the other day when i saw my ute we decided to see if the speedo was tellin me the right speed
at eighty the speedo is showin 110 and at 100 it shows around 150 WTF!!
wats the standard wheel size for a 77 1200 ute it got 13s on it now

standard was 12s, but ive found speedos in the datto are crazy different. i had to run 17s before my speedo was correct. but in saying that even brand new cars are not 100% correct they usually are out about 3kms at 100, so when it says 103 you actually only doing 100.

my recomendation either put up with it or get a gps thats all i use. or pay the big bucks and get it recalibrated

i can easy put up with it
but wouldnt it be defectable?

running the non-standard tyres may be defectable depending on the state law which applies to you, but the accuracy of the speedo cant really be determined by the police on the side of the road without a dyno.

Dont forget that diff ratios and gearbox ratios also affect the speedo reading.

i know that the previous owner rebuilt the gearbox and diff so maybe thats what messed every thing up
who knows?

I dont think that just a rebuild would throw the numbers out that much, you'd have to change the gears inside to some very different ones to get the inaccuracy your talking about.

You'r not by any chance running REALLY low profile tyres on your 13's??

maybe they change the gearing when the rebuilt it???
na they are not low profile i think there about 45-65s not sure tho

Just an after-thought, with that kind of innaccuracy, you may be clocking up alot of extra K's on your odometer as well.

If your speedo reads 150 when your really doing 100, it will clock 150Km's for every 100 that you really drive. I think. Someone may correct me later.

When my speedo reads 0km/h I'm actually doing 208km/h, what the hell is up with that...

I'm sorry I couldn't resist...

Seriously though, speedo's are generally 10% optimistic, but your's seems to be up to 50% optimistic, which is a bit much. What you could check, is that there isn't some dust and/or metal filings that got stuck inside the cup that drives the speedo needle. There will be either a magnet turning inside a cup, or the cup will be turning around the magnet, although I think the Datsun one is the prior arangement. The magnetism drags the cup along, and that is what causes the needle to rotate.

Any dust or metal filings will either make direct contact or lessen the gap between the magnet and the cup, and cause cup the needle to turn faster in relation, and indicate a higher speed. The cup might even be distorted, but you'll have to disassmble the speedo to see this.

Quote:

Unless the gearing has been changed that physically turns the cable, the odo won't be incorrect. The odo is driven directly from the cable with gears, where as the speedo is driven with the magnet in a cup arangement as per my previous post.