Weedy rear brake

Have you tried RGM as they have high friction shoes which work well.

Fitting the disc brake Mk3 wheel would also need the swinging arm as it has caliper location points though am not sure if it would fit to the early gearbox cradle. Then the is as you say the matter of rear master cylinder but you would benefit from a better cush drive set up.

You can open out the hole in the brakeplate for the stub axle, this allows the brakeplate to float when the nut is loose, to centralise the shoes to the drum apply the brake while tightening the nut. Without the ability to float the shoes wear on the leading edge and then do not make good contact.

Chris

Karl has mentioned the high friction brake shoes:

http://www.rgmnorton.co.uk/buy/rgm-rear-brake-shoes-high-friction-mz-gold_2471.htm

Also have you considered getting the drum and shoes looked at by a specialist, e.g.

http://classicbrakeservices.vpweb.co.uk/About-Us.html

See also others under Services section on this website.

In my experience the rear drum brake can be made effective enough for 'normal' use.

Andy

Previously chris_ankcorn wrote:

The rear drum brake on my 1973 850 is hopeless, I'd welcome any advice from folk about making it less of an ornament.

Failing that, what would be the level of difficulty (and expense!) involved with converting to a later type disc? I'd like to keep left foot braking but I don't see that as a problem.

If you really want to find out if disc brake fits your swinging arm- The caliper locates on lower suspension bolt and axle - come to Doncaster and try the one in my mk111. If your really keen I might do you a swap. Yes - my experience and that of rolling road at MOT is that standard disc is no better than drum, but drums don't seize up if left standing.

If you drum has become worse, here are 2 ways it can happen through maintenance. 1 dismantle and paint backplate, on assembly put shoes on opposite way round to how you took them off. 2 Decide play in cam spindle bush is too much and swap it/backplate for a better one - but put old shoes back; the leading (worn) one now hardly contacts the drum.

My advice for what it is worth is clean drum with emery cloth to remove any rust /oil contamination and try a set of new shoes.

If you are from Yorkshire linings and rivets come up on auction quite regularly!

regards Martin

Back in 2012 I wrote up and theorised about the lack of bite with the 7" drum brake and came to the conclusion that John Holmes has suggested above. The weakness or lack of power is because of the brakes inability to self centralise the two shoes. By far the most braking force created by a single sided drum brake is produced by the leading shoe...however as this shoe wears more quickly because of the extra work it's doing it gradually loses the ability to contact the drum with any force because the less worn thicker trailing shoe is controlling and limiting the outward movement of it's partner as it meets the drum first and stops further rotation of the cam.

Enlarging the brake plate's central spindle hole just a millimetre or two will allow better re-centralisation before tightening. But eventually you will have to do this again but it only takes a minute. Better brakes allow the operating cams spindle to float (Royal Enfield is one example) where the spindle is held in a sliding plate that is held loosely on the main brake plate. Having a floating cam will ensure that both shoes can touch the drum exactly at the same time but more importantly allow the leading shoe to really pull itself onto the drum hard and continue to receive pressure from the cam which is now free to follow it up and not have its turning action stopped by the thicker trailing shoe.

I suggested a very simple but crude improvement could be created by slightly enlarging the cam spindle hole as well as this would allow the cam to have some float. As the cam is always loaded by the tension on the brake rod or cable and the shoes springs it does not rattle...Once again just 1 mm helps quite a bit. If one could fit a sprung pressure washer behind the brake arm sandwiched to the brake plate to stabilise the cam spindle then I reckon even a bigger clearance could be created allowing enough float to really cater for the shoes uneven wear rate but you don't have to over do it either.

I have done these mods to my 7" front brake and found the brake acceptably powerful even with the old shoes but will shortly try the RGM ones.

Les

Plenty of good set up advice above, though I have by-passed the rivet on linings and had oversize (1/4" thick) modern #3915 high friction lining materialvulcanised on to the shoes. Then, mount them on the back plate and turn the diameter to exactly suit the drum with a 10 Thou (.010")shim wrapped on the cam. When the shim is removed, the plate with shoes will slip into drum with minimum clearance. Pull brake on hard as the axle nuts are tightened to positively centralise shoes in drum.

The #3915 frictionliningis used on older vehicles with manually operated brakes, this gives excellent bite on the drum, the only trade off is it will not last as long as the harder, less effective linings. My front brake, with moderate cable pull, will easily sink the forks rightdown.