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Username Post: Master cyl bore        (Topic#348955)
Airlifter 
"3rd Year" Gold Supporting Member
Posts: 469
Airlifter
Age: 72
Loc: Tazewell county, Virginia
Reg: 06-07-15
01-01-18 10:27 AM - Post#2719662    

I installed a dual master cylinder kit from Ecklers last winter. I wound up with a corvette type master cylinder so I could use the remote fill. The car stops great but there is a lot of travel in the brake pedal. I believe that the MC that I have is a 1" bore. I think that the original MC had 7/8" bore.

If I understand correctly, the smaller the bore the less travel but it also takes more leg pressure to stop the car. I would like a little less travel even if it takes a more pressure. If this is the case, I am going to start looking for a MC with smaller bore.

I have adjusted the brakes and bled the system.

1951 styline deluxe sport coupe w/54 engine & powerglide


 

50hotrod 
"6th Year" Silver Supporting Member
Posts: 951
50hotrod
Age: 61
Loc: Wisconsin
Reg: 07-25-11
01-01-18 10:55 AM - Post#2719671    
    In response to Airlifter

I believe its the opposite. A smaller bore master requires less leg pressure then a larger bore.

I have the same outcome after changing to the dual master with a 1" bore. Excellent stopping but more pedal travel. Yes, all the brakes are new and adjusted properly. If you change to a larger bore master please let me know how that works out.

I kinda like the pedal pressure but a little concerned about the amount of travel also.


Well, you know what's wrong with the world today

People done gone put their Bible's away

They're living by the law of the jungle not the law of the land

"Simple Man" By Charlie Daniels



 
junky 
Valued Contributor
Posts: 2507

Loc: Northeast CT
Reg: 06-27-10
01-01-18 06:32 PM - Post#2719723    
    In response to 50hotrod

The additional travel is a result of the dual master cylinder. The rear brakes are applied first, and as you push on the pedal further, it applies the front brakes. I honestly don't believe that changing the piston diameter is going to change the basic design of the dual master cylinder.

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
raycow 
Honored Member
Posts: 27492
raycow
Loc: San Francisco, CA
Reg: 11-26-02
01-01-18 10:35 PM - Post#2719748    
    In response to junky

Guys, you still have it backwards even though you seem to have arrived there by different routes. All you have to remember is one very simple formula:
F = P x A, which can also be written as P = F/A.

P is the hydraulic fluid pressure, which you can think of as the system pressure being applied to the wheel cylinder pistons to stop the car. F is the linear force your leg applies to the master cylinder piston through the pedal and linkage. A is the area of the MC piston.

For a given set of wheel cylinders, increasing the MC bore size will increase the pedal force required to develop a given amount of fluid pressure and will reduce the amount of pedal travel required, because you are moving a larger volume of fluid for a given amount of pedal travel.

Conversely, reducing the MC bore will reduce the pedal force required to stop the car, but will increase the pedal travel required.

As a practical example, Chevy had a MC bore of 1" up through 1952. The MC bore was reduced to 7/8" for 53-54 because GM had received complaints about the pedal force required to stop the earlier cars and also because the car weight was increased in 53. You can install a 53-54 MC in your 52-earlier car and you will feel the difference.

Now you know why you should have stayed awake during class.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 4233
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
01-02-18 01:00 AM - Post#2719755    
    In response to junky

Hi Junky, that's not really how dual masters work. One piston only pushes the other piston when there is a leak. The pressure that forces the first piston to move also acts on the end of the second one so they both move in unison.
its only when one side has a leak that one piston hits the other and holds pressure in the remaining circuit.

Changing the bore diameter does very much affect the force you need to apply and how far you need to push to take up the free-play.

Cheers Kiwi

48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


 
bobt 
Contributor
Posts: 160

Loc: colonial heights va
Reg: 06-28-14
01-02-18 04:19 AM - Post#2719757    
    In response to Airlifter

I read that you have adjusted your brakes. What is your method of spooning? How much "free travel" do you have on your brake pedal? When I upgraded to a dual master cylinder, I had to lengthen the push rod from the master cylinder to the brake pedal until I had about one inch of free travel.



 
Airlifter 
"3rd Year" Gold Supporting Member
Posts: 469
Airlifter
Age: 72
Loc: Tazewell county, Virginia
Reg: 06-07-15
01-02-18 06:23 AM - Post#2719758    
    In response to bobt

Tanks for all the input. I think that the length of the push rod might be the culprit. The rid is adjustable so I will try to adjust it out when I can get back to the car.






1951 styline deluxe sport coupe w/54 engine & powerglide


 
50hotrod 
"6th Year" Silver Supporting Member
Posts: 951
50hotrod
Age: 61
Loc: Wisconsin
Reg: 07-25-11
01-02-18 10:06 AM - Post#2719777    
    In response to Airlifter

Just wanted to add....My push rod is adjusted with 1" of free play.


Well, you know what's wrong with the world today

People done gone put their Bible's away

They're living by the law of the jungle not the law of the land

"Simple Man" By Charlie Daniels



 
62chevy427 
"12th Year" Silver Supporting Member
Posts: 2113
62chevy427
Loc: laurens sc
Reg: 04-13-06
01-02-18 09:21 PM - Post#2719841    
    In response to Airlifter

be careful not to adjust it too tight. you need some free play, about an inch , so that the pistons retract enough for all the fluid to return to the master cyl. otherwise your brakes will drag/lock up

56 bel air ((since 2002)
62 impala ss (since 1965)
65 el camino (since 1969)
66 nova (since 1987)
67 malibu convertible (since 1981)
72 el camino ss454 (since 1985)
83 gmc 4wd (since 1991)
95 impala (new)
14 camaro (new)


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 4233
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
01-03-18 12:22 AM - Post#2719847    
    In response to 62chevy427

Hi Guys, I think you are confusing two different methods of free play checking.

The pedal travel is relevant to drivers for feel but as pedals have a levering ratio one inch at the pedal means different things at the master cylinder for different cars.

First thing is to make sure the pedal return springs will pull the pedal off the master, and hold it off so the master cylinder internal springs take it right back to the rear stop. Check the spec for your car or master at the push-rod.

There must be some clearance. But be absolutely certain it can't fall out

If the pedal rises up too far form the point of application, check your at wheel adjustment. If that's OK the pedal may also have a top stop. As others have said once you have the system and master clearance sorted you can play with pushrod length and pedal height to suit different size drivers.

Cheers Kiwi

48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


Edited by Bel Air kiwi on 01-03-18 12:23 AM. Reason for edit: No reason given.

 
belairbob50 
Contributor
Posts: 268

Loc: OH where rust never sleep...
Reg: 03-17-13
01-06-18 07:09 AM - Post#2720196    
    In response to raycow

Raycow, I changed the Huck style brakes on my 1950 to the Bendix style brakes from a 1953. I kept the original 1950 MC but used the wheel cylinders from the 1953. I purchased and installed the larger 5/16" brake lines prior to the switch, so I cannot return them. I had to use fittings to attach the brake lines to the newer wheel cylinders (1/4"). Here is my question: if I switch the master cylinder to a 1953 (7/8" bore), will the larger size brake lines affect the system in any way?



 
Gene_Schneider 
Ultra Senior Member
Posts: 12132

Loc: Wisconsin..USA
Reg: 09-27-02
01-06-18 01:30 PM - Post#2720228    
    In response to Airlifter

I have a 7/8" master cylinder on my 1950 replacing the original 1". The pedal travel is only slightly less and barely noticable.
Chevrolet called the change to the SMALLER DIAMETER LINES IN 1951 AS BEING "INCIDENTAL" AND LISTS NO ADVANTAGES IN THE 1951 eNGINEERING MANUAL.

ChevGene 1934 Master sedan 1939 Master DeLuxe Town Sedan 1950 Styline DeLuxe Power Glide 1957 Nomad 283 PG 1963 Corvair Convertible


Edited by Gene_Schneider on 01-06-18 01:38 PM. Reason for edit: No reason given.

 
raycow 
Honored Member
Posts: 27492
raycow
Loc: San Francisco, CA
Reg: 11-26-02
01-06-18 02:23 PM - Post#2720233    
    In response to belairbob50

Gene is totally on target, The change in line diameter caused no perceptible effect on braking performance.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Bel Air kiwi 
"3rd Year" Silver Supporting Member
Posts: 4233
Bel Air kiwi
Loc: New Zealand
Reg: 04-24-14
01-08-18 05:03 AM - Post#2720414    
    In response to raycow

Hi Guys, I am with Gene and Ray on this. Hard brake pipe diameters don't change anything. Brake fluid doesn't flow around the system like fuel or coolant.
As soon as the pedal takes up all the free play it shouldn't move any further. Things tend to flex a bit but it doesn't move anymore, just the internal pressure rises.

Changing the master piston diameter does, as it changes the force/area input, and a smaller piston will tend to move a little further initially to take out the free-board which is the volume of fluid that needs to move to take up the calipers or brake shoes from rest. And any pedal/master or booster/master clearance.

The only advantage I can see in small diameter brake pipes is that for a given material they should be stronger if they have the same wall thickness.

Cheers Kiwi




48 3100 RHD, 51 Deluxe 4DR RHD, 51 Bel Air parts car, 52 Bel Air P-Glide LHD. Others 23T, 32 Tudor, 58 Edsel pacer 4DR HDT, 79 F250 351C RHD. 69,70,82 Capri. No mobile, no TV, and no Jap cars.

And when it was laid to waste, they called it peace.


Edited by Bel Air kiwi on 01-08-18 05:09 AM. Reason for edit: No reason given.

 

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