Quattro Squad

Twin Brake Master Cylinders

We decided some time back that this car would dispense with the hydraulically powered brakes and employ dual master cylinders with a bias bar adjuster but were never quite sure how we’d accomplish that. Then a friend turned us on to Compbrake in England who have a bolt-in kit for the Quattro. How could we say “no”? 

So we ordered one up and it arrived in just a few days. Seems to be very comprehensive. It even has a bracket and lines for remote reservoirs. 

  

The first job was to figure out how to mate up its four bolts with three on the bulkhead. It was seemingly not as “bolt-in” as we’d hoped. We made a template and transferred it to the car and immediately discovered that the four required holes would interfere with the pedal mounts. Something did not seem quite right. 

Close-up view of a white car panel with several holes, showcasing part of a mechanical assembly and visible components in the background.
A rectangular cardboard device with four protruding bolts and a central black lever, held by a hand against a dark surface, surrounded by various tools.
A top view of a black mechanical part with four protruding bolts, accompanied by a cardboard template with a circular hole and marked alignment arrow, placed on a blue fabric surface.

Then a gentleman and fellow Quattro rally car builder called Frank pointed out that the kit is designed to bolt to the OE brake booster not the firewall. He also highlighted how far into the engine bay this would make the assembly protrude because he had installed one himself. However, he had engineered a solution by way of an interface ring that was only about an inch thick rather than the 5″-6″ of the booster. A few more emails and some PayPal and one showed up at our shop. 

Close-up of a metal flange with a circular mount and multiple holes for attachment, featuring a rough, welded seam and a rusty finish.

This made all the difference and we were able to mock it all up in short order: 

Close-up view of a mechanical component featuring a circular metal base with threaded bolts and a black top housing.
Close-up view of a metal circular flange with bolt holes, mounted on a vehicle chassis, showcasing an open center and adjacent mechanical components.
Close-up view of a car's chassis with a mounted brake master cylinder and plumbing components.

We then set about making it look nice by trimming it and painting it: 

Close-up view of a metalworking machine with a circular metal part positioned, showcasing tools and machinery in a workshop setting.
Close-up of a mechanical component with several bolts and nuts, next to a circular object with a worn surface on a brown textured background.
Close-up of a mechanical component with welded metal and bolts, featuring a cylindrical section and a black top.
Close-up of a metal flange with a circular opening and multiple bolt holes, resting on a wooden surface.

Frank also included some DOM tubing to replace the 5/16″ threaded rod that came with the kit as this linkage was going to end up quite long. The DOM would be much stiffer and didn’t take much work to cut it to the correct length, thread it and attach a couple of short, threaded rods to each end. We will probably have this assembly plated before the too long. 

A metal threaded rod with a forked end, commonly used in mechanical applications.
Close-up view of a mechanical assembly showing a metal rod, couplings, and connectors within a machine or vehicle.

And here it all is installed. We attached the reservoirs directly to the cylinders for now as we don’t yet know where everything else is going. The Group B cars had them mounted to the strut bar but we are not that particular. We’ll see what seems the best location later in the build. 

Close-up view of a black brake master cylinder and reservoir installed in a vehicle's engine compartment.
Close-up of two brake fluid reservoirs mounted on a mechanical assembly inside a vehicle.
Close-up view of automotive brake components including a master cylinder and mounting bracket inside a vehicle chassis.

Next on the list is engine prep. Look out for that one soon.

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