Speedometer/odometer accuracy

dotcentral · Post by **dotcentral** » April 16, 2007, 4:03 pm

That's one way to keep your mileage low. :wink:

I've wondered about that myself, but figured they'd be the same, both either hi, low, or just about right. Mine aren't quite running yet but will be interesting to see what others find out.

Garbz · Post by **Garbz** » April 16, 2007, 5:53 pm

Gears were changed. You need to go down one tooth on the driven gear to bring the speedo back in line.

This gets you in the ball park, however remember the insturement is above 40 yrears old. 10% above or below is the average...Ever wonder why the PD gives that ten MPH break on ticketing on the freeway?

Garbz

Ford4jack · Post by **Ford4jack** » April 16, 2007, 9:27 pm

As Garbz said one tooth should do it. When I was setting mine 1 tooth = 1/10 per mile.

Im loseing 1/10th for every 3.2 miles last time I checked.

Speedo wise who knows. mile markers are sparse around here and every body seems to speed

Think mines within a couple of MPH though I just can't prove it.

willy3486 · Post by **willy3486** » April 16, 2007, 10:13 pm

Don't forget the gear in the transmission that goes to the speedo. If you have changed the rear end chunk it can cause it to be off also. I changed the rear end once and the plastic gear in the tranny was way off for it. I got a ticket to prove it.

blackagatha · Post by **blackagatha** » April 18, 2007, 1:06 am

your odometer may be getting sticky, causing the gears in the speedo head to skip.

My odometer completely jammed up and exploded a few years back. I got another one from a different head unit. It was all stiff too. So I soaked it in a glass of water for a few hours, dried it out real good, and filled it up with graphite (FULL). shook it around, and blew it all out with a duster can. Works as slick as new. Twisted the dials around to read an approximate value for my new engine. I think it keeps perfect time now.

When I put my c6 in my truck, I had 3.89 gears in the back. Car tranny + Truck diff = 10 mph wrong. I threw in a 2.75 diff to help on the freeway, and guess what, speedo is dead on the money.

If you have issues of the sort that I had with incompatible ratios for the speedo gear selection, I've heard of gearboxes that go on the end of the speedo cable to put it in a proper ratio band.