RP Rear brake cables

[Tony Press]

Whilst on the subject of front cotters , I make my own, about 3 inches long and jutting forward, with a light extension spring between the cotter and backing plate. This to help the brake shoe springs counteract the weight of  front cable and fittings.  cheers  Russell

An article I wrote for our 'The Light Shaft' Club Magazine in 2010-

Front Brake Return Spring by Tony Press.
 
 With the Austin Seven front brakes, there is often a problem with making sure the levers return fully to ‘off’, to prevent the Brakes from dragging when turning.
 One way to assist with this is to add a short external tension spring to the brake lever, one end hooked around the neck of the ball end of the Brake Lever, the other attached to a hole drilled in the backing plate.   
 Another better way is to make up a special 3 1/2" long cotter pin.

 A piece of 5/16” dia. rod about 4” (102mm) long is turned eccentrically one end and threaded ¼” BSF with a filed taper flat like the original cotter pin. The outer end of the pin has a couple of flats filed and a small hole drilled to accept one end a ‘pull of’ tension spring about 4” long. The other end of the spring is stretched up and inserted in a hole drilled in the backing plate. You will have to experiment with the spring size, length and position to get a good return tension, but not so tight that the front brakes are difficult to apply.
 
 This modification was fitted to my Chummy in the 60’s and is still in place
  If you look closely, this ‘return’ system was also used on my Austin 7 chassis on the Club Website History pages.
  http://www.austin7club.org/Tony-Press/target4.html
 
        
It is interesting to note that in the late front brake shown above the lever has a twist at the ball end making the levers left and right handed which change  appears to have been introduced around 1936.

Tony.

[Ruairidh Dunford]

I used brake pull-off springs, similar to those described above, each winter; the road salt here is aggressive and these helped to ensure the cams did not seize (most of the time)!

[dickie65]

I seen to remember that a lot of the replacement brake cable ends were wrongly made which is why they foul the front backplate.
This has been the case since the 1970's ( might even be earlier than that )
I have just had a quick measure on my car. The offset from cam centre line to the outside of the cable end is 3/8" ( 10mm )
The end caps on the cable are about 1/8" thick.
The other problem with the aftermarket cables was the ball neck being worn away by the slot for the ball neck being incorrect.
This means the cable slot pulls the brakes on via the neck.
The cable end should be free to rotate around the ball at a greater angle than the available steering lock.
There should be no need to bend the brake lever. ( Unless you have incorrectly made replacements )
The end of the alloy brake shoes will be badly worn but at least new ends are available. ( This affects the brake lever angle at rest )
The rear cables should be unaffected by the above.

[squeak]

I seen to remember that a lot of the replacement brake cable ends were wrongly made which is why they foul the front backplate.
This has been the case since the 1970's ( might even be earlier than that )
I have just had a quick measure on my car. The offset from cam centre line to the outside of the cable end is 3/8" ( 10mm )
The end caps on the cable  are about 1/8" thick.
The other problem with the aftermarket cables was the ball neck being worn away by the slot for the ball neck being incorrect.
This means the cable slot pulls the brakes on via the neck.
The cable end should be free to rotate around the ball at a greater angle than the available steering lock.
There should be no need to bend the brake lever. ( Unless you have incorrectly made replacements )
The end of the alloy brake shoes will be badly worn but at least new ends are available. ( This affects the brake lever angle at rest )
The rear cables should be unaffected by the above.

I seem to remember that a lot of the replacement brake cable ends were wrongly made which is why they foul the front backplate.
This has been the case since the 1970's ( might even be earlier than that )

...some replacement cable ends have been cut off square instead of round, the advice given is to use your old ends.   

The other problem with the aftermarket cables was the ball neck being worn away by the slot for the ball neck being incorrect.
This means the cable slot pulls the brakes on via the neck. 
The cable end should be free to rotate around the ball at a greater angle than the available steering lock.

...observing the works drawing supplied by Ian Dunford the eagle eyed Tony Press has noted the lever is TWISTED, shown by the offset ball position. Austins must have realized  the necking problem and I submit the fault lies not with the cable but with the ball position.
  
There should be no need to bend the brake lever. ( Unless you have incorrectly made replacements )

...unless you have earlier or non twisted replacements

The end of the alloy brake shoes will be badly worn but at least new ends are available. ( This affects the brake lever angle at rest )

...this is interesting, one imagines that at rest the brake shoes will be fully retracted and the cam will be nearly horizontal. The brake lever angle is therefor  fixed until the brakes are applied and it approaches vertical. In Rodgers case the front levers are well forward of the optimum 90 deg but this may not be a bad thing! If the drums are oversize or the linings worn there will be some travel in the lever before brakes are on and the lever is hopefully at 90. So if we adjust the excess travel out by tensioning the cable, and if our operating range remains around 90, then we should not experience front grabbing brakes on cornering. A minor extra benefit is that as our cam rotates the lift versus effort ratio improves.

[Bob Culver]

Austin may have originally intended that the shoes always fully return and this may be the reason for the very short levers initially fitted. But with worn shoes and the later long levers the pre semi Girling brakes at rest are often in a state of part operation to avoid very long pedal travel. 
If the front balls are not near the kpin axis, even when off, the tendency to grab is increased. 
The handbook photos, and diagrams and factory dwgs show the direction of the cotter which certainly suits new linings and also semi Girling but most insist on the reverse.
It is vital the brakes are never operated in a state where the cam may jam on. Can cause excitement when all the other brakes release. Nevertheess the wedging leverage near this conditon is considerable.
A colleague claims to have rolled his Seven years ago when one front wheel grabbed on turning. It may have been a 1920s model where the swivel has little effect.

[Tony Press]

Austin may have originally intended that the shoes always fully return and this may be the reason for the very short levers initially fitted. But with worn shoes and the later long levers the pre semi Girling brakes at rest are often in a state of part operation to avoid very long pedal travel. 
If the front balls are not near the kpin axis, even when off, the tendency to grab is increased. 
The handbook photos, and diagrams and factory dwgs show the direction of the cotter which certainly suits new linings and also semi Girling but most insist on the reverse.
It is vital the brakes are never operated in a state where the cam may jam on. Can cause excitement when all the other brakes release. Nevertheess the wedging leverage near this conditon is considerable.
A colleague claims to have rolled his Seven years ago when one front wheel grabbed on turning. It may have been a 1920s model where the swivel has little effect.

"The handbook photos, and diagrams and factory dwgs show the direction of the cotter which certainly suits new linings and also semi Girling but most insist on the reverse."

The cotter pin in from the outside- front and rear, as often shown in the handbooks (not all) may suit as you say when the brake assembly is new but after much wear and the lever moves past vertical then the little gained by reversing the cotter is often useful.

My extended cotter with pull off spring puts the cotter 'in from the front'.

I can't remember the brake assembly on my cars but the levers look to be around vertical at application.

The replacement cams seem to show a good forward or rearward offset to the levers- is this the experience ?  


  Early Brake Cams.jpg (Size: 102.31 KB / Downloads: 155)

Cheers, Tony.

[Roger]

Tony,
I checked as best I could and the angle machined on the brake camshaft is about 30 degrees, I have new linings and when applied the lever is still well forward of 90 degrees. This amount of angle moves the ball further away from the centre of rotation of the king pin. It would only ever reach this point if the brake linings were worn away and not shimmed to compensate.

Surely the ideal position for the lever ball viewed from the top would be perpendicular to the cable when the wheels are straight ahead.

I have adjusted my front cable quite tight at present so brakes are nearly applied, I can now turn the wheels lock to lock and the brakes do not affect the wheel rotation.(car is still on axle stands) does this sound ok?

Roger

---

Bob,
Surely if the cam can rotate to the point of jamming on it means the linings are so worn, or the end of the shoe is worn and should have new linings or shim added to the shoe?
One of my brake shoes was reluctant to return to the off position because a previous owner had used too wide a shim on the shoe so it jammed in the cam sides. If all is free surely they will always return to the correct position.

Roger

[Roger]

I thought this collection of levers May highlight the way the levers can be worn away by the Narrow slot in the socket.

   

Roger