i got my disc brake kit!

yorgatron wrote:

i'll post updates in the days to come.

Which kit did you get?

While I'm all in favour of upgrading stepdown brakes, I must sound a word of caution about the kits that hang the caliper bracket off the back of the stub axle, rather than bolt it to the face of the stub axle where the drum brake backing plate used to go.



Hang the bracket off the back? Bolt it to the face? What's the difference I hear you say.



There is a big difference to the amount of force being placed on the mounting points, ie the 4 little "ears" that protrude from the stub axle. And remember the "ears" are only 3/4" diameter, 1/4" thick and have a 3/8" hole through them.



If the bracket is mounted off the front of the stub axle, ie where the drum brake backing plate used to go, the mounting points only have to resist the rotational braking forces, which is what the Hudson engineers designed them to do. Any shear forces and bending forces are taken by the machined face of the stub axle.



Hang the bracket off the back of the stub axle and the situation changes dramatically, the 4 little "ears" have to absorb all the forces - rotational AND shear AND bending.



Theoretically the bracket only has to deal with rotational forces. But those very large rotational forces only have to get out of true by one half of a percent, not unheard of in the real world, to generate considerable sideways forces on the mountings. This may explain reports of vibration and calipers jamming that have been seen on these pages.



"Hang off the back" disc brake kits are in daily use, but there is definitely an unknown regarding the long term strength of the mounting points for that set up. They are being stressed a lot more than they were designed to be. Not to mention that they are 50 years old and have been round the block a few times.



The attraction of the the "hang off the back" caliper bracket is of course that it can be cut relatively cheaply from plate steel.



The right way of doing it is to make a caliper bracket that bolts to the front of the stub axle. It's way more expensive, and involves a lot of machining and milling of a big lump of steel, but it is definitely do-able.



This something I'm going to do "soon". I did buy a "hang off the back" stepdown disc brake kit, and after mounting it on a spare stub axle, studying it, and coming to the above conclusions, I'll make a bracket the hard way. I'll let you know how I get on, drawings will be freely available when I'm done.



Bob Ward coldesig@gil.com.au