Doing a full refurbishment on the brake cross tube on my 1933 AH tourer.
There is quite a bit of movement in the two end bearings, part
numbers BN51 and BN70 in the spares book.
I cannot find complete units (bracket and bearing) and wonder if
these are available anywhere ?.
Both 'floating' bearings in the assembly are very worn, especially the
nearside which is close to falling out. This explains why the nearside rear
brake hardly works !.
I suspect I will have to take the brackets off and try to either make
up new inner bearings, or try to squeeze the bracket to tighten them
onto the bearing as another possibility.
Did look at some pillar block bearings as a full replacement but think
this might be approaching major surgery.
Most importantly, it is necessary for these bearings (and the whole assembly) to have a fair amount of 'slop' in the set up. a nice tight engineering fit of the shaft in the bearings will lead to the shaft binding as the chassis flexes. Something that you don't want...
These are self-aligning bearings, and the bearing rings with the part-spherical outer faces are supposed to be a reasonably tight fit in the two halves of the chassis bracket but not so tight as to bind. I suspect this was partly to accommodate assembly tolerance and partly to allow for chassis flex. They certainly shouldn't rattle or rotate, rotation only happens when the inner bearings seize up. You could try some shimming/packing between the spherical parts and the chassis brackets, but this needs to be robust enough to stay in place reliably. A custom turned brass ring might be the best bet. The two halves of the chassis bracket are riveted together, these may be drilled out and replaced with cap head screws and nylocs if you need to disassemble.
The shaft rotation takes place between the inner steel shaft and the "top hat" zinc liners. I think Austin chose zinc as it is to some extent self lubricating and could withstand lack of oiling. Maybe not 90 years of no oil though.... You can buy new brass versions of the top hats, but I seem to remember they may need slitting and filing to reduce them to the exact diameter needed. I would describe the ideal shaft to liner clearance as an easy fit, i.e. looser than a nice tight fit but not a fair amount of slop.
Fair comment, John. Just as long as the OP doesn't think that a perfect bearing fit is what is required and that an allowance needs to be made for chassis flex...
You can easily make the top hat bushes from Zinc sheet and personally I find Zinc bushes far superior to brass. As for the spherical bushes they should be a close fit in the chassis brackets or braking efficiency WILL suffer, if they are badly worn you have no choice other than to make, or have made bespoke replacements.
Managed to take some pictures this morning to show the problem.
The bearings onto the cross shaft are all in fairly good condition, including possibly an original 'Zinc' one.
The problem is as per the photo's. Both sides have a lot of movement but the nearside is very bad.
Suprisingly there is NO bearing on the N/S, just cross shaft straight into the ball, which is probably why
this end is the worst.
I suspect the problem started with the bearings being too tight onto the cross shaft meaning movement
was from the cross shaft and bearing with the bearing mount ball to socket doing all the movement, but
with no bearing on the N/S this has the worst wear.
There are a few options to fix:
1, Weld the ball part to the bracket. Bit final as if it does not work I will have to fabricate brackets for a full replacement
2, Glue the ball into place. Possible, and reversable if it did not work.
3, Take the brackets off and as suggested use packing or bending to make the ball firmer in the housing.
Option 3 is probably the better idea, but with garage temperature at +4C I think I will wait until
the weekend when temperatures are supposed to go up.
I've experienced this problem and found that the bearing hangers have spayed out in one case I could slide the spherical portion out. I had an old Ford Cortina void bush removal/fitting tool which I found was perfect for squeezing the hangers back together.
