line is corroded under that plastic crap 'wrapper'.

You'll have to pressurize the system to find the line that's leaking; clean the area, fill it, bleed it, and pump it hard, and see where the **** spurts out. :)

If it actually is the block, you'll see it.

There's a residual pressure valve under the drivers plastic fender liner, at the firewall; see if they are leaking. There are kits for those, too.
 

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Discussion Starter #5 (Edited)
Ok, so here's what we found:

We cleaned up the area and tried to narrow down the leak. It wasn't squirting out, but then again the battery was out and we weren't running the engine, so it's not like we were working with full line pressure. But we did spot something. The first area to show signs of wetness was where the valve blocks are mounted to their bracket. All of the lines stayed dry.

So we continued with disassembly, removing the entire valve block and bracket assembly from the car. Despite a generous dousing of penetrating oil, two of the flare nuts insisted on twisting their respective hard lines as they were unscrewed. So if we didn't have leaking lines, we do now.

The aluminum blocks appeared to have a rectangular stem that was peened over to fasten it to the bracket, so we ground off some of that material and freed one of the blocks. There is a small rubber plug in either valve retainer cap, and both plugs were dislodged from their caps. I guess the only thing keeping them from falling out a long time ago was that they were mounted so close together. I suspect that this is where our leak was coming from.

I continued with disassembling one of the valve blocks, leaving the other one alone for reference. Everything looked pretty clean inside, except for the end of the green piston. It has a hollow on one end (which faces the cap & plug), and there was an accumulation of gunk inside that hollow. But it doesn't seem to be blocking an actual fluid passage or affecting piston movement.
 

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Discussion Starter #6 (Edited)
Here's my theory: I'm thinking that fluid might have worked its way past the piston (perhaps due to a worn-out O-ring in the center of the retaining cap), and popped out the rubber plug. That rubber plug doesn't seem like it would stand a chance of ever holding back hydraulic pressure anyway, so maybe this is meant to be a weep hole to help indicate worn internals, not unlike the weep hole in a water pump. Maybe the rubber plug is just a dust plug.

The Muscle Car Research site finally went live again today, but it turns out that their Thunderbird proportioning valve page doesn't cover these valve blocks. Rather, it focuses on the same downstream double-barrel units covered in the "Where's the Proportioning Valve?" thread. They don't offer rebuild kits for these. They do have rebuild kits (and write-ups) for Mustang valve blocks, but I'm not sure if the O-rings would be the same size or not.

The local Ford dealer confirmed that these valve blocks were indeed long since unavailable. No rebuild kits, either. I'm sure that I can get some O-rings elsewhere (I actually have an O-ring assortment, but I don't think they're rated for use with brake fluid). But I don't know where I would find the ridged seal on that goes in the middle of the piston. Thoughts?
 

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Here's my theory: I'm thinking that fluid might have worked its way past the piston (perhaps due to a worn-out O-ring in the center of the retaining cap), and popped out the rubber plug. That rubber plug doesn't seem like it would stand a chance of ever holding back hydraulic pressure anyway, so maybe this is meant to be a weep hole to help indicate worn internals, not unlike the weep hole in a water pump. Maybe the rubber plug is just a dust plug.

...
This is very likely; the oring in the bottom is the seal, as the valve needs air as a reference for pressure.


I swear, looking at how these are made, I think they're residual pressure valves again. :)

Look at the mustang version; the additional brass valve does the proportioning...

https://www.musclecarresearch.com/valve-rebuild-kh


The terminology on all this crap is just bad. :)

All these different valves seem to have the same partnumber, differing only in the final letter.

Is there a partnumber on that assembly anywhere?

According to this part for sale, with box and visible partnumber, our partnumber is this:
E9SZ-2B091-C

https://www.ebay.com/itm/NOS-1989-1997-Ford-Thunderbird-Cougar-Brake-Pressure-Valve/152805718029?_trkparms=aid=222007&algo=SIM.MBE&ao=1&asc=41375&meid=2e5d44abd9db48629d11ba530ba83b7e&pid=100011&rk=1&rkt=9&sd=161883603595&_trksid=p2047675.c100011.m1850


Also, in the book, Ford refers to the two residual pressure valves as proportioning valves, and they're not.

We have the Red valve; Red means 10 pounds, from other vendors of these.



But there's hope. :)

Note this little blurb I found:

" Ford also used this valve as a later service replacement for the cylindrical C7OZ-2B091-B proportioning valve."

They are talking about this valve:



Does this look familiar? :D

As far as I can tell, this is the same part; You'd want to keep your spring and valve, but all the rubber should work fine. :grin2:


It's a AMC-Ford-GM-Mopar Kelsey-Hayes Proportioning Valve, apparently first used by GM in the 60's, lol.

The ford partnumber is C7AZ-2B091-A, apparently.

The original patents are online, btw, if you want to know how it works.
 

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Discussion Starter #8 (Edited)
Haha, can't believe I forgot to include the code stamped on it. Yeah, it's F6SC-2B091-AA. It's only stamped on one of the valve blocks, which tells me that Ford considers the entire bracket with both valve blocks to be all one part.

You're right about the terminology being weird. I've been treading carefully, trying not to call this thing a proportioning valve, as I've been hearing that term applied to the downstream double-barrel part, stamped F6SC-2B091-CA.

Do you have the Ford book on these? I only have a Mustang one, and it calls the 2B091 block a "brake pressure control valve", which is pretty vague. It refers to this spring-loaded piston valve in the block as the "proportioning valve", which I haven't quite wrapped my head around. (The Mustang block also has another valve inside, referred to as the "shuttle valve", which MCR calls a "differential valve", but looking at it I think "bypass valve" would be better...).

I'm also not sure why the pistons come in different colors. Seems like (aside from the presence of the "shuttle valve") the spring strength would actually be the deciding factor in making these blocks application-specific? Maybe not, I must be overlooking something...

But I digress. At any rate, it appears that Kelsey-Hayes was the OEM for Ford on these things, and that C7OZ unit really does look at lot like the ones I've got here. However, I did notice that there are some slight differences between these Mustang and Thunderbird seal kits. So I think I'm going to have to take some careful measurements and contact MCR to see what they recommend before I go and order the wrong part.
 

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I've learned in car parts, they wo'n change something if they don't have to, so odds are these are correct.

The kit is what, $10 or there abouts; if it's wrong when you get it, after you talk to them, I'll buy it from you if it doesn't work.
:)
 

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Discussion Starter #10
Well, MCR didn't have a rebuild kit available for this application, and none of the other kits are a direct match. But I took some careful measurements, and they've been able to put a kit together for me. I have a hunch that they're going to start offering this kit on their website, now that they know which pieces to include. This is great news for anyone else who wants to rebuild their valve blocks.

I'm being asked which other applications this kit will work with. I think it's safe to say that this will fit '96-'97 Thunderbirds and Cougars, but are there any others that can be added to that list? Do the Mark VIIIs use the same valve? Can we expand the year range to include earlier models too? Does it matter if the car has rear disc brakes, or ABS?
 

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Discussion Starter #11

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Discussion Starter #13
Great! It's nice to know that rebuilding these things is finally an option.

I should also update this thread while I'm here- rebuilding the valve blocks did indeed fix the issue. There is no longer any fluid weeping from the blocks, and all air has been purged from the lines. The brakes feel great, and that one rotor that was showing surface rust earlier is back to keeping itself clean again.

If yours is leaking, be sure to take care of it ASAP! I know that sounds obvious, but this one must have been leaking for a while, and it really did a number on the metal underneath as it ate away at the paint.

And a note on rebuilding: Because these valve blocks face one another, at least one must be removed from the bracket. I left one mounted while I ground away some of the peened-over aluminum on the other in order to release it. Once the rebuilding was done, I just fitted it back onto the bracket and secured it tightly with a zip-tie.
 

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