I am wondering if all mechanical tachometers are the same gearing wise. Are the tachs built knowing that the cable's speed input is 1/2 crank speed(as most I have seen are driven from the distributor) and then doubled mechanically in the tach itself, or just compensated for on the faceplate? I have only owned one thing with a mechanical tach, and that was an old (1952) John Deere It needed a new cable, and worked well. Are all the cables the same also? (except for length)
Back in the day VW midgets ran a mechanical tack off the crank. It had a box on it and that could have reduced the revs, I don't know. They used a cable exactly like a speedo. I had one made at Speedometer Service in the Springs.
no. I have seen three different cable ends in perf. applications, hex, square, and round with a tang, there may even be more.
My advice is....... get the one you want and adapt it to fit. They make speed reducers/multipliers, and cable ends would be an easy fix.
Early Corvettes ran the tach off the rear of the generator. It ran the cable at a different speed than the ones from the dist. When I tried to run the tach in my '61 Vette from a dist. with a tach drive, the tach ran at approx. 50% of actual RPM.
Mechanical tachs run at cable speed and twice cable speed. The Corvette tachs that ran off the generator were cable speed, the ones that ran off the distributor or ones that run off the cam are twice or 2X cable speed.
The one on my old truck build? I'd love to hook it up somehow? The geek in me could do it with a electronic pickup and servo motor but? the hillbilly in me thinks it should be just a cable drive like it was on the other engine. Simple is better. THE SW cable looked just like a speedo cable. Any pictures of "how to do it off a small block chevy"?
I had a vette with mechanical tach [ the distributor drive and cable were the same ] so it needs to read 2 x that. I switched to a mallory tach drive distrubuter [same gearing ] but the cable was different. The solution was to shorten down a Tach drive cable off an early Yamaha. It has the same Tang on the cable as the mallory drive but fits perfect inside a corvette cable. So I can ***ume 70's Jap bikes are another source of mechanical Tach's
A good speedo shop will have those things and the abi8lity to make a custom length cable too. The reducers/multipliers aren't cheap, but they can be custom ***embled with whatever combination of gears are needed to get the ratio you need.
COMMERCIAL SPEEDOMETER SERVICE, INC. West Sacramento, CA These folk have built two cables for me..... They do excellent work!
I remember back in the mid 60's going to a company named Jones Motorola is Stamford, Connecticut when they were making tachometers for submarines. They had just started making the tachometers for **** Moroso and it was cool being in their factory and looking around at just how they manufacture them. Jimbo
A Jones Motorola mechanical tach is "period correct" with vintage road racing cars [ F5000's and CanAm cars etc ] They have the cool factor!
It is Jones-Motrola, not Motorola. Those tachs were "chronometric". The needle periodically jumps from one point to the next rather than sweeping smoothly like a "normal" tach.
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