The Great Lotus Europa / Datsun F10 Master Cylinder Swap (Part 3: The Bleeding From Hell)

Last week, I admitted to you something that most folks would share only with their therapist—that seeing the adjective “straightforward” applied to retrofitting a Datsun F10 master cylinder into a Lotus Europa triggers me into a Three Stooges’ NIAGRA FALLS! (“Slowly I turned …”) level of rage.

But I got it done, only to find that the symptom that caused me to replace the master cylinder in the first place—a brake pedal that was soft and with travel that was obviously too long and that pumped up firm with a single pump but repeated the whole thing just 10 seconds later—was unchanged. In other words, I hadn’t fixed it. Grrrrrr.

So I’ll admit something else—I’m magnifying my level of annoyance because, well, because it’s funny. Really, the swap went about as expected. The issue of the troublesome unadaptable 7/16-20 fitting on one of the brake lines was just a detail, albeit a vexing one. In a perfect world, we’d all be alerted to these sorts of stumbling blocks up front. When I write my version of the swap in detail for one of the Lotus Europa forms, I’ll do exactly that; I’ll say, “Understand that you have no choice but to cut the flare off the line with the 7/16-20 fitting, substitute a more conventional fitting, and re-flare the line, because there is no commercially-available adapter.” The world doesn’t always spoon-feed us the information that we think is the crux of a project. We usually only know what that is when we’re done and it’s bitten us in the behind.

I did, though, still need to solve the problem of a brake pedal with too much travel that pumped itself up with a single stroke, only to repeat the symptom 10 seconds later. The fact that it did exactly the same thing with both the old master cylinder and the new pretty much took the master off the table as the cause of the problem.

To recap, the problem appeared last fall when I was driving the car on a leaf-peeping trip in western Massachusetts. I noticed the long pedal travel, then stopped and found that I’d been driving with the handbrake on for some unknown amount of time (more than five, less than a hundred). I assumed that I’d probably shaved a goodly amount of life off the rear brake shoes—on a car with rear drum brakes, badly-worn shoes will certainly cause unwanted brake pedal travel. However, when I pulled off the drums, the shoes had some visible wear, but weren’t the worn-down-to-metal nightmare I expected. Plus, my Europa is a Twin Cam Special, and this model has self-adjusting rear brakes, so I thought that I was doubly let off the hook as this being the source of the problem.

I did a manual adjustment of the supposedly self-adjusting brakes, then bled the system, but the problem remained. That was what sent me down the path of replacing the master cylinder, about which I was apparently wrong.

So, with an apparently unnecessary new master cylinder installed, I went back to basics. I did some reading on the Europa forums regarding the Special’s self-adjusting rear brakes, and learned that the general opinion is that they’re about as useless as you-know-whats on a bull—if the shoes are completely unadjusted, they may move them a bit closer to the drums, but they don’t get them close enough to take out all the pedal travel. Some Special owners drill a hole or cut a slot in the backing plate to allow a screwdriver to be used to manually turn the teeth on the adjuster with the drum on, as is the design on many cars. I didn’t really want to take the time to pull the shoes off, which appeared to me to be necessary to properly cut a hole or slot, as that meant having to deal with the pesky springs that all brake shoes have. Plus, it wasn’t clear to me how I’d be able to rotate the adjuster backward if I got the shoes to the point of rubbing, as the automatic adjuster would prevent that, and as removing the automatic adjuster completely looked like it would allow things to spontaneously loosen or tighten—that is, there would be no detent or other mechanism holding the adjuster wheel in position.

Instead, I carefully adjusted the shoes. If I did this last fall, I apparently did a terrible job of it. This time, I was methodical. For each rear wheel, I pulled off the drum, clicked the adjuster by one tooth at a time, put the drum back on even if I had to tap it on with a rubber mallet, pulled the handbrake, released it, and stomped the brake pedal to seat and center the shoes, then repeated this process until I found the point where the shoes were just beginning to drag on the drum. This lessened the brake pedal travel by about half, but the pedal still did the pump-up thing on the remaining travel.

A soft brake pedal that pumps itself up is usually symptomatic of air in the brake lines (air is compressible; fluid is not). Thinking back to last fall when I left on the handbrake and drove the car an unspecified distance before I noticed it, I had to admit that it was possible that the rear brakes got hot enough that the brake fluid boiled. This phase change from liquid to vapor can create bubbles, the very definition of air in the brake lines. As was the case with adjusting the brakes, I did bleed them last fall. Maybe I did a poor job with that as well.

As I mentioned last week, part of my master cylinder swap included installation of a remote ATE reservoir from a BMW 2002 I’d parted out decades ago. The goal of this was to be able to use the same Motive power brake bleeder that I use on the vintage BMWs.

Last fall, I installed a set off SpeedBleeders—bleed nipples that have a little check-valve in them that allows one-person bleeding; just open up the valve and push the pedal up and down.

Now that I had the Motive, however, I unfortunately found that the SpeedBleeders didn’t play nicely with it—the Motive didn’t build enough pressure to overcome the force of the spring in the check valve. So I pulled the SpeedBleeders out and reinstalled the old passive bleed nipples. I bled the system three times, but the brake pump-up issue remained.

I bounced the problem off some friends as well as posting it on one of the Europa forums. One senior Europa guru in England had a genius-level idea: Engage the handbrake, then try the brake pedal. If both the too-long pedal travel and the pump-up problem went away, then I’d know the issue was still being caused by the adjustment of the rear shoes. If not, the issue was likely air in the lines. I tried it, and it made no difference. Back down the bleeding hole I went.

I should add two things. The first is that I’ll admit that I didn’t “bench-bleed” the master cylinder (put it in a vise, feed it brake fluid, manually push the cylinder in and out until the bubbles stop, then plug up the ports) before installing it. The reason was that with all the twists and turns in the installation, I thought that the odds I’d get it installed without the fluid leaking out and air leaking in were small.

The second is that among the Europa’s many strange features is that Twin Cam cars like mine have dual power brake boosters. Because it’s a mid-engine car, the boosters aren’t mounted on the master cylinder like they are on nearly every other car but are in the back—in the engine compartment where they can be easily connected to the intake manifold. With 50 years of age, it’s very common for these boosters to die. Like the original Girling master cylinder, they’re long since out of production, so the only choice is to have them rebuilt, or to bypass them, which isn’t crazy since the earlier non-Twin-Cam Europas don’t have power brakes at all (hey, you can get away with a lot on a 1600-pound car). So, when I got the car running four years ago, I went the bypass route, buying a few short brake lines, bending them into “U” shapes to bypass the boosters, and splicing them in with unions. While this was successful, it does create a geometry that’s almost tailor-made for air bubbles to lurk in the high spots of the inverted “U”s and be difficult to push out.

At a friend’s suggestion, I tried something I never would’ve thought of: I re-installed the SpeedBleeders and used them and the Motive power bleeder and manually pumped the brake pedal. Normally, you use a power bleeder so you don’t have to pump the brake pedal yourself or rope a spouse or child or friend into doing it for you. The only reason I had the SpeedBleeders was because the original Girling master cylinder had threads on it that no cap—from Motive or homemade—would seal against. So using all three at once was sort of like using belts, suspenders, and a staplegun to hold up your pants. But my friend’s logic was that this was the best way to push fluid and air out while minimizing the chance that, when the pedal was lifted, fluid and air would backtrack.

He was apparently right, because finally, on the eighth bleeding, the pedal became firm.

So, my post-mortem is that the problem appeared to have indeed been caused by my leaving on the handbrake—specifically, the long pedal travel likely was due to the brake shoes losing some material, and the pedal being soft and pumping back up was likely due to the brakes having been overheated, likely boiling the fluid and creating air in the line.

Oddly enough, I’m not unhappy with the way this worked out. Even though I was less-than thrilled that going to all that work to replace the master cylinder didn’t solve the original problem, the end result—having a new brake master cylinder rather than the 50-year-old one (the only original bit of brake hydraulics left on the car)—was a huge plus for what was really a modest outlay of money, only a few more evenings than I’d anticipated, and a bit of cursing.

However, I’d be remiss if I didn’t point out that the textbook symptom of a bad brake master cylinder is the brake pedal slowly sinking to the floor when you stand on it. The car never did that. So while I’m glad that the Lotus now has a new master cylinder to go with the new calipers and rear wheel cylinders I installed four years ago, I also must admit that, had I been my usual unrelentingly cost-conscious self, it actually would’ve helped me come up with the correct diagnosis at the beginning rather than the end of the repair.

Live and learn.