Rapide front brakes

A-BCD

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I'm fairly sure that girder forks, and particularly Girdraulics, do not compress the springs under braking, rather the reverse, and the front end can rise and extend the springs ? Also I think Girdraulics tend to not move at all under heavy braking ?
 

davidd

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I'm fairly sure that girder forks, and particularly Girdraulics, do not compress the springs under braking, rather the reverse, and the front end can rise and extend the springs ? Also I think Girdraulics tend to not move at all under heavy braking ?

That is my point. If I run over a speed bump under full braking, my Girdraulic forks go up and down. The springs will compress under heavy braking. With stock springs the front end can only rise or go to full extension. It will not return to its static position until you release the brake. Girder forks will go up and down under full braking if you are in the middle of their range and not at the extremes. This effect alone has generated a lot of affection for the Bramptons among many owners.

David
 

danno

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Dan,

Stumpy's reply is a good template. The best way to start is to make sure the cables are new and big (resistant to flex). All the mods are beneficial, but do the cheap improvements first to see if you are happy. A good brake lining is important. Old ones tend to be hard and slippery.

Clever Trevor discovered that the sponginess in the brakes may be due to a geometry error. The various attemps to rectify this is truing the brake linings on a lathe, the Burt Weiz floating pins mod in MPH and the Tim Kingham mentioned mod. This last mod was a favorite here in the States used Rick Voshel and Marv Kummet. They would file the axle hole in both brake plates so it was a little large. When they installed the wheel they would leave the hollow axle nuts a little loose. With the wheel still in the air they would hold the brake lever tight causing the shoes to align the brake where it should be. They would use a special thin wrench to tightn the hollow axle nuts while the brakes were on. The wrench is now made by Niel Videan in Australia (see adver in MPH).

There are three popular upgrades. The 8 inch brakes, the 4 leading shoe conversion and disc brake conversion. The first two are easily available the third you will need to do yourself. I have been told the 4 LS conversion in quite good. I use the 8 inch brakes as 4LS brakes are illegal in the racing rules I have to comply with. I find them quite good on the track. If you have Rapide drums you should consider new Black Shadow drums if you are doing the 4LS conversion. I have shattered Rapide drums.

Finally, if you are running stock springs on the front end your stopping distances will be longer because the front end does not go up and down very easily during braking. Glen's video seems to show this as his tire flattens so much. Even with low tire pressures the front springs should be compressing as the weight transfers to the front end but because the forks are seizing the springs do not compress, the tire does. Very impressive!

David

Great thanks. Plenty to go on there.
I'll see if I can improve things with the current setup first.
Regarding the 8" brake upgrade, my brake drums are 8" diameter.
Dan
 

danno

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I measured outside diameter. They have a chrome surround riveted on which measures just over 8".
No air scoops so guess they're standard Rapide drums.
 

davidd

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Dan,

The measurement is the inside diameter of the brake drum. The stock drums are 7 inches. The Club shop sells an 8 inch brake that has Lightning style alloy plates and the shoes are much wider. Glen has the same type of plate on his Rapide in the video. These Lightning plates are alloy, the originals were Elektron, and are stiffer. Vincents with Lightning plates have no thin hollow axle nuts as there is not enough space with the thick brake plates. Most owners like them because they provide more stiffness while having an original racing look to them. If your drums do not have fins, they are 7 inch Rapide drums. If they had fins, they could have been 8 inch drums but they would have to have the special 8 inch Lightning style plates. The stock 7 inch racing brake plates do not use the alloy water excluders (the "surround"). On the 8 inch brakes the appearance of the water excluder is turned into the alloy plate itself.

I think you will do well if you do the simple items first. It may take a while to get used to all of the adjustments. The best brakes are always adjusted well and there is a bit of experimentation involved.

Best of luck!

David
 
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clevtrev

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Dan,

The measurement is the inside diameter of the brake drum. The stock drums are 7 inches. The Club shop sells an 8 inch brake that has Lightning style alloy plates and the shoes are much wider. Glen has the same type of plate on his Rapide in the video. These Lightning plates are alloy, the originals were Elektron, and are stiffer. Vincents with Lightning plates have no thin hollow axle nuts as there is not enough space with the thick brake plates. Most owners like them because they provide more stiffness while having an original racing look to them. If your drums do not have fins, they are 7 inch Rapide drums. If they had fins, they could have been 8 inch drums but they would have to have the special 8 inch Lightning style plates. The stock 7 inch racing brake plates do not use the alloy water excluders (the "surround"). On the 8 inch brakes the appearance of the water excluder is turned into the alloy plate itself.

I think you will do well if you do the simple items first. It may take a while to get used to all of the adjustments. The best brakes are always adjusted well and there is a bit of experimentation involved.

Best of luck!

David
And even if they have fins, they are 7" brakes.
 

Peter Holmes

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And even if they have fins, they are 7" brakes.
I do not think that Trevor quite understood the point that David was making, the club 8inch brake drums are only manufactured ribbed, not plain, the original 7inch drums are made ribbed and plain, therefore if you are looking at an 8inch drum it can only be ribbed, a 7 inch drum could be either be ribbed or plain.
 

redbloke1956

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I have some very good info from a club member in AJS club that has been comprehensively tested, it involves removing about 2 inches of brake shoe from all trailing edges, therefore forcing the leading edges to make contact first. Kevin
 

Matty

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Hi again
Surprised to hear that there is some dive on people's Vincent forks - mine have never dipped appreciably on braking and I was always led to believe after 60+ years of ownership, that this was their greatest merit.
Perhaps it is because my brakes have never worked properly and the bike has only been used as a tourer for the last 100,000 miles or so!!
Matty
 
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