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TR2/3/3A speedo/tach discrepancy? TR3A

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NutmegCT

NutmegCT

Great Pumpkin
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Earlier I posted about my tach showing 3000rpm while my speedo shows ca. 60mph. Thanks for the replies regarding possible incorrect cable and/or internal gear ratios.

My speedo has some small numbers on the face:

SN 6307/04 over a 1180.

A friend's TR3A speedo shows SN 6325/00 - 209187 over a 1184.

My tach's face shows:

RN 1402/09.

Friend's tach shows RN 1417/00

Are these numbers anything more than "serial numbers"? Do my speedo/tach numbers look correct?

Just wondering if I might have "mis-matched" gears inside the instruments themselves, or if they're just fine. Before I work to replace the missing trip reset on my speedo, I'd like to know if it's the proper speedo/tach combination.

Thanks.
Tom
 
Tom, here's some information I gleaned from the net.
Jeff

1. Speedometer - There were several different speedometers fitted to the cars.TS 1 to TS 8637 (?) were fitted with Smiths' unit #SN 6307/04. This unit featured a deep casing, rigid trip stalk covered in black vinyl or painted black, and a dull red high beam warning light set into a lip in the gauge face. These gauges fit all U.S. specification TR2's, and are found on 3.7:1 ratio cars well into theTR3A range.TS 8637 (?) to TS 10545 were fitted with different speedometers depending upon the rear axle ratio of thecars. Non-overdrive 3.7:1 ratio cars were fitted with Smiths' #SN 6319/00, and overdrive cars Smiths' #SN6319/02. These units featured a more shallow casing, flexible vinyl covered trip stalks, and a bright red high beam light in a more exposed setting.TS 10546 to the end of production were fitted with Smiths' #SN 6319/06 (non-overdrive) and Smiths' #SN6319/04 (overdrive). Visually, these are identical to those immediately above, and probably were not always fitted after supposedly introduced in May, 1956.

2. Tachometer - There were only two types of tachometers fitted to U.S. specification cars, generally.TS 1 to TS 8637 (?) were fitted with Smiths' #RN 1402/09. These units had deep casings similar to the early speedometers. These tachometers were fitted well into the TR3A range despite the introduction of a later unit. TS 8637 (?) were fitted with Smiths' #RN 1411/00. These had the more shallow casing.
 
NutmegCT said:
...My speedo has some small numbers on the face: SN 6307/04 over a 1180...
Click to expand...

That means the speedo cable should turn 1180 times in a mile for this speedo to be correct.

I believe the 1180 speedo head is correct for the 3.7 rear end on a TR4 with sotck tires (noting that almost no one uses stock tyres).

The 1184 head would possibly have been for a 3.7 rear end with stock tires of a slightly smaller diameter. I think the original tires on a TR3A would have been different from the original tires on a TR4 -- but the difference between 1180 and 1184 is negligible.
 
Here's some more info on the speedos.

BTW, I've got a Jaeger speedo and tach in my TR3, not Smith's. IIRC, that's what they all came with.
 
My TR3 always travelled at 60 mph at 3000 rpm. I hope it continues to do so when I get it back on the road.
 
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