Wednesday, July 13, 2016

Brake Bits pt. 1 - the distribution block

I changed my mind. The coil springs are still scary and so they'll have to wait. I have some brake parts to work on still.

The brakes are a pretty involved project, and there seems to always be one more thing to do. While I have all the front and rear brakes rebuilt and installed, there's still a lot left that's brake system related --- a parking brake to connect, brake lines to mount, a distribution block to rebuild, the master cylinder to bleed and and power booster to bolt to the firewall, the the brake pedal assembly goes in. Turns out there's a lot of parts in the brake system.

The distribution valve is a little brass block that serves two purposes - it splits the brake fluid coming from a single line out of the master cylinder into two separate lines for each front wheel, and it houses the Brake Warning Switch (which lights up an angry red BRAKE lamp when the brake system develops a hydraulic fault.) The valve has a tendency to seize up after time from old brake fluid, especially if it hasn't been driven in over 30 years like my car.

Here again, the factory service manual is super handy. There's a fantastic page on how this thing works and a cutaway drawing. I can't really describe how great the FSM is - I love this book. The descriptions of the systems, the old school cutaway illustrations, the exploded parts drawings, the tables full of torque values - I could go on. Even if you're not doing a full blown rebuild like me, this manual is easily worth its weight in Cobalt (look it up). 

67 mustang distribution block
Here's the distribution block as it came out of the car. It's a brass block, but the janky rattle can black paint job makes a mess of things. The brake warning switch is the plastic socket on top. The front brake line comes in at top right and is split out the right and bottom ports. The rear brake line simply passes in through the top left port and exits out the bottom. 


All blown apart. The little shuttle valve is what makes the warning switch work. Normal operation has balanced pressure between front and rear brakes. If a line opens up when the brakes are pressed, the shuttle will be pushed to the low pressure side and depress the plunger switch, lighting up the "you gonna crash" lamp on the dashboard.

The secret for getting it apart is a couple of specific tools. First, line wrenches to get the old brake lines off the block, and then a hemostat (medical locking scissors) to grab and pull the shuttle out. I had to push the shuttle in a bit with a punch to "unstuck it", then use the hemostat to pull it out. 


67 mustang distribution block rebuild kit
A rebuild kit is available for about $10. A replacement part is $70 and has different sizes of ports, so you'll very likely have to re-flare all your brake lines to get it to work. The rebuild kit has a copper crush washer and 3 o-rings. The '67 block only uses two of the o-rings (the square edge ones), whereas very late '67 to '69 I think) will also use the third o-ring.


Everything cleaned up on the bench grinder (brass wheel!) and ready for reassembly. Only use brake fluid for lubricating the o-rings and shuttle. The bore of the valve body is cleaned with a brass bottle brush and some brake cleaner.


 A rebuilt distribution valve. Shiny!

I wanted a quick and easy win, and after the pedal assembly turned out to be neither of those, this was fun and rewarding. It only took a couple hours to do this, and $10 in parts. What's not shown is all the messing around with the replacement valve and finding it won't work with my lines without a lot of work, shipping it back, trying to figure out how to get the shuttle out. and then driving around town looking for a hemostat (Communist Freight, naturally).

OK, seriously, I'm doing the coil spring cutting and install next. Really.



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