13" cobra brake problems

Cobain03 · Nov 26, 2009

my front brakes will not hold the car, if im doing a line lock assisted burnout or they wont even lock up when i totally slam on the brakes from 50mph. im almost positive my master cylinder isnt big enough to push the big calipers. being a 65 coupe, clearance is a BIG problem and i cannot find another master that is small enough to put in there. i currently have a booster in there and my question is, could i go with a non power master that has a larger bore to solve my problem? is the booster needed?

2+2GT · Nov 26, 2009

No, a larger bore will make it worse. What booster do you have? If it's one of the "modern conversion" types, straight line, like this:

They suck and everybody I know who has used them has had problems. I know where there's a couple of brand new ones lying on the floor in a shop, where they were yanked off and thrown in disgust.

The only one that seems to work well on 64-66 cars is the replica of the original, which comes with single or dual master. It also has the advantage that it works with stock clutch linkage:

ForceFed70 · Nov 26, 2009

I think you want something with a smaller bore. Smaller bore = more pedal travel but less effort.

tx65coupe · Nov 27, 2009

I have a master cylinder that is similar to the first one, but no booster. It works very well. I have Granada brakes though.

What so bad about that type?

I have seen quite a few people that use a later model style MC that has the transparent plastic reservior. They all say that it works well.

The statements about the bore size are correct. A smaller bore is what it sounds like you need.

Before you go and replace it make sure that there is not something else that is wrong and that the system if properly bled of air.

Cobain03 · Nov 27, 2009

ya mine looks like the top one and its a super tight fit.

YourBaby'sDaddy · Nov 29, 2009

What's the bore size on your master cylinder now? I'm looking to swap to 13" cobra brakes as well.

2+2GT · Nov 29, 2009

tx65coupe said:
What so bad about that type?

Nothing, in theory. Frequent defects, in practice. They tend to be too sensitive, due to the short leverage of the standard pedal, and they often end up with too much pedal travel due to the leverage. This means that even a minor variation in function makes them work lousy.

The stock type reduces the leverage, allowing better "feel", in 65-66 with the bracket and lever on the booster, and with a longer pedal on 67-70.

Cobain03 · Nov 29, 2009

i dont know my bore size, dont know how to measure it either.

rbohm · Nov 29, 2009

what car did you get your master cylinder from?

Cobain03 · Nov 29, 2009

65, called up a mustang parts place and thats what they sent me

rbohm · Nov 30, 2009

thats going to be part of your problem then. if you still have drums in the rear, then get a master cylinder from a later model vehicle like a late 80's grand marquis since you have power brakes, or if you have rear disc brakes as well, get a master cylinder from a late 90's or later cobra mustang. these are designed to work best with the system you have. the stock master cylinder for your mustang isnt.

Cobain03 · Nov 30, 2009

only bad thing is the measurements. i HATE my car because of its small spaces. i iwill try to find the dimensions online

latamud · Dec 4, 2009

I'm having the same issue swapping from Granada to 13" Cobras. I'm standing on the pedal and doesn't seem to stop me as well as it did before. But even then with the Granada setup it was tough. My pedal never had much travel with this current master cylinder which leads me to believe I have a 1" or more bore based on what I've been researching. My master cylinder is the manual disc/disc from Mustangs Plus $85 or something around that price.
A friend of mine has a disc/disc SVO master cylinder and his pedal has more travel, kind of feels mushy but the brakes grip hard and tight and lock up well. It has 21mm bore (aprox. 7/8"). The only CON I have is that the lines plumb into the other side of it.

StangDreamin' · Dec 5, 2009

You might look at/get some measurements on a late Fox M/C.

Also, THIS STUFF HAS BEEN DONE BEFORE! The pictures are of a '68; but read the text.

GT350R · Dec 5, 2009

latamud said:
I'm having the same issue swapping from Granada to 13" Cobras. I'm standing on the pedal and doesn't seem to stop me as well as it did before. But even then with the Granada setup it was tough. My pedal never had much travel with this current master cylinder which leads me to believe I have a 1" or more bore based on what I've been researching. My master cylinder is the manual disc/disc from Mustangs Plus $85 or something around that price.
A friend of mine has a disc/disc SVO master cylinder and his pedal has more travel, kind of feels mushy but the brakes grip hard and tight and lock up well. It has 21mm bore (aprox. 7/8"). The only CON I have is that the lines plumb into the other side of it.

If I recall, the SVO unit is around 1 1/16th bore. Look into Ranger master's. The ca be had in different bore size from 1 inch down to 7/8th's if I recall, AND the lines are on the driver side of it.

latamud · Dec 5, 2009

GT350R said:
If I recall, the SVO unit is around 1 1/16th bore. Look into Ranger master's. The ca be had in different bore size from 1 inch down to 7/8th's if I recall, AND the lines are on the driver side of it.

SVO power brakes is 1-1/16"
SVO manual is 21mm (7/8)

ddonaca351 · Dec 6, 2009

Also of note is that "cobra" brakes ran diff bore size m/c and also diff size pistons in the calipers in diff years.... so get what was factory designed to work with your parts and it will do just fine.

If size is a huge issue for ya, you can call up willwood and get a cute little alloy m/c that will get the job done. (but first you'll have to know what you want, cuz their sales guy doesn't know your car...)

Wicked65 · Dec 8, 2009

I would call up strange. Tell them what your doing. And get the master cylinder for manual brakes. Saves room and should be strong enough.

ForceFed70 · Dec 9, 2009

ddonaca351 said:
Also of note is that "cobra" brakes ran diff bore size m/c and also diff size pistons in the calipers in diff years.... so get what was factory designed to work with your parts and it will do just fine.

If size is a huge issue for ya, you can call up willwood and get a cute little alloy m/c that will get the job done. (but first you'll have to know what you want, cuz their sales guy doesn't know your car...)

Good point. The early SN95 Cobra brakes used a 38mm piston. The 40mm piston is much more common. If you are running the calipers with 38mm pistons it will require more pedal effort than the calipers with 40mm pistons.

13" cobra brake problems

Cobain03

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