Following my post regarding the changing of my differential on my 240 Mk2 to suit my new 340 engine I now wonder if the speedometer will also need changing, if it does will an S Type 3.4 speedo be ok or must I find a Mk2 3.4 or 3.8 speedo?
once again many thanks in advance. Jim

 

I would say you could use the speedo from the 3.4s as they are the same as the 340 speedo and if you are using the rear diff with the 3.4 ratios and the 3.4 gearbox it should read the correct speed. You could also replace the rear diff and gearbox then send your original speedo to https://speedycables.com/ who can calibrate it to the correct settings. This way you can keep the correct mileage for the car instead of having to fiddle with the new one.

 

Thank you Cass I will look up your suggested company and see what they can do for me.

 

I used them several years ago when I built a Lotus Seven and had to have the Smiths Speedo calibrated for the IVA. You have to count the revolutions of the speedo cable compared to the number of wheel revolutions over a set distance which is why you have to have all the new parts in the car first. It sounds complicated but they explain it all to you and it is quite simple. Cost I could not tell you now as it was several years ago but cheaper than a second hand Smiths speedo for a Jaguar.

 

On the face of the speedometer is a number that gives the number of rotations per mile, (at least there used to be !). The value for 2.4s will be higher reflecting the lower gearing of those cars in order to give a reasonable performance. The 2.4 ran out of puff before 100 mph, the 240 just about got past 100. Today it doesn't really matter as these cars are not daily drivers any more and rarely is the performance of the larger engine needed.

 

Please tell me if I’m wrong but I’ve just realised that all Mk2 speedometers are identical and that it’s only the faceplate that changes. Please tell if I’m wrong.

 

The internal gearing will be different, thus the number of turns per mile on the faceplate. Jaguar didn't change the speedometer gear on the transmission between different axle ratios, they changed the speedometer.

 

There were four speedos for the Mk2

C15600 for the 4.27:1 ratio diff on the 240 for MPH

C15907 for the 4.27:1 ratio diff on the 240 for KPH

C15466 for the 3.54:1 ratio diff on the 340 and 3.4 and 3.8 in MPH

C16402 for the 3.54:1 ratio diff on the 340 and 3.4 and 3.8 in KPH

Jagboi64 is correct that the internal gearing on the speedo would have been altered to get the correct gearing for the rear diffs which were different between the 3.4/3.8 and the 2.4 engines.

 

There are more options, the cars for Canada/USA had 3.77 rear axles, and you could get speedometers calibrated for either 185 radial tires or 6.40 bias ply tires in both MPH and KM for each axle ratio. Lots of options!

Don't you mean a 3.54 axle, not 3.45?

 

Sorry Typo which I have edited.

The above speedos are the only ones listed for the Mk2 in my parts book so if there are others I apologies but they must have been special orders.

 

Hi Jagboi
Yes the axle I have has a 3.77 differential so must have come from the USA then, I have emailed speedycables and awaiting response will let you all know when I get a reply.
many thanks
Jim

 

Reply from Speedycables:-
The cost to convert this speedometer which will include the overhaul/calibration would be £140 plus carriage (£12.50 to a UK address) and VAT (20%)
Received this reply yesterday so all told including sending mine off to them would be around the £200.00 mark.
They require the car to be pushed for 6 wheel revolutions and count how many revolutions of the speedometer cable turns so they can correctly calibrate it, they say not to lift the wheel and do it but push the car. Not sure if that would work with an automatic will have to ask.

 

It should work fine. The speedometer is driven off the tailshaft of the transmission, so it should turn with the car in neutral and being pushed.