Author Topic: Rear brakes  (Read 239 times)

Offline UncleD

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Rear brakes
« on: 03.01. 2019 04:00 »
1958 Super Rocket.

My rear brake is very spongy to the point of being ineffective.  I have tried multiple adjustments to the arm position on the spline but while I can get some pressure in the pedal, not enough to provide stopping power. 

I have what I understand to be the shortest brake cable but it is still a poor fit as you can see from the photos.  Even with the rear wheel almost fully Adjusted out (to provide the appropriate tension on the chain), the inner brake cable still seems too long (and the outer too short). I probably should remove a link from the chain and bring the wheel forward but this would make the cable length problem worse.

I fitted a new rear tyre so also repacked wheel bearings and checked out the pads.  I was firstly surprised how loosely the brake assembly sat in the drum (slops around and easily fell out); is this normal?   This would mean a lot of movement would be required simply to make pad contact with the drum let alone apply the necessary pressure. 

The pads ranged from 5-6mm in depth (leading edge to the back). They look to be in good condition but I don't really know what I am looking for.  I cleaned them with fuel and wire brush however this has not improved anything.  Is this measurement sufficient for pad depth or do I simply have worn pads?

Despite much fiddling and adjusting, I don't feel like I understand the relationship between all the components and am not making the most of these efforts.  Is there an order of process or any tips for adjustment people can give me?

Northern Territory, Australia

Offline muskrat

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Re: Rear brakes
« Reply #1 on: 03.01. 2019 06:53 »
G'day UncleD.
Yes that outer is about 1.5" too short.
Push the wheel all the way forward, you may be able to take two links out. That would help matters.
Yes once you remove the axle and spacer the brake plate will fall out. 5-6mm of lining is OK.
To centralize the shoes (I think it works on your model) loosen the nut opposite the lever on the brake plate. Spin the wheel and apply pressure to the lever (I use a spanner in it's nut) to lock the wheel and while keeping pressure on the lever tighten the nut.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Online Peter in Aus

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Re: Rear brakes
« Reply #2 on: 03.01. 2019 07:08 »
I had to shorten my inner rear cable by 1 1/2 ins on my 58 A10 There is quite a lot info on the forum about the rear crossover  brakes, so have a look, but they are known to be crap brakes and as Musky says "brakes only slow you down"
Peter *eek*

Busselton West Australia
49 A7 longstroke
58 A10  SA

Offline Swarfcut

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Re: Rear brakes
« Reply #3 on: 03.01. 2019 09:07 »
G' Day Uncle D... Your brake operating lever appears to be over centre with the brake applied. So you will not achieve  the maximum  available force to apply the brake. The wheel is on the rear limit  for chain adjustment, and consequently the hub brake lever at rest is set too far forward.
    You need to adjust the operating lever on the cam spindle so that at rest  it points further to the back of the machine with the linings just kissing the drum. With the brake fully locked the lever and cable should never pass over that 90 degree angle. Any stretch in the outer cable must be overcome first before the inner can exert any real force, so this is another source of wasted pedal movement and a spongy feel as the spiral wound outer acts as a compression spring.

  The secret of good stopping is to achieve full lining contact, with both shoes initially contacting the drum at the same time so follow Musky's advice and see if the fixed pivot is adjustable to centre the shoes.
 
  The cable run is really suspect.... it looks too short and also wound through the frame will give an additional friction loss. A nice straighter cable  run is what you need. It has been run like that to make it reach. Plus S/A movement could have stretched the outer  as detailed above. However, the front lever is not set up correctly.  Moving the cross shaft on the pedal splines to allow the front cable lever to point  backwards  to be almost parallel with the sloping frame tube and with a correctly set rear hub lever will increase the mechanical advantage of the system. It will also effectively lengthen the inner cable and allow the cable adjuster to be backed off so the drum lever can be set to point further backwards. As set now, the more you apply the brake, the less force you have, as again the front arm and cable are on the wrong side of the magic 90 degrees.

  Get the brake internals set up properly to achieve minimum drum/lining clearance.

 With a bit of luck some cable dimensions will be along soon from other forum members, so you can see if it is the correct cable, just badly fitted. Or simply the wrong one. I reckon it should be a bit longer and run outside of the frame loop, and be supported by a P clip on the vacant torque stay mounting.


  My first post of 2019, so Happy New Year to you all, and may a small drip of oil from your breather pipes be your only problem.

    All the best for whatever 2019 brings.

   Swarfy.

Offline UncleD

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Re: Rear brakes
« Reply #4 on: 03.01. 2019 10:40 »
Thanks swarfy...plenty of new learnings for me in that post...my logic has had me working in the opposite direction.

I centred the brakes today (another new learning) with some minor improvement however I have plenty of opportunities with a repositioning of the arm on the spindle, re-routing the cable outside of the frame and also removing some links to bring the wheel forward.

Cheers all

Northern Territory, Australia

Online worntorn

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Re: Rear brakes
« Reply #5 on: 03.01. 2019 17:43 »
Swarfy nailed it.
So well in fact that I had to check my 63 SR to see if it meets Swarfspec.
It does and the rear brake works well.
With some effort it will skid the rear tire on pavement when riding solo.
To my way of thinking, that's about as strong as the rear brake wants to be.
I did install new shoes and fitted them to the drums using stick on Emery.

Glen

Offline Swarfcut

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Re: Rear brakes
« Reply #6 on: 03.01. 2019 18:07 »
Thanks Glen. I hope you stuck the emery to the drum then lapped in the shoes.....not stuck it to the shoes and lapped the drum.

  New word.....Swarfspec.   First noted on this forum, today. Fame at last!

  Swarfy.

Online worntorn

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Re: Rear brakes
« Reply #7 on: 03.01. 2019 18:32 »
In that case the emery was used to shape the shoes as the drum was already round.

The front 2 ls which had extreme pulsation due to an out of round drum, needed both treatments.
 I started by trueing the drum using Emery stuck to the shoes.
It essentially turns the brake shoes into a slow speed lathe cutting tool.
A C-clamp was used on the linkage to slowly move the shoes out while rotating the brake plate in the drum.
Initially you feel the tight spots and the free spots. Eventually you get one perfectly even amount of drag.
The Emery was renewed two or three times during the process, which took about an hour in total.
It worked beautifully to remove all pulsation.
The front brake is almost like a modern disc brake now, two finger operation.
The lathe wasn't quite big enough for turning the drum with rim in place, 19" wheel and 18.5" swing on the lathe.

After getting rid of pulsation on the BSA brake with the Emery,  the same method was used on my Vincent, with same result.
A couple of members here have also tried this and had a good result.

Glen

Offline chaterlea25

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Re: Rear brakes
« Reply #8 on: 03.01. 2019 20:40 »
Hi All,
With the earlier setup where the cable anchor moves with the wheel it is inevitable there will be some bends in the cable outer,
Any and every pattern cable that I have tried has not fitted correctly *problem* *problem*

On the models with the upwards pointing brake lever the lever cannot be reversed to take advantage of moving it a 1/2 spline. moving one spline is usually too much

Most replacement linings and shoes (which are crap!!!!) are too thin in lining thickness resulting in the arm coming too far forward for best results

For best results fit oversize linings and have them turned to the drum diameter with the cam end packed out 20 thou
Get the longest cable you can and modify it to get the correct "approaching 90 degrees" when the brake is applied
Make absolutely sure you know how and are able to modify the cable or get someone who has the proper equipment to do it  *warn* *warn* *warn*

It is sometimes possible to pack the shoes  with steel pads wrapped around the shoe ends to get the lever to a better operating angle

Some time Ago I posted about how I sorted the rear brake on my own SR and it has proved well worth while taking the time to attend to the above

John


1961 Super Rocket
1963 RGS (ongoing)

Offline morris

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Re: Rear brakes
« Reply #9 on: 03.01. 2019 21:50 »
Get the rear end sorted as described above. This already will make a huge improvement.
Not clear what type of shoes you got, but if it's the modern "bonded" type, get rid of them and find a set of riveted shoes with "old style" linings. Set up well they will transform the brake from virtually non existent to a tyre squealer
My '58 SA has the rear FW hub with the lever pointing downwards but with the frame lug high on the frame like yours for the upward lever. In my case the best fitting cable is one from a B31, but I still had to make up a small ferrule to get the lever at the right angle.

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