Joined: Aug 2017 Posts: 1,436 Threads: 59
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Interesting Paul
I too have found that budget Morris Minor linings can be, shall we say, variable. Whilst not going to the extent that you have (3.50x19 is my weak link) I've settled on a Mintex branded linings.
Be fascinated to know more.
Charles
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26-08-2020, 02:29 PM
(This post was last modified: 26-08-2020, 02:29 PM by Chris KC.)
An interesting read Paul and for what it's worth I think your analysis is essentially right.
Friction materials are tested exhaustively on dynamometers and actually deliver a considerable range of friction coefficients depending on the specific conditions of speed, temperature, humidity, pre-conditioning, etc. And guess which value the supplier likes to quote? Even though it may only occur under very specific circumstances.
Just how much analysis suppliers do on 'vintage' materials I wonder; it's not a huge market and probably doesn't have the budget OE applications command. Rather I suspect they supply what the majority of people ask them for. Even in the modern car industry, material selection is largely a question of what worked well on the last model, it is (for good reason) a very conservative business.
The area you might explore if taking this study further is the geometry of the drum brake itself. Many configurations were conceived 'back in the day' to deliver ever more 'self servo'. It's a road fraught with peril though, as the higher you push the output the further it has to fall. The fundamental reason drum brakes were almost entirely superseded by discs is stability; they are not more powerful than drums but continue to deliver a more or less steady brake torque when the nearest drum brake car is parked somewhere in the hedge. Maybe less a worry for sprints and hill climbs where there isn't time to cook them properly.
Yes, and tyres. It is more or less a given nowadays that - with the help of ABS - the brakes are capable of locking the wheels, so stopping distance in the modern world is all about tyre compounds.
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Fascinating article - I eagerly anticipate the follow up with details of the supplier and materials used
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Remarkable Paul. A big thanks for sharing all that with us. Waiting for the following.
Renaud
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HI Paul,
Interesting reading,
To my way of thinking the best thing was taking the drums and shoes to a brake specialist and having them matched ie skim drums and match thickness of linings to the correct Dia of drums giving maximum contact.
the other item I would fit is 10lb Residual valves one to each brake cyl
two things they do they retain 10lb pressure in the wheel cyl which holds pressure on the seals
which is also handy if the car is not used all the time
less chance of air entering the system
mount them directly after the master cyls
and (No ) they will not hold the lining against the drum it takes about 70psi to over come the return springs
Colin
NZ
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Assorted observations. I do recall trying to roughly work out the force on ends of shoes for Austin, semi girling and typical hydraulic. Seem to recall the hydr worked out much higher.
Linings certainly make a huge difference; my everyday 1964 car had acquired shoe by shoe used 1970s rear linings off other same cars. (economy has always been an objective!) The handbrake had become very poor and the foot (unassisted) braking heavy. I replaced the rear leading shoes with NOS Ferodo woven MZ (with zinc and asbestos!)and the difference was remarkable. Can lock wheels with handbrake.
Some hydraulic master cyls incorporate a valve intended to maintain line pressure. My 1960s Lockheed car has but 1950s Girling does not, although with cooling I wonder how much pressure is retained..
For those with mech brakes having the shoes radiussed off the car can be dubious as the shoes are not free to self centre as a modern.
Modern lining materials are intended for powere assist and a very extended life.
Joined: Aug 2017 Posts: 216 Threads: 7
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Location: Edinburgh/Lothians
Car type: Seven Special
Hi Colin,
Just by way of information.
I have twin ap racing master cylinders with adjustable balance bar and 10lb residual valves on both lines also m/c's below height of slaves.
M/c's started as 0.625 but changed to 0.7. pedal ratio is currnently 6:1. I can generate 1200psi line pressure without very much effort as measured with a Wilwood test guage. Could generate more if I pushed the pedal very hard but dont need to. Linings are arched by supplier as part of their racing service and double checked by me to the actual drum using my bedding in tool. Very little bedding in required, just a check really, compared to off the shelf commercial shoes.
I also changed from Silicon to Mineral fluid and accept I will have to flush annually.
If I'm brutal I can lock the wheels and thats on racing rubber. The balance bar allows for ideal set up for the prevailinbg conditions.
Not very 'vintage' agreed but a lot more confidence inspiring!
Paul N-M
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HI PAUL,
Sounds like you are right on the Ball.
When you build your own car for competition it is all ways satisfying developing new ideas and set ups that suit your style of driving,
and Knowledge keeps on expanding all the time
I would not be concerned about it not all being vintage build it for you.
Have fun
Colin
NZ
