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Correct Master Cylinder?

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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. 


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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.

Edited by Stanglover


 I learn something new every day!

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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.

73 modified Grande 351C. (Finally back on the road woohoo!) 

71 429CJ. ( In progress )

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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.

When a man is in the woods and talks and no women are there is he still wrong??:P


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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!!

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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.



“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein


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