Hot Rods Trouble shooting brakes

I have started working on the brakes but after looking things over everything appears to be done correctly,the car has a dual master cylinder and a proportional valve and residual valves for front a rear brakes.

The car has brakes but they a sketchy,I have to stand on them to stop the car and the brake pedal has a very short travel.

The car has disc up front and drums in the rear.

I am told Austin Speed Shop built the rolling frame.

Anyone have any ideas on what my be amiss? HRP

 

If it is manual brakes, I would say it has a master that is a little too big. I'd recommend finding some or someone that has pressure gauges and testing exactly what pedal pressure you are stating with. Now with that being said I would be inclined to pull the master, find out what it is ( make, model ) measure bore and drop it a size. Like if is 1" drop it to 15/16" or even 7/8", the smaller bore will increase pressure, make it easier to push, at the cost of more pedal travel. The gauges are nice to use since you know the pressure before and after. Remember the pedal ratio is important also.

 

What Johnboy said makes good sense.

 

Any idea what the master is.

 

No sir,I set Ron a conversation asking him did he remember what he used but I haven't heard back from him yet. HRP

 

Be nice if all that info was written down..... Like on a build sheet.

 

Johnboy34 nailed it, what he said is exactly what I would do if it were my car. Smaller bore master will give you longer pedal travel and more pressure to the wheel cylinders or calipers.

 

Yeah,I do that but I have been building hot rods a long time and I believe it's something that you learn to do after you have a few builds under your belt,especially if you have a car for a long time,we tend to forget what we used and remembering parts numbers? forget that! HRP

 

Are the residual pressure valves facing in the correct direction? I heard that installing them backwards could increase braking effort, and reduce the pedal travel.
I had problems with the front residual valve on my disc/drum setup and I ended up just removing the valve from the front system and the brakes worked 100 times better.

 

There are so many variables in the system is why I recommend checking pressure. Since you said it was built in a shop one would hope it was put together correctly, parts not installed backwards and the like. If the pedal ratio is close, should be at least 6 to 1 for manual. You can read a ton of books on this subject and you can accomplish an improvement in many ways, from smaller bore calipers and wheel cylinders, more pedal ratio and on and on. What I pointed you to would be a quick and easy way to start to make it better. And to add a picture of the master here would get you a good idea as to what it is, even easier if it were in your hands.

 

Ron thinks he used a '79 Corvette master cylinder. HRP

 

Yep! There's lots of tweaks. And Johnboy has given some great info.

The short pedal travel would certainly lead to an investigation of the pedal ratio. When stuffing 10 lbs of stuff into a 5lb bag it's tempingly easy to alter the amount of movement needed with in the bag to get stuff to fit.

Manual brakes require 6:1 ratio so that your foot can create the desired clamping pressure at the brakes. In between your foot and the brakes you can gain or loose that mechanical advantage by altering bore sizes.

If the pedal ratio is short due to size limitations and constraints then every advantage to gain should be utilized, certainly you can't afford to loose in mechanical advantage. On the other hand, if you can afford to get the pedal ratio in line everything will improve.

 

make sure its s deep bore master for manual brakes good luck , fighting similar issue, just changed front pads turned rotors and change the hardware. Floating pins on bottom gummed up, pads were poor quality, also change pedal ratio from 5 to 6 to 1, doing rear brakes now seems to have helped. A lot of dirt etc from open wheels on the bottom we just dot see, good to do an inspection on regular basis. Part of my issue was sticking pads.

 

That corvette master would be for disc / disc.
Otherwise - johnboy

 

Trouble Shooting Brakes - Why do you want to shoot your brakes and how is that giving you trouble? Or was it Troubleshooting Brakes?
Sorry, it just reminded me of ;
Let's Eat Grandma, versus Let's Eat, Grandma
A little Monday morning blues levity.

 

It's amazing how much trouble a simple " 's " can cause.

 

Yeah,but ain't it amazing how many arses worry about punctuation and sentence structure.

When I was a kid,I remember my granddad, High-pockets, tell my grandmother if she would turn off the light he would eat it,I thought he was a glass eater.

BTW,if I continue have these problems I may end up shooting the brakes. HRP

 

Danny are these power or manual???

 

The brakes are manual. HRP

 

If you have a Corvette master, It's most likely 1" or 1 1/8", This one for a 78 Monza Manual disk-drum should fit in it's place. Chevy didn't make many small bore masters. Increasing caliper bore and/or wheel cylinder bore would do the same thing. If pedal ratio is 6 to 1 dropping from 1" to 7/8" will decrease pedal effort by about 30%. As another note Ford made more bore sizes to switch with but fit could be a problem without moving and/or changing tubing. Then there is always the Wilwood, big size and big money. But back to my first suggestion, get a hold of pressure gauges ( they screw into bleeders front and rear ). That way you know exactly what there is and what you need to do to remedy your problem, anything else is a guess.

http://www.rockauto.com/en/catalog/...056675,brake+&+wheel+hub,master+cylinder,1836

 

Thanks a lot,nice to know there is something that probably will fit the same as whats already in place. HRP

 

Just make sure it is for a manual brake and has a deep brake rod hole.

 

Here is a good reference to the pedal ratio.....

 

I suspect that all 79 Corvettes had power brakes and a quick parts search shows a 1-1/8 inch bore master cylinder. As has been mentioned, all 79 Corvettes were disk/disk. Another consideration is which is front and rear on the Corvette as it determines which brakes actuate first. The front port isn't always for the front brakes.

 

Some Camaros and Novas had disc/ drum setups and had manual master cylinders. Power brakes were optional. I have had good luck with a Mustang 2 master cylinder used in a manual disc/drum setup. They are compact ,easy to find and cheap. Used on my last Morris Minor street rod with a Speedway Model A pedal assembly. Adjustable proportioning valve and residual valves.
Had same issues with the same Corvette master you are using in a 35 Ford. Ended up putting an 8 inch power booster in the car.

 

Before you start changing anything, disconnect the pedal push rod and make sure the pedal can fully travel without any binding. The last two rods I trouble shot had pedals that would not fully travel without binding, resulting in the exact same problem you're having. Then verify the pedal ratio and master bore.
Note-ALL Corvette dual masters are disc/disc, jfyi.

 

I had the same issue. F100 brakes up front and maverick Brakes in the rear. I think I had a 1 1/8 bore master cylinder, brakes were rock hard but had no stopping power. I put a 7/8 master from wilwood. They work perfect now. I would have liked to use a master out of a production car but I could not find anything that would work for me.

 

I was going to agree with Engine man. When i put mine together, i mixed up the lines. Make sure the front line goes to the right place.

 

the master cylinder for a manual brake 1973 Elcamino has a 1 inch bore.
http://www.autozone.com/brakes-and-...ter-cylinder-brake-system-/706812_0_2558_3482
There is one for 72 Monte Carlos and other GM rigs with a 15/16 bore.
Here is the link to that one to use as and example. http://www.oreillyauto.com/site/c/d...173925_4398&pt=01292&ppt=C0066#itemDetailTab_

Both of those are quick search examples of what might work and an idea of what to look for. I'm going to have to dig one of my old auto mechanics text books out and study the brake section to remember the exact mc bore size vs pressure and travel thing though.

 

You need all the components to be correct. In my 54 truck with disk drum, I just used the components from a 70 Chevelle. Booster master, proportioning valve, etc. put it all in bleed the brakes and stop on a dime. If your not sure, get a good shop to fix it right. 1000 hp, and no brakes not a good combo.


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