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Hi all,
As I have converted which was originally a 2.4 to all 3.8 running gear, as expected the speedometer is in now inaccurate. Now, do I get the original speedo recalibrated (I do have a spare one which I could send off) or do I purchase a second hand 140mph unit from a 3.4 or 3.8 which they tell me is the same. I've noticed on the latter two the main beam warning light is in a different position and there is no low fuel warning light or am I looking at the wrong speedo
Cheers, Ray
Last edited by MK2 1962; Jan 14, 2022 at 03:25 AM.
This is the correct speedo for a Mk2 or S Type. Note the small printing on the dial below milometer for Match. No frills. Some Mk2's might have had a fuel light.
Last edited by Glyn M Ruck; Jan 13, 2022 at 10:38 AM.
The key thing is the differential, as the two cars are identical transmission-wise. A 3.8 will probably have a different ratio. This is normally on a little tab attached to one of the bolts holding the diff cover on. I had a 2.4 and AFAIL, the diff had a higher ratio, to allow of reasonable acceleration. The car couldn't exceed 100 mph, whereas the 3.8 was good for 120+, so had a lower ratio. What you need is a speedometer off a 3.8. Whether a 2.4 litre speedomter can be altered to match a 3.8 I know not, but others will.
This is the correct speedo for a Mk2 or S Type. Note the small printing on the dial below milometer for Match. No frills. Some Mk2's might have had a fuel light.
Cheers Glyn,
All of the speedos from a 2.4 that I have seen and in fact the one in the car have a low fuel warning light and it seems like all of the sender units have a tab for them it works in mine. Is the low fuel warning light situated elsewhere in a 3.8, I cant seem to find the information in any my Jaguar MK2 service manual
The key thing is the differential, as the two cars are identical transmission-wise. A 3.8 will probably have a different ratio. This is normally on a little tab attached to one of the bolts holding the diff cover on. I had a 2.4 and AFAIL, the diff had a higher ratio, to allow of reasonable acceleration. The car couldn't exceed 100 mph, whereas the 3.8 was good for 120+, so had a lower ratio. What you need is a speedometer off a 3.8. Whether a 2.4 litre speedomter can be altered to match a 3.8 I know not, but others will.
Hi Frazer,
I have installed a complete axle from a 3.8 I cant remember the ratio but it is obviously higher than a 2.4 and is correct for the 3.8 although it doesn't have a powerlock diff (Lower Ratio = higher acceleration, Higher Ratio = more top speed !) The 2.4 120mph can be recalibrated no problem but I would like to install an140mph speedo and I'm trying to establish if they had a low fuel warning light like the ones on the 2.4 that I have, I cant find this information
Cheers Glyn,
All of the speedos from a 2.4 that I have seen and in fact the one in the car have a low fuel warning light and it seems like all of the sender units have a tab for them it works in mine. Is the low fuel warning light situated elsewhere in a 3.8, I cant seem to find the information in any my Jaguar MK2 service manual
Yes. The S Type has twin tanks & pumps & the gauge switches across.
The Mk2 3.8 Fuel light always bottom right orange. Same for Kph cars.
Last edited by Glyn M Ruck; Jan 13, 2022 at 01:50 PM.
I have seen a Mk2 without fuel light but that might have been a CKD thing here. We built 2050 Mk2's here in SA or just a car that had been fiddled with.
Last edited by Glyn M Ruck; Jan 13, 2022 at 05:03 PM.
I have seen a Mk2 without fuel light but that might have been a CKD thing here. We built 2050 cars here in SA or just a car that had been fiddled with.
Just seen a couple of 140mph ones with the low fuel lights on ebay I reckon they could be the right ones I will try and find out what engine size car they came from
The standard speedos for 3.8 and 3.4 litre cars are identical to those in 2.4 cars for warning lights etc. The only differences are the calibration and the maximum reading. As noted above, you should check if the axle ratio is 3.54 or 3.77. If you keep a lookout on eBay or search around on a spares day, it's possible to find one at a reasonable cost. Some sellers are a touch ambitious on prices.
Hi All,
I think I have found a couple original 3.8 of speedos with all of the warning lights. Does anyone know what the SN number relates to??
Cheers Ray
If I remember correctly, the figures immediately after the SN (to the left and above the centre of the dial) specify the general type of speedo; that is does it go in any Mk2. The important part for calibration are the last four numbers situated to the right and above the centre of the dial. They give the turns per mile or TPM on an instrument in miles per hour (I'm not sure about ones in km/h). I'm not certain, but I think a TPM of 1150 is correct for a 3.77 axle and 1080 for a 3.54. I'd check my own, but it's buried under a pile of other parts. A speedo for a 2.4 or a V8 would be more like 1400 or higher.
If you want to do some arithmetic TPM = (axle ratio) / (2 x 2 x 3.14 x rolling radius), where the rolling radius of the rear tyre is converted to miles.
Last edited by Peter3442; Jan 14, 2022 at 06:30 AM.
I found my speedo and the TPM number is 1152. The car is a 3.4 MOD with a 3.77 axle.
I think there's a mistake in the equation I gave. I'd assumed a ratio of 2:1 on the drive from the gearbox/overdrive. It's more likely to be 2.5:1 so that
TPM = (axle ratio) / (2.5 x 2 x 3.14 x rolling radius)
For a rolling radius of about 13.2 inches, that gives the TPM printed on the dial. That value of rolling radius was probably what someone in Jaguar assumed for the old Dunlop RS5 cross ply tyres. Of course, modern tyres might well have a different value.
I found my speedo and the TPM number is 1152. The car is a 3.4 MOD with a 3.77 axle.
I think there's a mistake in the equation I gave. I'd assumed a ratio of 2:1 on the drive from the gearbox/overdrive. It's more likely to be 2.5:1 so that
TPM = (axle ratio) / (2.5 x 2 x 3.14 x rolling radius)
For a rolling radius of about 13.2 inches, that gives the TPM printed on the dial. That value of rolling radius was probably what someone in Jaguar assumed for the old Dunlop RS5 cross ply tyres. Of course, modern tyres might well have a different value.
Thanks Peter,
I've found this information very useful it seems like the TPM number needs to be 1152 as you have said. I've just bought one on eBay
Cheers Ray
Speedometer
