Our thinking too. We fitted a 1:1 and it made no difference. Same error. as far as I can tell we’ve eliminated any problems from back wheels to speedo (though have not changed cable). So I’m mostly just wondering if a speedo CAN develop a fault that makes it run fast? My concern is having it recalibrated (about $300 I’m told) only to end up back where I started.
It may be the angle drive. There is some conflicting information on the net. It was my understanding that E Types all had a 1:1 ratio.
Chris Vine however says that E’s had 1.27:1 and other Jags had 1:1, and that they are externally identical.
Marek, however in this thread says that for non overdrive boxes, the turns ratio is 1:1 and for overdrive boxes, the ratio is 11:14 (1.27:1).
Looks like you may have the wrong angle drive.
I suppose it’s worth double checking your rear axle tag is right by seeing if you get about 3.5 turns of the prop shaft per turn of a rear wheel.
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Thanks John. That helps narrow it down then.
Should know that tomorrow. Thanks.
Yes, that’s throwing me a bit. Seems like it should be the cause but a new 1:1 angle gear shows same error. If this was an Agatha Christie mystery I think the 1.27 drive might be a ‘red herring’.
Just saw that you have replaced the angle drive already; ignore my post above.
WRT running fast. The speedo calibration is basically a fight between the spinning magnet and the spring on the pointer. It’s an incredibly crude system. Usually the problem is that the magnet fades over time and so the speedo under-reads. To over read, the spring must have got weak or someone has made the magnet too strong.
This still doesn’t explain why your odometer is equally inaccurate. It is connected directly to the speedo cable by a gear set. So if you have the correct speedo and angle drive for your rear axle it should read correctly, regardless of inaccuracy in the speedo itself.
It will be interesting to see what the problem turns out to be.
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Thanks for this. That’s some proper trouble shooting! 
Thanks Andrew. The plot thickens. I’ll report back when I’ve got it sorted.
Though I rarely use eBay as a definitive source for technical information, this Ad seems to support the “wrong angle drive fitted” theory:
It lists an angle drive Smiths Part# BG2402-08, Jaguar Part# C25547 for the E-Type with ratio 1.25:1 (actually 14/11:1 = 1.27). It notes that this drive is similar to drive BG2402-07/C24589 which is the angle drive for Overdrive Equipped cars (xk140 through MK 10 4.2) which has ratio 1:1.
In one of your posts you said you switched the drive for a 1:1 and it made no difference, implying that the original one was 1:1 also. If the above eBay Ad is correct, you need a 1.27:1 for your E-Type, so you have the wrong angle drive. I believe that the Smiths part number is stamped on the angle drive. If yours is a BG2402-07 it is 1:1 and the wrong one. You need a BG2402-08 which is 1.27:1.
Of course, I could be completely wrong…
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Thanks David. You had me up to the last sentence! 
I was of the understanding that the 1:27 was for overdrive cars (I don’t have overdrive). I need to check this again. My (admittedly dodgy) thinking led me to think that if the speedo was running fast due to the wrong angle drive then the drive in the car must be the one that ran fastest (1:1.27) and this seemed to broadly match the measured error in speed (1.3 on average**). So the obvious gear to fit seemed to be the 1:1. We did this and nothing changed, suggesting that a) we had a 1:1 in the car all along, and b) the problem is not with the angle drive. We did not try a 1:27 gear (which would have completed the experiment) mainly because once fitted and run I could not return the parts. I’ll take another look at this though.
A 1.27 to 1 angle drive will make a difference over a 1to 1 drive. The question is will the difference be .27 higher speed or .27 lower speed. I do not know the answer to that. You could contact sng barratt or one of the other suppliers and ask them. Other option would be to obtain a 1.27 drive and count the output revolutions vs the input revolutions.
My thinking is stuck at exactly that question. My point of confusion is which side of the ratio is the input and which is the output. I’m guessing 1 in and 1.27 out (in which case that would make it read faster) rather than 1.27 in and 1 out (in which case it would read slower). Also I may be over thinking this.
Mechanic checked rotation of real wheel today and gets 3.5 rotations of prop shaft.
Perhaps start a new thread with the title reading “angle drive ratio question” or similar. Then ask the question about if the 1.25 (1.27) angle drive is a step up or a step down reducer. Someone on the forum will know.you just have to get their attention.
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If the angle drive was the culprit wouldn’t the percentage of error be constant? Per the chart below that’s not what Philip is seeing.
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You CANNOT assume that the tag on the diff, and the marking on the speedo are correct. The diff gears could well have been changed, and the old tag retained. The speedo could well have been re-calibrated, leaving the same face. The ONLY way to be sure is to actually check both.
Regards,
Ray L.
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My mechanic checked these:
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"Speedometer in your car is sn 6332/01A. This indicates a 1312 turns per mile speedo for a 3.54 rear end (which is what your gear casing tag shows, 46/13 gearset ratio).”
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He then reports that “one rotation of rear wheel turns prop shaft 3.5 turns.”
But you’re right, we can’t know if the speedo face or internals are original. Looks like I need to have the speedo recalibrated, giving the restorer all the info and measurements I’ve got so far (as he won’t have the car).
Why am I reading here. Cuz my lump is way off. I know why and have the fix. but, it is electrical and I do not want to screw it up worse!! A definite possibility !!!
Here, The mention is made of fitting a 1.1 angle drive.
Was the original a different ratio ? And, 1.1 means no change in the rpm’s of the cable. So, clear, it can not change. So long as it works. That is rpm going in and rpm coming out.
OTH. a corrective angle drive may be available. Reduce the rpm on the 1.5 scale.
Side bar: I checked my speedo against that on a cop radar speedo warning trailer. 25 on the radar, 40 on my speedol!! Did not seem that badly off at freeway speeds.
Then I checked against my now obsolete Tomtom GPS. Aha, error only minor. durn close. ???
Or, I have no reason to believe that my tacho is not reasonably accurate. So, I could dig out the formula including tire circumference and compute… perhaps, probably not…
Insurance requires a mileage report for premium purposes. The odd numbers I give them seem to make no difference…
Carl. …
Did you find the Smith’s part number stamped on the angle drive? I agree that the ratio 1.27:1 is ambiguous, as it doesn’t make it clear whether it’s a step up, or step down ratio. Given the preponderance of the evidence, I still think that you have the wrong angle drive, and that the one you need is the BG2402-08 (1.27:1). As for the non-linearity that you see in the measurements, that may not be that abnormal. As someone has already noted, the speedometer part of these instruments are pretty crude, and rarely accurate at a wide range of speeds. The best you can do is set them up to be correct at some intermediate speed (say 50 mph) and accept that they become more and more inaccurate the further that you go from that speed.
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