Single system brakes

[ecoloney]

Friends,

I've seen two photos (1975 & 1976 year cars) where the front reservoir was capped. Thus, there was only a single brake line. I don't recall when ALL cars had separated brakes. Most disc/drum combo brakes require separate lines due to the difference in pressure/volume requirements of discs and drums.

So, what's the deal? How do they work from a single source? Why would the master cylinder have 2 reservoirs?

Thanks,

E Coloney

[Gunslinger]

I'm not sure I completely understand your questions, but beginning in 1967, Federal law required all cars to have dual master cylinders regardless of whether the car was equipped with disc or drum brakes. I have seen at least one '67 and a '68 Avanti still equipped with single circuit master cylinders, which I assume was due to small manufacturers such as Avanti Motors being granted an extension to many regulations, but they did have to comply, only by a later date.

I do know most, if not all, cars with disc/drum combinations used distribution blocks, sometimes incorrectly called proportioning valves, in the brake line fed by the master cylinder, which regulated the brake line pressure between front and rear brakes. True proportioning valves are adjustable...distribution blocks are fixed by their internal machining to give specific front/rear proportioning brake line pressure. Studebaker also went slightly different, or maybe it was Bendix since they supplied the brakes, but the rear hydraulic wheel cylinders were fairly small in inside diameter to further limit rear brake pressure. I found this out the hard way...when my '70 was rebuilt I discovered that the rear wheel cylinders were the same application as certain Jeeps...wrong!!! While the wheel cylinders were visually identical and fit exactly the same, as soon as they were installed and the car tested, when the brake pedal was touched the rear brakes would lock up. It was due to a larger inside diameter to the wheel cylinders allowed greater fluid volume and pressure to the rear brakes. My only solutions were either install the correct rear cylinders or install an adjustable proportioning valve...I installed the correct wheel cylinders. NAPA's application guide was wrong...just because something is an exact bolt-in doesn't mean it's the correct part.

I don't know if this answers your question, but I hope it does.

[ecoloney]

Gunslinger,

That's very helpful. I'd post a photo to help show what I'm speaking of except I don't know how to (post a photo)...

E Coloney