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Rapide front brakes

danno

Well Known and Active Forum Website User
VOC Member
Hi
Are Vincent brakes good when setup properly?
I've been riding my restored C Rapide when weather suits since last summer and find the front brakes
a bit spongey.
It's quite easy to pull the lever back to the bar so there might be some flexing happening somewhere.
Brakes are standard and haven't done much milage since restoration.

I need to spend a bit of time setting them up and any tips or info on this would be appreciated.
If there's not much improvement after that are there any upgrades available?
Dan
 

bmetcalf

Well Known and Active Forum Website User
VOC Member
In KTB, there is a balance beam outrigger mod. Heavier cables are available, but I can never remember who sells them. Also, gussets can be added - http://www.vincentownersclub.co.uk/photos/showphoto.php/photo/2842/title/brake-mod/cat/646 and http://www.vincentownersclub.co.uk/photos/showphoto.php/photo/2843/title/brake-mod/cat/646

You can also "preload" the angle of the brake arm before tightening the brake cam nut to minimize the travel before the lining contacts the drum. It is also important to set the brake arms so the the angle of it and the cable is never more than 90 deg, the serrated washers can be rotated on the square shank for a vernier effect to enable fine tuning.
 

stumpy lord

Well Known and Active Forum Website User
VOC Member
Hi,
you have here three different problems.

1 flexure of the fork bridge plate.

2 Flexure of the brake back plates.

3 flexure of the brake shoes.

number 1 can be cured by fitting an outrigger plate.


Number two by fitting gusset triangls to the back plates.


Number three is a lot harder to sort out due to the fact that when the brake is first applied , the first part of the shoe to contact the drum is the trailing edge, and from then on it is the shoe, due to its fixed pivot points, being forced to bend to contact the rest of the drum. Trever Southwell has a brake set up that has a cut away back plate that allows you to see the opperation of the brake, thats how I know that. The only answer that I know off is to have over size linings fitted to you brake shoes , mount them on your brake bake plates with a shim between the heel of the shoe and the cam, and turn them to suit the dimension of your brake drums.

You do not say how good your brake are ? Do you have to pull the lever right back to the bars to get a decent brake effect? or is it
a case that they are O.k. but you dont like the sponge feeling.


When I had drum brakes on the Vin I would always adjust the cables so that when the front left hand brake was just touching the drum, the right hand one was just about to touch its drum , I mention this because I have seen many members bikes where the right hand brake is trailing a long way behind the the left hand brake,
. where as both brakes should be sharing the work evenly.


with all these mods it is possible to have front brakes that will squeal the front tyre.

cheers stumpy lord.
 

Monkeypants

Well Known and Active Forum Website User
VOC Member
"Are the Vincent brakes good when setup properly?"

Well they outdo the 1st generation disc brakes on my MK3 Commando.

The link below is a dramatic reenactment of an actual Vincent braking/dog on the road event that occurred earlier that day. Sort of. With a lot of poetic license and a fair bit of plain BS. But the stop is real, and pretty quick too!

http://www.youtube.com/watch?v=amMPrwtuz2U
 
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Monkeypants

Well Known and Active Forum Website User
VOC Member
Yes, it squishes down quite a lot from the weight transfer. I checked it afterward and it was just a bit lower than I usually keep it . It was at 23 lbs.
Pull just a little harder on the front brake lever, the wheel locks up. This happened to me a couple of times at speed until I got accustomed to the brakes.

My other Rapide has decent brakes, but nothing like this one. I guess everything is in sync.
Green Ferodo linings, Lightning type back plates , aluminum copies, not the original Magnesium type


Glen
 
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vibrac

Well Known and Active Forum Website User
VOC Member
Wow! well into this thread and nobody has trotted out the well used but never the less true fact
loosen the front spindle ,pull on the brakes hard, hold them on, and do up the spindle

(you can let the lever go now :)
 

danno

Well Known and Active Forum Website User
VOC Member
Blimey! Nice stoppers.
I need to study how the brakes work as I've not worked on them before.
I've got both Paul Richardson's book and KTB.
Also not sure what brake parts Conway Motors fitted during restoration so may take a look at the drums.
 

davidd

Well Known and Active Forum Website User
VOC Member
I need to spend a bit of time setting them up and any tips or info on this would be appreciated.
If there's not much improvement after that are there any upgrades available?
Dan

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
 

Monkeypants

Well Known and Active Forum Website User
VOC Member
Hi David.

After reading your post I had to view the video a couple of times to see what was happening with the front end. The part of the clip where the bike approaches the stop firstshows the front end after the brakes have already been applied. It is difficult to gauge fork action until the braking ends when the bike stops. When the bike stops, you can clearly see springs pop up and my upper body get thrown back. It looks to be quite a lot of fork action, difficult to say exactly how much.

It looks as though the springs compress about as much as they can then, as you say, the rest is done by the tire.
Glen
 
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