A Special Builder's Notes


The Special Builder's Breakfast Club

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04 September 2012

Something I've Eaten...

...has set the synapses off and a message that must have been trying to get my attention for some days, has finally got through. 'The brakes - there's something you're missing about the brakes - think Austin 7', was my first conscious thought this morning.

Of course! In reversing the front brake levers and setting the pistons at the back of the drums, I've replicated what's generally accepted to be a design fault in the Austin 7 front brakes. As brake pressure is applied, the axle has a tendency to roll in the direction of rotation of the drum and is helped in this by the force being applied in the same direction to the brake lever. The theory is that the more you press the brake pedal, the more the axle will rotate - in effect releasing the brake pressure. So you'll need to press the pedal a bit more which will continue to rotate the axle and further release the pressure until the garage wall is in your lap.

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Mr Bowden came up with a fix for the 7 and routed the brake cables over the top of the king pins so that the levers pulled up - in the opposite direction to the rotation of the drum - and everyone was happy. I'm not going to be able to get out of this so easily (I'm not going to put the cylinders on the front because they'll look awful) but, in adopting the hydraulic system, I notice that the mounting holes in the axle for the various brake lever pivots are left unoccupied. I can rig up an anti-axle-roll-bar going back to a point on the chassis rail that will help to counteract the twist of the axle under braking, but realistically, if I'm winding up the axle when I'm braking, I'm doing something wrong.

I popped the front axle on over the weekend....

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...which threw up another problem. I've measured the springs; they're exactly the same except that the offside has an extra leaf - this is how it was originally. I've also checked the squareness of the chassis by measuring the diagonals - there's 1/8th in it. Somehow, the offside of the axle beam is 1/2" forward or the nearside is 1/2" backwards. It may be something to do with the clattering the chassis had with the wall way back when or ..... what? Dunno gov.

There's something a bit odd in that the shackle at the rear of the front offside spring doesn't hang exactly vertically but the extra leaf in the spring is possibly making it a tighter radius: it'll probably flatten out when loaded up. I'm not particularly worried about any of this lack of precision because in use, the chassis flexes so much it's never in line anyway. But I will have to address the 1/2" stagger across the width and the only way to do that will be to re-position the locating points on both the axle and the bump stop that sits on top of the spring. I can't re-position the axle clamping bolt because a: it's blinkin' dangerous and b: it'll affect the Centre of Boing.

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The headlamps which were arriving any-day-now a week ago, haven't. A message from Monsieur Marchal informs me that they have arrived safely - at his. La Poste have delivered them to the sender.

As a Francophile, I have over time adopted and perfected the Gallic shrug.

previous post Further Distraction.....
next post Decisions....


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