M/C 15/16 bore

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Cuda 1964

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Hi everyone
I have a 64 barracuda that has been converted to dis/drum brakes
It seems that I can not get the front brakes to lock up the M/C is a 11/8 bore would a 15/16 bore M/C give me more pressure to the front and yes I do do have an adjustable brake valve
Thanks for your info and help in advance
 
Hi everyone
I have a 64 barracuda that has been converted to dis/drum brakes
It seems that I can not get the front brakes to lock up the M/C is a 11/8 bore would a 15/16 bore M/C give me more pressure to the front and yes I do do have an adjustable brake valve
Thanks for your info and help in advance

A 15/16" master cylinder would increase the line pressure vs a 1.125" master cylinder, yes. It would also lengthen the pedal stroke to achieve that pressure.

Larger bore M/C= higher, harder pedal with less line pressure
Smaller bore M/C= longer pedal travel with more line pressure

There could be a whole host of other problems that could cause the front brakes not to lock up though, so you should definitely investigate other possibilities first. Contaminated brake pads, for example, can cause the same thing and are a much cheaper fix. Heck even brand new, not bedded in pads can cause that issue and they just need miles. Could also be issues with the calipers themselves, the brake lines, the caliper brackets, etc, etc.

What conversion was used? What disk brakes are on the car?
 
A pirate jack kit was installed for 73 up including M/C and calipers

Ok, well those are pretty simple. If they're brand new consider that the pads may not be bedded in yet, which does make a significant difference.

Other things to look at would be to check that you're getting good fluid flow out to the calipers, just because the hoses are new doesn't mean they're good, especially with the cheap offshore stuff that comes in those kits. I've had brand new brake hoses separate internally and limit flow. You can also check to make sure that the calipers are sliding well on the caliper brackets, all of those surfaces should be new so it shouldn't be an issue but if the callers aren't sliding like they should it can effect stopping power.

And if you've just got the brake pads from the kit you might want to grab a part number and see what they actually sent you, brake pad composition and quality also makes a big difference and if you figure out what pads you have you can look them up and see if they have a break in procedure listed.
 
and yes I do do have an adjustable brake valve

I'm assuming you are using a DUAL-brake, front/rear system.
So, in which line did you install it the adjustable valve, and where?
On a MOPAR Dual M/C, the front brakes have to run directly to the REAR reservoir on the M/C with NO pressure modifications and no hold-off valves. Thru the Distribution block is fine, BUT, the M/C line comes in on the END, and then splits. In a MOPAR system the lines from the M/C are coded by size and only fit the appropriately coded valve but one way.
Mopar has used at least three different types of valves that I know of, so knowing which one you have is kindof important. The kinds are; a simple distribution block, a combination distribution front with a straight out rear valve, and the same valve with a proportioning valve tacked into the back. This type usually has a safety switch incorporated into it.

This safety switch is supposed to be self centering. But I have seen cases where it it has shifted to one end or the other. When this happens, whatever side the shuttle has moved to, that side of the brake system fails to work, by design.
If you have this type of valve, you can check the position of the shuttle valve by checking the continuity thru the switch to the brass body. In centered position there should NOT be continuity. If there is continuity, it can only be that the shuttle is not in neutral. But you don't know which way it has gone.
In your case, it seems to have shut off the fronts. The only way to move it is to open the rear line and slowly press the pedal until no more continuity is found, then close the leak.
I mean, I'm guessing, right.
Other notes;
>If you do not have a MOPAR valve, then IDK how other brands work.
>If you have clamped the rubber soft-lines, they may have been damaged beyond use.
>If you do NOT have a high and hard pedal, then you have a problem, and
it may not be hydraulic

Hope that helps
 
I'm using the original distribution block with the rear feed blocked off and a straight line to the rear brakes distribution block. The front brake line is in the rear reservoir down to the front distribution block. The rear brake line is connected to the front reservoir to the porportioning valve and then out to the rear brake block
 
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