67 Brake Master Cylinder Retrofit

A single-circuit to dual-circuit upgrade for old cars is a fairly common conversion. The conversion provides no additional performance, but does provide a level of safety. In a single-circuit system, if a brake cylinder fails, you will lose pressure in your entire braking system. In a dual-circuit system, you will lose pressure in only half your braking system. The benefit is obvious.

As I pointed out previously, this is a common upgrade for many older cars (my mom's 65 mustang is next). So you can search on "single dual master cylinder" and find quite a few hits. Many of the issues and solutions are the same no matter what marque you own.

There are two options available for upgrading your single-circuit system to dual-circuit:

The first solution involves using a 67-style dual-circuit master cylinder and brake reservoir. Originally, this was a one-year part - as the braking system was changed in the 68 model year. ATE now reproduces the 67-style master cylinder. It is a fairly low-production item, so the cost is relatively expensive compared to a single-circuit reservoir or later dual-circuit reservoir which enjoy higher production volumes.

Another solution available for VW is the use of a '71 or later master cylinder using an adapter kit (shown at right). This is available from Wolfgang International for around $40 (part #2611011). The benefit of this method is that later master cylinders is that they are cheaper than the 67-style master cylinder, and they are readily available at most auto parts stores (in metropolitan locations of course). If you need a master cylinder in the future, it will be easier to find/replace than if you go with an earlier style master cylinder.

If you were going this route, and couldn't find a 67-style brake fluid reservoir, you would be on the lookout for a rabbit reservoir. Prices on these are going up because they are harder to find (as Rabbit's are harder to find in junk yards). If you don't mind paying a little extra, Wolfgang International sells a "Rabbit-style" reservoir for nearly $50. But you can probably find a Rabbit reservoir for around $15 at a junk yard near you.

Nate's article, linked at the top of this page, describes using an early 70's Volvo brake fluid reservoir (160 and 1800 series). The benefit is that it is not "tilted" as is the Rabbit reservoir. But the similar problem here is that you'd be lucky to find an early Volvo in a junk yard these days.

This is the old single-circuit master cylinder and brake fluid reservoir from my 65 Bus:

I put this in when I was in high school in 1984 - although it hasn't seen very many miles, the rubber plunger cover is shot, and it is very crusty.

When I started this side-project, I was struck by the cost of a 67-style master cylinder. ($145 or more) So I decided to get an adapter from Wolfgang International and bought a '71 (or later) master cylinder on eBay. Both cost be around $65.

Some time passed when out of the blue I lucked into finding a 67 master cylinder with reservoir. (applause) However, my luck ran out, when I broke the reservoir's plastic nipple trying to remove the reservoir from the master cylinder (boo):

[The ATE style reservoir should be removed by pulling straight up. That's easier said than done. In trying to remove the reservoir, I pulled as hard as I could, but I couldn't seperate the reservoir from the master cylinder. At first I soaked the parts in PB Blaster. But after a month, that didn't change a thing. I then tried putting a little extra pressure on one side, that side broke free, and the other side snapped. (Insert obscenities here.) This was a real bummer - there's nothing more depressing that breaking an original and irreplaceable part.]

Here's a closer look at the plastic nipple and how it fits in the rubber grommet:

In retrospect, I should have tried to cut away at the rubber grommets that held the reservoir nipple in place. Though it would have been a long difficult task due to the minimal clearance, and the fact that the nipple is well below the surface. Notice how the end "hooks" into the bottom of the grommet to ensure a tight fit.

My luck turned around though. On eBay I won a used 67 master cylinder with a very nice FAG reservoir. Note the difference in this reservoir - it is much easier to remove because it uses rubber nipples (grommets and nipples are one piece):

I am not sure what the reservoir came off of, but I assume that this is a replacement reservoir for the '67 style reservoir. It fits and is in good condition (which is the important point).

Here's a closer look at the nipples:

After reading some discussion on the VintageBus list, I decided to invest in the ATE '67-style master cylinder:

[The main benefit of using a '67-style master cylinder is that the brake pedal pressure will not be as hard as a later master cylinder. I would also assume that the ATE is a little higher quality than the brazilian Varga. You can get these through vendors such as Ronnie @ Old Volks.]

Here's a comparison of the two master cylinders (the '67 style ATE is on top, the '71 style Varga is on the bottom of the picture):

Notce how the the openings for the reservoir are offset. If the master cylinder were used in this manner, the plunger would be too long, and the reservoir would be moved too far forward.

And here is a side-by-side comparison of the two master cylinders with the wolfgang adapter attached to the '71-style master cylinder:

Notice how the aluminum collar moves the master cylinder back to align it with the '67-style master cylinder. The only difference being the location of the rear circuit line.

Here's a close-up of the wolfgang adapter on the '71-style master cylinder:

Obviously, the benefit of using the adapter kit and '71-style master cylinder is if something were to happen to the master cylinder on the road, you could easily find a replacement - which is not the case with the '67-style. (That is, unless you have an extra $145 for a spare master cylinder and take it along with you at all times.)