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master cylinder location

D

DIM

Member
Does the master cylinder have to be located above the wheel cylinders for the system to work right
 
well how do you expect the fluid to run uphill to the wheel cyl's if the master is lower? never saw one lower yet. be fun bleeding too. no gravity there.
 
NO many of the older cars and trucks had the master cylinder under the floor board so they would be below where the wheel cylinders where. Like on say a 1950 Chev pick up. where you had a place in the floor you took out to fill the master up
 
Now OLD if you think about the old chev the master cylinder was just a little above the wheel. Not much but a little. Hope this finds you finding your goats alive and things looking up.
 
Doesn't have to be, but the reservoir does have to be highest point or it will try and drain back over time when brakes are released
 
That might be true some of the time depending on the load in the truck LOL'
As for the goats already found one dead and have not found any of the other 3.
 
Hello DIM,

Old style drum and shoe brakes have a residual presure of 7#. Location of the master cylinder does not matter!

Guido.
 
(quoted from post at 14:51:31 01/01/16) Now OLD if you think about the old chev the master cylinder was just a little above the wheel. Not much but a little. Hope this finds you finding your goats alive and things looking up.
Click to expand...
I went out and looked at a 48 Suburban and 53 sedan. Suburban looks level, and the sedan looks like the master cylinder is lower. But I don't believe the elevation makes any difference. Brakes are a closed hydraulic system, if the wheel cylinder cups would hold pressure, they will hold air under a little vacuum. Try draining a wheel cylinder by unhooking the hose and sticking it in a cup of brake fluid. It won't drain. On the positive side, if the wheel cylinders are high it should make bleeding much simpler. You don't have to force the air down hill, you just have to encourage it to go up.
 
It is actually easier to bleed because bubbles in fluid go opposite of gravity. Like on a motorcycle removing the master cylinder from the handle bars and holding it below the caliper to bleed.
 
(quoted from post at 16:13:38 01/01/16) Hello DIM,

Old style drum and shoe brakes have a residual presure of 7#. Location of the master cylinder does not matter!

Guido.
Click to expand...
I'm always surprised when Guido is right!
 
Ya,on Car Talk one time,they were telling about a guy who had both calipers off at the same time to rebuild them and got them back on the wrong sides so the bleeders were at the bottom. He tried to bleed them,took the car to a shop where they tried to power bleed them,nothing worked until one mechanic noticed they were on the wrong sides,so upside down.
 
I think it does.

Old is also right that the early master cylinders were under the floor boards, but I bet they were still above the top of the wheel cylinders.
 
My master cylinder is about the same level as the brake cylinders but the brake lines go higher going to the master cylinder. Master cylinder and all wheel cylinders were rebuilt and all brake lines new. Setting for a short time the fluid returns to master cylinder, take 3 or 4 pumps to get brakes.
 
My jeep (1957) and my 51 GMC 3/4 PU, and my friends 34 ford, and a 46 Chevy I had, all are lower than the cylinders. The 34 is a hotrod with Corvette front disks, and ford 9" rear drums. Jim
 
yes, i know that. but when u leave the bleeder open with the master lower there is no way that the fluid will leak out of wheel cyl. on its own. with the master higher... u can fill it and leave the bleeders open and come back later and will see fluid dripping out of the wheel cyl's.
 
Hello DIM,

Adjust the brakes, bleed ALL the air out of the system. No pumping required!!
Chrysler school on brakes 1964

Guido.
 
What happens is the return springs squeeze the fluid back into the master and the shoes away from the drums. Takes a couple pumps to push the shoes back out.
 
I have bleed brakes and there is no adjustment on the brake shoes and shoes like new only 350 hrs on vehicle
 
okay, the answer to your question is YES. i did some digging and the master cyl. is mounted most time as high as possible. when that is not possible a residual valve is installed in the system to prevent the fluid from running back to the master cyl. when this happens you must pump the pedal to get the fluid back to the wheel cyl's or calipers. now you know the rest of the story.
 
Every Harley with hydraulic drum brakes [ and disc] has the master cyl, below the wheel cylinders. .And as mentioned the location on many street rods. Gravity is irrelevant.
 
the lines being higher than the master cyl. is part of the problem. lines connect to btm of master and never are looped higher than the cyl.the master cyl. fluid compartment is the highest point in the brake system. the fluid is draining back into the master which causes you to pump the brakes to get the fluid back to brakes. that is where the residual valve comes in ... to stop this and keep a bit of pressure on the line.
 
Hello DIM,

I assumed the master cylinder has the proper clearance.
If all was right, no pumping required
Guido.
 
In the master cylinder down at the footboards. No residual valves required. Wheel cylinders are higher. Plus I'm not going to argue AS IT IS LIKE THAT ON A WHOLE LOT OF STREET RODS AS OTHERS POSTED. oops
 
Hello rustred,

The answer to his question Is a resounding NO! A have some questions for you though.
1: Do you know what a residual pressure valve is.?
2: Do you know what is its purpose.?
3: Where is it located.?
4: Is it even part of the braking system.?
Most importantly: could you answer all the above questions on a multiple question test?

Guido.
 
well smart man ... what is your reasons for saying a resounding NO!???
i just told you what the residual valve is. and the system will not work properly if the master is lower than the wheel cyl's. because the fluid will be draining back to the master.
so whats your best answer here? besides a big NO! where is the facts?
and it would be nice to know what vehicle DIM is working on.
 
(quoted from post at 20:23:49 01/01/16) Hello rustred,

The answer to his question Is a resounding NO! A have some questions for you though.
1: Do you know what a residual pressure valve is.?
2: Do you know what is its purpose.?
3: Where is it located.?
4: Is it even part of the braking system.?
Most importantly: could you answer all the above questions on a multiple question test?

Guido.
Click to expand...

I know the answers to all of those.
Can I play?
 
All Right. I decided to weigh in on this. I went out and looked at my 51 Chevy 1/2 ton and the answer is no. The master cylinder does not have to be above the wheel cylinders.
Old had it correct in the beginning of this thread.
Richard in NW SC
 
A master cylinder is just a manual activated hydraulic pump for a closed circuit system with a spring loaded return. The supply has to be above the pump. The out put can be anywhere. Air can only get in from bad seals or openings in the system. This system could be used to raise a flag on the roof.
 
Hello rustred,

I did some digging of my own. If you look close you will see two numbers. 64 and 11. First number is the year, second number is the month. That is what I was doing November 1964. They call us technicians even then. Up to 1965 , that is the year I left the dealership, I did 90% of all brake work,

Guido.
a210269.jpg
 
(quoted from post at 19:46:45 01/01/16) the lines being higher than the master cyl. is part of the problem. lines connect to btm of master and never are looped higher than the cyl.the master cyl. fluid compartment is the highest point in the brake system. the fluid is draining back into the master which causes you to pump the brakes to get the fluid back to brakes. that is where the residual valve comes in ... to stop this and keep a bit of pressure on the line.
Click to expand...
Not arguing, I just don't understand how brake fluid could drain downhill into a master cylinder unless there was an air leak or air in the brake fluid. Vapor pressure of brake fluid has got to be pretty high, it wouldn't break into a vapor until well over 30 ft of elevation change.
 
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