Brake Master Cylinder Mock-Up

It’s been far too long between updates, I admit, but a lot of custom Harley work has kept me very busy for the past few months along with some pretty major occurrences at home that have demanded just about every spare moment I had (more on that is the coming weeks).  However, much to the chagrin of most of my neighbors and even a few family members, I am NOT dead in spite of the rumors and wishes to the contrary!

This update will be a quick one and somewhat out of sync with the most recent work on the Boss.  I find myself having to step back from a certain line of thinking for a while to regain perspective and let the matter “breathe” now and again, and one way I like to do that is to pick up a project I have let lay and drive it through the goal post if at all possible.  One of these projects has been to have my original brake booster rebuilt and the other is to configure a modern aluminum master cylinder as a replacement to the old iron original that, in my opinion, has too small a fluid reservoir capacity for rear disc brakes.

The booster rebuild was ultimately a disappointment.  No because it wasn’t successful, but because the condition of my original booster was not up to my standards.  When it was all said and done, the two case halves were pitted from rust when cleaned to bare metal and plated in zinc dichromate and because the rebuilder was a bit less than tidy in the reassembly process, leaving many tool marks and gouges along the seam.  I guess I had higher hopes given the rebuilder was perhaps the most highly recommended outfit around but I can’t complain too much as the price was hardly arguable.  The bottom line is it works and will function as a good spare, but I will be replacing it with a new unit from NPD very soon.

The master cylinder solution was quite a while in the making as I ended up using a combination of parts from three different vehicles to get the entire booster/master cylinder setup I was looking for.  The key features I was after was a nice, 1” bore, modern aluminum master cylinder with the fittings on the outboard side just like the original.  Also, I wanted a clean, see-thru fluid reservoir and the whole works needed to work within the stock packaging space.  As it turns out, I might have actually created something that could have some potential for aftermarket sales if I put my mind to it (but that is another issue altogether).  In the meantime, I will continue to refine the setup with a Wilwood distribution block with built-in bias valve and a mounting bracket designed to mount the valve and the reservoir for the hydraulic clutch as well.  But that being comparatively easy work, I might let that lay a bit while I return to working on the doors and mirrors!

Lots of research went into getting this master cylinder combo to work on the original '70 Mustang Bendix booster.  This booster is my rebuilt original and will only be used as a mock-up donor and spare.  It's just not looking good enough for the project, but you get the idea.

Another shot from the top shows how much cleaner and slimmer the modern master cylinder is over the old iron unit.

Almost all of the popular master cylinder conversions that use the plastic fluid reservoirs have the ports on the inboard side.  This complicates many aspects of working on the engine and looks too cluttered for my taste.  This setup puts the ports in the same (outboard) location as the original master cylinder and offers a lot more working room on both sides.

Clearance to the shock tower is exactly the same as the stock iron master cylinder!