In my post about the truck interior a couple of weeks ago I talked about the broken odometer and inaccurate speedometer. Last weekend the new speedometer came in and I installed it before making the trip down to my brother’s place.
Driving on a marked freeway is the best way to test the accuracy of your odometer. At one of the mile markers (not an exit), note your odometer reading. Drive 10 miles (by the markers) and note how far your odometer said you travelled. Mine was showing about 11.8 miles each of the 3 times I checked it, so it was about 18% high. When I compared the speedometer to a speed app on my phone it was even more inaccurate.
After testing the odometer you basically have two choices: 1) swap out the speedometer gears inside the transmission, so the speedometer cable spins at a slower rate, or 2) put a ratio adapter between the transmission and the speedometer cable. The first option is much cheaper and the second option is much easier.
I went with the easier option so I could fix it myself. You can buy adapters that either speed up or slow down the rate that the speedometer spins. This is where you need a bit of math. My odometer was 18% high, but that doesn’t mean I want to slow it down 18%. To go from 11.8 miles to 10, it’s about a 15.3% decrease (1.8/11.8). I didn’t feel like getting a custom ratio adapter built, so I found one close enough (17.6% slow down), which cost me $91. It was an easy install…
I took the truck out for a test drive and after 2 miles the speedometer dropped to 0 and the odometer stopped turning over. What the fuck?!
The next day I started troubleshooting and quickly found the problem when I unscrewed the speedometer cable from the ratio adapter. When I tugged on the inner cable a bit, the end came right out!
I must have either bumped the cabling around during the install or this was really bad timing. The outer cable housing must have been sitting on the exhaust, which melted right through, jammed up, and prevented the inner cable from spinning freely. The transmission kept spinning the end and the inner cable unravelled, completely snapping.
I picked up a brand new speedometer cable and outer jacket from Advanced Auto Parts for less than $14. I’m glad the closest they had to 72″ (length of my old one) was 83″ because I ended up needing the extra foot. I installed the cable, properly routed it up to the dash, and zip tied it in place so it can’t come in contact with the exhaust or any moving parts.
After a test drive, the odometer was about 3% high, which was to be expected. Remember that I needed to slow it down 15.3% and the closest adapter I could find slowed it down a bit more, by 17.6%. Speeds were about 2-5 mph fast until I got on the freeway where it was dead nuts while going 70-77 mph. Close enough for me!
I have an idea of the gas mileage from the first trip with the odometer (after adjusting for the inaccuracy), but now that everything is working I’ll be able to track it and see for sure what I’m getting. Stay tuned!