Rear Brake cable

[jhg1958]

A little apologetic for bringing these two well worn subjects up but I thought it was worth it and I have a question (or two)

Whilst working on my 1961 Golden Flash I put pressure on the rear brake to move it out of the way.  There was a sudden clunk.  I quickly found that the cable had pulled out of the rear fitting.  Glad it did not fail whilst I was riding.

I cannot remember where I bought the cable from, but it is less than 2 years old and I have only done 300 miles on it (first service -still!).

Since the cable was too long anyway I was not too upset in having to buy a new one.  It had an outer of 14" and inner of 23", with a bottom entry full width rear brake drum it should have been 12" outer and 21" inner.  Since I wanted to regularise the oil tank fittings (after seeing a post on this forum) I manage to get a new cable from Priory Magnetos in the same order. I see the new cable has a crimped fitting whereas the one that failed had a small soldered fitting (see photo).  Assuming the new one will last, it is probably worth looking at what is fitted to your bikes.

Now I have the right (probably) length of cable I am a little unsure of how to thread it through the frame.  Currently I have put it through the rear footage loop.  This gives a poor approach to the lug on the frame.  However, other routes seem to be wrong where it is tied into the brake drum.  Is there a correct way to route this cable?

When I refitted the oil tank I found the brake arm, now more upright, fouls the bottom of the oil tank.  I managed to pad the rear of the oil tank so it is front of the brake arm.  Is this correct?  Could I have the wrong oil tank as I know some Golden Flash did not have the brake spindle passing through the swinging arm.

John

 

[limeyrob]

That failed cable is terrible.  The hole in the clevis should be tapered and the cable should have the individual strands turned over and pulled back in, then soldered. At the least there should be a wedge. the force is enough to pull the steel through the solder, I know, I used to make up my own cables.  Where did you get it from?

[Billybream]

Here,s my rear brake cable run, brake works well

[limeyrob]

One thing that puzzles me is the angle between the short lever and the cable. I would expect it to be close to 90 deg but its not. Mine has the earlier straight) cable mount but the angle is still acute very much like yours.  This does give more force but less travel.

[Swarfcut]

  From a brake efficiency point of view there is something amiss in the length of both cables pictured.

  In each case the cross shaft lever is over the 90 degree angle and the further the brake pedal is pressed, the less the applied force.  The cable length should be such that the angle between the levers and cable approaches 90 degrees at either end to apply the greatest leverage as the brake comes on hard, but does not pass over the magic 90.

 This is also often seen in the case of front brake cables and levers. Getting it right will improve the amount of force transmitted.
 
  I'd like a cross lever lying slightly to the rear of parallel to the frame tube at the start of its arc of travel, and well under 90 degrees on the drum lever, in other words hub lever pointing a little more slightly to the rear than Billy's rather than downwards when at rest as many do.

 A stretched outer cable also reduces efficiency, here the first movement of the pedal is compressing the spiral windings of the outer together rather than moving the drum lever.

 Lucky escape there and a timely reminder to stick to branded offerings where possible, where safety critical stuff is concerned. I reckon this is one area where one size does not fit all or the cable making community do not have the right information to produce cables of a length to give the best efficiency.

 Swarfy.

[JulianS]

My rear brake cable. Outer approx 12.5 inches inner approx 20.25 inches. Yes its not an A10 silencer it is A65.

[limeyrob]

Swarfcut - that's my issue. Mine too is well past the 90 deg and it only fits that way.  I looked at a lot of pictures inc ones in books of new bikes and they are all like that.  The acute angle makes the effective radius smaller so it increases the leverage and brake force at the expense of travel as its the "pulling" lever not the "being pulled" lever, but it still looks wrong to my eyes.  I wasted a lot of time trying to set it up nearer the 90 deg but its not possible, the lever socket is shaped for this angle.

[JulianS]

Below from the 1961 Trader Handbook is the only place I have seen cable dimensions listed. If the current offerings are made to these figures they could well be too long

[RogerSB]

Here's my 1960 A10, lever is maybe a slight obtuse angle to the cable which then goes through the loop.

  Note my swing arm & loop is cleaner than Julian's 

Edit: And a very handy chart Julian, thanks.

Rog.

[limeyrob]

That's the best angle I've seen. On my earlier frame with the cable higher up that's just not possible.

[bikerboy]

Just fit a disc back wheel 

Just need a different swinging arm, move the mudguard a bit, make up hydraulic pipes, mount a resevoir, weld something on the brake pedal, mount the operating piston thingy and its all done 

That will keep you busy for a while lol

[Swarfcut]

 Roger's set up is exactly what I meant. The difference in the length of the two levers give some mechanical advantage, and to rely on a decreasing effective radius as the brake is operated goes against my logic. Rob's right, and it does seem all wrong.

 Also if that cross lever is too far forward, is there a chance of the cable exit on the ball being flexed and bent against the rest of the cable if it fouls on the lever fork? A potential source of fatigue fracture. Like clutch cables the nipple needs to turn so no angular deflection occurs to the cable where it enters the nipple and must not be trapped.

 Roy Bacon's Twin Restoration, page 119 in my book, has a picture of a 1958 Shooting Star with full width hubs. Here the cable mount is higher up the frame tube, the cable exiting horizontally to the rear "above the spindle" brake lever. The cross lever is a shade past the vertical. Beats me.....but the eventual cable routing is somewhat decided by the position of that cable mount on the frame tube.

 Swarfy.

[limeyrob]

Mine is like that photo with the higher bracket. I looked at that picture very closely before giving up and leaving it

[chaterlea25]

Hi All,
I am not sure if the list above is correct or not?
The earlier SR and A10's have the brake arm pointing up and the cable anchors on the brake plate and the later
ones anchor where the torque arm anchors to the brake plate
They require different cable lengths.
Another issue is that 99% or replacement brake shoes do not have the correct thickness linings.
Somewhere in the past posts I showed how I modified the cable in order to have the correct arm operating angles and the outer cable as short as possible to minimise the bends

John

[JulianS]

The Trader Handbook was an annual publication so the information in the one above only relates to 1961.

There were 4 different rear brake cables, 1 for Ariel type hubs. 1 for iron hubs lever pointing up early 1958 models, another for later 1958 and 1959 lever pointing up then the final one for the  1960 on iron hub ever pointing down,

Some parts sellers offer the same cable for the 3 iron hub versions. Below shows the part numbers but no dimensions.

I think that the other issue is the position of the brake pedal when the footrest is moved to adjust the rider.