I have a Bosch tach that looks like my old Sun Super Tach in my 55 Chevy. Occasionally (3x over the past 4-5 years it shows no reading, then reads low, then corrects itself. Points ignition. Coil is good, and I’ve verified grounds, continuity and all connections. Suggestions? Sent from my iPhone using H.A.M.B.
You'd think it would do it regularly? What are you running for plug wires? There are a couple threads on here about bouncing tachs with some good suggestions. Do a search on bouncing tach.
Try replacing the condenser in the distributor. It's fairly common for them to develop an intermittent connection inside, because they are not made very well. But another symptom would be a slight misfire at the same time the tach acts up.
On boat tachs in saltwater marine environment this is common. One of the "fixes" is to access the screw on the back of the tach that is used to select 4, 6, or 8 cylinders and cycle it back and forth a half dozen or so times. It seems to help it restore a better electrical connection. I've done it on the boat tach a couple times over the past few years and seems to work.
Any device with moving electrical contacts, wiper switches or rheostats that acts erratically will likely benefit from a shot or two of DeOxit contact cleaner.
I don't recall saying that. But tubman was doing something with the old Mallory big condensers https://www.jalopyjournal.com/forum/threads/new-big-brass-condensers-now-available.1033298/
I was going to suggest a bad connection or corrosion inside the tach. Cycling the switch would be the cure for that. Sometimes if you look at a circuit board you will find that a wire connection is not as good as it could be. De-soldering and cutting back to good wire and re-soldering is the cure for that. Unless you play with older electronics a lot this is not recommended.
The factory tach in my 68 Olds does the same thing. It reads fine most of the time, then nothing...sometimes for a day or more. I have an axillary tach I installed for racing which reads perfect and never took the tach out of the dash to diagnose. But the 442 does have MSD ignition and 8mm wires, so rule out the points, condenser, wires and other triggers. That leaves me with a dirty tach with periodic connection issues, in my case.
Shutt. I have one of those too. Sorry to say they are a cheap imitation of a look we like. They are made under a few names. Sometimes mine doesn’t move until I smack the side of it. In my opinion they are not inexpensive to buy but not what I had expected...
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