Black89Z51

Hello all. My first post here, but I think it may be useful in the future.

I have a 1989 Z51 with a black tag ZF. Pretty much stock L98 (for now). I purchased this car to replace my other project car (Mustang) for the sole purpose of road racing.

Anyways, on to the question. My Power Brake Booster died on me the other day, and I know getting a new one is pretty easy, but since this is in slow process of being a road racer, I've decided to switch to manual brakes.

The problem I am having is finding out is what size master cylinder I need. I have stock brakes with the HD 13" front rotors with stock calipers in all 4 corners. I know I need to change the size, since you have to stand on the brake pedal to stop, making heel-toeing impossible.

Any insight is appreciated. Thanks in advance!

PS I searched for roughly 6 hours total and didn't find a whole lot, only drag racing stuff.

davidfarmer

Tilton has engineers that can help you find the sizing info you need, but unfortunately finding a dual-bore OEM style master cylinder is going to be nearly impossible. You'll probably need to go to a dual master cylinder setup, which is going to cost a lot of money, and not worth doing unless you are going to racing calipers and rotors. I personally can think of no reason to not just put a booster back on it.

trackboss

Of done a few manual conversions on mustangs. If the brake balance was good with the power brakes there's a good chance you do not need to change the m/c. What does need to be done is to change the pedal ratio. If you drive on the street it will suck cause a lot of effort is required to stop. On the other hand that is what is needed on track to make brake modulation easier. That being said, installing a pedal assembly with proper dual m/c's, as mentioned above, will be the best way to go. You can dial in your brakes exactly as you like them.

mousecatcher

What's the difference? If you change the MC ratio you are still decreasing the effort at the pedal and as long as you keep the same ratio front:rear in the new MC the balance is the same.

I think what you probably meant was, what can be done instead is to change the pedal ratio, which could be much much easier than getting a custom OEM style MC.

Please clarify if that's not right.

Either way, the pedal travel is going to change, which should be considered.

I'm with David on this one.

Black89Z51

Thanks for all the information. Maybe putting on a new brake booster will be the most economical for the time being.

The reason I would like manual brakes is because I drove a friend's Mustang race car (93 LX) and just loved the way they felt. He's got Baer front calipers and C4 rear calipers on his setup, and was hoping to somewhat duplicate the feel of it. He runs a manual m/c with the stock pedals and an adjustable brake bias valve.

trackboss

You could go down in size on the m/c to decrease the pedal effort and keep the same ratio pedal, but it is not ideal and the wrong way to do it. The problem with that is the pedal goes past 90*. Anytime the brake pedal goes past perpendicular you reduce the pressure that is being placed on the pedal (once past 90*). The target is to have maximum brake pressure when the pedal is at 90*, or less, and never go past 90*. In my first conversion I actually found a factory manual brake pedal and it had a different ratio.

mousecatcher

perpendicular to what?

trackboss

brake pedal to pushrod. Its a motion ratio and when angle is in there it reduces the effectiveness. I'm not very good at explaining this with words, but it is common knowledge when setting up a brake pedal. More angle=less pressure at the pushrod.

mousecatcher

gotcha. that makes sense. obviously i had never considered that before!

trackboss

you actually made have to dig into my brain. I almost forgot why and had to think a bit harder than I normally do. Thanks!

flink

I have the no-boost, no-ABS, dual-master Tilton setup on the e36. The pedal effort is really very reasonable on the 2500 lb car. In fact I'm thinking I need a larger diameter master on the front because it's still front-biased and the balance bar is at full-rear. That will increase pedal effort, but that's OK - I have no problems with pushing harder.

But I do use high Cf pads (Hawk DTC-70's) to keep the effort down.

Would I recommend boosterless brakes? Dunno, really.

Advantages: Simple! There's hardly anything there, very little to go wrong. Also, unless the pedal snaps you'll always have at least two wheels which have brakes.

Disadvantages: very small amount of caliper piston travel for each pedal stroke. This means that is you have any pad knockback, pad-taper-induced piston cocking or if you have insufficiently stiff calipers (koff-wilwood-superlites-koff) the you're going to get a long pedal. To the point of pedal-on-the-floor, not-enough-braking-happening. I have to be very careful to rotate the pads to get even wear to prevent this. Again, the high Cf pads help - with low Cf pads (koff-wilwood-h-compound) you have to press harder, and the calipers just bend.

I guess that on balance, yes, I prefer the manual setup, because of the safety/reliability benefits.