Brake Cross Shaft bushes info (RP Saloon 1934)

[John]

Hi 

This is the first time of posting on this forum, so any help would be appreciated!

 I am currently refurbishing a 1934 RP box saloon where I have completely stripped it down to the bare bones and am now rebuilding the chassis. I have been researching on this forum and found it really helpful but could do with a little extra help with how the cross shaft works (or moves) when the brakes are applied. The cross tube bearings were loose on the n/s but seized on the o/s (it also has a centre bush housing). After reading on the forum there is a zinc liner between each bush and the cross shaft, does the bush move in the housing its riveted into when the brakes are applied or is this part pinched tight in the housing and the shaft moves between the shaft and liner and bush? 

 I have also bought some new liners (brass) from the Seven Workshop but they only do 2 sizes and I need a third for the larger o/s bush, is there anywhere else in the UK that sells them (the shaft O/D is 1 21/64, and  the bush I/D is 1 3/8)?

       

[John Cornforth]

Hi John

The bearings have a semi-spherical part which is sandwiched tightly between two stamped bracket halves riveted together. This is supposed to form a self-aligning bearing, and the semi-spherical part can just about swivel to relieve any angular misalignment strain. It's not supposed to be able to rotate freely, though this can happen if the inner bearing seizes and it starts to turn and wear. If it's too loose you may need to pack out the space with shim stock, after drilling out the four rivets and replacing with high tensile fasteners. Your photo shows that the rivets have already been done.

Inside the semi-spherical part is a thin wall zinc liner, and the shaft rotates freely inside this. Zinc is tolerant of owners who forget to lubricate the bearing, but brass will work. You might have to make up your own liner, ideally this is a continuous tube but one with a slit will still work and is easier to make. It will need a "top hat" end to stop it working sideways. The fit on the shaft isn't ultra-critical but you want better than a rattling gap.

You may or may not know that (in theory at least) the torque from the foot pedal travels down the hollow outer shaft towards the centre of the car, and is then conveyed (via a weld) to the middle of the solid inner shaft to give symmetrical left/right braking. The amount of differential movement between the pedal lever and the offside rear brake lever is miniscule - I doubt if you could see it unless you added a long bar and really heaved. Nevertheless, with cable braking systems its all about the torque and tension in the various parts - any movement you see does nothing except take up slack before the real braking begins.

[Hugh Barnes]

And to re-iterate a point that John alludes to, these dont want to be a 'bearing' fit, a bit of play (but not too much) is needed otherwise the cross shaft binds when the chassis flexes..

[John]

John / Hugh

Many thanks for getting back to me so quickly and explaining how it all moves (or is supposed to!). In theory then it looks like my n/s bearing housing and bush is warn, I can work on this to make it tighter. The centre of the shaft support will be fine as it is a sliding fit between the brass liner, shaft and bearing and the housings in the centre and o/s are tight, I will just have to make another liner for the o/s. I think I will get away with using some 20swg zinc or brass.

I had to remove the shaft so drilled the rivets out, after much research on this forum understood it was the only way! the photo shows it bolted back together as I was trying the fitment and took the photo. 

I think I am getting an understanding now of the tube torque as well and why it was made this way. 

Many thanks both.

John.