Brakes

[Geoff Lewis]

Hi All, I need some advice regarding brakes. I am currently using a Grimeca front brake of 125 mm diam. as per moto morini 90 cc in the current VMX mag and a 125 mm moped rear brake. Both are at best pathetic and at worst dangerous. I have been told that compound type is critical, others say leverage rate is more important. I have heard of self servo effect with drum brakes etc. Some help here would be most appreciated.I have some single sided CZ hubs that seem better even with the 50 year old linings! Help!
Regards Geoff.

[David Lahey]

I say the most important things are:
The friction contact area is maximised (smoothness of drum surface, matching diameters of drum and linings)
Cam followers to cam face angle less than 5 degrees when linings touch drum
Perfect wheel bearings
Shoes centralised - beware that some bikes (OSSAs are known for this) have an axle hole that is not exactly in the same centre as the OD of the linings. Enlarging the axle hole fixes this common problem.

Most brake drums that have been used for a while have developed grooving and have worn bigger in diameter. Standard size shoes are made to fit the diameter of a new drum, so by the time the new shoes have been bedded into the diameter and grooving of the old drum, the cam is so far around that there is friction generated as the cam edge slides across the follower.

If you want great brakes - it doesn't matter what bike they are off - it may take machining of the drum, getting oversize linings fitted and then machine the linings to fit the drum diameter, but it can be done and they can be made to work well.

[Greg Harding]

Hi Everyone,

Geoff, maybe I can help, but first can you post some photos of your existing brake assemblies? Side views with brakes on and axle axis in the centre of frame would be nice. Do both of your bikes have the same setup and if not, photos of all please?

GO CZ, now lets work on STOP CZ !!!!!!!