While driving around the neighborhood the engine began stalling every time I applied the brakes. It didn't happen while sitting still, but once moving (and building up a vacuum in the booster) the engine would stall as soon as I hit the brake pedal. Luckily I wasn't too far from home. To isolate the problem I plugged the vacuum line running from the intake manifold and the booster. I've driven it with no power assist and made dozens of stops and the engine hasn't stalled once.
To troubleshoot the brake booster you hook up a vacuum pump to it, apply a vacuum, and step on the brake pedal. You're supposed to get 2 or 3 applications of the brake pedal before using up the stored vacuum, In my testing I only got one. I'm guessing that there is a leak in the booster that only manifests itself once I've built up vacuum and then applied the brakes. Maybe this is the only time the booster diaphragm moves, which would explain why I don't have a vacuum leak in the garage. Makes sense to me, I guess. Anyway, the booster is around 10 years old.
I decided to drop the idea of a power brake booster and go with a new master cylinder designed for manual disc brakes. It turns out master cylinder sizing is much more complicated than you could imagine. If the piston is too big then the line pressure may be too low requiring lots of effort at the pedal. And if the piston is too small then the line pressure will be fine but the pedal travel may bottom out. Wilwood makes a tandem master cylinder with a 7/8" bore that should be perfect for my application.
As you can see my existing master cylinder is almost hitting the shock tower and is partly covered by the export brace. Removing the booster will move the new master cylinder over 6" rearward, making access a lot easier. Unfortunately I'll have to rebend the brake lines since they'll never match up with the new position.
Here's the new Wilwood in place. It came with an adjustable push rod so I had it in and out several times getting the push rod the proper length. If I had been smart I would have worked on the brake lines now before bleeding the master cylinder. Hindsight... The front line goes to a distribution block before continuing on to the front wheels while the rear line goes to the SSBC proportioning valve.
This Wilwood is really a piece of art. I splurged on the polished version for an extra $50. Before being installed master cylinders need to be bench bled. Wilwood supplies the kit to do it (even though Summit let me order a second kit). Basically, you fill the reservoir with fluid and work the piston in and out. This forces fluid and air bubbles through the hoses and back into the reservoir. The only problem is that the little red fittings are cheaply made out of plastic and leak. Once I started this operation I had two slow leaks to contend with. Now you see why I should have bent the brake lines first. My attempt at reusing the existing brake lines didn't go so well either. The two lines are both less than a foot long and bent fairly easily. I first cut some wire the length of each brake line and then shaped the wire to the fittings on the car. Then it was just a matter of bending the lines to match the templates. However, I couldn't get a good seal when connecting the lines to the master cylinder. When I pulled them off I could see that the flares were poorly formed. So I ordered some new lines along with a nifty little tubing bender--what I should have done in the first place.
Here's the new lines bent to match my wire templates. I bought 12" lines, which were a few inches longer than the originals so I'd have plenty of room to make some nice defined bends. The old ones looked like they were hand formed--really sloppy.
Here's the new lines in place--no leaks so far.
UPDATE: July 2017
Wouldn't you know it, 3 months after I get the new master cylinder working and Wilwood issues a recall. They emailed me a shipping label so all I had to do was box up my old (new) one, ship it to them, have them repair it and ship it back to me. The guy on the phone said it would only be a 2-day turn around once they received mine but it ended up taking 2 weeks. So with shipping both ways it was closer to 3 weeks of down time. My son helped me take the old one off by crawling under the dash to disconnect the brake pedal.
Wilwood wanted me to remove all fittings and the pushrod before shipping it back so I used my combination square to measure the pushrod. When it came back I reinstalled the pushrod and adjusted it to the correct length before putting it back in the car. Last time I bench bled the master cylinder before I installed it but this time I figured I'd try bleeding it on the car. It sits very level in the car so I didn't think it would make a difference. It was definitely easier, I had my daughter pump the brake pedal while I watched the bubbles get purged.
Last time I lost a lot of brake fluid while trying to bend and connect the new brake lines, but this time the lines knew where to go so I hardly made a mess. Bleeding the brake lines using the two-person method of pumping the brake pedal while opening the bleeder screws can prove to be quite tedious so I looked for an alternative this time.
I bought a Motive Power Bleeder with an adapter that clamped on the top of the Wilwood master cylinder.
This bleeder is designed for you to pour a quart of brake fluid in the pressure tank which will then fill the master cylinder as the level goes down. At first I couldn't picture how this wouldn't just fill the reservoir up to the top and make a mess when you took it off, but then I realized that the volume of air in the reservoir would remain constant, so the fluid level would never change as long as the tank had fluid.
After all this, the swap was successful. The brakes work great. So far...
