Topic: '65 Disc Brakes -- Proportioning Valve Bypassed??

[drummingrocks]

Hi guys, some of you may remember I was looking for the correct master cylinder rod for my '66 GT fastback.  Several people offered to help, but they needed to know the length I needed.  I ended up taking the master cylinder off of my '65 disc brake convertible this weekend, as I knew it had good brakes and the correct length pushrod.

While I had everything apart, I happened to notice that the proportioning valve on the '65 has been bypassed.  It looks like the valve leaked sometime in the past, and rather than replace or rebuild it, someone used a line coupling to bypass the valve entirely.  There were no lines at all going to either port on the proportioning valve; they went directly into the master cylinder.  I can understand why someone would do this, but my question is: How in the world did it work?  I've owned this '65 for seven years, and I've been underneath it many times.  There isn't an aftermarket valve plumbed into the braking system anywhere that I can see. 

So again, how did this work?  I always thought (and correct me if I'm wrong) that the purpose of the valve was to equalize line pressure between the disc setup in the front and the drums in the rear.  This car had excellent brakes, but how?  It seems that without the valve one end of the car would be braking much harder than the other.  At the very least, it should've been noticeable, but I've driven this car a good bit, and the brakes were always great.  How is that possible?  I've been puzzling over this all weekend!     

[CharlesTurner]

You can still have decent brakes without the proportioning valve.  If you ever get on the brakes hard, I would expect the rear to lock up before the front.

The brakes will be a little better when the proportioning valve is routed back through the system.  Especally as the front pads wear more.

[drummingrocks]

You can still have decent brakes without the proportioning valve.  If you ever get on the brakes hard, I would expect the rear to lock up before the front.

The brakes will be a little better when the proportioning valve is routed back through the system.  Especally as the front pads wear more.

Thanks, Charles.  I was thinking that under extreme braking conditions, the unequal braking could be severe enough to make the car try to spin around.  I certainly don't want to find out!

[CharlesTurner]

Thanks, Charles.  I was thinking that under extreme braking conditions, the unequal braking could be severe enough to make the car try to spin around.  I certainly don't want to find out!

So long as the rear brakes are adjusted right, I don't believe that would happen.  As the shoes and front pads wear out, you'll begin to notice uneven braking.

[sgl66]

I've had an after market prop valve for a long time...KH leaked. Now that I'm replacing all brake lines, I will be sending mine out to White Post Restorations in Va for a rebuild so new lines will fit correctly.

I've seen a few for sale on the net but no idea if they are painted leakers.

I tried going without the prop valve and was locking up rear brakes....not a great idea.

[drummingrocks]

I've had an after market prop valve for a long time...KH leaked. Now that I'm replacing all brake lines, I will be sending mine out to White Post Restorations in Va for a rebuild so new lines will fit correctly.

That's who I used too.  I had White Post rebuild the original in my '66 fastback, and just mailed the one off of this convertible yesterday.  I can't believe my car wasn't locking up the rear brakes, or otherwise not using the rear brakes.  It worked, but I don't know how.  I'm usually of the mindset "Don't fix it if it isn't broken," and this '65 always had excellent brakes.  I hope I'm not opening a potential can of worms by reinstalling the proportioning valve.  I know I'm going to have to replace the brake lines they've sectioned, and it may all be downhill from there...

[CharlesTurner]

Probably best to do a thorough inspection of the whole system including pulling the rear drums off.  Your rear shoes may be completely worn or the drums turned too much and out of spec.

[drummingrocks]

To give a somewhat happy ending to the story, I have two words: project creep.  That's when you know you have one thing to fix, and you start thinking, "Hey, while I'm in there, let's do this...and this...and this."

Making a long story short, I ended up replacing all of the brake lines with carbon steel replacements from NPD.  I figured if that one original line was bad enough to wring off, the others couldn't be too far behind.  While the master cylinder was off, I noticed it was leaking out of the rear seal, so I went ahead and replaced it too (though I did save the original).  With the new lines installed, it was pretty easy to plumb the rebuilt proportioning valve back into the system and get everything hooked up like it was originally.

At this point, I've not driven the car more than 10 miles (from the shop back home), and it does have a slightly spongier pedal than it did before.  However, I figure there's probably still some air in the lines somewhere, and now that's it's had a chance to sit, I want to go back and bleed everything again.  Other than that, the car stops much like it did before.  I can't tell a noticeable difference, but at least I now have the peace of mind that everything in the brakes is functioning like Ford intended.