Beck TD, Part 69: The MGA Master Cylinder

 When Beck TD came to live at the Grant Street Garage, the brake and clutch plumbing worked, but was definitely in need of some attention. The brakes used the stock MG TD master cylinder, and the clutch used a Volvo part, mounted on a bolt-on bracket:

Both of those master cylinders were past their best days, and in addition, the clutch cylinder was actuated by a crude fabrication that sported some of the worst welding I've ever seen. The torque applied to the arm by the extension and stack of washers had twisted the arm, and cracked the weld.

I did a lot of rebuilding that first year, including removing the pedal shaft and rebushing the frame (Part 15 and Part 16). I replaced the brake master cylinder with a new one, and rebuilt the clutch master cylinder. I also added a new clutch slave cylinder. But as for that crazy pedal shaft... I just cleaned up the weld and stuffed lots more weld there, and gave it a try. It worked fine, but it was always on my mind.

The brakes worked great after I added front discs (Part 23 and Part 33). But the clutch, while it worked well enough, never was that pleasing. The action was heavy, and the throw was so long that I had to point my toes to fully disengage. I knew that Charlie Baldwin was a big fan of the solution in his car, which uses an MGA double master cylinder to provide hydraulics for both brakes and clutch. Charlie kindly provided this picture:

I decided to give it a try, and I knew that I would have to start with that crazy pedal shaft. The photo below shows an eBay find, along with my nasty old shaft. The new/used one even had a yoke for the rod to actuate the master cylinder, which I definitely needed.

Of course, used parts are often well-used. The eBay shaft was worn in exactly the same was as my old one, and when I took the yoke off, this very worn hole presented itself. If that shaft had stayed in service in a stock TD for much longer, the owner would have been surprised by a big bang followed by no clutch! But it's not a problem, because I needed a new hole farther up the arm anyway.

Once that hole was drilled to match the one in the brake pedal, I needed to fabricate the rod to push the piston in the cylinder. In the next photo, on the left you see the solution - the stock TD brake rod to the left, and a stainless steel rod threaded on one end to match the yoke, and rounded on the other end like the brake rod. The right photo shows the linkage mocked up on the bench, proving it aligns.

Moving to the car, I had to create clearance for both rods. To the left you can see the round hole in the stock TD pedal box. On the right, simply extending the hole to the edge worked just right. You can see I also did some long-delayed cleaning and painting under the dash as part of the process.

Nothing is ever straightforward on these cars. The MGA cylinder needed to be spaced out from the frame, and Charlie had already figured out how much: 7/16". Making those spacers was easy on the lathe, but the longer bolts were problematic because those bolts are Whitworth standard, 3/8-20 BSF. Charlie had bought the threading die long ago, and managed to come up with it and loan it to me. Those are hardware store 3/8" bolts with a long shank. I cut off the "American" thread and then used Charlie's die to make the new threads.

Finally, I could mount everything and proved that it all lined up.

Now for some plumbing, and the first order of business was at the clutch slave cylinder. When Beck came to me, the metal and rubber hydraulic hoses were just hanging in mid-air, and I temporarily jury-rigged a mount with wood and zip ties. Time for a more standard solution. I needed a bracket that was only 1/16" thick, and I used an aluminum bracket from the scrap bin. Here's before and after:

Then I went to drill holes in the frame to mount it, and found that I had zero clearance for a drill! I guess Charlie drilled his while the engine was out. I settled on a mount that clamps to the lower flange of the frame rail. It's upside down in these photos:

And finally, after almost four years, a safe mount for the slave cylinder hose!

Next came the copper/nickel pipes, and that taught me the next problem: fittings. In this photo, the one on the left is what the TD uses, a long Whitworth fitting threaded 3/8-20 BSF. The MGA master cylinder, being newer, has 3/8-24 UNF threads, and I had that standard fitting, but it was too short! Charlie clued me in to the fact that I had to order special British standard fittings that looked like the left one, with an unthreaded part at the end, and he also told me that the best source was Federal Hill.

Once I got those fittings, I laboriously plumbed the system. I'm not an expert at this, but I'm happy to say that nothing leaked and everything worked once I got the system bled. Clearance was very tight on these fittings. I had to be sure the left hand one (the brake, oddly) was good and tight before installing the clutch plumbing to the right.

There's more work to be done elsewhere before I can drive the car, but testing seems very promising. The brake pedal is high and has a short throw. And the clutch seems to be absolutely transformed. It is light enough action that I can push it by hand, which was difficult to impossible with the old setup. The throw seems to be about half the old system, and there's something more to explain about that.

The bore of both sides of the MGA cylinder is 7/8", and the stock Volvo clutch uses a 3/4 bore. Charlie had his clutch side sleeved to 3/4" and has been happy with it, but I volunteered to test the system without doing that. I had an ulterior motive, because a larger bore will have two effects: a shorter throw, and more effort. It seems to me that I lucked out, because the effort is very reasonable, and I no longer have to point my toe to engage the clutch!

Continue on to Part 70....