Brakes: Dual master cylinder and no brakes?

[Ron Dame]

I converted my Champ to a dual master many years ago, and keep up with fluid changes and maintenance.
Yesterday, I backed down a slope to turn around and the brake pedal went to the floor!
Thankfully, my E brake and God's will stopped the truck from going over a steep slope. After a few minutes of catching my breath and offering thanks, I pulled back up to a flat area, pumped the brakes a few times, and had a full pedal.Checking the fluid, the MC was full.

The MC is about 5 years old, as is the rest of the system, including Turner Brakes, hoses, tubes, cylinders, all is about 5 years old. I flushed the system (DOT4) back in the summer and had no issues since.

Two questions: WTF happened, and why did I not have at least once brake circuit working?

This was very very scary.

[RadioRoy]

Glad you are OK. That must have been scary, especially since your upgrades should have improved the brakes.

Some questions may shed light on the problem, if you do not mind answering them.

Does the truck have a power brake booster?

How long had the truck sat unused before you backed down the slope? Was this episode the first application of the brakes after some period of sitting?

How often do you back down a slope in this truck on your regular driving routine?

Does the truck have a hill holder?

Did you try pumping the pedal when you were out of brakes, out of control going down the slope backwards, or only after you stopped and got back up to the level or flat area?

I am wondering about the angle of the truck affecting something, or maybe an air bubble in some part of the system.

p.s. Whenever I have a nightmare about driving a car, it's always that the brakes don't work, especially going backwards. I can understand what a terrifying episode that must have been.

[JoeHall]

Were the front wheels turned sharply when this happened?

[jclary]

I’m just speculating here, but I suppose even dual chamber master cylinders have a common reservoir air vent somewhere on the cap. I’m wondering if the vent was clogged and the reservoir had developed a vacuum from cooling off while sitting? If so, that would explain why no brakes until frantic pumping broke the vacuum. Study the cap and find the vent and make sure it is clean of dirt or corrosion.

[Dwain G.]

I don't remember what year your Champ is, but I'm thinking '62? If this is an under-floor master cylinder it should have in-line check valves front and back. If it does, they might be defective.

[Ross]

My best guess is that one of the MC cups stuck and bypassed when you first hit the brakes. Several of the dual MC conversions I have seen do not provide enough pushrod stroke to operate the second half of the system when the first half of the system has failed for whatever reason. I would therefore further guess that if you opened any one bleeder screw on your truck you will have no brakes. I would be interested to hear.

In any event, if you don't find any cylinder or line leaks it is time for a new MC.

[JoeHall]

I had the exact same thing happen several times in a 56J, and it took awhile to figure it out. It was none of the suggested problems mentioned here so far. That's why I asked the question in post #3.

[r1lark]

I had the exact same thing happen several times in a 56J, and it took awhile to figure it out. It was none of the suggested problems mentioned here so far. That's why I asked the question in post #3.

Don't keep us in suspense Joe! What did you find when this happened to you?

[JoeHall]

Come to think of it, it happened in a 56J, and later in a 63GT. The 56J had my own version of 'big disc brakes' and the 63GT had Turner vintage from the 1990s. The 56J's steel braided lines were too short and, when the wheels were turned max, when backing up, would pull the inboard side caliper inward and push the piston in slightly. Then, the pedal would go to the floor and required 1-2 pumps before the piston would push the pads far enough to contact the rotors, then the brakes pedal would return to normal. It only happened when backing up and turning the wheels max, left or right. Longer caliper lines fixed it.

The 63GT had the same issue, but caused by a different problem: The Turner calipers reversed, right on left and left on right (possible, but hard to do unless you are an idiot). The calipers were positioned in front of the king pins, instead of behind, as Turner designed. When I first got the car, it had a notched, steel plate welded to the frame behind the steering bell crank, to limit max steering, right and left. I could not see any reason for it, so removed it. That's when the brake problem began: when turned max left or right, the calipers would kiss the frame, and push the caliper piston in just enough to require 1-2 pumps of the pedal before any brakes again, same as the 56J. When I consulted Jim Turner, he suggested the calipers were reversed, and re-installing them correctly fixed the problem. The idiot who originally installed them had also notched the frame where the calipers touched, in addition to welding the travel limiter behind the bell crank. WHO could possibly be that stupid? The car had all maintenance done at a Stude repair shop in Long Beach in the 1990s...

In addition to the above, I found several other things insanely done to the 63GT, for example the rear motor mounts were reversed, and front mounts in the wrong hole. Again, hard to do, but possible if you are an idiot. Also, the Turner adapter plate bolts on the spindles were loose, and one was 1/4" from even being seated. People who smoke marijuana should never be allowed to work on Studes. LOL

Back to the OP here, I am pretty sure he'll find something is 'cocking' the caliper(s) when the wheels are turned max.

[Ron Dame]

More info: It's a '63 with suspended pedals. Turner brake conversion 8-10 years ago. Brake fluid was flushed last year, brake inspection while doing wheel bearings this year, indicated no problems. I've never had any leaks in the system. No Hill Holder, no power booster. I've been driving the truck daily for the past two weeks. RadioRoy, no I don't normally back down a slope of this degree, but I do on occasion. The wheels were turned, but not sharply, and I've never experienced this on tight turns when the steering is against the stops. Pumping the pedal got me enough brakes, including the emergency brake, to stop. the more I pumped, the higher the pedal got until it finally was back at normal height, so got up to the top of the slope , popped the MC cover, and both chambers are full.

I'll check the reservoir cap vent, and if it's clear like I think it is, I'll get a new MC. That's interesting about the pedal stroke and push rod length not being enough to engage the secondary system. How could I check that?

Either way, it's out of service until I have this fixed, even though they fell OK now.

[JoeHall]

Since it occurred while backing down a slope, and the front wheels were turned, the front suspension likely raised up a bit, so it still may be something pushing a caliper out of kilter.

As for both axles losing brakes at same time, I noticed long ago, if it's a minor problem i.e. a seeping wheel cylinder or rear shoes real loosely adjusted, the pedal will go down but still activate the other end's brakes. If catastrophic, as in this case, the pedal will hit the floor with no sign of brakes whatsoever. It would be interesting to hear Jim Turner's comments on this.

[Ron Dame]

I suppose that is possible, I'llraise it by teh frame and turn. and check. I'd be surprised since Ive not had this in 8 years with this set-up, but you never know.

[WCP]

Regarding the flex lines for the Turner brake system, I recommend using Wagner #F98913 & 4 or equivalent. These are shown on chart #102 in my 1982 catalogue. They come as rt. and left with metal hose retainer brackets and are 16 5/8' OL. The brackets are simple to pry off as they are not needed on Stude applications. The hose mounts parallel to the rear surface of the caliper, loops forward by the kingpin and the back to the frame mount and has a rubber jacket over the section that may contact the kingpin, With this setup there is no way that the hose can interfere with the movement of the caliber, Hoses should never pass directly laterally to the frame mount. I have seen cars with hoses stretched to the limit on full lock turn!

[Ron Dame]

Jim Turner makes his own hoses with fresh rubber and good fittings. That's what I have, and I did confirm that the hoses pulling are NOT and issue. I have a new MC on order, but still surprised that the secondary system did NOTHING without a $#itload of pumping.

[Mark L]

As for both axles losing brakes at same time, I noticed long ago, if it's a minor problem i.e. a seeping wheel cylinder or rear shoes real loosely adjusted, the pedal will go down but still activate the other end's brakes. If catastrophic, as in this case, the pedal will hit the floor with no sign of brakes whatsoever.

Not to detract from the main topic, but I've also had the problem that Joe mentioned in post #11 on non-Studebaker vehicles with discs in front and drums in the rear. I found that as the drum brakes wore or were out of adjustment, when I pushed the brake pedal, I could momentarily feel some small resistance in the pedal as the front discs touched the rotors, but then additional pedal travel as the brake compensator shifted and the rear shoes continued to travel until they touched the drums. Once all pads/shoes were against their braking surfaces, only then did I truly get a firm pedal and any substantial braking action. Adjusting the rear brake shoes took care of the problem. I usually rotate my own tires, so on those vehicles, I just made it a habit to check and adjust the rear brake shoes every time I removed the rear wheels for a rotation.

If the emergency brake also activated the main rear shoes on those vehicles, I also found that I had to periodically loosen the emergency brake adjuster before adjusting the rear shoes, then re-adjust the emergency brake. Otherwise, the emergency cable interfered with the regular adjustment of the rear shoes, and adjusting the rear shoes alone was ineffective.

[Robert Crandall]

In the 1980's we had a 1970's Ford truck that would intermittently have no brakes. The problem turned out to be a master cylinder that failed at around 10 years of use.