Clock Setting Knob

[Rob Reilly]

On my TA tachometer (rev counter), I have discovered that the knob for resetting the clock is missing, broken off.
What remains of the shaft appears to have had a hole drilled through it, and that's where it broke.

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The shaft is 0.119" diameter.
I can weld an extension on the shaft.
I have a machine shop so I can make the knob part if I knew what it looked like.
Can anyone provide a picture of their knob?
It is held in by a brass sleeve that unscrews.

[Rob Reilly]

Or how about a picture of the clock viewed from the back, so I can get an idea of the knob and length of the shaft?
I think it must hang down below the dashboard, right?

[Steve Simmons]

Every tach I have here is missing the knob so I was hoping someone else would chime in. Here's a photo of the area on my TC, which I assume is the same as TA. The distance from the bottom of the clock to the bottom edge of the dash (through the hole where the knob goes) is just over 1/2". Hopefully this helps.

[Duncan M]

Replacement knob, also. One pushes up a fraction of an inch and then turn to adjust clock. When the battery is re-connected due to service, the clock hands must be moved forward to start the clock ticking, on the TC clock.

[Rob Reilly]

Well, this answers a couple of questions that weren't yet asked.
Apparently mine is not the only broken clock knob shaft. Someone has done a clever repair on Duncan's.
And I see that metal strap spanning the gap in the plywood dash panel on Steve's. I was wondering if on mine it was some sort of old repair job. I see now that the gap was necessary for the clock shaft to extend down there. Then the strap strengthens the plywood there.
I've been combing MG books, and the only pictures I've found are long distance shots of the whole dash.
But it looks like the knob is the same as the one on the speedometer.
My odometer reset shaft is a flexible spring.
Maybe the clock reset should have also been a spring so it wouldn't have got broken.
I begin to suspect the clock knob had a sleeve that fit over the main shaft, with a hole and a cotter pin to hold it on the shaft. But when you drill a hole in a .119" shaft, the remaining material is pretty weak at that place, easily broken there by hitting the knob with your knee.
That's my working theory anyway, until something better turns up.

[Steve Simmons]

I wonder if a better idea would be to thread the shaft, then thread the knob on with a locknut above it. Or maybe the shaft is too thin to cut threads into without making it even weaker. I haven't seen the shaft since the tach was out.

[Rob Reilly]

Thinking about this some more, I think it probable that Jaeger would have used the same knob for both clock and odometer resetting shafts.
The knob on my odometer is brass, 25/64" OD x 21/64" long, with 33 grooves around the outside of it and a hole through, where a shaft is inserted and soldered.

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I can make that.

There is a coil spring pushed over that knob shaft and over another shaft coming out of the speedometer.
So most of the spring length is flexible, but not at the ends where it is pushed over the shafts.
The spring is .215" OD with about .063" wire diameter.
A spring that size could be pushed over what remains of my clock reset shaft.
I'm thinking it would make more sense to have a springy clock resetter.
So I'm going to look for a spring with something close to those characteristics, and copy the idea from the odometer resetter.

[JonnyP]

Whilst mine is a TC, rather than a TA, I can confirm that the resetting knobs on both appear to be the same and they are springs with a brass knob on the end. I cannot be sure how the spring connects to the threaded fitting because on both resetters the spring part is covered by what I would describe as a canvas tube covered in thick black paint, I guess for aesthetic purposes.

Of course, they may not be original parts, but they are certainly very old.

[Rob Reilly]

Thanks very much for that confirmation of the spring. That is what I will do. I've already found a suitable spring in my stash of miscellaneous springs.