Speedo Swap

[79Series]

Would this speedometer work in my 1967 Series IIa with 235/85/16 tires?
http://www.famousfour.co.uk/new_parts/ff_part?part=666

Or is there another replacement out there I might use since originals are NLA?
Jack

[warrenperkinson]

Hi Jack,

You'll need to take care with the speedo cable connector at the back. I've seen a number of variations on the connector - some push in, some screw in. Because my truck is a mish-mash of every series LR out there, I don't know what is what any more (mine's a sIIa and has a screw in connector). There are also some variations on the trip meter reset cable too.

I'm pretty sure that there is a subtle difference between the IIa and III as far as the connector at the back of the speedo goes.

I swapped mine out with a second hand one - but I had to buy about 3 speedos before I was able to cobble one together with the right tyre size compatibility and connector that actually worked! (But that said, it still worked out way cheaper than buying a new one).

Cheers,
Warren.

[SafeAirOne]

The SIII speedo has a push-on connection for the speedo cable. Converting is simply a matter of getting the correct style cable for the speedo in use.

The trick is to get a speedo that will read correctly for the tire size. The number of turns-per-mile for the particular speedometer is printed on the speedometer face.

A 235/85R16 tire is approximately a 31.5" diameter tire so that's...um...31.5 x pi = 98.96" of travel per revolution of the wheel.

So that's...63360 inches per mile divided by 98.96" per rev = 640 revs of the rear WHEEL per mile so...

With a speedometer cable that turns 2.136 times for each revolution of the rear wheel, then the speedo cable will turn...640 x 2.136 = 1367 turns per mile.

You'll need a 1367 TPM speedometer to be very accurate with those tires, however, the choices in Rover speedos are generally as follows:

1500>1536 are for swb landrovers on 600 or 650 tyres
1408 is for 750 tyres
1344 is for 900's

[79Series]

Great info. Thanks for your responses.
Jack