DIY speedometer calibration

[Solamar]

Par for the course, the speedo I acquired (12/75 180 MPH electronic) read wildly inaccurate. At 20mph it read ~40 and at 60 it read over 90.

I searched the Pelican archives and found several threads on the topic, but the info was vague and most of the photos were missing. At least I knew it was possible, in theory, to adjust the speedo calibration.

First thing I did was remove the plastic electrical connection panel to get a better look at the internal circuit board. Just as I had read, there was the trim pot, right side of picture -



Unfortunately you can not get to the trim pot with the speedo body intact, unless you drill an access hole. Not wanting to get metal shavings into my speedo I used all the tricks I've gathered over the years. Filled the drill bit flutes with grease, painters tape on the inside and drilled upside down into the speedo so gravity would help displace the metal chips.







I didnt do a great job guestimating the alignment for the hole. Wound up a bit further from the back than needed, but could still get a small screwdriver onto the trim pot.



I believe the trim pot travel is from ~ 7:00 to 5:00. Mine was initially set at ~2:00. I spun the pot to 5:00 and went for a test drive. Immediately obvious I had adjusted the wrong direction, reset at ~ 9:00. Much better, but still indicating faster than actual. Set to the low limit, 7:00 and it's pretty much perfect

Small patch of tape over the new hole and buttoned everything back up.

Couple hundred $$ saved that I can now send to Pelican for a new master cylinder (whats that dripping on my feet?)...

[Bill Douglas]

Very clever!!!

[theenico]

Super cool! Thanks for posting that.