Have been trying to post new thread red light comes on then flashes for a few seconds then stops, if any interest in brake shoes send me a pm with your e mail address I will pass on to the guys making them
H: Hubs, Wheels and Tyres Eight inch brake ?
- Thread starter Julian R.
- Start date
no no no ofence, tom, i was just kidding, or is/was my correct english been to short.
But not with woven linings. Woven linings need to be ground/sanded to size..John
Just been playing around with a modified Conical rear hub to look like a Manx one, and I see that the shoes are completely floating, with single cam and flat shoe plates at either end of each shoe. The linings do start around the shoe more so than a Vincent shoe, but both are the same. A large washer at the static end and two return springs. This is not too different to the twin leader 8 inch that Triumph and BSA used. I asked my local brake specialist about the possibility of the shoes jamming or self energizing too much, but he said "No that never happens", so this tells me that you could do the same to Vincent brakes, with a vast improvement to be had. Anyone who has ridden one of these bikes knows that the front brake is very good, and a lot of racers put 2 together back to back for racing.........Maybe we need to improve Vincent brakes in this way like we did to overcome the steering geometry fault in the Girdraulics. Cheers.................Greg.
Power is Work over Time! Oder Leistung ist Arbeit pro Zeit! [P] = W = Nm/s
Greg,
I have reviewed all of the brake articles written in MPH through the wonderful work of Graham and others on the Database. Thank you to those involved!
Unfortunately, it does happen! It used to happen quite a lot at road races in the 1960's. A rider would grab the front brake and the bike would go down due to the drum brake locking. Brake engineers call this "spragging" and often the only way to release the brake is to roll the wheel backwards. This is the ultimate good news/bad news story. The good news is you could make a 7" brake do a stoppie, the bad news is it might do this anytime you grabbed the brake! As the engineers say, the the twin leading shoe is less stable than the single leading shoe or two trailing shoes (which is the most stable drum brake of all) The duo servo shoe brake is the most powerful drum brake, more powerful than 4 leading shoes, but is the most unstable. Patrick Godet uses the duo servo or dual servo brake on his new Flashes based on the old G 250 single leading shoe brake used by Seely.
What would make the brakes lock up easily? Two things, the geometry of the brake and the coefficient of friction of the lining. It is usually the lining we get to fool around with although we can mess with the geometry a bit. Drum brakes are rated by something called "brake factor." It is essentially the ratio of the drag of the shoes on the drum to the amount of squeeze on the brake lever. Each shoe has a "shoe factor", like the leading shoe has a factor of 1.75 and the trailing shoe has a factor of .5. The brake factor is 2.25 when both shoes are added together. This number gives you an idea about how little squeeze you have to put in to get a lot of braking. A brake factor of 2 is not memorable, but a brake factor of 6 might be grabby (or it might sprag).
For example, a Vincent front brake with Ferodo MS3 (the green non-metalic linings) has a coefficient of friction of .38 and will create a brake factor around 2. If you switch to the AM4, which has a coefficient of .44 the brake factor jumps to 2.75. That is quite a bit more self energizing. I think that is why it is so well-liked.
I have just had some linings put on that are .61 coefficient of friction. This runs the brake factor up to 9.0. I suspect that I will find in testing that this lining may be too unstable to use and will grab or sprag, but I have to start somewhere.
I don't believe there is any value in relining stock Vincent brake shoes. I think Trevor is correct and these shoes are junk. They are not hardened correctly. Assuming the replacement shoes are the correct material and hardened properly, that should be the first course of action.
There are lots of linings that are as good or better than AM4. It is just difficult to find this info. I would not get a lining without knowing its coefficient of friction. The Ferodo MZ41 that I believe Martyn is using has a coefficient of friction of .43 cold and .45 hot, which is essentially better than AM4, which goes down to .40 when hot. I am not sure if they have asbestos. I would pass if they did and choose a similar non-asbestos lining.
...and yes, I was trying to improve the brakes this way, much like the Girdraulics. Drum brakes, however, are wildly complex, unlike the Girdraulic!
David
I have reviewed all of the brake articles written in MPH through the wonderful work of Graham and others on the Database. Thank you to those involved!
Unfortunately, it does happen! It used to happen quite a lot at road races in the 1960's. A rider would grab the front brake and the bike would go down due to the drum brake locking. Brake engineers call this "spragging" and often the only way to release the brake is to roll the wheel backwards. This is the ultimate good news/bad news story. The good news is you could make a 7" brake do a stoppie, the bad news is it might do this anytime you grabbed the brake! As the engineers say, the the twin leading shoe is less stable than the single leading shoe or two trailing shoes (which is the most stable drum brake of all) The duo servo shoe brake is the most powerful drum brake, more powerful than 4 leading shoes, but is the most unstable. Patrick Godet uses the duo servo or dual servo brake on his new Flashes based on the old G 250 single leading shoe brake used by Seely.
What would make the brakes lock up easily? Two things, the geometry of the brake and the coefficient of friction of the lining. It is usually the lining we get to fool around with although we can mess with the geometry a bit. Drum brakes are rated by something called "brake factor." It is essentially the ratio of the drag of the shoes on the drum to the amount of squeeze on the brake lever. Each shoe has a "shoe factor", like the leading shoe has a factor of 1.75 and the trailing shoe has a factor of .5. The brake factor is 2.25 when both shoes are added together. This number gives you an idea about how little squeeze you have to put in to get a lot of braking. A brake factor of 2 is not memorable, but a brake factor of 6 might be grabby (or it might sprag).
For example, a Vincent front brake with Ferodo MS3 (the green non-metalic linings) has a coefficient of friction of .38 and will create a brake factor around 2. If you switch to the AM4, which has a coefficient of .44 the brake factor jumps to 2.75. That is quite a bit more self energizing. I think that is why it is so well-liked.
I have just had some linings put on that are .61 coefficient of friction. This runs the brake factor up to 9.0. I suspect that I will find in testing that this lining may be too unstable to use and will grab or sprag, but I have to start somewhere.
I don't believe there is any value in relining stock Vincent brake shoes. I think Trevor is correct and these shoes are junk. They are not hardened correctly. Assuming the replacement shoes are the correct material and hardened properly, that should be the first course of action.
There are lots of linings that are as good or better than AM4. It is just difficult to find this info. I would not get a lining without knowing its coefficient of friction. The Ferodo MZ41 that I believe Martyn is using has a coefficient of friction of .43 cold and .45 hot, which is essentially better than AM4, which goes down to .40 when hot. I am not sure if they have asbestos. I would pass if they did and choose a similar non-asbestos lining.
...and yes, I was trying to improve the brakes this way, much like the Girdraulics. Drum brakes, however, are wildly complex, unlike the Girdraulic!
David
Back in the 70s, I was racing My Blue Twin, Not very fast, After a bad road crash my head was / is in a bit of trouble, I had a pair of Slater alloy brake plates, The ones with the hole not in the centre, So I thought lets try and make a 4 leading shoe set up, So we sawed 8 shoes up so that we wound up with 4 shoes, Each shoe had two flat ends,ie fully floating, Maybe it was 4 trailing shoes ??, Can't blame Ron, It was my idea, He did the welding for me. It was better than before, But not as good as I needed, It did not grab or do anything bad, Maybe the linings were not good enough.
After a while I fitted a pair of Norton Commando front forks with the small soft pads, They were super, Then Nortons took the soft pads off the market because they wore out too quick, I then fitted the Norvil disc with the bigger caliper, Not as good because I for years could not get a soft enough pad, I don't think I found a soft pad until after I stopped racing the Special.
Cheers Bill.
After a while I fitted a pair of Norton Commando front forks with the small soft pads, They were super, Then Nortons took the soft pads off the market because they wore out too quick, I then fitted the Norvil disc with the bigger caliper, Not as good because I for years could not get a soft enough pad, I don't think I found a soft pad until after I stopped racing the Special.
Cheers Bill.
Looks like I had David's Springs in the 70s too !!, We had a race where we had to have a petrol stop at Cadwell,
Jim Duly with the Can. Cheers Bill.
Jim Duly with the Can. Cheers Bill.
A great period picture. (Just like a modern Formula1 pit stop.
)I can't see anything like that happening nowadays with Health and Safety ruling the roost.
Cadwell Goose circuit was very challenging for the brakes as you were on full fade downhill into Mansfield and so were lucky to have much brake when you got to the hairpin shortly after.