Master Cylinder Sizes

[gjkrv8]

Originally Posted by Aussie Mike

So what we have with our Cobra is a car with a rearward weight bias and low center of gravity. Add that to firm suspension and you have a car that won't transfer nearly as much weight as say your average ford falcon. This means a Cobra can use more rear brake and less front brake in comparison with that family sedan.

What the net result of having the same size master cylinders front and rear is that we may not bet the right bias between front and rear braking forces. You may end up with your balance bar wound right accross to one side and have enough adjustment to get the bias right where fronts and rears are close to locking at the same time.

Hey Mike, I've got dual 3/4" in my CR and have to have my brake balance bar wound all the way to the left (front) to get what I believe is a front bias. Although I think my problem is that the Front Discs are std VZ and the rear Std VE. I think maybe if I had higher performance fronts I might get a better balance gived the weight transfer dynamic you mentioned in the Cobras.

What do you reckon professor Mike?

[Aussie Mike]

Originally Posted by gjkrv8

Hey Mike, I've got dual 3/4" in my CR and have to have my brake balance bar wound all the way to the left (front) to get what I believe is a front bias. Although I think my problem is that the Front Discs are std VZ and the rear Std VE. I think maybe if I had higher performance fronts I might get a better balance gived the weight transfer dynamic you mentioned in the Cobras.

What do you reckon professor Mike?

So your rears are locking way before the fronts? What size are the rear rotors and calipers?

Slowy,

If your fronts are locking way before your rears you need to add more line pressure to the rear circuit or take it out of the front circuit. That means an increase in crack pressure (that's if the valve is in the rear circuit).

The problem with Tandem master cylinders that most regular cars run is they have the same piston bore for front and rear. This means the caliper piston sizes need to be dialed in to suit. Easy done if you are a big manufacturer as you can ring up PBR and give them the spec of what you want. When we are taking parts from these production cars and adapting them to ours we end up with missmatched systems. Proportioning valves are used as a band-aid fix when they should be a tuning aid.

Cheers

[gjkrv8]

Originally Posted by Aussie Mike

So your rears are locking way before the fronts? What size are the rear rotors and calipers?

Mike

I am pretty sure my balance is ok now, but my problem is that the Balance bar is wound all the way to one side (Front bias) to get them to lock up first. So my adjustment range is gone. I thought maybe down the track if I put in higher perf Front Brake I might get some range back. Works ok for now.

Rgds

Gregg

[Aussie Mike]

I'd try some grippier front pads first. Might be a cheap and easy fix.

Cheers

[gjkrv8]

Originally Posted by Aussie Mike

I'd try some grippier front pads first. Might be a cheap and easy fix.

Cheers

Yes not a bad idea.

Whats those red pads that people seem to get for better braking ?

I'd need them to fit VZ standard Calipers.

Rgds

Gregg

[NASSTY]

I had my rear end rebuilt by a jag specialist when I built my kit so the rear disks work reasonably well but as this discussion has stated it's pretty hard to adapt donor brakes to cobras and get the balance right. It's certainly not right in my cobra. Given our jag diffs are 30 odd years old I wanted to make sure they were working properly from the start.

I know of a fair few cobras, with jag diffs and falcon master cylinders, who have removed the proportioning valve altogether to improve the brake balance and their fronts still lock up first. I'll plan to do this mod myself when I next change the brake fuild.

[trularin]

A little late but well done Aussie Mike.

A lot of guys have a mix of calipers front and rear, so a little work with the caliper volume may be in order to get the balance you are looking for. I know I changed the rear master when I swapped out the Lincoln setup for the GM setup.