Why is my front brake still useless?

[berger]

ok chaps I know my front brake is good but I am trying the emery method on the rear and now can't get the shoes in the drum without taking the brake operating pivot  out , I have two strips of emery the same size as each shoe , has anyone else had this problem, at the moment I will put the lot in the swing arm and use a spacer and screw driver to open up the shoes and then turn the back wheel. I don't think I can make it any worse than it is because looking at the shoes it is way more miss than hit at present.

[morris]

A while ago I did my rear drum that way because slightly out of round. The shoes with the stuck on emery where a tight fit but went in with a bit of persuasion without having to take the pivot out.

[A10 JWO]

Think the drum needs a skim on a lathe, my local shop charges £20. Probably gone oval.

[berger]

brake drum had to be sorted when I bought it new, couldn't get a ball race in it so it was set up and skimmed to get the bearing in then the drum skimmed. think I,ve found  what could have been the problem in the topic on rear single sided brake drum

[berger]

just to clear up some confusion , I put the emery in the drum to get the high bits off the shoes because looking at the shoes they had very little contact with the drum. now they are nicely uniform, some nice weather will be the time to find out.

[philwhitelaw]

Having read the posts here I feel a bit more knowledgeable about setting up the shoes I have had relined. I understand the role of a fulcrum pin on semi-circle recessed shoes. With floating shoes however, when they are pushed into the drum, does the fulcrum end get drawn outwards along its flat face and create this self-servo effect? What prevents the shoes from sliding down the cam and pin under gravity and rubbing on the drum with nothing to positively locate them? Can anyone recommend any reading material on the subject.
Cheers.

[JulianS]

There is only very limited movement on the floating shoes. Movement limited by the drum.

See the photo you can see the pivot marks on the pads which will give some idea about how much or little they slide.

(left is a Triumph and right is BSA)

[philwhitelaw]

Next is incorrect radiusing of the shoes.
To work as intended the shoe must have a LARGER radius than the drum so the initial contact will be at the end only. ***
The leading end digs into the drum which locks onto the shoe and forces it back against the pivot end which can not move so the shoe flexes into the drum.
Thus the rotational energy in the drum is supplying the breaking energy , not your grip.

Do you mean like this?

A trailing shoe marked 68-5525 which is 197mm across and only touches at the extreme edges as seen in the second image, the gap is about 1.5mm. Next to it is a leading shoe which is 191mm across and has good overall contact as shown by the blue ink. Obviously not a matched pair so which size is the best fit?

[Swarfcut]

    A conundrum!    Whether to substitute a full contact  "191mm" shoe for a larger "197mm" trailer?  The  leading shoe does most of  the braking, and  the bigger shoe as leader is well worth a swap. Once the trailing shoe makes contact, no appreciable further cam movement takes place. Up to that point continual pressure on the cam and consequent servo action is forcing the leading shoe against the drum.

   If they are identical and can be swapped, well worth giving them a go, remembering brake performance may not be up to spec to start with.  Don't forget to adjust the pivot pin position if your backplate has a slotted pivot mount.

 Swarfy.

[JulianS]

Dont swap leading shoe for trailing shoe if linings are asymetric.

The result is a considerable reduction in brake power.

[mikeb]

Phil - I believe the late A10 floating shoes are 'handed' being 68-5524 leading and 68-5525 trailing.
see here: http://bsa-info.nz/service-sheets/?f=1zv5Ztk8sucQpvKPoci9lBU1-iwFoZ1mL
I don't think they are supposed to swap (as Julian says). I have some in the shed but haven't examined them as to why - no doubt Julian can expand on that point.

are you saying your two shoes are different sizes (radius)?  they look so in the picture. do the part numbers match as above? are they a set?

it looks to me in that close-up pic that the lining is not arced tho that drum. any difference in round should be negligible, way less than 1.5mm

i think i'd be making sure I had a set of matching shoes then getting them relined and arced. start fresh.

cheers

[Swarfcut]

 Phil. Following my earlier comment, I am concerned that in this case there is something very wrong with those shoes. A closer look indicates the basic castings don't match lengthwise. I hope these are not the ones which were relined. In this case swapping them around is a bad idea.

 As mikeb says, start with the correct parts. If it's any help we've all been down a blind alley like this at some time.

 Swarfy.

[orabanda]

Unfortunately, when we reach the end of the blind alley, our brakes aren't going to work!

[JulianS]

The 8 inch front floating shoes (Parts 68 5524 leading and 68 5525 trailing ) are handed in 3 ways;

1. The cam and pivot ends are different sizes, the pivot pad too small to fit over the cam end.

2. Asymetric position of lining on the shoe.

3, The width of lining is not symetric to the cam, it is displaced towards the brake plate side.

So they only fit one way.

Non floating 8 inch front shoes as point 3 above.

Above for genuine BSA shoes, I cannot make any comment about pattern shoes or Triumph shoes (part numbers starting W)

The 7 inch rear full width with floating shoes points 1 and 2 above so only fit one way.

7 inch non floating shoes same part both shoes and interchange with each other.

[philwhitelaw]

Yes Swarfy, a conundrum, and potentially a dangerous one. I wouldn't have liked to fit them and then discover I couldn't stop. Mike they are of different radius and were bought as part of a job lot of brake shoes. Julian I think they might be aftermarket items (they are marked MC ltd) as the ends are identical in size so in theory they could be swapped over, keeping the assymetry, but I wont be trying that, I can hear the metal of the wider shoe rubbing against the drum, not good.  I will keep my eye out for a 191mm trailing shoe and will try those at some time. The lining offset explains why the shoes are just 1mm from the outside edge of the contact area with about 4mm of unused inner drum face.  The shoes I had relined by Villiers are of the fixed pivot type swarfy and he did a good job of sizing them with thicker cloth woven sintered material.
  As I was arcing them in I noticed two things. First, when I operated the brake arm in the opposite direction mimicking the reverse fit of the arm, as in a previous post here, the brake worked better and was sharper so I would say it works!  Second, when I centered the shoes, the brake didn't work well. BUT, when I operated the arm in the reverse way (anticlockwise) and then tightened the fulcrum they became quite good. I can't determine how good until the lockdown ends but will keep you informed. Thanks for your input guys.