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Autometer Speedometer

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Dr_EluSivE

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Hi, I have a 73 Midget, and i have killed Yet another Speedometer. Im not sure why, but the only seem to work a year or so. I have replaced the cable, and swapped in atleast 3 spare heads. The current one reads like 25mph faster then what i am actually going. So i give up... Has anyone ever put an Autometer Gauge in their Midget? Looking at their specs it appears as though they will drop right in the hole, so i wont have to modify the dash at all, but the Cable connection size is different. Anyone know of a cable that will work? And does anyone know how many Revolutions Per mile the stock guages are? I just want a reliable guage that is accurate. Im open to ideas though.

Dr.
 
If you look on the face of the Midget speedo you should find a three or four digit number near the odometer window. This will NOT be the serial/model number but a group of numbers typically by themselves over to the "right" side of the gauge. Those digits are the turns-per-mile (TPM) number.

If you're lucky you'll have a stock speedo with a TPM number like "980". The AutoMeter gauge will probably be 1000 TPM. If you use the 1000 TPM gauge directly in the Midget this will give you a 2% error on speed and mileage. That's not too bad. If your Midget speedo is something other than 980 (like 1248 or 1280), you'll need to consider another solution.

The other solution is related to your other question about cable sources. The AutoMeter gauge will probably have 5/8-18 threads on its back. The Smiths speedo cable will have M19x1 threads on the gearbox end and M12x1 on the speedo end. Your easiest option is to buy a brand new cable and send it along with the AutoMeter gauge to a local speedo shop and have them crimp a new speedo end on the new cable. They can also build you a ratio-box at the same time. The ratio box will convert the TPM from your gearbox to the TPM needed for the input to the AutoMeter gauge. All this of course means money.

Another option for you is to buy a programmable AutoMeter speedo and a digital sending unit. I doubt you'll get out for less than $300, but you won't have any cables to break and you can calibrate the speedo to exactly match your combination of final drive and tire size (without a ratio box).

AutoMeter makes good stuff but I prefer VDO. Both brands show up on eBay regularly so you may want to start there if you don't mind a speedo that already has a few miles on it. For some reason these used instruments are frequently take-off from project or collector cars and they seldom have more than a thousand miles on them.
 
'73 Midget should be 1376 TPM. IIRC
 
thanks for the responses guys, Sounds like going the autometer route wont be easy, or cheap.. SO.. i grabbed a few spares and my power drill and tested some. 2 of them tested 20mph on the drills LO speed, and 50 on the high... The one that was in the car tested 35, and 63ish.. So i swapped to one of the other ones and took a drive. It seems much more accurate now, but its still a bit wobbly at low speeds. without someone to follow and test.. its accuracy is just a guess. We shall see, Oh, and trevor, you are correct, the 3 heads i have all say 1376.

Dr.
 
A simple way to get an accurate reading of speed may be to get a gps and put it in your car. They will tell you your speed. I find they are more accurate than the speedos. Speedos are usually under by about 2 mph. from the manufacturer. I bought the Garmin I2 gps for $230. I learned that my speedo was slow by about 5 mph. and drive by tac or look at the gps.
 
I'd like to have a GPS. The only problem I see with them in a car is the lack of an odometer. I'm out of touch with that stuff though, perhaps by now they've added an odometer function you can dedicate to your car. I know a lot of motorcycle drivers have been using them for a while.

Another way to address this if you don't mind adding something to your car's dash is to buy a Sigma BC800 bicycle computer/speedometer and mount it on the dash. Properly set up they are remarkably accurate and at about $25 they are also economical. The downside is the BC800 has no internal lighting so for night driving you'll have to pay attention to the Smiths gauge.
 
Some of the gps's have odometers, and will give you all sorts of reports, average milage, distance, time to destination and other good stuff. Mine just tells me how to get where I want to go.
 
I would agree about the bike speedo. Ive got one fitted to my 3000 and it is mileage and speed accurate. Mine cost ÂŁ5 from Halfords, but as above doesnt have a backlight. Only problem is that over 110mph it doesnt read anymore! I dont suppose many cyclists do that tho
 
If I see a street legal Spridget going 110 mph I'll pull over and watch from a distance!

A lot of bicycle speedos can't read above 45 mph which is why the Sigma is often suggested for cars and motorcycles. The Sigma can read higher than 180 mph IF the number of input pulses per second isn't too high. It's a question of choosing where and how to mount the magnet on a rotating component.

BTW Neil, if you are using the stock Sigma speedo pickup and magnet, try orienting the magnet differently. The standard configuration has the magnet making a parallel approach to the reed switch. On the bench I found that if you keep the gap to a minimum and turn the magnet 45 degrees to the switch you can increase the operating (top end) of the speedo. If you can reposition your magnet it may help. However, don't go much over 110 on the street to test it!
 
Have you actually taken apart and cleaned, lubed a speedo before installing it? It lasts longer that way. I aslo would suggest checking the speedo with a gps. You can always take the face off the sppedo and change the starting point of the needle so it reads right at about 60-70 mph even if it is off at 0.
 
Thanks Doug, mine isnt a sigma speedo. Its just an own brand unit from our car/bike supermarket. I dont regularly push my Healey that hard but I am building a Sprite which should acheive that if Im brave enough!
 
Neil, I did a lot of web searching before installing the Sigma as a supplement to my Smiths speedo. They cost a little bit more than others but are a well designed gauge with a higher display speed capability than most. If you ever have trouble with the one from Halford's, I wouldn't hesitate to try the Sigma.

DrElusive, if you decide to work on your speedo yourself (to clean it up) be sure to google for Anthony Rhodes' PDF document on Smiths & Jaeger Speedometers. It is a "must have" for working on these gauges. Also, if you take Regularman's advice and reposition the needle, do so in combination with the Rhodes document. Remember the needle is spring biased against a stop. To reposition it you need to be able to hold the works in your hand with the components held in a "fixed" position while you reposition the needle.
 
some interesting suggestions, i would have never thought of using a bike speedo, As for GPS.. i dont think it would last long on a car thats impossible to lock. I am thinking i had several problems, I put in a guage that failed previously, but now i have a new(er) cable and it seems to be doing ok so far. I have only driven it about 10 miles though. Thanks for all the Input.

Dr.
 
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