Brakes (HELP!)

Good morning! I need some help with my brakes. I bought my 1930 Brookville Roadster from its second owner. It has manual Wildwood 4 piston discs up front and drum brakes in the rear. No power.

Ever since I purchased the car, it seems the braking isn't what it supposed to be. I started driving in 1963, so I know you have to apply more foot pressure than with power brakes. The problem is they won't allow me to bring the car to a quick "emergency stop".

I had a mechanic friend drive the car and he agrees with me on the lack of stopping power. However, when he looked at the brakes, he found that the front pads and rear drums are fine.

The car is equipped with a Wildwood Adjustable Proportioning Valve (APV). I'm new to street rodding. Will adjusting this help and if so, what is the proper procedure for adjusting the valve? Is this something I can do or should I trust this to a professional?

Thank you in advance

Denny is probably right....what sizes are the master cylinders?

Typically, someone uses a big bore cylinder with these calipers and the system wont get enough pressure.....

Do you use the Wilwood balance bar?

What is your pedal ratio?

Wow! Thanks for the replies.

Like I said this is all new to me. I have no idea what a balance bar or my pedal ratio is and no idea what size master cylinder I have. I'm at work now but will check this weekend.

All I know is the original owner said that when the car was built, it used to stop on a dime and give you a nickel change back. Evidently something has happened.

a dime aint what it used to be

Does it feel like you need to push harder to get it to stop.....like
really hard?

If you stab the brakes really hard, can you lock up the wheels at either end of the car?

Do you have a single master cylinder or two separate ones?

Did the car ever stop well enough in your opinion?

Robot...thanks again for trying to help me.

It have one dual master cylinder under the floor board. The brakes have been bled.

I've tried stabbin' the brakes and I can't get the front or back to lock up. This is why I came to CHR for suggestions.

Yes; I do need to push harder to stop the car. Luckily I can judge stopping distance pretty well and give myself plenty of time to stop. My only concern is that if I have to stop in an emergency.

Usually, the proportioning valve is used to adjust the front to rear balance. For instance, if the back brakes locked up earlier than the fronts, you would turn the valve knob to make the back brakes less effective. In your case, it doesnt sound like a balance problem.

A single master cylinder under the floor gives more information. There is a pivot point on the brake pedal. The ratio of the lengths is your pedal ratio.....it is the leverage. For instance, if from the pivot to the pedal pad measures 12 inches and from the pivot to the master cylinder rod measured two inches, your ratio is 12 divided by 2 or 6:1. Most cars run somewhere in this range.

There is no balance bar in your setup.....a balance bar exists when you have two separate master cylinders. The balance bar connects both cylinder inputs. The brake arm pushes on the balance bar somewhere between the two cylinders. If you move the brake arm pushing location, you change the force ratio between the master cylinders....but you dont have one so it's not a worry.

Next, the brake force is determined by the pedal ratio and the master cylinder bore. This is because there is a nominal force that you can push with your leg. That force is multiplied by the pedal ratio......let's say that you can push with 75 lbs times your 6:1 ratio so the master cylinder "sees" 75 x 6 = 450 lbs. Disc brakes need to operate at about 1000-1400 psi (drums less). Therefore, you need to run the equation PSI = Force/sq. inches

SO 1000 = 450 / sq in equals about .45 sq inches for the bore AREA. A 3/4 bore master cylinder give about .44 sq inches. To see what happens when the typical 1.25 bore master cylinder is used, we can calculate 450 lbs times 1.227 (area) equals 552 lbs! This is using the same ratio, same right leg, etc. but just a different master cylinder!!!!

mike

Robot/ Denny...thanks for the plethora of information. I will definitely do my homework this weekend.

Pat

One last suggestion....ask the previous owner if he knows what the master cylinder used is from....if it can be identified, it is easier to find the diameters (as opposed to taking it apart and measuring it).

Mike...Ask the original owner about the master cylinder is a great suggestion. However, since I originally spoke with him back in December, the number has been disconnected. I've searched the internet for hours and can't seem to locate him. Too common of a name (Robert Young from New Hampshire)
I'll have to measure it.

Have a great weekend!

Has anyone checked the rear brake adjustment? If theres slack u lose stopping power.

Couple of questions:

Does the system have residual flow valves: If the master is under the floorboard, you need a 2# RSV in the line going to the front disks, and a 10# RSV going to the rear drums.

Have you bled the brakes?

One thing I have had happen is I replaced my front discs without getting my rotors turned and my truck didn't stop worth a darn, same simptoms you have. The discs I guess didn't break in properly to rotors so no stopping power. The truck was down right scary to drive. Had the rotors turned and put new discs on it and now it will through you through the windshield.

pat, not knowing what I had, one thing i would do is get on a dirt road or some place not to hard to slide the wheels and id find out what each wheel was doing. lock the brakes up, slide the wheels and then get out and see if all of them are working, whether the front and rear brakes are balanced(locking up at the same time), all you would be doing is getting as reading on each wheel and then you will know what to work on. you don't have to get fast , just enough to slide the wheels. if all are working as they should then you will need to put a booster or something else to get it to stop. your front brakes should slide a little before the rear, if they don't that's where the(ATV) comes in. if you are use to power brakes then reg. brakes don't feel to good. do the slide test and let us know what's going on with each wheel. just go fast enough to slide the wheels on dirt now, don't wreck the car.:HMMM:

Thanks Mike...great suggestion. Now to find a dirt road???? (LOL) :)

Pat

I'd like to thank Pat for starting this thread and all the contributors. It has helped me a bunch.
Mike

Well call me stupid for even asking you this but I would think the first thing you need to do is bleed the brakes and maybe going ahead and bench bleeding the mc in case whoever put it on forgot to do it. Remember, you can't really trust other peoples work. Now I am sorry if I sound like an idiot here but you didn't say if you bled them or not. I don't know if you knew if they were bled or whatnot. But the thing that should be done FIRST (even if it doesn't seem like this is the problem) is check for ANY leaks. I just did a brake job on my truck and looked all over and rechecked everything 5 times or more and then out of nowhere noticed on the fitting from the brake hose to the caliper there was a small leak and when pedal was pushed it dripped and (probably) sucked air back in.
So...
1.) Check for leaks
2.) Bleed the whole thing starting from the wheel FARTHEST from the mc
3.) Do whatever else anyone here said to do in whatever order you wan't.

The Proportioning valve wouldn't be the problem that's for sure. Like someone said earlier all that does is keeps the rear brakes from locking up.
I remember someone on here (I think it was Southerner) telling me that if you run master cylinders under the floor that it's setting lower than the brakes so you need some kind of valve. Anyone know what I am talking about? I don't remember the name or nothing, but maybe that can be your problem if you dont have one.

That's all the info I can really give. Anything beyond that I am not 100% sure of and don't want to give you any false information.

Hi guys;
I just bled the brakes on my 54 Merc today and I made sure there was no air just brake fluid coming out. I took it for a test run and it just brakes like on the spot ....to a screeching halt...what did I do wrong???

Shawn,

My post about residual pressure valves is five above yours.

If your master cylinder is under the floor, you need a 2# RSV to the front disks and a 10# RSV to the rear drums.

My cylinder is behind the firewall, above the steering column.

Henry, thanks man. I didn't catch that. I did that post last night I was pretty tired so didn't read all the posts carefully, I kind of skimmed them. But yeah residual pressure vavle, got it heh.