Hi, I have the rear wheel out of th bike and I have some questions about the brake hub. What is the correct internal Dia (Mine has a slight lip then is a chamfer to main braking surface, it measures 140mm on lip but I cannot get measurement beyond this as I only have a vernier not an internal Micrometer) Next what should the surface look like and is it a replacable liner or an integral part of the hub. If necessary can it be relined easily? Finally what thickness is the brake shoe when new so I can judge wether replacement is due?

Cheers

The inner surface is an integral part of the hub. They came from the factory with a chrome plate layer on them which wears out and becomes pitted. The hubs can be relined (Bultaco UK do this service

Re your query

I rarely use Bultaco Model numbers M80 etc

If it rusts it will be a liner, if there are any shiny flaky bits its crome and probably due fora re-line.

I use a dremel type thing to get rid of the lip, makes it easier to get the shoes back in.

Edited February 18, 201016 yr by B40RT

Thanks everyone, its definitely an M-80 and there does seem to be some signs of rust developing whilst it has been standing. I will try to post decent photo for clarification,

Graat advuce as usual,

Cheers

Hi, finally got photo of hub, it is definitely a diferent material to rest of hub but is it to worn to run?

Myson

Edited February 21, 201016 yr by myson

It depends on how serious you are about having good brakes

If the drum diameter where the shoes run is different to the diameter of the shoes when they are on the backing plate, the contact area will be small = poor brakes.

Standard shoes + worn drum = poor brakes

Oversize shoes machined down to worn drum diameter = slightly better brakes

Oversize shoes machined to fit + skimmed flat drum surface = great brakes

Resleeved drum + shoes that match diameter = great brakes

The picture is out of focus so impossible to tell if it is worn too far for skimming or requires a new sleeve.

Cheers for that. I have contacts in several CNC companies that could skim or re sleeve for me. How do you secure sleeve to prevent slippage and what material would you recommend?

I believe correct ID is 140mm is that about right?

Thanks,

Myson