I thought I’d try and fit an MPH speedo to convert from old KPH unit fitted to my South African built '73 S1
On consulting the parts book there seem to be quite clear variations (see photo below). The one I have in should be part number C34717 and for MPH I want C38203 or C29273 (chrome bezel, it’s easy to swop bezel)
I bought a cheapo MPH speedo of unknown source car which over reads by about 40%. Maybe from 2.8?. It’ll have to go back on ebay.
But nowhere on the speedo I have, or the one I’ve bought is there any indication of the part number or model suitability. So I don’t know what to look for when buying.
The bought unit has markings of SN-6330/12A and the number 960 Sticker on rear says 030
Existing unit 6330/30 and the number 625 sticker on rear says 050
An ebay listing shows 6330/illegible and the number 1020, sticker on rear says 060 or 090
I put the original KPH speedo back on after a cleanup and I can live with it, I have got quite adept at the mental calculations involved and it is actually very accurate.
Does anybody have any clues on how to identify the correct unit?
You need one with 625 turns per mile if you want to match it with the one in your car.
You can calculate turns per mile with the circumference of the tyre and the rear end ratio.
I don’t know if the screen printed part is a direct swap from kph to mph…?
Mine is also a 625 with a 3.54 rear end. The two you gave sound like 2.8 auto or manual and 2.8 od because they need much more turns per distance. E type internals could work, they were 3.54 most of the time and are also 7” smiths. But the face has more lights.
Thanks - I think that’s solved the issue - I need one with that 625 reference number on it. Found one for sale relatively locally so will go down and test it. Mine’s a 3.54 Diff also - 75MPH at 2500RPM in overdrive is about right for good cruising.
Just about to get new diff in (mine’s a bit noisy) this winter and my Jag specialist did ask me about putting a bit more power in the engine and running a longer than standard diff, but I love the way it pulls in 4th from less than 15MPH and don’t want to lose that.
The other takeaway from the exercise is how much nicer the chrome ringed instruments on the earliest cars look.
Lucky you, mine’s automatic so 3000 rpm at 60 mph. So I’m not that unhappy about the differential whine I get. 2500/75 sounds so much better. The chrome does look nice and no downside to it either.
