Hi all
Have just got my 3.8 FHC back on he road after a two year restoration. Car runs well but the speedo reads low. Indicates 18 mph/1000 rpm in top gear instead of 22.5 which I think it should. Rev counter has been checked against an electronic one is is pretty accurate. My speed has the number 6322/00 on the face, which believe to be correct for the 3.31 rear axle which my car has. The speedo is smooth and progressive in operation and appears to read 20% low up to 60 mph which is as fast as I want to go as the engine has only a few miles on it. Before the restoration the speedo did stop working which I traced to a worn out angle drive on the gearbox. I replaced that with a repro item from one of the UK suppliers, but the threads were too tight to allow it to be screwed fully onto the gearbox. I replaced it with a good second hand drive which worked but now I have the low reading. A bit baffling. Any thoughts much appreciated. Too many speed cameras to tolerate a low reading speedo.
David
Speedo reading low
#2
Check the calibration. Details here: http://etypeuk.com/forum/viewtopic.php? ... alibration
David Jones
S1 OTS OSB
1997 Porsche 911 Guards Red
2026 Lexus LBX
Add your E-Type to our World Map: http://forum.etypeuk.com/viewtopic.php?f=1&t=1810
S1 OTS OSB
1997 Porsche 911 Guards Red
2026 Lexus LBX
Add your E-Type to our World Map: http://forum.etypeuk.com/viewtopic.php?f=1&t=1810
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#3
A couple of thoughts.
Firstly if you have a smartphone get one of the free sat nav apps which give you a GPS speedo function. I use NavFree on my iPhone. This makes checking your speedo on the move easy.
Secondly, establish if the error is a constant or is speed-dependent. Constant means under -reading by the same amount at every speed, speed dependent would be for example 10 under at 35 and 20 under at 70.
If the error is constant it may just be that the needle is in the wrong place on the axle and needs moving-fairly easy.
If it is speed-dependent then it is gearing. You mention you replaced the angle drive. Do you know for sure that the replacement has the same ratio as the original? You can get those drives with different ratios, and I had the problem that the one in my car had a different ratio to the readily-available replacements. In the end I had to have mine rebuilt as I could not find a replacement with the same ratio. If your speedo was accurate before the rebuild of the car and that drive is the only bit you've replaced, odds are that's your problem.
Firstly if you have a smartphone get one of the free sat nav apps which give you a GPS speedo function. I use NavFree on my iPhone. This makes checking your speedo on the move easy.
Secondly, establish if the error is a constant or is speed-dependent. Constant means under -reading by the same amount at every speed, speed dependent would be for example 10 under at 35 and 20 under at 70.
If the error is constant it may just be that the needle is in the wrong place on the axle and needs moving-fairly easy.
If it is speed-dependent then it is gearing. You mention you replaced the angle drive. Do you know for sure that the replacement has the same ratio as the original? You can get those drives with different ratios, and I had the problem that the one in my car had a different ratio to the readily-available replacements. In the end I had to have mine rebuilt as I could not find a replacement with the same ratio. If your speedo was accurate before the rebuild of the car and that drive is the only bit you've replaced, odds are that's your problem.
John '62 S1 OTS (now sold)
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#4
Many thanks for these ideas. I didn't realise that the angled drives come in different ratios so that looks like a good place to start. GPS app sounds like Good idea too just to find out how accurate the speedo really is.
David
David
Life in the fast lane
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#5
I had the same problem about 15 years back and didn't know there were different ratios for the angle drive. I'm seeming to recall 1:1 and 1.25:1 but I could be wrong. Anyway, having in the end got the right one to my cost the inner cable snagged and broke it. I'd advise a new inner to go with the correct angle drive!
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#6
Hi
Well I've managed to repair the original angle drive and it does indeed have a different gear ratio 1:1.25 (gearing up) compared with the replacement one I used (1:1). This accounts for the 20% low error on the speedo. Thanks for the advice. I just need to get the odometer working properly now. It decided to jump ahead 20 miles for some reason. A problem for restricted mileage insurance policy!
David
Well I've managed to repair the original angle drive and it does indeed have a different gear ratio 1:1.25 (gearing up) compared with the replacement one I used (1:1). This accounts for the 20% low error on the speedo. Thanks for the advice. I just need to get the odometer working properly now. It decided to jump ahead 20 miles for some reason. A problem for restricted mileage insurance policy!
David
Life in the fast lane
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