Correct Master Cylinder?

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Omie01

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Good Morning Gents and Ladies. I have yet another question. As I am sure you can tell I am gathering parts for another repair/resto. Last night I had my wife order a master cylinder and she says there are 2 available. One has a 1" piston bore and both brake line holes are 3/16" I believe. The other has a 15/16" piston bore and the front brake line hole is bigger than the rear. Which one is technically correct for a 72-73 Mach 1? I have a pic of the 1" bore MC. 

DSCI0363.JPG

 

SVO2SCJ

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I think you will find that is the difference in drum/drum OR disc/drum applications.  Since she is doing the internet ordering provide her with all the info for the planned build, if you are adding a power booster and if you have the correct proportioning valve for the final build.  My guess is she just started with an internet search and thinking of shopping by price.  

We needed a master cylinder in a pinch on a Sunday , last month and NO ONE had one......ended up driving to NPD and got one cheaper that the parts store!  Lately I have been CONFIRMING avalablilty on anything ordered on line.  Many suppliers aren't stocking (to cut costs) and are drop shipping BUT you don't see the jobbers inventory to confirm stock.        https://www.npdlink.com/product/master-cylinder-assy-brake/103676?backurl=search%2Fproducts%3Fsearch_terms%3Dmaster%2Bcylinder%26top_parent%3D200001%26year%3D1972&year=1972

 
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I just looked at my Ford 1971 manual for master cylinder piston/bore sizes. For both drum and disc for Mustang and Cougar except Torino and Montego, it states 1.000". Torino and Montego are .9375" (15 /16th). So if you got the 1" it's right. On the Drums, it shows for both power and non power being the same. 

EDIT note:  For some reason, I thought Omie01 had a 71 car. Sorry if I confused the issue.

I have no idea why Ford would have needed to change the bore size over probably the entire vehicle range other than expense.

 
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Fabrice

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if of any use, I was having issues with my brakes (they sticked a bit) and MC was an obvious piece to check as it was new. 

Turns out it was the callipers pistons, but before I've found the prob, i've checked my orders on NPD for both my 73 and 71.

There are not the same for 71-72 and 73. and ofc also different if for drums. so 4 kinds to pick from, at least by NPD.

 
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I am pretty sure that 1971 had 1" even for PDB. 72 & 73 with PDB had 15/16" bore. 1" with drum. I have the components to rebuild the booster you can get the master rebuilds from NPD is who i use. Those differences are the reason not much of a reason to go to DB unless racing.

 

Omie01

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Sorry for the confusion, the next car I will be fixing up is a 73 Q code Mach 1. My wife did get a 15/16" "New" MC in last night for me so I will go with that one. Thank You for all the insight gents. Yet another part that can be confusing with these old steeds!!

 

Don C

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I believe the one with different size output fittings are for power disc/drum brakes. The ones for power disc/drum brakes also have different size 'humps' on the master cylinder cap, the drum brakes have the same size.

 

lurbanow

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I believe the one with different size output fittings are for power disc/drum brakes. The ones for power disc/drum brakes also have different size 'humps' on the master cylinder cap, the drum brakes have the same size.
Backwards. Disk brakes need more fluid. The smaller resovor is for the drums.
 

Don C

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I was referring to the size of the humps on the drum/drum master cylinder cover, they are the same size. Yes, the larger hump on the disk/drum master cylinder is over the larger disk reservoir.
 

mrgmhale

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And more non-Big Nose Mustangs/Shelbys

[url=https://ibb.co/ZYR2dW1][img]https://i.ibb.co/RBGj2z4/IMG-4852.jpg[/img][/url]

[url=https://ibb.co/KzfYYJ7][img]https://i.ibb.co/M5tbbmp/1073-Mach-I-From-Right-Front-Above-With-Gil-20180608.jpg[/img][/url]
Here are some thoughts I have saved in a file. The info may or may not be applicable to you. But, if you are using disc brakes be sure to heed the info re: the Residual Pressure Check Valve below.

When replacing front and/or rear drum brakes with disc brake components on a First Generation Mustang or Cougar you do not want to go cheap. This is a fairly serious, even if fairly easy, operation. Use high quality parts, preferably in a kit designed to do a full upgrade. I like Wilwood, a reputable brand with a lot of years in this end of the business. Here are the most important things to be aware of:

• Replace the Master Cylinder with one designed for Disc Brake systems. Often the MC bore size is different compared to Drum Brake system MCs. Also, for Drum Brake MCs the fluid outlet port(s) for drum brakes has/have a Residual Pressure Check Valve (RPCV) under the outlet port’s brass seat. The RPCV is needed for drum brakes to keep fluid pressure on the wheel cylinder cup seals so they do not suck air into the cylinders when the fluid cools off. But, for Disc Brake systems such a valve puts needless pressure on the caliper pistons and causes the pad to drag on the rotor under pressure. That results in reduced vehicle performance, overheating of the front pads and rotors, and rapid wearing of the front pads.

https://www.youtube.com/watch?v=WxT9vLO6pOc (00:42)

• Flush the old brake fluid and replace it with fresh DOT3 Disc Brake Fluid. DOT3 is totally compatible with Drum Brake hydraulic components, and differs from DOT2 Drum Brake Fluid in its boiling point is higher – which is needed for Disc Brake systems. Do not mix newer brake fluid types with DOT3 fluid. And never use petroleum fluids (oil of any type) - ever.

• Get a Power Brake Booster, as the Disc Brakes are not a self-actuating design like a Drum Brake system is. I have driven Disc Brake systems without a power booster before. No fun. They work, but power boosted Disc Brake systems are much better.


• Never use copper lines for hydraulic brake systems (Nickel-Copper alloy metal lines made for brake systems are fine). The copper metal alone is too soft and the lines can and will rupture if enough pressure is applied. Use only properly designed steel or Copper-Nickel alloy lines with double flare endings.

• Do not go cheap on brakes, suspension, or tires, ever.

For front disc calipers, be sure to put the calipers on the correct side, otherwise you will never be able to properly bleed the air from the hydraulic system. Refer to the attached graphic file, apparently created by Richard Ackerman (I got it from Dennis Keegan), to see how the calipers ought to be oriented. Many thanks to Richard and Dennis for allowing me/us to share this excellent graphic.
 

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