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Misc: Everything Else Brakes, Linings, Drums and Shoes

davidd

Well Known and Active Website User
VOC Member
Brake linings contain many odd materials to make them work better and I don't think that they all age at the same rate. I tend to look at linings like tires: fresh ones seem to work better. Additionally, adhesive technology has improved considerably over the decades.

When the friction of a lining is increased it makes the brake slightly less stable. Squeal is one of those problems that arises from improving the mu. Squeal, being a result of vibration, can cause mechanical destruction of the springs or the hooks. The lining itself tends to wiggle around and vibrate, which is why we chamfer the leading edge of a new, tall lining. You don't have to chamfer worn linings because they have lost enough mass to be much more stable.

Manufacturers tend to "detune" the rear brake to prevent the rear wheel from steering the bike by stepping out sideways during heavy rear braking. Vincent detuned the rear brake by activating the trailing shoe most. On the front brakes, it is the other way around. the leading shoes are activated most.

With the detuned rear brake, the AM4 linings cannot get the bite they need to cause squealing. Almost all brake linings are hygroscopic, so they will absorb water if they are left idle for a period. This will also increase the friction of the lining which results in that early morning squeal or harshness that disappears quickly with a little heat.

David
 

Albervin

Well Known and Active Website User
VOC Member
Interesting thoughts here. I have always been able to get maximum retardation out of my rear AM4 brakes on the Rapide. Almost lock up levels on dry tarmac. I can still barely get decent power on the front. Yes, I have tried truing, centring etc. My next step is different compound on leading and trailing shoes. All good fun.
 

vibrac

Well Known and Active Website User
VOC Member
I must admit that the rear on the Comet racer was if anything too fierce coming down through the gears to Cadwell club circuit hairpin (in the days when the club ran meetings :rolleyes:) you had to be gentle on the rear or the whole lot would lock I have sorted something softer for the twin racer rear (Its one drum as well)
 

timetraveller

Well Known and Active Website User
VOC Member
I have failed to understand something important in David's remarks. On the front, the brakes are handed and yet both activating levers point forwards. So I do not understand the bit about activating the trailing shoe more or less. Similarly with the rear. On 'B's and 'C's there are two handed brakes and on the D the lever is upside down compare with the same side on the earlier bikes. Sorry if my brain has ceased to function. If necessary I can blame the lock down.
 

bmetcalf

Well Known and Active Website User
VOC Member
When the cam rotates, it either contacts the H48 plate at the outer or inner edge. The outer edge contact spot is ~1" farther from the shoe pivot point and has that bit more leverage to press the shoe against the drum.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Statement.
Vincent detuned the rear brake by activating the trailing shoe most. On the front brakes, it is the other way around. the leading shoes are activated most.
David my handsome,
Please explain the detuning of brakes? As far as I know, the cam operates the leading and trailing shoes simultaneously. Top shoes at the back are leading and lows are trailing.
Front lower are leading and forward uppers are trailing.
bananaman
 

davidd

Well Known and Active Website User
VOC Member
Just as Bruce has indicated, when using a flat cam the brake lever turns in one direction. This means that the cam hits one shoe high on the H48 and the other shoe activated by being struck low on the H48. The shoe that is struck low on the H48 is pushed further than the shoe that is being struck high on the H48. The designer has a choice to have the leading shoe or the trailing shoe move further simply by deciding which way the brake arm is pulled.

I have been told that the rule is if the brake arm is activated in the direction of wheel rotation that the trailing shoe is moving the furthest. If the brake arm is moving in the opposite direction of the wheel rotation, the leading shoe is moving the furthest. I think this rule should at least help with the "handed" question. Phil Irving was a proponent of having the front leading shoe activated by hitting low on the H48. The reasoning was the desire to give the leading shoe the benefit of the mechanical advantage. On the Vincent, the brake lever moves opposite to the rotation of the tire, so it fits the rule.

The rear brake, on the other hand, has the brake lever moving in the same direction as the rotation of the tire. Thus, the trailing shoe is being activated to move the furthest. This will not provide the same braking as the front shoes. I think if you note how the cam is turning you will find it is pushing the lower shoe on the lower edge of the cam, which is the trailing shoe.

On some series Ds with one brake, the brake arm lever is pointing down. Thus, it is activating the top shoe (the leading shoe) on the rear to move the furthest. The brake arm is now moving in the opposite direction of the tire rotation.

David
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Thank you, David, my handsome, a good explanation. Question:- Both my "A" & "B" Raps have model "P" braking system at the back,(this giving equal pull like the front brake), will it work better if the torque arms hang down like a "D"?? when it was done I had double the movement on the brake pedal so cut and shortened the brake arms by an inch.
bananaman
 

Matty

Well Known and Active Website User
VOC Member
My comet brakes have always been bad ever since I bought it in 1956.
It originally had the old green (Mintex?) linings which were not too bad if I remember but since then I have tried 4 or 5 different makes of professionally fitted on linings and have also tried the following tricks.
The brakes however seem to work well once or twice in the morning but then just fade away - which I had put down to a fine layer of rust, - but this happens every day !!
1. Had oversized linings turned to fit the drums - no improvement.
2. Cut about a quarter of the trailing shoe lining off, reasoning that the leading shoe wears most just leaving the pretty ineffective trailing shoe to push on the drum. - this also means there is more leverage on the trailing shoe because the metal shoe is longer than the lining and perhaps the shorter trailing shoe wears faster. This gives a small improvement.
3. Tried different brake reliners who promised their linings would fix it. This did not work.

I know that the brake arms are set to operate at near 90degrees and the cables, compensation arm etc are all set to optimum and have rebuilt and owned many bikes both British, German, Italian, and Japanese over the last 60+ years and have only ever had poor brakes with the Comet in all the 100,000 miles I have done on it.
I am surprised that the forum states that the brake cam has a different lift depending on which way it is operated, I have never noticed this which could account for my problem if the cams are reversed - will go out now, take the front wheel out and have a look but have also had thoughts in the past of making the cams shorter to give more leverage but obviously more movement at the handlebar lever.
I have been through this before on the forum many years ago but will have another go when the Corona virus shutdown is in operation, or will use the Fireblade when I really want to stop !!
Matty
 

Matty

Well Known and Active Website User
VOC Member
Hi - Have just understood about the relative leverage of the two ends of the cam on the brake shoes and the reason for a small difference in leverage to the leading and trailing shoes.
So that is not my problem and will have to think of something else - tried the trick of slackening the spindle,
applying the brake and doing the spindle up again, some years ago to little effect.
I still wonder if it is really the material of the drums or if ribbed Shadow ones are the answer.

This however would be an expensive experiment unless I could borrow a front wheel with Shadow drums from somebody to try !!
 

greg brillus

Well Known and Active Website User
VOC Member
Matty I have to ask if you know what material your front brake drums are made of........The early ones are steel and no modern normal linings will work, only the very course woven linings work with these drums. From your description this sounds like your problem........A change to cast iron either plane or ribbed drums will make all the difference. Cheers.......... Greg.
 

davidd

Well Known and Active Website User
VOC Member
will it work better if the torque arms hang down like a "D"?? when it was done I had double the movement on the brake pedal so cut and shortened the brake arms by an inch?
I think that it will have the opportunity to work better with the levers hanging down. I am not certain why the lever would move further. A friend of mine walked into the shop when I had all the Vincent brake plates on the bench. He asked what I was doing and I mentioned the problem stated above. He told me that he had changed the lever on his Suzuki rear drum from down to up and in the last race he realized that his rear brake did not work as well as it did before. After I explained what he had done, he moved it to the original down position and it regained its former performance.

If you notice that your brakes tend to work better in reverse, then switching the arm would be logical.

I still wonder if it is really the material of the drums or if ribbed Shadow ones are the answer.
If your drums are cast iron I suspect you will find them about the same as Shadow drums. I tend to agree with Trevor that the major problem with Vincent brakes stems from the soft shoes. The shoes are not up to the task. Having changed the shoes I went with high friction linings and the combination seems to work well.

However different the performance is from the cam and the trailing shoe, the real culprit is the "equal work condition" problem that has been discussed before. It is almost impossible to get shoes to wear equally. What happens is that the leading shoe is pushed into the drum aggressively and wears very quickly. You are now stuck with the slow wearing (and performing) trailing shoe hitting the drum first until it wears enough to allow the leading shoe to hit the drum aggressively again. Matty has described how this happens. By eliminating or minimizing the trailing shoe you will get better performance. The reasoning is that the trailing shoe is preventing the leading shoe for doing a good job. A soft, high wearing lining on the trailing shoe would be an advantage. This is what Bill Hancock used to advise.

Apologies to Corey for the divergence.

David
 

Marcus Bowden

Well Known and Active Website User
VOC Member
I think that it will have the opportunity to work better with the levers hanging down.""" I am not certain why the lever would move further."""
David.
With normal set up with the cross shaft, cranks & rods to brake arms, if brake pedal pulls the cable 1/4" then rear arms move 1/4". With model "P" system where a continuous cable goes from brake pedal to LHS arm round the back of the wheel to RHS arm to an anchor point. Now 1/4" movement of cable will move LHS 1/4" but as the cable sheaved around the back of the wheel it has to be moved another 1/4" for the RHS arm to move the same as the LHS. Does that make sense? any way it is better but will look into hanging the arms down as sons "D"Rap ear brake has always worked better than the "B"&"C" rear brakes.
 
Last edited by a moderator:

Albervin

Well Known and Active Website User
VOC Member
A bit off tangent so sorry. Douglas was experimenting with expanding brake shoes and disc brakes in the 1920s. They had a combination of cable and rod for the front brakes operating on spun or pressed steel drums. Using the rod reduced sponge but braking was still woeful so they tried different linings and bang. If only they had used steel discs and fibre callipers instead of the reverse they would have nailed it.
 

Matty

Well Known and Active Website User
VOC Member
Thanks Greg - going back a few steps it could well be that my drums are steel - I will have to try with a file to try to find the texture of the metal. I have always felt there was some sort of incompatibility between the lining material and the drums.
I will have a look on the spares site for prices which will no doubt be high for plain or ribbed ones .
But does any one have some plain ones I could buy that they have taken off to replace with ribbed ones to make a Shadow wheel please.
Matty
 

Matty

Well Known and Active Website User
VOC Member
Yes the cost of new brake drums is very high, but where can I get some of the course woven linings to try as a cheaper option please
Matty
 

davidd

Well Known and Active Website User
VOC Member
I know that McMaster does not sell to the UK, but I think these linings are Green Gripper Woven (GGW) made by Scanpac. They have a high coefficient of friction at .52 cold. This is much higher than AM4 at .44. However, when hot the friction goes down to .43, still very good when compared to AM4 as AM4 drops when hot also. I think the static friction is very high at .56. This is good at stoplights on hills.

The cold friction performance is very good because the lining contains aluminum oxide, which is the material in your grinding wheels. Some complain about the higher wear, but I don't think I would be one of them. Several Vincent owners have used these linings for years and like them. I know that Carleton Palmer just put these linings on his Godet front brake. This is not a racing lining, just street.

I would see if your local brakeman can install Green Gripper. It cost me $35/shoe.

David
 

Hugo Myatt

Well Known and Active Website User
VOC Member
Yes the cost of new brake drums is very high, but where can I get some of the course woven linings to try as a cheaper option please
Matty
Villiers Services do relining of brake shoes for all bikes. They claim to suit linings to the particular model. The ones they supply for Vincents are woven. Whether they are coarse or not I would not know.
 

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