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Brake efficiency
#1
I was thinking of fitting 1 1/4 brake shoes to my front brakes but concluded that although the linings would probably last longer, they wouldn't generate any more friction. Can anyone confirm whether they make any real difference?.

Looking at the picture of Damian's asymmetrical shoe I was wondering about fitting the wider shoes but trimming the linings down to say 3/4 of their usual length so that the shoe would be unlined towards the cam end. In theory you could maintain the same lining area (or maybe even slightly reduce it) but get more pressure due to the increased leverage. That is probably not an approved procedure but could be tested fairly easily if you don't mind experimenting and relining shoes a few times... In any case, my car has had the same front brake linings for 15 years and they are still going strong so wear doesn't seem to be a bit issue at the front.


Are there any other mods to get more pressure at the front without resorting to hydraulic or bowden brakes, such as using longer levers?
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#2
The 1 1/4” shoes provide no more braking power than the 1” but do last longer in my experience.

The offset shoes are arguably the best brakes (pre full girling rod-type) fitted to Sevens, in my experience.

Fitting a Girling front axle and radius arms will help prevent twist considerably which can help with braking efficiency - you can still use Austin stub axles...
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#3
Friction force = friction coefficient x reaction force, it has nothing to do with area. As Ruairidh says wear life should increase simply by virtue of there being more material. By the same token they will take longer to bed in.

Improvement due to Bowdenex conversion tends to be negated by excessive friction. I've converted back and although it still needs proper adjustment I'm already enjoying better braking.

The geometry of drum brakes is a complex topic - that's one reason why disc brakes are so popular! By all means experiment but the results may not please you. Keep in mind that a lot of heat can be generated during braking and that even and distributed contact with the drum is desirable.
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#4
Experimenting with shortened linings etc would likely encourage fracture of the alloy shoes, not uncommon anyway.
The closer the end of the lead lining is to the cam, supposedly the more forceful application (and tendency to grab).

It woud likely lead to bent cams but often wonder how brakes work with a very used trailing shoe so that  it does not contact.  (The trailing shoe obstructs the cam from further applying the lead shoe)
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#5
If Friction force = friction coefficient x reaction force, then an increased shoe area would reduce the reaction force, wouldn't it? Then a reduced area would increase the reaction force, however I probably have got it wrong.
Bob
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#6
(05-10-2018, 10:52 AM)Chris KC Wrote: Friction force = friction coefficient x reaction force, it has nothing to do with area. As Ruairidh says wear life should increase simply by virtue of there being more material. By the same token they will take longer to bed in.

Improvement due to Bowdenex conversion tends to be negated by excessive friction. I've converted back and although it still needs proper adjustment I'm already enjoying better braking.

The geometry of drum brakes is a complex topic - that's one reason why disc brakes are so popular! By all means experiment but the results may not please you. Keep in mind that a lot of heat can be generated during braking and that even and distributed contact with the drum is desirable.

I would have thought you could have an open cable running to a mounting point near the front of the radius arms and then a short bowden cable from there to the brake cam, this would deal with problems of axle twist and steering geometry and keep steering to a minimum. Or how about a bell crank mounted on the radius arm to reverse the movement of the cable and then a push rod to the brake lever, this would mean that the axle twist would pull the brakes on rather than off? - maybe they would tend to grab though .
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#7
(05-10-2018, 11:55 AM)bob46320 Wrote: If Friction force = friction coefficient x reaction force, then an increased shoe area would reduce the reaction force, wouldn't it?  Then a reduced area would increase the reaction force, however I probably have got it wrong.
Bob

Pressure, yes; force, no.
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#8
In response to Bob C's idea of using much thinner trailing shoes to aid braking, Bedford petrol powered trucks and buses used this system from at least the 1930's up to the 1960's. Like Sevens once retardation efficiency had been reached no amount of extra pushing of the brake pedal made any difference.
Still as exciting today, giant Austin Sevens.
Peter.
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#9
It was common to reduce the thickness / length of trailing shoes simply because they do less work than leading shoes and wear less (= saves money).
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