manual brake upgrade

[edwards54 15]

I am almost finished with a 1969 mustang restoration and I am unhappy with the manual brake stopping power. (4 wheel drum obviously) I know there are expensive solutions to this problem and I may look into those down the road. The question I have is there a master cylander set up out there that would increase performance without putting on a booster?

 

Please let me know if you know of something,

 

and thanks for looking at the post

 

Bob

[Max Power 74]

I really don't know for sure, but I am guessing that there isn't a master that would make a difference. Your stopping power is determined by swept area of your friction material, and a master has no effect. Ease of braking is based on power assist or pedal leverage, and a master wont help you there either. Your master is doing it's job if it is functioning properly. Upgrading to a master that can displace more fluid isn't gonna make your wheel cylinders or your drums/shoes any bigger.

[foothilltom 33]

Agreed with Power Maximus. Assuming your wheel cylinders are working and your shoes are good, you're not going to see any benefit by adding mechanical advantage.

 

4 wheel drums just don't match the stopping power of discs, but you will get used to it. You just learn to plan ahead and be more alert. Plenty of folks got by just fine over the decades with drums, but if you're used to a modern car, it's a big culture shock.

 

That said, I upgraded my boys drums on his 69 coupe to front discs mostly to satisfy his mother. She is still on me to add an airbag :)

 

Good luck,

Tom

[Max Power 74]

 

That said, I upgraded my boys drums on his 69 coupe to front discs mostly to satisfy his mother. She is still on me to add an airbag :)

 

Good luck,

Tom

 

 

LOL....a rim blow airbag. The mind reels....

[edwards54 15]

Thanks for the input guys. After putting on new shoes, hardware, and a new line I still don't like the braking power. I feel like I still need to pump the brake to build pressure. Is there a way to test the master cylandar on the Car? Could there be air traped in the M.C. that's not being bleed? If the master is working properly and I want to upgrade to a power booster what is the easiest kit to install?

 

 

Thanks again for the help

 

Bob

[CandyAppleRed 10]

I hate to disagree with the above knowledgeable gentleman but I believe a master with larger bore would help. Would it be enough, I doubt it. It's all about pressure on the wheel cylinder. Pressure is measured in pounds per square inch. A piston with more square inches results in more pressure. That's what hydraulics is all about. A given amount of leg pressure on a small bore master cylinder is going to result in less pressure at the wheel cylinder than a master with a larger bore.

 

edwards54. If you press hard on your brake pedal does it hold solid, or fade slowly to the floor? A solid pedal means the master cylinder is in good shape. If the pedal slowly finds it's way to the floor it's time for a replacement. If it holds it's place but feels soft you likely have air in the lines somewhere.

Edited July 13, 2010 by CandyAppleRed

[foothilltom 33]

Well, I think we're all right. (And it's always cool to disagree, that's how we learn). My comment (agreeing with MP) was that increasing mechanical advantage would not actually provide more braking power.

 

Your comment about sufficient pressure at the wheel cylinder is totally relevant, though I was assuming that was not an issue. If there is not sufficient pressure to push out the pistons of the wheel cylinder, there is a big problem.

 

Given edwards last comment about pumping the pedal to build up pressure, I would back up and suspect more elementary problems (air in the lines, bad MC, etc.).

 

I'm interested in hearing edwards answers to CARs last question.

[CandyAppleRed 10]

My disagreement is that adding mechanical advantage will indeed increase braking power. It's all about pressure. The harder you push the faster you stop, that happens because you're increasing the pressure in the brake line. I don't think anyone would disagree that a brake booster increases braking power. It does it by using mechanical advantage to increase pressure on the master cylinder piston which in turn increases brake line pressure. Or at least allows you to use less leg power to achieve a given line pressure. Surface area, materials, methods and pressure all come into play in a brake system. Given the same same surface area, materials and method (staying with drum brakes) increasing pressure will increase braking power. Increasing master cylinder piston surface area will increase pressure.

[Max Power 74]

That's all well and good, but drum brakes rely on servo action to applying stopping power as much as any mechanical force or hydraulic pressure. Yes, a larger bore master can produce more hydraulic pressure, but can the rest of the system use it? Highly debatable. I don't think Ford would engineer it that way, but I could be wrong.

[CandyAppleRed 10]

I'm not sure what you mean by servo action. But hydraulic pressure is exactly what brakes rely on to function. Whether it be a caliper piston in the case of disc brakes or a wheel cylinder in the case of drum brakes, they exert force in direct relation to the pressure exerted on them by the brake fluid. More brake fluid pressure, more stopping power.

[Max Power 74]

I'm not sure what you mean by servo action. But hydraulic pressure is exactly what brakes rely on to function. Whether it be a caliper piston in the case of disc brakes or a wheel cylinder in the case of drum brakes, they exert force in direct relation to the pressure exerted on them by the brake fluid. More brake fluid pressure, more stopping power.

 

In the most base terms, yes. Press the pedal harder, stop faster.

 

Servo action is the rotating force of the shoes forming a wedge in the drum. It is why there are springs in drum assemblies, and why one shoe is longer than the other. It is the very principle on how drum brakes work.

 

Applying pressure to brake shoes via hydraulic force is not completely how the mechanical force of stopping works.

 

From Wiki:

 

 

Drum brakes are typically described as either leading/trailing or twin leading.[1]

Rear drum brakes are typically of a leading/trailing design(For Non Servo Systems), or [Primary/Secondary] (For Duo Servo Systems) the shoes being moved by a single double-acting hydraulic cylinder and hinged at the same point.[1] In this design, one of the brake shoes will always experience the self-applying effect, irrespective of whether the vehicle is moving forwards or backwards.[1] This is particularly useful on the rear brakes, where the footbrake must exert enough force to stop the vehicle from travelling backwards and hold it on a slope. Provided the contact area of the brake shoes is large enough, which isn't always the case, the self-applying effect can securely hold a vehicle when the weight is transferred to the rear brakes due of the incline of a slope or the reverse direction of motion. A further advantage of using a single hydraulic cylinder on the rear is that the opposite pivot may be made in the form of a double lobed cam that is rotated by the action of the parking brake system.

Front drum brakes may be of either design in practice, but the twin leading design is more effective.[1] This design uses two actuating cylinders arranged so that both shoes will utilize the self-applying characteristic when the vehicle is moving forwards.[1] The brake shoes pivot at opposite points to each other.[1] This gives the maximum possible braking when moving forwards, but is not so effective when the vehicle is traveling in reverse.[1]

The optimum arrangement of twin leading front brakes with leading/trailing brakes on the rear allows for more braking force to be deployed at the front of the vehicle when it is moving forwards, with less at the rear. This helps to prevent the rear wheels locking up, but still provides adequate braking at the rear when it is needed.[1]

 

 

Manual disc brakes are not very effective because of the amount of hydraulic force required to get the car to stop. There is no mechanical servo action, only pure clamping force. Early discs were all manual, and required quite a bit of hydraulic force to apply effectly, which is not pleasant for the driver. That is why "power assist" was developed. While not applying "more" hydraulic force at a maximum, it enabled the user to apply the maximum amount of force comfortably and repeatedly, using engine vacuum as an assist. The stopping power of disc systems relies on swept area of friction material more than hydraulic force.

 

Ford tried power assist drums, but found that heat dissipation was a problem. And if you think the master cylinder swept volume is key to stopping faster, look no further than 69 Mustangs. The 69 428 Cobra Jet cars used the same master cylinder as the smaller engined cars, yet bigger drums. What does that tell you?

 

All systems, when operating properly, can easily achieve lock up. No more hydraulic force is necessary when you can achieve lock up, as you already have more hydraulic stopping power than other components in the system can handle. Since pretty much every factory system can achieve lock up, very few will benefit from more hydraulic force. Ease of use and effective rate of stopping power are where more sophisticated systems are of great benefit to the user. And of course with discs, superior heat dissipation.

[CandyAppleRed 10]

:surrender:

That's a lot of info and I appreciate your taking the time to type it all out. You are obviously thinking way more in depth than I was. The OP asked if a different master cylinder would "improve performance". All the things you state (larger brake shoes, brake booster, disc brakes) would be better and more effective routes to a better brake system. But at this time he wasn't interested in going those routes. He just wanted to know if a different master cylinder would make a difference. You stated "Your stopping power is determined by swept area of your friction material, and a master has no effect." I simply disagreed with that, and actually still do.

 

Everything you laid out in your post, servo action and swept area of friction material are quite true. But they require hydraulic pressure to function. It is also certainly true that once you achieve enough pressure within the system to lock up the wheels more pressure is pointless. But, being able to get to that point using less leg force is achievable and desirable.

 

Rather than stating a larger master cylinder piston will build more brake pressure (even though it is true), I should have said it could build the same pressure with less leg force. I never said master cylinder swept volume is key to stopping faster. I simply said it will have an effect.

 

To boil this all down. A 4" master cylinder piston is not the route to braking bliss. But given the OP's parameters of leaving the balance of his system as is, a larger master cylinder bore is going to take less leg force for him to reach the point of tire lock-up. Or any braking point shy of lock-up. And I still have to say that is true.

[edwards54 15]

I haven't taken the car for a ride yet since posting the original question. When sitting in the drivers seat and I apply the brake pedal there is a solid hold on the pedal and it does not sink to the floor. I have an area that I will do some test driving tomorrow and see if it continues to consistanly hold pressure or if I have to pump up pressure. Ill post again tomorrow with my findings.

 

Thanks a-lot

Bob

[Crazyhorse 21]

:surrender:

Rather than stating a larger master cylinder piston will build more brake pressure (even though it is true), I should have said it could build the same pressure with less leg force.

 

This is actually backwards. A smaller master cylinder will build higher pressure, but move less volume. A larger master cylinder bore will move more volume at less pressure (for the same force input on the brake pedal). If your pedal hits the floor, and you have to pump to stop, and their is no air or leaks in the system; then you need a larger bore master cylinder (not possible with a stock system.) If on the other hand, both feet are on the pedal, and lifting you out of the seat and the car still isn't stopping you may benefit from a slight reduction in master cylinder diameter. The tradeoff is that you will have a longer pedal throw to compensate (still have to move the same amount of fluid). Again though, with a factory system this probably won't net anything substantial.

 

I went through all of this on the Bronco, as it has stock F350 front disks, and rear disks using Dodge 1 ton front rotors, and Caddilac calipers, all with a manual brake setup. Now that it's dialed though, I can jump on the pedal at 50, and lock all 4 of the 39" diameter, 200 lb wheel and tire assemblies.

[CandyAppleRed 10]

This is my last post on the subject as obviously I have a lot to learn. But... I always thought that if you put 1lb of pressure on a 1 square inch piston in a closed hydraulic system you will achieve 1psi of pressure within that system. If you put 1lb of pressure on a 2 square inch piston in a closed hydraulic system you will achieve 2psi of pressure.

[Crazyhorse 21]

It's Cool, we're all here to learn. Pressure is force divided by area. If you put 1 Lb of force onto a 1 square inch piston, you will have 1 pound/1 square inch, or 1 Lb. per Sq. Inch. If you now apply that 1 Lb of force to a 2 square inch piston, you will have 1 pound/2 square inches, or 1/2 Lb. per Sq. Inch. On the other end of the hydraulic system, at your wheel cylinder or caliper ti works the opposite direction. You take that 1/2 Pound/sq Inch of pressure and apply it to a wheel cylinder with a 2 sq Inch piston you will get 1 Pound of force output from the piston (1/2 Pound/sq Inch * 2 sq Inch = 1 Pound)

 

Hopefully this helps

[danno 128]

Great discussions, I am reading it all and thankful I have factory discs and do not need to worry too much.

[CandyAppleRed 10]

Oh! Sure!... Maybe in YOUR universe things operate that way. In mine they obviously operate quite differently...

 

Excuse me while I go hang a "For Sale" sign on my toolbox and go join a knitting club. :P

[edwards54 15]

I took it on a test drive, it wasn't far, I dont have working guages yet either. When I drove it the pedal held firm and I didn't need to pump the brakes. So at this point I believe I have functioning drum brakes. I understand that I could always switch out the master cylander but it probably will have little or no effect. If one day in the near future I decided to upgrade (I will need to keep the switch as affordable and easy as possible) what kit do people like?

[foothilltom 33]

I think this discussion was fascinating. I don't know about your experience, but I am pretty certain a similar discussion happening on any other forum would have degenerated into name-calling and insults. This forum is populated by intelligent (present company excluded), self-effacing, and humble folks who can disagree yet still remain completely civil and informative.

 

Well done, dammit.

Tom

[CandyAppleRed 10]

I think this discussion was fascinating. I don't know about your experience, but I am pretty certain a similar discussion happening on any other forum would have degenerated into name-calling and insults. This forum is populated by intelligent (present company excluded), self-effacing, and humble folks who can disagree yet still remain completely civil and informative.

 

Well done, dammit.

Tom

 

 

PEACEMONGER! :tongue_smilie:

[foothilltom 33]

Cheesehead!

[Burn 14]

OP, do a search for 1974 Maverick master cylinder. Its bore is 15/16" (compared to your stock 1"). Most the guys selling the Granada front disc brake conversions seem to be using the 74 Maverick Master cylinders...They must know that bigger isnt always better.

 

I'm using one for my manual front disc/rear drum setup and will give an update once I have it install.

[Burn 14]

OP, do a search for 1974 Maverick master cylinder. Its bore is 15/16" (compared to your stock 1"). Most the guys selling the Granada front disc brake conversions seem to be using the 74 Maverick Master cylinders...They must know that bigger isnt always better.

 

I'm using one for my manual front disc/rear drum setup and will give an update once I have it install.