Technical Weird Brake Problem - Can anyone recommend a good dual drum/drum master cylinder?

KEY WORDS - BRAKE PEDAL RETRACTING -

Not - MC PISTON RETRACTING SPRING -.

Without the BRAKE PEDAL ASSIST SPRING, the push-rod would continually beat against the MC PISTON (especially on rough road), causing annoying rattles and possible damage. This is not what is causing the brake drag. The weight of the un-sprung pedal linkage cannot overcome the return pressure of the MC PISTON RETURN SPRING (internal). I understand what you are saying but this is not the cause of the OP brake drag problem.

Correct on the clutch anti-rattle spring. The un-sprung linkage weight/movement (depending on design) may not cause the T/O BRG to actually spin (resting foot on pedal or incorrect adj would do that) but will play havoc on the pressure plate fingers and bearing face.

 

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PROPORTIONING VALVE (PPV) or RESIDUAL PRESSURE VALVE(S) (RPV)?

 

The actual problem was ID'd many posts ago.

 

From the website.
Weighing in at only five pounds, the MCPV-1 aluminum master cylinder has all the features of a modern braking system in one master cylinder. It has a double-adjustable proportioning valve, removable metering valve (for 4-wheel disc brake cars), stop light switch port, larger capacity (1-quart) and a smaller size than a conventional iron master cylinder. It's approximately the same size as an iron Corvette master cylinder, only much lighter. The MCPV-1 has two circuits: a front circuit with a metering valve for disc front/drum rear brakes, which is removable for 4-wheel disc brakes and a rear circuit that has the double-adjustable proportioning valve and a maximum rear pressure adjustment. The proportioning valve controls the brake pressure between front and rear brakes, while the rear pressure adjustment controls what the maximum pressure is to the rear brakes. Available with a polished finish.

 

Hmmm...I always thought proportioning valves limited pressure rise time. Never heard of one that regulated pressure. Interesting.

 

An OEM VALVE controls cut-in pressure (knee-point) and rising pressure while an ADJ ANTI-BIAS VALVE (as incorporated into this design) has an adj knee-point and you are on your own after that.

Want to get hurt?

EXCERPT FROM C99 INSTRUCTION SHEET -

It's pretty and serves the same purpose as a freestanding anti-bias valve but hides the feature.

And I don't see any reference to a RESIDUAL PRESSURE VALVE for the drum circuit.

 

One thing being overlooked here is the fact that by their very design an under floor brake pedal assembly at rest exerts more pressure against the brake master cyl. piston than does a hanging pedal arrangement. The O/P needs to check EVERYTHING from the brake shoe retracting springs, through the wheels cylinders, to the brake pedal retracting spring to find the cause; hopefully, he's done that already...

 

Sounds to me like you have an M/C piston that doesn't move freely. If you are continually adjusting for more freeplay, it is an indication that something is moving in the master cylinder OR the linkage, taking up that slack that you are continually adding.

"Pedal height assist" sure sounds like a pedal return spring to me. Your young varmint experiences in early models indicates that those vehicles had weak or missing pedal return springs and/or pedal bumpers.

This has now become entertaining to those of us who understand reality versus supposition.

 

No, what I find entertaining are endless threads concerning "brakes don't work, what do I do" being the problem(s) that are never correctly diagnosed/answered.

You would think at some point most would actually realize how hydraulic brakes work and correct the problem(s).

Some of these posts are frightening considering you may encounter one in traffic.

 

So to summarize, you are entertaining yourself.

 

Actually, yes. Reading posts from someone like you makes my day. It demonstrates how ignorant some people can be.

If your reading comprehension level was just a little more advanced and you could actually cipher what has been posted within this thread, you will find this was suggested many posts ago.

Bad day or just retaining water?

 

There are RPVs internal, I had to add those (5 pound in back and 2 up front if memory serves). Hard to make out but this pic is from the rear facing forward. That CPP chrome M/C I posted is on the right alongside the Wilwood clutch master with a remote reservoir on the firewall. The brake M/C is filled through the floor. RPVs are visible in both circuits. Been years now and the M/C has performed as expected.

Here is a pic of the style return spring I used on both the clutch and brake pedals. Practically invisible once installed, work great and very sanitary.
The aluminum attaches over the end of the M/C (set screws to secure) and the spring around the rod seats inside the cup. I can't for the life of me recall where I bought those but they work slick.

 

First, that is a beautiful build. You are an artist Sir ...

You misunderstood the original post. The VENDOR (in it's adv) , made no mention of the MC having an RPV (drum circuit) or if one had to add an external valve or use another method.