I'm now looking at uprating the brakes on my car - it was the old M16 set-up, but I've recently bought a pair of Wilwood Powerlites for the front and I'll try keeping the Ford Calipers at the back with uprated pads.

My old Master Cylinder was a rather large single unit with two apertures - one each for front and rear brake lines. Is there a great deal of benefit to be had by changing to 2 indepent Cylinders? I had thought just to renew the old cylinder with a similar style but more performance orientated one and put a proportioning valve in the rear brake line so I can fiddle for balance.

I know very little about braking - is this a sound suggestion?

A few questions to get things clear
(1) From your description I take it your original build had Cortina front suspension with Cortina solid discs and M16 calipers at the front and Sierra Discs at the rear ?
(2) In normal use did the front brakes lock before the rears ?
(3) When driven hard did you get brake fade to extent you could no longer lock the front brakes ?
(4)In normal driving iIs excessive pressure required on the brake pedal ?
(5) or do you get excessive pedal travel before the brakes work ?
(6) Are your front discs solid or vented ?


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Assuming the answer to question (2) is yes --- you don't need a proportioning valve as a proportioning valve is only any use if you start out with a vehicle that is over braked on the rear axle. A proportioning valve or other type of valve can only reduce the brake pressure going to the rear axle it can't increase it to more than the line pressure.

Fitting a dual master cylinder balance bar set might give you a little more braking by allowing you to increase the hydraulic pressure to he rear brakes but remember the rear axle only contributes less 30% of the vehicles stopping power and the brake bias must always be set to lock the fronts first so any gain from the rear will be tiny.

Again referring to question (2) If you can lock the front wheels during normal road driving then changing the front calipers won't make your brakes any better.

Referring to question (3) if you can no longer lock the front brakes after a spirited drive then you have brake fade --- changing the calipers will make very little difference to this --- only larger or vented discs or high performance brake pads will make any noticeable difference .


Referring to Q(4) If you need excessive pedal pressure to lock the front brakes in normal driving , you might want to consider changing the master cylinder & or pedal box to one that either has either a smaller bore master cylinder or a higher mechanical advantage (leverage ratio) so you get more hydraulic pressure for less effort on the brake pedal.



Referring to Q(5) If you have excessive pedal travel before the brakes work (or a spongy pedal) you might want to look at changing the master cylinder and pedal box but it could be other problems which should be checked before doing major work.

[Edited on 6/5/07 by britishtrident]

Have a look at the post by Dern in this thread http://www.locostbuilders.co.uk/viewthread.php?tid=42257

Cheers.

I've changed the fronts as they were very poor in all area's. No feeling and braking was very hard work (had tried different pads - not much difference).

So, I've ordered the Powerlite's and Cross-Drilled Discs.

The pedal was super spongy as well, so I would like to change the master cylinder to a smaller one, but I'm not sure if a smaller unit will be up to the job on front AND rear.

I'm going to leave the rear's alone - the proportioning valve was only a thought in order to tone down the pressure at the back if need be.

You need to track down the cause of the spongey pedal before you start changing coponents. Particularly as the only easy way to reduce the pedal effort required is to fit a smaller bore master cylinder or increase the pedal leverage both will make a spongey pedal worse.

If you had a spongey pedal and needed excessive pressure on the pedal to slow the car something was wrong eg faulty --- most likely a seized piston in one of the brake calipers --- this problem is very common on M16 and P16 calipers. Only way to check this is remove each brake pad individually and check the its piston is moving, also when you put the pad back in check the pad is moving freely in its guide slots.

The other thing you should check is the pedal box and mastercylinder mountings are stiff enough, as even a very small ammount of lost motion will give a spongey pedal.

Of course you will already know the problems bleeding Sierra calipers on Locost IRS setups.

There is a simple way to test if a mastercylinder or its mountings are the cause of the brake pedal sponegyness ---- remove the brake pipes from the mastecylinder, replace them with bleed nipples and give it a quick bleed. If the mastercylinder and its mountings are OK the pedal should be rock solid.




[Edited on 7/5/07 by britishtrident]