Stopping Distances

Bob Bidonde

Bob Bidonde

Well-known member
This topic comes up often, and it is mostly as an excuse by some to avoid touring on main roads.


Is there a table of stopping distances for a stock Model A?


The only person I have seen test stopping distances is Flathead Ted.
 
Such a weird rationale – as if dump trucks and logging trucks weren't out on these same roads. The only way I see it making sense is if you as a driver don't know your own stopping distance and thus don't feel safe, but it seems that you could establish this empirically pretty easily.
 
Bob, what a great idea. Car owners testing their stopping distance and reporting back to the Barn. I will do this when I get home in May. How do you propose doing the test? 25 mph, level dry asphalt road? Anything faster may be a safety hazard. And I would propose reporting the conditions and status of brakes, like stock, juice, FHT modified, etc.

Many year ago my uncle participated in a braking test. I don't know who sponsored it. A device was mounted to the car that fired a mark on the pavement. The driver would respond when they heard the bang. Another mark would be placed when the driver hit the brakes. That way the reaction time could be measured as well as the total stopping distance. I can see a paint ball gun being used today.
 
I would do it in a big empty parking lot. Also if there's a good free GPS speed recording app out there that folks could use, that would probably be a more reliable baseline than trying to get a timely read on a speedo that may or may not be accurate.
 
Such a stopping needs to start with a common base line and the GPS for measuring speed is perfect.

It should be limited to stock Model A mechanical brakes using correct size tires, with the notation of either cast iron brake drums or original pressed steel, woven or bonded linings. ('Cheating' could happen with bonded linings as there are various hardness available.)

'Gentlemen, Start Squealing Your Brakes !'
 
Our club recently did a workshop on brakes and afterwards, all of the cars were tested. One of them was so bad, we didn't allow him to drive home before we got all that was possible out of that worn out setup. The best was a stop from 20mph in 19 feet on dry bitumen. The wheels were locked so with stickier tyres, it would have been less.
 
A shopping plaza is under ideal conditions which rarely ever exist. Too many variables to compile meaningful results. JMO
 
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Synchro, Best was 19 feet but what was the range? Was the best newly rebuilt stock brakes with cast iron drums, or what? Inquiring minds want to know.
 
As part of a reliability check a couple years ago The Beaver Chapter MAFCA set up a special run to test braking power and stopping distance. I wasn’t on that committee, so I don’t know if the data was saved or, if so, by whom. But it was a worthwhile event and I encourage every club to do it, along with a regular pre-tour season reliability check: lights, horn, braking power, wipers, seat belts, tire wear, etc.
 
nkaminar said:
Synchro, Best was 19 feet but what was the range? Was the best newly rebuilt stock brakes with cast iron drums, or what? Inquiring minds want to know.
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I can tell you exactly what the setup was in the best car because it was mine but first, the range. The worst car just about disappeared over the horizon - the one we felt obliged to adjust for him. BTW, he has spent some $ and time on them now and can't believe how good the are.
The front brakes were fitted with those floating pin wedges, cast iron drums and woven linings rivetted on. The back ones were stock standard - woven linings rivetted on and steel drums. I had done it that way un an effort to get something like the correct front/rear balance right. The back ones still locked too early so I have replaced the front actuating levers with a pair of the longer ones from the back. I don't think that has improved the stopping distance much, is any but it takes less pedal pressure and I don't have near as much brake fade. My brother in law has Flat Head Ted brakes on the front and I would rate them as about the same.
Dammit! There goes another secret. I also like to use a cross shaft from a LHD car. I drill out the rivet holding the arm for the rod from the pedal and move it over to the right side. When it is lined up with the pedal, it is nearly out of that dip it has in it so it goes under the gearbox By then, the clevis eye is further from the axis of the shaft and I have more leverage
I know, I know. That's cheating. Tell the hand! Safety come first. As they say, it is not only cars that are recalled by their maker!.
 
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That's interesting because I find the need to stop quickly much more in city traffic than out on the roads. and highways. I do like the state highways and county roads better than driving the Interstates, but not for the fear of stopping as much as holding up 80 mph traffic. Drive defensively in any case!
 
Synchro909 said:
The back ones still locked too early so I have replaced the front actuating levers with a pair of the longer ones from the back. I don't think that has improved the stopping distance much, is any but it takes less pedal pressure and I don't have near as much brake fade.
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Synchro, do the rear actuating arms fit the front brake shaft without any modifications? Sounds like a good setup.
 
I set my brakes up with the fronts working first and the rears last. Big difference. Back in the day on gravel roads you wanted the rears to work first. All cars now the fronts work first.
Something to think about.
 
Wick said:
I set my brakes up with the fronts working first and the rears last. Big difference. Back in the day on gravel roads you wanted the rears to work first. All cars now the fronts work first.
Something to think about.
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Wick, I AGREE! But try convincing some old(er) and not so old "Model A Mechanics" that insist on setting up brakes "as Henry did" or using the Brake Board. :p:p
 
I agree with Wick. My brakes are set up with more braking in the front. The "weight transfer" is towards the front when braking. By the way, the only time when locking up the brakes will result in shorter stopping distance is on gravel or dirt roads where the tires act as plows.
 
Y-Blockhead said:
Synchro, do the rear actuating arms fit the front brake shaft without any modifications? Sounds like a good setup.
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No, they are not a direct fit. The shaft on the rear brakes is bigger than the front actuating shaft so I made a sleeve. After removing the original arm, I put the sleeved rear arm on (oriented so the clevis is facing the wheel) and secured it with a rivet I also made. Be prepared to have to grind down the rivet at the back or it will hit the spring perch. The fact that the clevis is now higher than it was means the anti rattle springs have to be modified a little to keep the brake rod straight and that's about it. You will also have to twist the lever to get it lined up with the direction of pull on the front rods. I have a Philips head screw driver with just the right diameter shank to fit the clevis. I mount the lever on the actuating shaft and hold it in the vice while I give it a good nudge till the screw driver and shaft are parallel.
 
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Brake testing by humans, especialy old type humans will seldom yield results even close to the way they were when fresh out of the factory. While locking them up and skidding to a stop can be repeated many times close enough for every day use, a professional driver can normally shorten the stopping distance by at least 5% by pulsing. A lot of bent fenders and dead people could have been saved if they taught that in driver education 101.
 
Synchro909 said:
No, they are not a direct fit. The shaft on the rear brakes is bigger than the front actuating shaft so I made a sleeve. After removing the original arm, I put the sleeved rear arm on (oriented so the clevis is facing the wheel) and secured it with a rivet I also made. Be prepared to have to grind down the rivet at the back or it will hit the spring perch. The fact that the clevis is now higher than it was means the anti rattle springs have to be modified a little to keep the brake rod straight and that's about it.
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Thanks Synchro. Sound like something I want to investigate further. Always willing to learn something new.
 
Yeah, mine should be set up with more front bias. I can grab a hand full of E Brake if things get too serious to balance the rears. :)
 
Wick said:
I set my brakes up with the fronts working first and the rears last. Big difference. Back in the day on gravel roads you wanted the rears to work first. All cars now the fronts work first.
Something to think about.
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Agreed. That's why so many vehicles have disc brakes up front and drums out back and not vice-versa. Something like 70% of the stopping power comes from the front brakes.
 
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