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Differences between BN2 and BN4 speedometer gears??

blueskies

Jedi Warrior
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The speedometer on the 1956 100-4 BN2 had issues. It looked fine but was disconnected when I bought the car. On hooking it up, I found that the needle bounced and floated all the way up to 120 mph, when the car was going about half that speed. Also, both odometers did not work. I took it apart and found both small phenolic? odometer gears chewed off, and that part of the mechanism appeared jammed.

So, I looked in the box of Healey gauge parts and found a number of speedometers from 100-6 and 3000 cars. Picking what looked to be the oldest one (almost certainly from a 100-6), with the best chance of matching the workings of the one from the 100-4, I took that one apart. The parts inside looked identical in design to the one from the 100-4 (Smith's made three different types over the years), and both of the little odometer gears were good. So I put that together with the face and case from the 100-4 and hooked it up. For those that don't know, the 100-4 uses a black face for the speedometer, while the 100-6 cars have white faces for the speedos, which is why I couldn't just install the newer speedometer and have it look correct.

It's much better now than before, but a couple of issues remain. I played around with calibrating the "new" speedometer, using the GPS speedometer on my phone as a reference point. After another disassembly of the speedo, I got the needle in the right spot for accuracy at 20 mph. But as the speed rises after that, the speedometer reads high. By 60 actual mph, it reads about 75 mph. Also, while both odometers now work, they turn the miles over every 8/10 or so of a mile.

The only thing I can think of is that the speedo from the 100-6 is geared differently internally than the speedo from the 100-4. I could disassemble it again and count the number of teeth on the gears, but prefer not to do that without the correct parts to put in there.

Does anyone here know the difference in gearing in these two speedos? I could send it off somewhere, but where's the fun in that?
 

Jake

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