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Master Cylinder PSI


 
Edited

I'm having trouble getting enough hydraulic pressure to the rear wheels. Only enough pressure to deploy one shoe at a time ????? I've purged & bled all lines.
So I'm going back to basics & testing the new master cylinder. My calculations say that the 1" bore should produce about 127.4  PSI. Can anybody
verify that fact?

Thanx, Skip D


James Dlapa
 


Did you replace your wheel cylinders, they very well may have accumulated rust  restricting movement. 


On Mon, Jul 27, 2020 at 3:15 PM Tilden Drinkard <TILDENLD@...> wrote:
I'm having trouble getting enough hydraulic pressure to the rear wheels. Only enough pressure to deploy one shoe at a time ????? I've purged & bled all lines.
So I'm going back to basics & testing the new master cylinder. My calculations say that the 1" bore should produce about 166 lbs PSI. Can anybody
verify that fact?

Thanx, Skip D


Butch
 

My guess is, you have a stuck piston, a bad rubber line or the shoes are not properly adjusted. You do know that each shoe, on each wheel, must be adjusted separately and the each shoe has two adjustment points on it.

Butch

On 7/27/2020 6:15 PM, Tilden Drinkard wrote:

[Edited Message Follows]

I'm having trouble getting enough hydraulic pressure to the rear wheels. Only enough pressure to deploy one shoe at a time ????? I've purged & bled all lines.
So I'm going back to basics & testing the new master cylinder. My calculations say that the 1" bore should produce about 127.4 PSI. Can anybody
verify that fact?

Thanx, Skip D
--
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dale@servicemotors.net
 

Its not the master you have a plug somewhere or the pipe is smashed somewhere.


On Jul 27, 2020, at 3:20 PM, James Dlapa <crosley1980@...> wrote:



Did you replace your wheel cylinders, they very well may have accumulated rust  restricting movement. 

On Mon, Jul 27, 2020 at 3:15 PM Tilden Drinkard <TILDENLD@...> wrote:
I'm having trouble getting enough hydraulic pressure to the rear wheels. Only enough pressure to deploy one shoe at a time ????? I've purged & bled all lines.
So I'm going back to basics & testing the new master cylinder. My calculations say that the 1" bore should produce about 166 lbs PSI. Can anybody
verify that fact?

Thanx, Skip D


Jim Bollman
 

If you are working with new wheel cylinders did you put the right size in?

Wheel Cyl - 1” front 7/8” rear

If they are not new/rebuilt that would be a good place to start looking, could be a stuck cylinder.

Jim...

On Jul 27, 2020, at 7:39 PM, dale@... <Dale@...> wrote:

Its not the master you have a plug somewhere or the pipe is smashed somewhere.


On Jul 27, 2020, at 3:20 PM, James Dlapa <crosley1980@...> wrote:



Did you replace your wheel cylinders, they very well may have accumulated rust  restricting movement. 

On Mon, Jul 27, 2020 at 3:15 PM Tilden Drinkard <TILDENLD@...> wrote:
I'm having trouble getting enough hydraulic pressure to the rear wheels. Only enough pressure to deploy one shoe at a time ????? I've purged & bled all lines.
So I'm going back to basics & testing the new master cylinder. My calculations say that the 1" bore should produce about 166 lbs PSI. Can anybody
verify that fact?

Thanx, Skip D




Butch
 

Jim,

While the original rears were 7/8", all of the replacements, for many years have been 3/4", as far as I know.
I do know, that all of the ones that we sol, were 3/4".

Butch

On 7/27/2020 8:12 PM, Jim Bollman wrote:
If you are working with new wheel cylinders did you put the right size in?

Wheel Cyl - 1??? front 7/8??? rear

If they are not new/rebuilt that would be a good place to start looking, could be a stuck cylinder.

Jim...
_._,_._,_


Virus-free. www.avast.com


Jim Bollman
 

Thanks Butch, I knew that, just forgot.

Jim...

On Jul 27, 2020, at 8:31 PM, Butch via groups.io <butch46988@...> wrote:

Jim,

While the original rears were 7/8", all of the replacements, for many years have been 3/4", as far as I know.
I do know, that all of the ones that we sol, were 3/4".

Butch

On 7/27/2020 8:12 PM, Jim Bollman wrote:
If you are working with new wheel cylinders did you put the right size in?

Wheel Cyl - 1??? front 7/8??? rear

If they are not new/rebuilt that would be a good place to start looking, could be a stuck cylinder.

Jim...


CHRIS BECKWITH
 

I’ve had hoses that  have collapsed internally in the past They don’t pass fluid and even hold pressure from returning crack the master cyl side of the lines and check that way 

Sgt. Chris Beckwith ,
US ARMY Ret

On Jul 27, 2020, at 8:36 PM, Jim Bollman <Jim@...> wrote:

Thanks Butch, I knew that, just forgot.

Jim...

On Jul 27, 2020, at 8:31 PM, Butch via groups.io <butch46988@...> wrote:

Jim,

While the original rears were 7/8", all of the replacements, for many years have been 3/4", as far as I know.
I do know, that all of the ones that we sol, were 3/4".

Butch

On 7/27/2020 8:12 PM, Jim Bollman wrote:
If you are working with new wheel cylinders did you put the right size in?

Wheel Cyl - 1??? front 7/8??? rear

If they are not new/rebuilt that would be a good place to start looking, could be a stuck cylinder.

Jim...


Bruce Derenski
 

The calculation of system pressure sounds about right. Rough eyeballing of the pedal leverage is about 5:1. Figure your brake foot applies about 50 lbs of force; you’d be getting 250 lbs of force coming into the master cylinder. Divide by the area of the master cylinder piston (sorry; I don’t know the bore size). If it’s a 1.5” bore (just a guess) that would be 1.8 square inches. 250/1.8= 141 psi. 


On Jul 27, 2020, at 8:36 PM, Jim Bollman <Jim@...> wrote:

Thanks Butch, I knew that, just forgot.

Jim...

On Jul 27, 2020, at 8:31 PM, Butch via groups.io <butch46988@...> wrote:

Jim,

While the original rears were 7/8", all of the replacements, for many years have been 3/4", as far as I know.
I do know, that all of the ones that we sol, were 3/4".

Butch

On 7/27/2020 8:12 PM, Jim Bollman wrote:
If you are working with new wheel cylinders did you put the right size in?

Wheel Cyl - 1??? front 7/8??? rear

If they are not new/rebuilt that would be a good place to start looking, could be a stuck cylinder.

Jim...


Jim Bollman
 

I believe the Crosley master cylinder is a 1” bore.

Jim..

On Jul 28, 2020, at 9:56 AM, Bruce Derenski via groups.io <bruce.derenski@...> wrote:

The calculation of system pressure sounds about right. Rough eyeballing of the pedal leverage is about 5:1. Figure your brake foot applies about 50 lbs of force; you’d be getting 250 lbs of force coming into the master cylinder. Divide by the area of the master cylinder piston (sorry; I don’t know the bore size). If it’s a 1.5” bore (just a guess) that would be 1.8 square inches. 250/1.8= 141 psi. 


On Jul 27, 2020, at 8:36 PM, Jim Bollman <Jim@...> wrote:

Thanks Butch, I knew that, just forgot.

Jim...

On Jul 27, 2020, at 8:31 PM, Butch via groups.io <butch46988@...> wrote:

Jim,

While the original rears were 7/8", all of the replacements, for many years have been 3/4", as far as I know.
I do know, that all of the ones that we sol, were 3/4".

Butch

On 7/27/2020 8:12 PM, Jim Bollman wrote:
If you are working with new wheel cylinders did you put the right size in?

Wheel Cyl - 1??? front 7/8??? rear

If they are not new/rebuilt that would be a good place to start looking, could be a stuck cylinder.

Jim...



 

All wheels cylinders are new.
Thanx


 

Yup.
Thanx


 

Most lines replaced & the others blown out, recharged & bled.
Thanx


 

All new wheel cylinders & replaced in the proper order.
Thanx


 

I only have hoses on the fronts, & I haven't gotten to them yet. That's good to know. Probably should replace
all hoses to be sure.
Thanx


 

My calculations are nearly the same.
Many reference materials say that on drum brakes you need +500 PSI at the wheel cylinders. I'm not a good enough
mathematician to calculate the result of hydraulic fluid leaving the 1" master cylinder at +/- 125 PSI & passing thru a 3/16"
line. I guess I'll call me Princeton educated physics professor buddy & give him the problem.
Thanx for your help


 

Thanx everybody. Your quick & informative responses were very helpful. It's very encouraging when you are stumped
to have Crosley buddies to turn to.
Many Thanx, Skip D


L.E. Hardee
 

The beauty of hydraulics is that the pressure at the end of the line no matter its diameter is the same as at the entrance, if not blocked, in a static state, ie: no movement.  The volume of fluid delivered is subject to frictional losses  due to a lot of factors including line size, bends and tube wall roughness. 

What i would do is disconnect one of the lines at one of the wheel cylinders not working right.  Direct the open line into a glass jar and get an helper to stomp on the brake pedal with all their might.  You should nearly blow the bottom of the jar out with the fluid squirt.  If it just dribbles, go upstream and repeat the procedure until you get a good squirt.  Make sure to refill the reservoir.  When you get the full squirt, you need to check the line or hose downstream for a restriction or blockage. 


On Tue, Jul 28, 2020 at 11:45 AM Tilden Drinkard <TILDENLD@...> wrote:
My calculations are nearly the same.
Many reference materials say that on drum brakes you need +500 PSI at the wheel cylinders. I'm not a good enough
mathematician to calculate the result of hydraulic fluid leaving the 1" master cylinder at +/- 125 PSI & passing thru a 3/16"
line. I guess I'll call me Princeton educated physics professor buddy & give him the problem.
Thanx for your help


 

That's great hydraulic physics to know.
After I disconnect the brake line, I'm gonna' attach the pressure gauge to the end of the brake line & see if there is any decrease in the pressure at the wheel.
I'm a little skeptical that +/- 125 psi is enough pressure to effectively deploy the brake shoes, but this is my 1st Crosley rebuild, & I'll certainly accept 
your experience in this matter.
Just for grins, I'll report back to you the psi reading.
Thanx so much for your advice.
Skip D


Dennis @ Recks & Relics
 

There is a hose at the rear also. The hoses get old and plug up the inside and restrict flow. A common problem on older cars.
 

From: Tilden Drinkard
Sent: Tuesday, July 28, 2020 11:45 AM
To: Crosley-Gang@groups.io
Subject: Re: [Crosley-Gang] Master Cylinder PSI
 
My calculations are nearly the same.
Many reference materials say that on drum brakes you need +500 PSI at the wheel cylinders. I'm not a good enough
mathematician to calculate the result of hydraulic fluid leaving the 1" master cylinder at +/- 125 PSI & passing thru a 3/16"
line. I guess I'll call me Princeton educated physics professor buddy & give him the problem.
Thanx for your help