Technical Some brake questions !!!

All brake system is new .
Master , wh cylinders , calipers , br. Hoses and lines .
I will test this to ensure they will work or dont work !!! This includes in the rain !!!
I have to try , should have the car back together in a couple if weeks and will post my happenings again then
Joe Mac

 

Of all the points brought out I still don't see how master cylinder size effects front to rear brake bias.

 

It doesn't, it's the fact that it doesn't match the calipers on the front that is the concern.

 

Somewhere in this , does the weight of the vehicle play a factor ???

 

Read post 26

 

It does because there is a force applied ratio between the master cylinder bore and the size of what ever cylinder it is feeding. For example, if the M/C bore is 1 sq in (not diameter) and the cylinder it's pressure is applied to is also 1 sq in, the force will be the same PSI. However, if the wheel cylinder has a 2 sq in area, the force applied by the M/C will be twice the force when applied by the wheel cylinder piston to the shoes/pads. You could change the M/C bore, not the wheel cylinder, and get the same effect.

Okay, if we are in agreement so far, now add a wheel cylinder/caliper bore of a different sq in area into the system and you can see they will be applying different forces to what ever they are pushing against.

That is the simplest and most basic example. When you add into the mix such things as drum or disc diameter, lining area of shoes/pads, friction coefficient, tire diameter and tread characteristics and weight transfer during a rapid stop, just to name the more conspicuous factors, you can see it gets real complicated real quick.

EDIT: but that also explains why most well engineered production vehicles typically have greater capacity brakes on the front where weight is usually greatest, static and especially dynamic (when stopping). They have more work to do and, in addition, in a panic stop, it's far better to have too much front brake than too much rear brake force. If not, be prepared to suddenly see what was beside you or in back of you (likely both) just a second or two before.

 

Read post #36.....

 

This is exactly what i was getting at. You just explained it. That's far better than the lame, no explanation response i gave!

 

I'm not sure what you are getting at here....Gimpy didn't say the bore size of the master has anything to do with brake bias, just that components need to be matched to one another. Ray posted an explanation above>

 

The complexity of all the variables is what has resulted in a relatively simple solution (the idea, not the hardware) that is applied by most new vehicle manufacturers, but is decidedly not HAMB friendly. That is the anti-lock brake systems that prevent wheel lock up within a wide range of variable operating circumstances. Far more effective than a mere proportioning valve.

 

Exactly.

 

Guess I will have to go back to school and get my engineers degee LOL.
I dont know if this set up is going to work or not , but I am going to try ..
I am getting an education from you guys here , and appreciate that ..

 

Not to be a smart ass or anything ..
Where does line size , play into this equation?
Would say running 3/16 line to front and 1/4 inch line to rear ??

 

The issue is that the old Ford master cyl (being larger diam piston than GM master cyl) will produce *less* force on the front brakes, for a given brake pedal applied force. So it may be that the rear brakes are able to lock up sooner than would be best. The larger master cyl bore has plenty of volume, that is not the problem. It is the psi in the lines that does the work against the caliper piston or wheel cylinder piston. The only way to really know is to do some brake tests and see when lock-up occurs and where.

Here is the math. A 1-1/8 master cyl has 0.99 sq in of area. A 3/4 master cyl has 0.44 sq in of area. So if a pedal has a 5:1 ratio (just used for ease of math), a 100 lb force on the pedal produces 500 lbs force acting on the master cyl area. PSI in the line = pounds/sq in area = 500 lbs/.99 sq in = 505 psi for the 1-1/8 master cyl. Same 500 lbs/.44 sq in = 1136 psi for the 3/4 master. The smaller master cyl produces more line psi for the same pedal force applied by your foot.

I have no idea what the optimum clamping force for the Chevette calipers is in the current modified brake parts setup. A larger diam piston in the caliper would produce *more* clamping force. Just like a smaller wheel cyl diam will produce *less* force on the shoes in a drum brake application. Optimum braking is when the rears lock up just before the fronts.

The best way to know if the OP's setup is good or bad is to have some real brake test results. Then we can all discuss what the best way to fix that is. It may be that putting Ford drums back on the front is the best fix, and of course is also best for traditional concerns. But I am not going to say that just because the parts are mixed, means the brake system is not capable of working good and producing acceptable braking results. Not until we have some actual test results, the proof is in the results.

 

Line size is irrelevant. In a hydraulic system, pressure is equal in all measured locations.

Line size would only govern flow, and 3/16" is plenty.

 

Line size does not have an effect. It is the psi in the lines that does the work.

 

The old adage is "pressure is pressure, and volume is volume! don't confuse the two"
It is "Clamping Pressure" that causes brake torque, Volume is only needed to take up clearances

The hydraulic pressure is equalized everywhere in the system [even on the walls of the tubing]
Bias is where hydraulic pressure is converted to clamping pressure by changing the Fr/Rr piston area sizes [wheel cylinders] The hydraulic pressure remains the same.

So It's not really a flow issue!
But a 3/16 line can run higher pressures than 1/4" so for extra safety stay with the 3/16"

Back onto the subject of explaining Bias [on your situation] . Because the front swept volume is smaller on your callipers ,you will need higher line pressures to compensate [pedal effort]
This higher line pressure which is equalized everywhere in the system will also go to the rear brakes causing premature lockup [especially with low traction conditions]

Altering the M/C size to match the callipers only raises line pressure without the need for increased pedal pressure [you will still get too much rear brake bias]

And don't be fooled into putting a "patch-up" proportioning valve in the system. They do NOT proportion at all, they limit the maximum pressure downstream.
Proportioning valves do not Balance the brakes [and shouldn't be used for that purpose]

Your best [and less invasive] solution would be matching the front brakes to the rears.

 

Hey Guy's Thanks for all the information and the education !!!!
I am going to try this set up and see how it works out , perhaps play with it a bit .
I do have extra front spindles backing plates and drums if all else fails .
Should have everything back together in a few weeks and will update with successes or failures and pissible fixes then .
Thanks Joe Mac

 

With the caveat that if you switched to 1/8", 3/32", or 1/16" brake lines, flow could be reduced enough to slow brake reaction time!

 

Or Cooking Oil for brake fluid
No Joking here, Cooking oil is what they use as hydraulic fluid in "computor gaming simulators" because they run indoors [and the consequences from failure are easier on the carpet]

 

Just be careful.
Your northern hemisphere winter should show up the flaws at relatively slow speeds

 

Thats what I was thinking too LOL
will tell the truth right quick what is locking up first !!!

 

Don't test on the road. Find a big, empty parking lot.

 

Brake tubing size does affect velocity of the fluid that is moving through the lines. For a given fluid pressure, smaller tubing increases fluid velocity as the same volume of fluid is going through a smaller space in (approximately) the same time span.....therefore it has to travel faster.......

That's the reason your garden hose squirts farther when the nozzle is more restricted or the hose itself is squeezed. Water pressure hasn't changed, only the area of the outlet.

 

I’ve said it before, less than a teaspoon of fluid “flow” in your average brake application


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Yep...but volume was not the point of the physics illustration.

 

I love physics!


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The reason a garden hose trickles water, is the volume is restricted upstream [at the faucet]causing a drop in pressure When the nozzle is used to restrict flow it restores pressure in the whole hose, equalizing with the pressure upstream from the faucet.

Not a good example to use on brakes [maybe to explain low idle oil pressure due to excessive bearing clearances]

"pressure is pressure, and volume is volume! don't confuse the two"

I've been told to "stop" on many occasions before I spill less than a teaspoon of fluid “flow”
[Would that be considered a "brake application" or "heartbreak application"?]

Is that physics or physical?

 

Don't think I am confused about the difference. I don't accept your rejection of my analogy of the water hose........my example supposed an unrestricted flow at the 'faucet' flowing through a hose (common scenario) with no further restriction passing a volume of water through the typical 5/8" ID common garden hose.....as compared to adding a restriction at the end of the hose (adjustable nozzle or pinching the hose) that reduced the useful diameter from 5/8" to something of less area.

That would result in the constant pressure moving a constant volume at a greater velocity to pass the volume through a smaller orifice. The restriction causes the fluid to accelerate....does it not?