Author Topic: Why is my front brake still useless?  (Read 1497 times)

Online mikeb

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Why is my front brake still useless?
« on: 27.01. 2019 07:27 »
My 61 super rocket has the standard 8” full width SLS front brake. I've read lots of brake threads on trying to improve things so I fitted a later floating shoe setup and replaced the old linings as they didn’t make good contact with the drum. The new linings are modern stuff but supposedly a soft material for cable operated vintage car brakes and used successfully on old bikes. The people who did the linings have a good rep down here.

Anyway, after centring the new shoes/linings (by adjusting the fulcrum pin) and doing a few hundred miles they are still pitiful, albeit slightly better than when first fitted. Possibly worse that the original fixed shoes that I swapped out. Photos below show the wear is somewhat more on the inside of the linings and mostly at the ends of the linings - ie the middle of the linings has little proper wear yet suggesting minimal contact. the drum looks ok (to my untrained eye) and feels fairly smooth - I don’t have means to measure the drum.

what to do? Should I get the drum machined in some clever way? Should I try the sandpaper trick (adhered to the drum) to rapidly bed in the new linings? Any thoughts?

Thanks
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Online KiwiGF

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Re: Why is my front brake still useless?
« Reply #1 on: 27.01. 2019 08:03 »
Do you know the theory on why it’s important to get the leading shoe to make contact with drum first? I ask as it took me a while to figure it out, but then I had a  *woo* moment when I did.

I made a useless 8 inch single sided brake (like the gold star one) go from completely useless to ok just by getting the leading shoe to contact first. There are a couple of ways of doing it but I built up the cam face of the leading shoe by 1 mm.

Using the emery double sided taped to the drum will probably improve things, but unless you put a spacer under the trailing shoe cam face whilst doing it you will end up with the trailing shoe contacting first which may negate any improvement!

My next mod will be to “reverse” the brake lever on the drum.

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Online Greybeard

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Re: Why is my front brake still useless?
« Reply #2 on: 27.01. 2019 09:33 »
Apart from shoe contact, how is the operating arm?

Online JulianS

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Re: Why is my front brake still useless?
« Reply #3 on: 27.01. 2019 10:03 »
The brake is wrongly assembled.

The steel pads go at the pivot end.

Service sheet below shows correct assembly.


Online Triton Thrasher

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Re: Why is my front brake still useless?
« Reply #4 on: 27.01. 2019 11:39 »
Mr Kiwi knows what he’s on about.

If the trailing shoe hits the drum first, it stops the cam from turning, so the cam can’t put any more pressure on the leading shoe.


Offline mugwump

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Re: Why is my front brake still useless?
« Reply #5 on: 27.01. 2019 11:50 »
I have found easing off the last 1/3rd of the trailing shoe helps quite a bit. This tip has been about for years.

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Online duTch

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Re: Why is my front brake still useless?
« Reply #6 on: 27.01. 2019 12:12 »

 
Quote
The brake is wrongly assembled.

The steel pads go at the pivot end.

Service sheet below shows correct assembly.   

 Unless my eyes are weirder than they were when I woke up, mike's shoes are assembled as in the factory drawing... *conf2*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online JulianS

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Re: Why is my front brake still useless?
« Reply #7 on: 27.01. 2019 12:27 »
No they are not as per factory drawing.

The end of the shoes with the steel pads in Mikes photo are at the cam end. The factory drawing shows them at the pivot end.

First photo is A10 8 inch front fitted with floating shoes.

Second shows the pads on floating shoes, they are not flat, you can imagine the problem of a cam opening on that shape shoe end. You can see the pivot marking on them.

Left is Triumph type and right is BSA type.

Offline Swarfcut

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Re: Why is my front brake still useless?
« Reply #8 on: 27.01. 2019 12:55 »
 A quick reassemble as Julian has indicated will certainly improve matters.  Here are a few other things to consider on any cam operated brake.

    Relieving the cam end of the trailing shoe lining will allow the leading shoe to have a bit more pressure as the cam can continue to turn, as T T says. Mugwump suggests 1/3 of the length, so start off gently and see how it goes.

   The drum operating lever should be set so that it never passes over the 90 degree angle with the cable.  Make sure there is no stretch in the outer cable, as this is is wasted effort. Worth checking you also have the correct handlebar lever, as regards mechanical advantage. Make sure the floating pivot is set up to work as intended, either fully floating or locked in place with the brake applied and the shoes centred, depending on type.

   Once full contact is achieved, by bedding in, sanding off high spots etc, the poor performance  can only be the retarding properties of the friction lining material.


  Swarfy.

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Re: Why is my front brake still useless?
« Reply #9 on: 27.01. 2019 12:57 »
 What's this then ? 


 And where did this come from..?...;

 

To me the drawing sure looks the same as mikes
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online JulianS

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Re: Why is my front brake still useless?
« Reply #10 on: 27.01. 2019 13:38 »
Not quite sure what you mean duTch.

The steel pads on Mikes photo are clearly at the cam end. His top shoe in photo needs to be fitted on the bottom side putting the pads at the right end. The linings will still be in the same asymetric position. The shoes are not interchangable, one is made a leading and one as trailing.


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Re: Why is my front brake still useless?
« Reply #11 on: 27.01. 2019 14:21 »

 What I mean is that mikes appear to me to be the same as in the factory diagram you posted;
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Swarfcut

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Re: Why is my front brake still useless?
« Reply #12 on: 27.01. 2019 14:39 »
  On any drum brake with linings fitted asymetricaly, in other words  more to one end of the shoe, just imagine that the rotating drum has pushed the lining along to the end. Works every time for assembling them correctly.  The start of the lining will be some way from the cam on the leading shoe. Slight sanding to remove the front sharp edge of this  leading shoe lining will minimise grabbing.

  The factory diagram would indicate cam at the bottom, pivot at the top. Steel pads fitted pivot end of the shoes. You can see how the rotation appears to have "moved" the linings along the shoes.

  Mike's shoes just need to be  rotated 180 degrees to put the steel pads at the pivot end. The linings will then be in their correct leading and trailing positions.

 Swarfy.

Online JulianS

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Re: Why is my front brake still useless?
« Reply #13 on: 27.01. 2019 14:44 »
Perhaps this helps.

The pads will only fit on one end of the shoe due to diffrent dimensions.

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Re: Why is my front brake still useless?
« Reply #14 on: 27.01. 2019 15:44 »

 yeah ok wahever- I really don't care so much, nought to do with me anyway- was just saying it didn't look right, but at 1:40am before some suds not much does....i had the same issue on my Gutzzi 20 yrs ago and sorted that similar, so probs the same stuff....
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia