Speedo drive for a datsun converted morry

[morrisman1]

G'day, I need to sort out my speedo at some stage soon. I have the datsun 56a gearbox, toyota starlet diff which I think is 3.9:1 if I remember correctly and 175/70r13 tyres. My speedo is 1472 turns per mile.

I know it will be incorrect if I do direct drive so I need to work out how much by and then get a ratio box. Would the easiest way to work this out be putting the ute on a rolling road and measure the turns per mile of the gearbox output then ratio it to suit 1472 or is there a better way?

Id appreciate feedback from someone who has done this before.

cheers,
Cameron

[grant69]

The instrument shop will be able to work out what ratio is required, the old days they went for a drive with another car at 60 and read what the speedo was on and did the calc's now the use a GPS. I was just having this conversation with a mate who makes the boxes here in cairns as I am in the process of working out how to do it for my project (I am wanting electronic though). He also said you could mark out 1m on concrete and count the turns of the cable at the speedo head, but this is less reliable as partial turns are hard to estimate, rolling diameter of the wheels will change speedo as well.

[Boeing Bob]

I run a 1098 engine with a MG Midget gearbox into a 4 cylinder LC Torana diff of 3.9. The local instrument shop guy near home goes for a drive with you over a measured kilometer with a counter attached to the speedo cable and then alters the gearing of the instrument to suit. He does a great job and it only cost me $25. Money well spent in my opinion. I will have get him to do it again shortly as I am in the process of changing to a Datsun A15 with a Celica 5 speed behind it.

Boeing Bob.

[Kel]

Boeing Bob
Could you please advise the contact details of the local guy ?

Regards
Kel