Watch out for wrongly made rear shoes.

[Vox]

Was doing a rear brake overhaul the other weekend (cylinders/pipes/etc) and realised after doing one side that the shoes I had bought from Rimmers (GBS813) made by Powertune were wrongly manufactured. They should be all the same with no lining at the end of the shoe with the rectangular hole for the brake lever but I had two correct ones and two with the lining coming all the way to the hand brake end.

I phoned Rimmers and to be fair they were very helpful and checked three sets from their inventory and they were all correct so said it must be a one off fault and they would send me another set.

As you may have guessed already the new set they sent had the same fault!

Between the two sets I had enough good shoes to do the job but it would be worth checking any Powertune shoes you buy straight away in case you need to send them back. They should look like these http://www.rimmerbros.co.uk/Item--i-GBS813

[Clifford Pope]

I think I'd have assumed that they were meant to be different - two leading, two trailing?
I'd have thought that on the leading shoe you wanted the lining to go right to the end to avoid over-leverage and too-abrupt braking?

[Vox]

Hi Clifford.
There should indeed be a leading and a trailing shoe but because the shoes are fitted alternate ways up (so all the holes for springs, handbrake etc are in the right places) both shoes need to be identical.
I have tried to attach a picture to show what I mean - these are the original shoes as fitted and you can see that the unlined part of the shoe is by the rectangular hole for the handbrake lever (which is at the bottom of the right hand shoe with the lever in it).
This is also how the Leyland manual shoes it.
The shoes as supplied by Rimmer would have the two unlined areas together (at the top in this case) and the two lined areas together.

Cheers
Chris

[Clifford Pope]

Interesting. I've never thought about it, just assumed that what was send was right.
So correctly, the unlined bit of shoe is always trailing, even if it's on a leading shoe? I think that's what I meant.

Why would it matter having lining running the full length ? (Assuming left and right were the same, of course)

[Vox]

I'm sure you could have more lining than that certainly.
That is the NS wheel in the photo so under braking any given point on the drum would hit the shoe after the unlined part - maybe that eases it into contact more gently?
All I know was that I wanted it to match what came off and what was in the manual but I did actually run it (not good practice I know) with the 'wrong' shoes in one side only (so both unlined areas were at the top) and the old ones in the other side just for the weekend and didn't notice any ill effects but then I didn't have to do any emergency stops...

[andyborris]

My understanding is that there's a "natural" servo effect with brake shoes, the leading "grabs" and pulls the shoe into contact with drum.

The trailing shoe is on in the opposite way to give the same effect when reversing.

[Clifford Pope]

Yes, I see that. (Although of course with a twin cylinder set up both will be leading when going forwards, with no servo-effect in reverse)

I was just wondering about the effect of the section where the lining is cut away.
If that is at the leading end of a leading shoe, would it magnify the servo effect? There would be more leverage from the piston, because the initial contact point would be closer to the fulcrum. (Like lifting a wheelbarrow - it's easier if you put the weight nearer the wheel)