TTur1996

If that rod is not perfectly straight going into the master. You are looseing leverage.

Corner Worker

Do you have to pump the brakes, or does it immediately feel like you are pushing a brick wall? If its rock hard, and not spongy at all, I highly doubt it has air in the system. 5.5:1 is low to me. I bet you are not generating enough line pressure. You either have to gain more mechanical advantage on the pedal or reduce the master cylinder bore. Either approach will create higher line pressures. Again, you cant cheat the physics of hydraulics.

StangEaterSS

iTrader: (41)

If i move the hole up higher to get more pedal ratio then it wont be straight. so which is it? people are telling me move it up higher and get 7:1 ratio. but it wont be a straight shot then.





Its rock hard and dont stop. pedal moved very little.

Corner Worker

If the angle is slight, it will be better than a short pedal ratio. remember, total movement of the master cylinder piston isnt very much. I dont think you have air in the system. You can bleed them until July, and you wont get any better.

On my Chevelle, I run Aerospace brakes at all 4 corners, Mopar 1.125" bore master, and a pedal ratio of 6.67:1 and it stops a 3100lbs car going 130mph in the quarter with decent pressure just fine.

If you can easily pop another hole in your pedal arm that will get you closer to 7:1, I would at least try it.

TTur1996

[QUOTE=StangEaterSS;19626787]If i move the hole up higher to get more pedal ratio then it wont be straight. so which is it? people are telling me move it up higher and get 7:1 ratio. but it wont be a straight shot then.

If you move the clevis up on the pedal arm and the rod is already angled. When you push the pedal down it will angle it even more causing a side load on the plunger. Thus loosing leverage. The only way to achieve your 7:1 ratio properly, would be to lower the pedal assembly to get it straight. And that is not attainable without a lot of fab work. I don't believe that's your problem. Do you have rubber brake lines? If you do, they could be broken down, and causing your hard pedal with low braking force. Otherwise, loose the stock proportioning valve and the 1/4 inch line going to the rear, and replace it with a 3/16ths line.

I'm not BSing. The rod is perfectly straight on ours under pressure, and is nothing to lock the tires up, with very little pedal pressure. We even put the GoPro (with the hood off) where you could see the master to see how bad the fire wall flexed, due to everyone saying how bad they flexed. When hitting the brakes to lock them up. It did flex a little. But not enough to worry about.

TTur1996

Here you go. To achieve number 1, number 4 has to be right. You could drill your pivot point on the mount lower so you can drill the Clevis mounting point higher and keep it straight to get the leverage you need.

TTur1996

Looks like the only other option you have, is to get a smaller bore master. But you still need to get rid of the stock proportioning valve and 1/4 brake line. That will help too. You might want to try that first. Along with replacing the rubber lines with braided. It just doesn't make sense that you can't stop at all. I mean, I can see you needing more force to push it down, but damn.

StangEaterSS

iTrader: (41)

So I had time this weekend to pull it all apart again. Aerospace brakes told me exactly how to measure pedal ratio and even had a diagram on the website which was easy to follow. You take the center of the pedal and measure to the center of the pivot point. then divide that number by what the measurement from the pivot point to the center of the rod hole is. I did exactly what my instructions told me on the strange master. measure up 1" higher and drill a hole. I was told this is close to 5.5:1. (which isn't even good if It came out to this) It actually came out to 4.8:1 ratio. this explains the super crazy hard pedal that would not stop the car even with both feet. All the info I could find showed that a manual brake system needs 6.0:1 up to 7.0:1 ratio. I moved the hole 3/4" higher and now have 6.8: ratio. The picture is hard to tell with the angle but its 1.75" center to center, so 12 / 1.75= 6.86. The pedal travel feels like double the distance. the pedal almost feels like it will hit the floor before feeling solid. I drove the car. it stops. it can lock up the tires now which it could not before. But it seems like the pedal sinks way too much. I bled the brakes again. still the same. This is an improvement and the car is derivable but I am worried about drag racing it and stopping. Somehow the ratio change also changed pedal height. I feel like i may have to pump the brakes from a fast stop.

Nostang

iTrader: (4)

Get a motive power bleeder and pressure bleed the system. The manual brakes are harder to push the pedal but should stop you just fine. If you are trying to lock up the brakes you will have to apply a lot of pedal pressure.

Corner Worker

Wow...imagine that. I said it before, and Ill say it again...you cant cheat physics. More leverage meant you were able to generate higher line pressure, which pushed harder on the caliper pistons. Alakazaam. The long travel pedal is a result of the change in pedal ratio. Make sure you have the pushrod adjusted so there is very little play in the pedal to master cylinder. My chevelle requires a second pump on occasion as well. I even installed 2psi check valves, and it still does it. Big bore master cylinder acts like a vacuum pump when the pressure is released. Sucks the fluid right back into the reservoir.
I worked at Aerospace for almost 5 yrs as a machinist and I took care of the tech calls at night.

RobsZ28

iTrader: (3)

I had manual master with 1.032" bore on my Camaro and the stock rotors, pads, and calipers on all 4 corners. I also relocated the rod hole 1" higher. The car stopped great, never a problem. Haul the car to a stop from 140mph just fine. After a while I forgot the brakes were even manual.

TTur1996

We had the same experience as RobsZ28. Then we went with Strange 4 piston calipers. And they even got better. If you are having to pump the brakes at all. You have air in the system. When they are right, you wont push the pedal down more than an inch, and rock hard. There has to be something else wrong to be that bad. Tried every type of bleeding. Gravity was what got our rock hard brakes. You don't have to stand on them to stop either. And just like Rob also said. You forget they are even manual. They work that good. Best of luck. I hope you get it figured out.

01ssreda4

iTrader: (96)

I wanted to update with my experience now that ive driven the car. The pedal is hard, and you have to lean on it pretty good if you want to stop, it does stop though. I dont have confidence in an all out panic stop (which wouldnt happen often), stopping with hot rotors (which takes even more force) or holding the car on the line to build boost. It was fun, but I have to re-route my brake lines anyway so I think Im gonna reinstall the stock booster. I guess i prefer the confidence of power brakes.

StangEaterSS

iTrader: (41)

my update is as follows... I did get the pedal adjusted a bit better so travel is closer to normal. its real sketchy street driving it. your on the brakes tripple as hard as any other car. First pass at the track I couldn't stop the car at all and went past the return road and made a big loop. all the rest of the passes I had to use the chute to stop. This will get me by for now but I feel its kind of dangerous. I will be upgrading to Strange drag brakes on all 4 corners this winter.

01ssreda4

iTrader: (96)

Thats exactly how i felt too.

Launch

There's also this..

https://www.ebay.com/itm/NEW-82-92-o...ZTXk-B&vxp=mtr

Gives you much more room in engine bay, can run any camshaft you want, vaccum from engine not needed.

Old Geezer

iTrader: (3)

" its real sketchy street driving it. your on the brakes tripple as hard as any other car. First pass at the track I couldn't stop the car at all and went past the return road and made a big loop."

^^the Darwin award...

StangEaterSS

iTrader: (41)

hey, places that sell this strange manual master conversion kit will tell you that this works fine. I trusted them. it does not work fine. thank god i had a parachute so i could finish the season of racing this year.

N2RACINGLS1's

iTrader: (2)

So I wonder why the suppliers that are offering the manual master cylinder kits for sale are telling F-body owners to drill the plunger rod hole 1-inch above the factory plunger rod location on the brake pedal when it does not provide the needed ratios per brake manufacturers to apply correct line pressures. That is a ton of work getting the pedal assembly out of the car to drill the needed hole.. also if you drill it at the needed location the plunger is at a greater angle, which is not good!

This is not good and is unsafe!! I suspect this error is also causing several folks to change out rotors and pads more often due to warping from low line pressures and heat from longer stopping distances.

Would love to see brake suppliers respond to this apparent oversight.

Thanks

HioSSilver

iTrader: (8)

I built a brake systems for a 56 belair using ls fcar brakes. Now this car had manual brakes from the factory so pedal ratio was already pretty good for manual brakes. I used a 7/8 wilwood master on it and the beakes feel very near like power brakes. You may have to do a combo of things like more pedal ratio and a smaller master to get the brakes to feel good.

Be sure to check your caliper sliders to just to make sure they are in good working condition.