Does the brake closest to Master Cylinder do slightly more braking?

[WobblyElvis]

During light diving/braking I find the front left rotor is slightly warmer than the right. [160F vs 150F]
All things being equal, is it possible that the left brake [being closer to the master cylinder] does a little more braking by being the first brake to apply?

 

[DriveHard]

During light diving/braking I find the front left rotor is slightly warmer than the right. [160F vs 150F]
All things being equal, is it possible that the left brake [being closer to the master cylinder] does a little more braking by being the first brake to apply?

I don't see how...it is a hydraulically controlled static system. Pressure applied from the master should be equal throughout the system as there is no flow.

 

[WobblyElvis]

What about this.....
The mass of the fluid is greater in the longer brake line and the resistance to flow is greater. This is not really a static system. The caliper pistons have to move out, although very little, in order to touch the pads/rotor. Would the left not apply first?

I am not saying this could account for a 10F difference it rotor temp, I am only interest in the physics.

 

[brianl703]

Wouldn't a difference in braking cause a pull to the side with more braking?

 

[Astro14]

You’re assuming flow.

There really isn’t much flow. The actual volume moved is tiny.

So the effect of flow is tiny.

And the pressure will balance to be equal, so that tiny flow variance will ultimately have no effect.

The difference in temperature isn’t statistically significant.

Go do some hard braking. Re-measure temperature. If it’s more than a few degrees off, you have a caliper, pad, or rotor problem, not an undiscovered hydraulic effect.

 

[SWS]

I suggest that your comment “all things being equal” needs reconsideration.

I have observed one front disk being much hotter than the other - the problem: The caliper slides were binding on that side. Interestingly, there was no ‘pull’ to one side.

I have also casually sensed a small difference in front disk temperatures that puzzled me until I knelt down next to each front wheel with the engine running after a 40 mile trip in the summer.
When the radiator fans turned on, there was MUCH more heat blowing past the hotter disk and below the wheel well compared to the other side. For your 10 degree difference, perhaps radiator & engine hot air flows are largely responsible.

 

[FowVay]

Think of the hydraulic line as being a solid rod. Whether the rod is 10" long or 10' long is irrelevant. Pressure applied at the input side will equal the pressure received at the output side. This is all assuming you have no compressible gas in the hydraulic line in which case you have to compensate for the compression of the gas (air in the line).

To answer the question... No.

 

[kschachn]

When the radiator fans turned on, there was MUCH more heat blowing past the hotter disk and below the wheel well compared to the other side. For your 10 degree difference, perhaps radiator & engine hot air flows are largely responsible.

My old Sienna is like that due to the transmission cooler located in the left wheel well.

 

[Number_35]

Very interesting discussion in any case!

To use an electrical analogy, if the calipers were operated by electric motors, and wires of equal gauge ran to each caliper motor, the motor at the end of the longer run would receive less voltage, and thus would operate slightly differently. It would draw a little bit more current to compensate for the reduced voltage.

So back to a hydraulic braking system ... if the steel lines were the same length but a longer rubber brake hose was used for the longer run, some hydraulic force would be lost in expanding the hose slightly, and there would be less pressure on that caliper's piston.

This is a thought experiment only - I suspect in real life it would make no measurable difference. It's fun to think about these things though.

 

[DriveHard]

Very interesting discussion in any case!

To use an electrical analogy, if the calipers were operated by electric motors, and wires of equal gauge ran to each caliper motor, the motor at the end of the longer run would receive less voltage, and thus would operate slightly differently. It would draw a little bit more current to compensate for the reduced voltage.

So back to a hydraulic braking system ... if the steel lines were the same length but a longer rubber brake hose was used for the longer run, some hydraulic force would be lost in expanding the hose slightly, and there would be less pressure on that caliper's piston.

This is a thought experiment only - I suspect in real life it would make no measurable difference. It's fun to think about these things though.

If wires of equal gauge were run, but nearly ZERO current was flowing, what would they test at the end of their runs? That is the situation we are dealing with. There is no return path for the hydraulic fluid. Going back to your electrical analogy, there is no ground wire...there is only potential.

Yes, for a small instant, you could calculate the flow rate based on the movement of the brake pistons, but as soon as they make contact, and your are braking, it is once again a static system.

Energy will be lost in the rubber hose as you apply pressure, but not for transmitting that pressure to the brake cylinders. The change to steel braided hoses with stiffen the system, but not change the force you apply to the brake cylinders, as there is no real flow in the system.

 

[hrv]

Wow this one may go 10 pages too...

 

[WobblyElvis]

A diagonally split brake system would further complicate things. Almost all vehicle are now this way.

As for the fluid being like a steel rod, one rod being longer than the other would have more mass. Fluid leaving the master cylinder has a choice of pushing one rod of the other, the shorter rod being lighter, would be the first to move and more fluid would be sent in that direction at the beginning of brake application. I am not talking about a lot of fluid.

Caliper pistons are retracted by a square section seal. It would follow that the piston furthest from the master cylinder would retract slower as the deformed seal has to push a greater volume of fluid in the lines back towards the reservoir.

 

[DriveHard]

A diagonally split brake system would further complicate things. Almost all vehicle are now this way.

As for the fluid being like a steel rod, one rod being longer than the other would have more mass. Fluid leaving the master cylinder has a choice of pushing one rod of the other, the shorter rod being lighter, would be the first to move and more fluid would be sent in that direction at the beginning of brake application. I am not talking about a lot of fluid.

Caliper pistons are retracted by a square section seal. It would follow that the piston furthest from the master cylinder would retract slower as the deformed seal has to push a greater volume of fluid in the lines back towards the reservoir.

If I pushed two steel rods of equal diameter into your chest slowly, could you tell me which one was longer? Could you measure a difference in force (hint, the answer is NO).

It is a NEARLY static system, the flow rates are negligible.

 

[Chris142]

If the system is properly working and no air in the lines the distance from the master to the caliper won't matter.

 

[Jetronic]

I suggest that your comment “all things being equal” needs reconsideration.

I have observed one front disk being much hotter than the other - the problem: The caliper slides were binding on that side. Interestingly, there was no ‘pull’ to one side.

I have also casually sensed a small difference in front disk temperatures that puzzled me until I knelt down next to each front wheel with the engine running after a 40 mile trip in the summer.
When the radiator fans turned on, there was MUCH more heat blowing past the hotter disk and below the wheel well compared to the other side. For your 10 degree difference, perhaps radiator & engine hot air flows are largely responsible.

There's no pull on a 1 piston caliper as long as the piston is free to move. The free to move side of the caliper simply does more work.

 

[Number_35]

If wires of equal gauge were run, but nearly ZERO current was flowing, what would they test at the end of their runs? That is the situation we are dealing with. There is no return path for the hydraulic fluid. Going back to your electrical analogy, there is no ground wire...there is only potential.

Yes, for a small instant, you could calculate the flow rate based on the movement of the brake pistons, but as soon as they make contact, and your are braking, it is once again a static system.

Energy will be lost in the rubber hose as you apply pressure, but not for transmitting that pressure to the brake cylinders. The change to steel braided hoses with stiffen the system, but not change the force you apply to the brake cylinders, as there is no real flow in the system.

That was just me doing a thought experiment, which woks best when taken to extremes - let's assume a situation which would never happen in real life, like one brake line being 1 m long, and the other being 1000 m long, etc.

I agree with what you say - once the short-lived lag caused by the rubber hose being expanded ends, the pressure at each cylinder would be identical, regardless of length.

 

[Jetronic]

That was just me doing a thought experiment, which woks best when taken to extremes - let's assume a situation which would never happen in real life, like one brake line being 1 m long, and the other being 1000 m long, etc.

I agree with what you say - once the short-lived lag caused by the rubber hose being expanded ends, the pressure at each cylinder would be identical, regardless of length.

And the reverse is true when releasing the brake pedal; the caliper that activated first (milliseconds before the others) will release first aswell

 

[DriveHard]

That was just me doing a thought experiment, which woks best when taken to extremes - let's assume a situation which would never happen in real life, like one brake line being 1 m long, and the other being 1000 m long, etc.

I agree with what you say - once the short-lived lag caused by the rubber hose being expanded ends, the pressure at each cylinder would be identical, regardless of length.

Well wave propagation in hydraulic fluid is about 1500 m/s so...about 2/3 of a second lag? A fully rubber hose will slow this, but most brake lines are steel, and only rubber at the ends.

 

[4WD]

Wow this one may go 10 pages too...

Nearing page 2 with 17 hairs split so far

 

[DriveHard]

And the reverse is true when releasing the brake pedal; the caliper that activated first (milliseconds before the others) will release first aswell

OMGOsh...

This is as good as a static system...those pistons move hundredths of an inch, the fluid displaced is drops. There is nearly ZERO impact of fluid motion on the system in the realm of how fast you can push the brake pedal. Now, ABS might complicate things, but it is still VERY low flow, and now more like AC current than true fluid flow.