A Special Builder's Notes


The Special Builder's Breakfast Club

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30 January 2018

Getting To Grips.

Counsel and I spent the day at The Great Collector's workshop, reinstalling the 1905 Darracq cone clutch. Charles Johnson in Norwich had done an excellent job relining the cone with the same material they used to reline the brake shoes on my Hillman. As the original material was leather, it would be interesting to see how this might work.

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The trial fit of the cone in the flywheel didn't see any improvement in the depth of engagement - the cone still stuck out of the housing by at least 3/8" so I popped it in the lathe and formed a small radius on the front edge.

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On the inside of the cone are 4 equally spaced spring-loaded plungers. They press on the inner face of the lining to create 4 high spots, the purpose of which is to provide a smooth take up on the drive. As the clutch is let out, the springs compress and the lining flattens against the cone. We thought that these might have been preventing the cone from engaging fully with the flywheel as the new material didn't have the same flexibility as the old leather, so out they came.

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There was some improvement so we decided to reassemble and give it a go. With everything back in place - it's not a terribly difficult job, just a bit awkward as we're not as flexible as we used to be - all the signs were that we had a perfectly serviceable clutch again and off we went down the road. It was quickly apparent that we were back to square one and the clutch slip that had prompted the new lining, had not gone away. Back in the workshop we noticed that the cone was now fully home in the flywheel, with no overhang at all. Hmmm. There's a very big nut and coil spring on the end of the gearbox input shaft and the Darracq Owner's Manual instructs the would-be mechanic to adjust this nut in order to alleviate the symptoms of slip. However, it doesn't say which way to screw the nut and when you do it doesn't seem to make the slightest difference to anything but the amount of pressure you need to apply to the pedal - though without a schematic of what's going on in the gearbox, I could be wrong.

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With everything in pieces again - we were becoming quite expert at this - we noticed a ridge of what looked like paint in the inner edge of the flywheel. It corresponded with the now very black and greasy lining on the cone. A Stanley blade scrapped away a 1/4" thick line of 100-year-old whatever-it-was-they-used-in-the-olden-days to keep the leather in trim. Back in the lathe, a liberal dose of brake cleaner and a scrub up with a soft wire brush, soon had things looking normal again.

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As a belt-and-braces fix, we decided to insert a 2mm aluminium spacer between the gearbox input flange and the cone. This, in theory, would help to push the cone home under a greater load. We also put the spring-loaded twinks back in their respective housings, popped everything back together again and whizzed off on a second test run.

Success! Not a hint of slip and, Mr Toad seemed pleased with the outcome.

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