Speedometer error - 1984 County

[I Love My Landy!]

G'day all,

I borrowed a GPS today and tested the speedometer reading in my 1984 V8 County.

-With 31x10.5 R15 tyres - speed on GPS: 100km/h, speedo reading: 125km/h.
-With 750 R16 tyres - speed on GPS: 100km/h, speedo reading 119km/h.

I know that most speedometers read a bit high, but is this amount normal for a County? Also, does the speedo reading affect the odometer reading?

Thank you,

Edward

[isuzurover]

My 110 county was dead accurate with 33.3" diameter tyres. (less than 0.5km in 100).

Yes the odo and speedo are driven from the same gearing.

[steveG]

Which transmission. If its a LT95 there are different output shaft speedo drive gears. If its not the original transmission then you might not have the correct gear. Relatively easy fix once you've got the correct part - but requires removal of the speedo drive housing from the rear of the transmission to change (the big alloy bit with the brake drum attached).

If you've got a LT230 transfer there are plastic speedo drive gears with different numbers of teeth so you can probably sort it out that way. Only need to pull the small speedo drive spindle and gear from the output housing to change.

Steve

[vnx205]

Also, does the speedo reading affect the odometer reading?

That depends on what you meant by the question. They are related, but they may not be inaccurate by the same amount. For example, on my Defender with standard 235/85x16 tyres, the speedo is out by 10%, but the odometer is out by less than 4%.

If I fitted bigger tyres, I could finish up with the speedo accurate, but the odometer reading a few % under.

The error on the odometer changes with any changes that affect the speedo, but the error on the odometer may be different from the error on the speedo.

[JDNSW]

On standard 7.50x16 tyres my County over reads by 7%.

John

[rijidij]

When I did my engine conversion in the County to a newly rebuilt 4BD1T, I pulled the speedo apart and wound it back to zero to start everything fresh. While I was in the speedo I physically moved the needle and tested it so at 100kph it was deadly accurate. It previously read 107@100kph/33" and 110@100kph/31".
I always run the 33's now.
The speedo is still not accurate at lower speeds, progressively less difference the closer you get to 100, but it's minimal and at least I know it's correct at highway speeds.
Probably not the correct way to calibrate a speedo, but it works for me.

Cheers, Murray

[I Love My Landy!]

Thank you everyone for your replies

Edward

[isuzurover]

When I did my engine conversion in the County to a newly rebuilt 4BD1T, I pulled the speedo apart and wound it back to zero to start everything fresh.



While I was in the speedo I physically moved the needle and tested it so at 100kph it was deadly accurate.

Isn't there a big fine for that???

Do you mean you bent the needle?

[rijidij]

Isn't there a big fine for that???

Do you mean you bent the needle?

I rotated the needle on it's shaft.........probably to where it should've been in the first place

The ''''repaired'''' speedo is noted on the engineers report including pre and post odometer readings......nothing dodgy going on here