Automotive Braking with one caliper out of four

[billiards_guy]

I debated with a friend tonight, and I need some unbiased input.

We were talking with a 3rd party that states that they only have one *working* brake caliper, of four. Assertion #1. (Basic four wheeled vehicle)

3rd party also states that there is no correction in steering needed, when braking, at any given speed. Assertion #2.

Party A, believes that a scenario exists where an improper alignment combined with a only single caliper working will result in no correction needed.

Party B, believes that regardless of any misalignment that a correction will have to be made at the moment of braking.

Sorry for wasting your time in this trivial matter, but would anyone mind weighing in? The more explanation the better, one party is a trained mechanic, the other party a physics dabbler.
Thank you in advance.

 

[Bystander]

Depends: single caliper braking single solid axle needs no correction; single caliper on prop shaft driving through a differential needs no correction so long as wheels don't slip; single caliper on leading or trailing point of a diamond shaped configuration needs no correction; any one corner of a conventional four-cornered rectangular configuration?

 

[davenn]

single caliper braking single solid axle needs no correction;

I'm not sure if you understood the problem ? sorry if you did

only one brake out of 4 working ... not an axle with only a single brake

I in my practical experience, on say, front wheels ( car), if only one is working, or is clamping harder than the other one, then the vehicle will strongly pull in the direction of the stronger working brake, which means you have to "oversteer" in the other direction to counter the brake pull

Not sure about rear wheel braking and the effect there, I haven't experienced that.
Suspect that it wouldn't be as dramatic as on front brakingD

 

[rcgldr]

Assuming a conventional rear wheel drive car, if only one of the front tires is braking, that will create a steering torque that would normally be opposed by braking at the other front tire, resulting in the car tending to steer in the direction of the braking tire, requiring the driver to compensate.

If a car has an open differential, that will allow the rear tires to rotate at different speeds without tire slippage, although the drivetrain (engine, transmission, driveshaft, ...) may change speeds. In this case, if only one rear wheel is braking that will also tend to steer the car into the direction of the braking tire, but the effect isn't as strong as single front tire braking. A limited slip differential would reduce this effect.

 

[sophiecentaur]

We'd need some more details but it sounds like driver, conditions and / or vehicle are non-standard (?). What speeds and what surface. What test was used to determine that only one calliper was working? Does "working" mean it squeezed the disc or does it mean that, despite high pedal pressure, all but one wheel could rotate?

 

[sysprog]

I'm not sure if you understood the problem ? sorry if you did

only one brake out of 4 working ... not an axle with only a single brake

I in my practical experience, on say, front wheels ( car), if only one is working, or is clamping harder than the other one, then the vehicle will strongly pull in the direction of the stronger working brake, which means you have to "oversteer" in the other direction to counter the brake pullD

That effect is what is relied upon when differential braking via 'toe brakes' is being used to steer aircraft when they taxi into position on the airfield.

 

[Ranger Mike]

Brake caliper not working on the rear brakes should not cause steering overload requiring steering correction. Typically dirt track race cars have a brake fluid shut off valve that kills the right front brake caliper ( left hand turn race track). The driver shuts off the right front brake when the dirt track condition makes the right front too overloaded. The left front snap turns the car. You WILL notice the brake pulling and have to correct with the steering wheel as the steering will want to pull the tires away from neutral ( going straight ) direction.
never do this on pavement on a standard production car.

 

[jrmichler]

I can tell you from experience exactly what happens when the brakes fail on one side of a car. These were drum brakes, and the brake cylinders had a habit of rusting and locking the pistons in place, with the result of no braking on that wheel. When a rear brake failed, I barely noticed. The car was a $60 rustmobile, so I ignored what I barely noticed. Then the front brake on that side failed. I noticed that when I stepped on the brakes, and the car suddenly swerved left. A hard correction on the steering wheel, combined with easing off the brakes kept me in the traffic lane. Honing all brake cylinders and new piston seals fixed it.

On another occasion, I had one brake fail during a night landing in an early model Beech Bonanza. Airplanes have separate brake systems for each of the two main wheels. The solution was to steer hard right, and brake left just enough to keep it straight. The passengers did not notice anything until after it was parked and I told them.

 

[sophiecentaur]

3rd party also states that there is no correction in steering needed, when braking, at any given speed. Assertion #2.

I am surprised that a 'trained mechanic' would be experimenting with brakes in that state at all. Isn't the rule that any brake fault should sorted out? Even if the experiment were off-road there are unnecessary risks involved.
I remember when a number of productioncars had double braking circuits - each diagonal pair being supplied by one of the circuits. That implies something.

 

[Ranger Mike]

up until the mid 1960s the prodcution cars had a single master cylinder. With popularity of the disc brakes (usually on front only) two separate master cylinder reservoirs were used. One for the disc front and one for the brake drum/shoe rear brakes. This was a safety feature even though differrnt pressures were required to active the two types.
in racing you never mess with safety items..too risky.