Front/rear brake bias

[Bill G]

Before I did my brakes, Mine were kind of like Fred Flintstone brakes!

[Synchro909]

Thanks guys, I have stayed quiet so far just reading responses. There is some very interesting info there and I appreciate them. Here's what I am thinking after reading all of it and I'd like responses to it.
Back in 1927, I believe Henry wasn't going to put brakes on the front wheels of his new car but was forced into it if he wanted his cars on the road. There was a belief amongst many designers at the time that the front wheels were for steering, not braking. That is understandable when you consider that the majority of roads were unsealed and any enthusiastic use of the brakes resulted in the wheels locking. The driver has no steering if the front wheels are locked so that was to be avoided. I think Henry set the bias heavily towards the back to avoid drivers (often not very skilled) being put in that situation and for the same reason, advised that the rear brakes came on first. Things are different these days. We hardly ever drive on anything but a sealed road. I believe that over the years, the design of braking systems has changed (Ford included) because of that and that hanging on to what Henry did 90 years ago when driving was VERY different from today might not be the best for our health. I see no reason to not update Henry's design for the sake of safety. I know there will be some who will throw a tanty at that but.......
My current plan is to install the longer arms and adjust the brakes so the front come on slightly ahead of the rear. I expect there will be some fine tuning done when I take to the road to get it just right but I think I will have good brakes at the end of it.
What is the consensus on that?

[heneste]

I'm not sure about why the cars were setup with more braking at the back but I've often thought about possible reasons it may have been setup that way. I've seen some cars that locked up the front (accidentally of course) and the front axle ended up with a very large twist and radius arm bend. I doubt you would risk having that occurrence if the rears locked up due to the reinforcement provided by the axle housings. I've also wondered with the possibility of "death wobble" occurring, would you want to have the fronts lock up faster than the rears? I think modern cars do have stronger front end suspension setups so possibly this was a reason but just guesses on my part.

[J Franklin]

Maybe take into consideration the fact that exact brake equalization is necessary for safe front wheel bias braking. Even early hydraulic brake wheel cylinders were sized to apply differently front to back. Not sure on modern setups.

[CWPASADENA]

Originally Posted by Synchro909

My current plan is to install the longer arms and adjust the brakes so the front come on slightly ahead of the rear. I expect there will be some fine tuning done when I take to the road to get it just right but I think I will have good brakes at the end of it.
What is the consensus on that?

I agree with what you are going to do.

Please let us know how things worked out for you when you get your car back on the road with these modifications.

Chris W.

[PC/SR]

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I agree with the idea of increasing front bias, but, would not increasing the length of the front actuating lever actually require more pedal movement to get the same movement of the actuating rod and wedge movement? Should you not shorten the front lever? A longer lever will give you more leverage, but require more movement for the same shoe engagement. If you want the front shoe to engage earlier, I think you want a shorter actuating lever. Just trying to think this through. Maybe I got it wrong, am missing something.

[Synchro909]

Originally Posted by PC/SR

I agree with the idea of increasing front bias, but, would not increasing the length of the front actuating lever actually require more pedal movement to get the same movement of the actuating rod and wedge movement? Should you not shorten the front lever? A longer lever will give you more leverage, but require more movement for the same shoe engagement. If you want the front shoe to engage earlier, I think you want a shorter actuating lever. Just trying to think this through. Maybe I got it wrong, am missing something.

On the one hand, what you say is correct. On the other, I figure that if I adjust them so the front ones come on just before the rear ones, I will be compensating for the longer arm. Like I said, there will be some fine tuning required. A shorter arm would mean less braking force - not what I want.
No one has mentioned and maybe I'm on the wrong bus but I think that under heavy braking, if the car is fitted with flota mota rear engine mounts, the whole engine, transmission and back axle assembly moves backwards a little in elation to the chassis because the two springs will distort. That action would increase the braking at the rear and lessen it at the front so I'd be fighting against myself. The original solid mounts Henry used will overcome this.

[J Franklin]

If you get into a wreck, don't mention your modifications. I think the lawyers ears might perk up!

[updraught]

It might not do much for your story ... but the front wheels need to lock up on unsealed road to stop quick. The gravel piles up in front of the tires. ABS doesn't do this, so can take longer to stop.

[Jim/GA]

Originally Posted by J Franklin

Maybe take into consideration the fact that exact brake equalization is necessary for safe front wheel bias braking. Even early hydraulic brake wheel cylinders were sized to apply differently front to back. Not sure on modern setups.

Yes, on "modern" American cars with hydraulic drum brakes on all 4 wheels, before you started to see disc brakes up front (mid- to late-60s), it was a common design practice to have larger wheel cylinder diameters in the front than you had in the rear. For example, 1.125 inch diameter in the front and 1 inch diameter in the rear. This puts a constant bias to the front axle. The diameters quoted above give you a 56/44 bias. This is fairly typical, though some put more in the front.

Ideally you'd like the bias to be proportional to the fully laden weight distribution of the vehicle, plus add some more to the front to account for the fact that weight shifts from rear axle to front on hard braking. So put a couple of adults in the front seat of your car and measure the front and rear axle weights. Shift a bit to the front. That's your ideal braking bias.

Until Anti-lock Brake Systems were in common use, this question about the optimal front/rear brake bias has been debated amongst designers for years (decades). Loss of steering (directional control) when the front wheels lock up was always cited as the reason you did not want too much bias in the front. To overcome this, we were taught in Driving School to pump the brakes (to give some steering in between hard braking applications).

If the rear axle locks up (a big problem with pickup trucks with nothing in their beds), the rear of the vehicle tends to "swing around" toward the front. We've all seen this. We were taught in Driving School to "Steer into the skid," which means steer to the same side the back end of the car is swinging towards, to prevent this. If you have enough road surface to work with, this maneuver works.

IMHO, you all are way over thinking this front/rear brake bias question. Get the entire braking system restored well, just like new. No need to modify anything. Follow Ford's original adjustment procedure with the pedal steps, but swap things around to have the front wheels start to brake first (instead of the rears) and have front locked up at the last step. Then you are good. When braking, try not to lock up the front wheels, but if you do, pump the brakes.

I have had other Model A owners drive my car and ask me if I had power brakes installed. No, I don't. When they are right, these stock mechanical brakes are quite good. I don't have floaters in the front. In a panic stop, I have all 4 tires squealing. I have not hit anyone yet!

[Growley bear]

Geometry and ratio of travel, one lever to another. Just like gear ratio.
If you must reengineer the brake system, a longer lever at the front brake will decrease the amount of rotational movement. If the movement needs to be increased then the lever needs to be shortened or the lever at the cross shaft needs to be lengthened. If the wedge and pushrod are properly set up, the forward angle of the lever will be in the 15 degree ball park. Both sides should be very close to the same forward angle. With wedge at maximum travel it will come into contact with the wedge stud. At this time the brake lever should not travel past vertical; if it does the push rod can be bent.
Take the advise of Jim Cannon and bring the brakes back to Ford specs.

[BILL WILLIAMSON]

AND, I fergot to add, I make SURE I have ALL good brake parts & lube ALL metal to metal contact points, with High Temp Wheel Bearing Grease. Those little touches make a BIG DIFFERENCE, in EASE of operation!!!---NEVER take SHORTCUTS!!!
Bill Babble

[Jim/GA]

Oh, I forgot to mention, Les Andrews will be giving a technical seminar on Brake Restoration and Adjustment at the MAFCA National Convention in June (in Sparks/Reno, Nevada). He's going to talk about the design and proper restoration of the entire system, plus how to adjust the wheels for best braking. Lots of good information to be shared there! (This is just one of several seminars planned.)

I hope to see you there!

[Synchro909]

Originally Posted by Jim/TX/GA

Oh, I forgot to mention, Les Andrews will be giving a technical seminar on Brake Restoration and Adjustment at the MAFCA National Convention in June (in Sparks/Reno, Nevada). He's going to talk about the design and proper restoration of the entire system, plus how to adjust the wheels for best braking. Lots of good information to be shared there! (This is just one of several seminars planned.)

I hope to see you there!

I'd love to be there - you gonna pay the air fare??
Please post a report here on any tips Les might share.

[CWPASADENA]

If the brake system is properly restored and adjusted, once the brakes are initially applied, there is very little additional movement of the lever required to achieve full application.

With longer levers, there is not a problem with not having a good firm pedal that is only about half way to the floor when the brakes are fully applied.

When the Model A was first designed, if Henry had his way, the Model A probably would have had only rear wheel brakes like the Model T.

As Ford designed the new cars thru the 1930's the engineers designed more and more front brake bias into the cars because they started to understand weight shift to the front during braking and how to design the brake system to take this into account.

Longer front levers will change the bias more to the front. This has been proven to be a definite improvement to the Model A brake system.

It would be very easy to make up a second set of front actuating shaft assemblies with longer levers. Install them and see how you like them. If you do not like the results, remove them and re-install the originals.

I made my longer levers by using an original lever and cut the top off right below the "Y" or yoke. I took a second lever and cut it off right above the bottom part where the shaft is installed. the two levers are long enough so they will overlap about 3/4 inches and achieve a length which is 50% longer than the originals.

I then tig welded the two overlapped parts together. PLEASE NOTE, I used ONLY original FORD forged levers, not reproductions. I am a certified Tig Welder and if a person is not proficient with a TIG Welder, have a certified professional do this.

Installing longer levers may not be for everyone but the original post on this thread asked the question about the use of longer levers and some of us have responded to this question.

Yes, we can take the position that the Model A should not be changed but restored just as the factory made it because that was the way it was designed. However, if we take that position, we would not be enjoying the many modifications and improvements that make our cars safer and more fun to drive. Improvements such as more compression, better camshaft profile, better radiators, better lighting systems, especially brighter rear lights and third break lights, syncromesh transmissions, overdrives, packless waterpumps and on and on and on.

Again, this may not be for everyone but for those who would like a very simple way to greatly improve the braking of their Model A, give it a try, you may be pleasantly surprised.

Please understand, this is only my opinion, based on my education, knowledge and experience.

Chris W.