Brake set up.....

nosbod

nosbod

Member
Good afternoon everybody from a wet and windy uk. If the cold hasn't ceased up everybody's grey cells in the US perhaps somebody could answer the question as to why we set our rear brakes to come on before the front ones when as far as I understand the exact opposite is true of more modern set ups ?
It has always confused me but there must an obvious reason that I have missed. I am off to compete in my first sporting trial next week so will need the brakes up to scratch.
Regards
John
 
From the Ford service bulletins:

"......pull the brake pedal all the way back until it is against its stop - then adjust the rod until there is about 1/16” clearance between end of rod and rear flange of center cross member (leaving a little clearance between end of rod and cross member prevents any possibility of the end of the rod rubbing against the cross member and causing a squeak).

"After adjusting the brake pedal to cross rod, assemble side pull rods to brake operating and cross shaft end levers. When assembling the side pull rods, pull the brake operating levers on the front axle back and the brake operating levers on the rear axle forward (taking up all idle movement). Then with the levers in this position adjust the side pull rods so they can be assembled to brake operating and cross shaft end levers.

Next adjust brakes by turning up the adjusting wedges as described on page 202 of the January, 1928, Bulletin. After the brake rods have been correctly adjusted car owners should be notified that this adjustment must not be altered. Service brake adjustments must be made only by means of the adjusting wedge at each brake."

From page 202:

"Make all adjustments with brakes cold. Jack up all four wheels. Release hand brake lever. See that wheels revolve freely. Turn the adjusting wedge at each brake (not the pull rod) until the brake drags, then back off the wedge 2 or 3 notches or just enough to allow the wheels to revolve without drag. On new cars brakes will sometimes drag slightly for ¼ or ½ revolution, due to slight high spots. Some judgment must be used in setting such brakes, for if the adjusting wedge is backed off sufficiently to allow the wheel to revolve freely, the brake pedal will go all the way to the floor board when the brakes are hot. A slight drag in one or two spots will do no harm, as the brake will soon free up when the car is driven a short distance and the brake drum slightly expands due to the heat generated. For this reason, brakes should not be adjusted with the drums hot, as when the drum contracts upon cooling it would cause the brakes to drag. To insure correct equalization have one man only check the brake pressure by rotating the wheel. If the above adjustments are correctly made the brakes should operate as follows:

1. Rear brakes should just start to hold when brake pedal is depressed approximately 1 inch.
2. Depressing pedal about 1/2 inch farther should tighten but not lock rear brakes and cause front brakes to just start to hold.
3. Depressing pedal approximately another l/2 inch should lock rear wheels and hold the fronts very tightly. With properly adjusted brakes this should not exceed one-half of the total possible pedal movement.
 
Many thanks Ron for your prompt and informative reply but it still does not explain why we set them up with the rears doing more work than the fronts , the opposite to more modern cars.
 
I was told that Henry's 'logical' thinking was that you could steer out of a skid. Now that slightly contradicts physics so I set mine to come one first in the front. I am sure someone will correct me if I am wrong though....

Mike
 
nosbod said:
Many thanks Ron for your prompt and informative reply but it still does not explain why we set them up with the rears doing more work than the fronts , the opposite to more modern cars.
Click to expand...

Technically we don't! They are that way by design and is based on the leverage applied. The rears have more leverage and come on SLOWER. The fronts are just the opposite. If you simply remove all the slack in the system that is the result. The front brakes start later but "catch up" to the rears making full contact with the drums at nearly the same time. However due to the increased leverage at the rear, the pressure is greater.

If you attempt to defy the system by either tightening the front rods beyond slack removal OR loosening the rear rods (introducing slack) you create another problem. When pressing the pedal the fronts will apply first and you will have difficulty pressing the pedal far enough to fully engage the rears.
 
Many thanks Marco , that does make sense and gives me confidence to set them up as Henry wished. Its not that I doubted him but I do like to know why when it seems counter intuitive to my way of thinking.
 
Hello John,
The way I remember it is that the mechanical reaction is slower for the rear brakes than the front, all 4 will catch up to each as they all approach fully applied, someone will correct me if this is wrong
Sorry I missed you last September for a chat and a few pints, how far from Stevenage are you?.

PS, I wish I could type faster Marco beat me to it, this was my brief explanation, his writing on any subject are so easy to understand.
 
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I'm pulling this out of the basement....
Originally, I think that they thought the car would flip over if you locked up the front brakes, so the T's never had front brakes at all.
Moving into the A age Henry still couldn't totally shake this belief, so the rears were primary stoppers.
 
Weight transfer during braking also has much to do with the front brakes on most all vehicles doing more work than the rears.
 
Hello Brian, yes it was a pity not to catch up. Maybe next time. We are about 2 hours or so from Stevenage which is small beer compares to the distances you will be use to.Back now to the garage to do what Henry told me to do in the first place. Many thanks everyone for your feedback
 
On modern cars, the rears still come on slightly before the fronts. This sets a fore aft weight transfer of the cars, allowing the fronts to be applied harder as there is now more car weight on them. The setup is performed in the master cylinder by a spring that separates the two hydraulic circuits.
 
On a Model A: Common sense reasoning & my own experience convinced me that ALL 4 brakes should apply at the EXACT SAME TIME!! (AND, you'll have a good high pedal.)
I'M THROUGH!!!! Bill W.
 
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The recent Model A Times magazine has a short article on these brakes. If or when mine need adjusting I might just try this method.
 
Maybe one may want to experiment & experience something with one's Model A mechanical brakes as follows:

A. For safety sakes, with no traffic in sight, carefully go down a fairly steep back-road hill on a partially slick wet paved road or a graveled road at about 35 mph or so, & immediately jam on your brakes with your Model A brake pedal as follows:

1. First: With both front brake rods disconnected & with both rear brake rods connected; and,

2. Second: With both rear brake rods disconnected & with front brake rods connected; and,

3. Third: Report back if you experienced any difference as to how your vehicle reacted while going downhill with locking only the rear wheels as compared to going downhill with locking only the front wheels.

4. Then, if one sets up one's Model A mechanical brakes such that one pair of wheels of wheels will lock up first, this very simple experiment may help a little to decide which pair of wheels one may want to lock up first.

5. Experimenting & gaining "actual" experience always beats trying to decide something from reviewing several different written opinions.

Hopes this helps.
 
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