Mechanical brakes, what i did

CWPASADENA

CWPASADENA

Well-known member
In an attempt to make the Mechanical Brakes work the good when I restored My Tudor, this is what I did:

Per Les Andrews Book, I rebuilt or replaced EVERY component.

I TIG welded and re-machined the tracks insted of replacing them.

I installed new Cast Iron Drums and properly turned them.

I used Scandinavian Woven Lining.

I arced the linings to the drums.

I "Centered" the linings when installing them on the backing plates.

I installed "Floaters" in the fronts.

ADDITIONAL MODIFICATION

I lengthened the front levers by 50%.

Reason for this;

As designed , as close as I can figure, the Front/Rear Brake Bias on a Model A is 40%Front/60% Rear.

Most modern Front Engine, Rear Drive Automobiles will have a Brake Bias in the range of 60%F/40%R to 70%F/30%R. This is because under hard braking, with weight transfer, weight if the car will be shifted more to the front wheels and the car will not have a tendency to lock up the rear wheels under hard braking.

By increasing the length of the front levers by 50%, I added 50% more brakes to the front which results in a 50/50 brake balance. This is a lot better but could be better yet. This also adds 20% additional overall total braking effort for the same pedal pressure.

RESULTS,

I have about 150 Miles on the car. When I first drove it out of the shop, I wanted to be VERY careful to be sure the brakes worked. After a few easy trips around the block, it was time to really try the brakes. Under moderate braking, it does not take a great deal of pedal effort, stops nice and straight. Under heaver braking, you can now see the radiator start to dip down and it really feels like the fronts are working.

Yesterday, I was running along about 45 MPH and was hurrying to make a green light up ahead. It turned yellow too soon and I had to stop in a short distance. I applied the brakes to the point where I started where I could hear the front brakes just want to start to lock up. Actually I applied more brake then necessary for the situation but wanted to see what a panic stop may be like. You could feel the weight transfer to the front and I was easily able to stop well short of the intersection. It really gives you a very comfortable feeling that you really have good brakes. :)

The woven linings with the Cast Iron drums are quiet and do not "Growl" or make noise when coming to a stop, even with the wheels not in the straight ahead position.

I am not saying this is what any one else should do, it is just what I did and the results I had.

My Experience.

Chris

100_0133.jpg
 
Actually, I am of the opinion that you took away front braking instead of increasing it due to the amount of travel it now requires vs. the normal amount of rear arm travel. The brake pedal now must pull the arm further to apply the same amount of brakes on the front.

.
 
I'm going to also agree with decreasing the breaking action. By adding a longer arm, you decrease the force needed, but you have to also apply more movement.

Perhaps this would make more sense if you had lengthened the levers on the brake cross shaft. that would have pulled the stock lever further back. Or you could have also lengthened the push rod inside that pushes on the wedge.
 
What did you do about the brake rod adjustment? To get the results you want you would have to loosen up the rear brake rods. The front to rear ratio is usually adjusted by the brake rods. If you shorten the front rods or lengthen the rear rods you get more front brakes. to get more rear brakes shorten the rear rods or lengthen the front rods. By lengthening the levers you have changed the distance that the break pedal has to move to to lock up the front brakes. Lets say it took 2" of travel for the brake pedal to go from a slight drag on the all 4 brakes to lockup. Now it will take 4" of travel to do the same for the front bakes. However the rears will lock up at 2" and the fronts will not be locked up. But if you lengthen the rear brake rods so the rear brakes do not start to drag until the pedal is 2" down. Then all 4 brakes will lock at 4" pedal movement.

Bob
 
CW, I'd eat my lunch off your car ;) so clean, i adjusted my brakes to work the way you have, the fronts doing more than before. They work great and i have to watch when stopping too quick, like i'm in my conventional car. I can forget what i'm driving sometimes. But i'm real happy with my adjustment.
 
BRENT in 10-uh-C said:
Actually, I am of the opinion that you took away front braking instead of increasing it due to the amount of travel it now requires vs. the normal amount of rear arm travel. The brake pedal now must pull the arm further to apply the same amount of brakes on the front.

.
Click to expand...

Bob C said:
I was thinking the same as Brent when reading what you did to the arms.

Bob
Click to expand...

Jason in TX said:
I'm going to also agree with decreasing the breaking action. By adding a longer arm, you decrease the force needed, but you have to also apply more movement.

Perhaps this would make more sense if you had lengthened the levers on the brake cross shaft. that would have pulled the stock lever further back. Or you could have also lengthened the push rod inside that pushes on the wedge.
Click to expand...

Bob Johnson said:
What did you do about the brake rod adjustment? To get the results you want you would have to loosen up the rear brake rods. The front to rear ratio is usually adjusted by the brake rods. If you shorten the front rods or lengthen the rear rods you get more front brakes. to get more rear brakes shorten the rear rods or lengthen the front rods. By lengthening the levers you have changed the distance that the break pedal has to move to to lock up the front brakes. Lets say it took 2" of travel for the brake pedal to go from a slight drag on the all 4 brakes to lockup. Now it will take 4" of travel to do the same for the front bakes. However the rears will lock up at 2" and the fronts will not be locked up. But if you lengthen the rear brake rods so the rear brakes do not start to drag until the pedal is 2" down. Then all 4 brakes will lock at 4" pedal movement.

Bob
Click to expand...

I KNEW THIS ONE WOULD BE LOTS OF FUN !!!!!


Lengthing the FRONT actuating lever will result in greater torque at the pivot of the lever for the same force (pull by the brake rod) on the end of the lever. With greater torque at the pivot (in this case the actuator shaft), you have greater force at the end of the lever on the opposite side of the pivot (in this case, the little arm on the other end of the actuator shaft that pushes down on the push rod). You could also accomplish the same thing by SHORTENING the lever at the cross shaft. I found it easier to work with the front levers.

As originally designed, the front brakes contribute to apx 40% of the total braking of the car. By increasing the length of the front levers you do increase the FRONT braking by 50% but the total braking (Front plus Rear) by only 20% (beings the front brakes originally only contributed 40% of the total in the first place).

IE, As originally designed, if you applied a force (pushed on) the brake pedal to the point where you had 1000 Lbs. of total brake retarding force, 400 Lbs would be contributed by the front and 600 Lbs by the rear. (400+600=1000).

By increasing the length of the FRONT levers by 50%, you increase the amount of braking effort that the front brakes contribute to the total by 50%. Example, with the SAME PEDAL FORCE required to give a total of 1000 Lbs. in the above example, you still have 600 Lb of retarding force contributed by the rear brakes (because the pull on the brake rods has not changed and you have not changed anything on the rears), but now, with the 50% longer front levers, you have 600 Lbs (insted of 400 lbs) contributed by the front brakes (400+50% x 400=600) or (400 x 1.5 =600). Now you have 1200 lbs of total braking effort (600+600) for the SAME PEDAL FORCE as used in the first example (unmodified configuretion).

As far as adjustment is concerned. I adjusted the individual brakes in the conventional manner, THEN I equalized the side to side and front to rear braking by adjusting the length of the rods. I did this with the BRAKES WELL APPLIED but not locked up. I had the car up on my lift and the wheels off. I made an adaptor that will hook over the lug studs and used an old, beam style, torque wrench to measure the braking effort of each wheel. You can also do this by having the wheels off the ground and try to turn each wheel to check the drag of each brake. YOU HAVE TO ADJUST THE FRONT TO REAR BALANCE WITH THE BRAKES WELL APPLIED, just like you should do with an unmodified system.

It does take an additional 20% of pedal travle to achieve the same pedal force, BUT you also have 20% more TOTAL BRAKING.

If you were to lengthen the front push rods you are not changing any of the leverages. All that would accomplish is you would have to lengthen the front brake rods to rotate the levers further forward to be able to release the brakes fully. What you want to do is to have more force on the front push rods for any given pedal force.

My goal was to get the BRAKE BIAS closer to optiumun and also to increase TOTAL BRAKING EFFORT for a given pedal force.

Again, I am NOT saying everyone should do this BUT this is what I did and the results I got.

Chris
 
Last edited:
1931 flamingo said:
How did you "safely" increase the length of the front levers.
paul in CT
Click to expand...

I used four levers total. I cut to top off of two and the bottom off of the other two so I could overlap them. I TIG Welded them together and normalized them. I am not concerned at all about failure BUT I will not do any for cars that are to be run on the street. I do fabrication work and will only do this kind of stuff on competition cars that only see track use or on my own cars. I also shortened my own steering arm BUT I will not do them for others.

AGAIN, I am NOT saying others should do this, This is just what I did.

Chris
 
CWPASADENA said:
I KNEW THIS ONE WOULD BE LOTS OF FUN !!!!!

Lengthing the FRONT actuating lever will result in greater torque at the pivot of the lever for the same force (pull by the brake rod) on the end of the lever. With greater torque at the pivot (in this case the actuator shaft), you have greater force at the end of the lever on the opposite side of the pivot (in this case, the little arm on the other end of the actuator shaft that pushes down on the push rod). You could also accomplish the same thing by SHORTENING the lever at the cross shaft. I found it easier to work with the front levers.

Chris
Click to expand...

You sure you got that right? For the same amount of pedal you are now moving the front brake only 2/3 as much. I didn't take statics and dynamics in school but....
 
Very very interesting; I understand the concept that the longer arm would require less energy to pull it back and that the longer arm would increase the distance needed. Very very interesting :)
 
Bob Johnson said:
Chris,

Please give more details on

" I adjusted the individual brakes in the conventional manner"


Bob
Click to expand...

With the brake rods not yet hooked up, I adjusted each individual brake to set the clearance between the drum and shoe using the adjuster in the backing plate. Tighten the adjuster until there is a heavy drag on the brake and then back off the adjuster until there is no drag (or a very slight drag with new linings).

Then, hook up the rods and with the brake pedal blocked about 1/2 way down, adjust the length of each pull rod until there is aproximately 150 Ft. Lbs of brake torque on each wheel. I use a beam type torque wrench and NOT a "Clicker" type wrench. The actual value is not too important but all wheels must be equal to each other. This will insure you have equal brakes side to side and a 50/50 bias under moderate braking.

Release the brake pedal and check to see that all the brakes are fully released. If the brakes do fully release, check to see if you can shorten the rods just a little more before the brakes start to apply. If so, repeat the above step with a little less pedal travel. Idealy, you want the highest brake pedal with the brakes applied BUT you also want to insure the brakes will fully release and do not drag.

Even with the longer front levers, with the brakes adjusted in this manner, there is actually little additional movement of all the levers required to apply the brakes from a moderate level of braking on to where the brakes start will start to lock up.

After the brakes are initially set up, future adjustments to compensate for wear can be made with the backing plate adjusters only.

PLEASE UNDERSTAND, THIS IS WHAT I DID BUT I AM NOT TELLING ANYONE ELSE THAT THIS IS WHAT THEY SHOULD DO.

Chris
 
dr.j said:
Very very interesting; I understand the concept that the longer arm would require less energy to pull it back and that the longer arm would increase the distance needed. Very very interesting :)
Click to expand...

The brakes are adjusted to a 50/50 bias when moderately applied. The longer front levers insure this bias is maintained as braking effort is increased. After the brakes are applied to a moderate level, the shoes are fully seated against the drums, and it takes very little additional rotation of the levers (and therefore movement of the rods) to increase brake application. You are escentially just increasing the pull on the operating levers.

AGAIN, THIS IS THE WAY I DID IT AND I AM NOT SUGGESTING OTHERS DO THE SAME.

Chris
 
Last edited:
I understand what your saying im only an enigneering student but I did make it to staticts, dynamics, and physics. You are saying is that by lengthing the front brake arms you trade force for distance. Simple mechanics, Like using a pully set up. You have a longer arm so you have more torque but you have to increase the distance in pedal throw.
just out of curiosity what feild of engineering were you in?
Tibor
 
CWPASADENA said:
The brakes are adjusted to a 50/50 bias when moderately applied. The longer front levers insure this bias is maintained as braking effort is increased. After the brakes are applied to a moderate level, the shoes are fully seated against the drums, and it takes very little additional rotation of the levers (and therefore movement of the rods) to increase brake application. You are escentially just increasing the pull on the operating levers.

AGAIN, THIS IS THE WAY I DID IT AND I AM NOT SUGGESTING OTHERS DO THE SAME.

Chris
Click to expand...
I have to agree with you Chris in that if the brakes are adjusted to a close fit to the drum very little extra rotation is required and the length is mainly to increase the pulling power of the brake pedal. Seems to me the actual results speak for them selves. Engineer or not.
 
OK now I get it. Once the shoes engage the drums there is very little movement of the levers. Thus the extra length of the front brake levers does not make much difference and the front brake shoes "see" a greater pressure than the rears. Thanks for the explanation.

Bob
 
So, let me get this straight. You lengthened the front levers to get more force and leverage to the front brakes but shortened the steering (pitman) arm to get more force and leverage to the steering? Seems like a contradiction here.
 
You must log in or register to reply here.
Back
Top