You could always use a few resistors to get an exact value you want. Or even use a trim pot. Most of the metal film resistors are 1% tolerance and are stocked in many values. You can probably calibrate it on the bench. It depends what the threshold of the tach signal is. I have built a signal generator for testing the idle ECUs that has two calibrated values 700 RPM and 850 RPM with a 400 volt signal level.
Dave M vin 03572
http://dm-eng.weebly.com/
...it is so touchy that I could run a moist finger along the cut and make it read correctly.
Schematic1669 160 Tac.jpg
PM me your address if you want to play with it.
Location: Bay Area, CA
Posts: 266
My VIN: 15190
Location: Bay Area, CA
Posts: 266
My VIN: 15190
Thanks to Christian Williams I replaced the trip reset shaft.
It’s a nice project, going really deep in the gauge...
My car's had a broken trip reset shaft since I bought it back in 2008 and it even came with a new replacement. I just never seem to get around to fixing it.
It looks like a fun project though. I actually kind of enjoy working on detailed/intricate projects like that vs. the rusty knuckle busting bolts I've been dealing with on my daily driver.
After seeing your pics I think I might dive into it this spring.
Posts: 4,808
My VIN: 3937
You already have a copy of the DMCH instructions?
DMCH - Trip reset shaft replacement.pdf
Sept. 81, auto, black interior
Location: Northern NJ
Posts: 8,581
My VIN: 10757 1st place Concourse 1998
While you are inside make sure none of the plastic posts have broken off. On more than one car I found at least one broken and because there is a metal clip on it, it got attracted to and jammed up the speedometer causing several angle drives to fail. Glad to hear the tach fix was cheap and easy. Replace all of the bulbs while you are in there too.
David Teitelbaum