VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Calibration of mileage recorder and speed indicato

In addition to the problem of fuel consumption, the speed and distance recorder is at least 20% too high. Is it possible to recalibrate this?
The accuracy was checked using a sat nav device, which recorded both speed and distance.

Hello Peterw,
Is it possible that the speedometer gear within the transmission is wrong with an incorrect gear ratio or that you are driving with other than the proper size wheels and tires or rear end gears different? As for high fuel consumption, don't know, maybe carb setting too rich or inaccurate fuel tank sending unit? Check the condition of the spark plugs for soot and monitor fuel tank levels using a dipstick. Make sure that you are not driving with the distributor spark retarded also. Use 35 PSI tire pressure. Also, let us know what year car.

The car is 1930, the wheels are 19", which is correct, not sure about the ratios. Part of the problem maybe that the car was laid up for many years. What the s possible or practical with the speedometer gears?

With this type of drum type speedometer,for every 1,000 revolutions of the cable,the trip meter should show 1 mile,and the speed on the drum should show 60m.p.h.
As for the poor M.P.G.,try tuning both the timing and carburettor with a vacuum gauge.Try and aim for the highest steady reading you can get for both the timing setting and carburettor high speed and low speed adjustments.

There not really the best on fuel at the best of times. Im lucky to get 15mpg on my 32.

Your question on calibration is yes it can be calibrated. We used to do this where I worked. We had a counter and a measured mile. You read the count on the counter and build a gear box that goes between the transmission and the cable. You may have trouble finding someone that still does this. The correct ends may also present a problem. It will be someone that has been in business for many years and still does this kind of work.

I had similar carb and speedo problems. I tried to fix myself, but gave into the experts. I sent my carb to Forest Street, and the speedo to Junkyard Dog. (JYD). Both jobs were done quickly, and the work is superior. The 29 runs better than it ever has, and the speedo is dead nuts on. By the way, I believe JYD can do both carb and speedo work.

Speedometer shops have a speedometer calibrating machine that is used to calibrate the speedometer. On the old drum type speedometers the speedometer is mounted on the calibrating machine and then an electromagnet is used to "zap" the speedometer to either speed it up or slow it down to the correct calibration.

I have now been able to check the speedo more definitely. The whole thing (speed & mileage) are reading about 25% high. This seems more than just need ing re calibration. Presumably the gears that drive it in the transmission are not correct, or damaged. As the FS does not list any gears for a 1930 car is there anything that can be done, bearing in. Mind that I am in UK. I am considering getting a GPS unit.

Hello Peterw,
A GPS unit will be useful so do that. You then should research your speedo gearing. If I understand you correctly, 25% high/over what is actually occuring does seem out of tolerance. For my convenience, using miles per hour, you're saying, let's say at 30 MPH indicated on the speedo, the GPS shows that you are actually doing 22.5 MPH? Am I understanding that correctly? I hope that you are able to figure it out. Maybe some 1930 owners can tell you the proper speedo gear teeth count.

Hi
Sorry I expressed it wrongly. At approx 30 mph the speedo shows about 45. At 50 it shows about 70 ( difficult to be precise as the reading swings wildly).
The mileometer showed around 80 miles for a 50 mile journey.
Hope that helps

The solution is to get an adapter that reduces the speedometer cable speed 25%. The both the indicated speed and mileage will be close.

Here is one place that can help with an adapter.
http://www.partshp.com/speedometer_gears.htm

Thanks for all the advice. A friend, who rebuilds old cars, has recommended a UK technician. I need to supply various details and he can build a conversion gear, which will sit somewhere in the cable and convert to a more accurate reading. I will probably still get a GPS speedo as being RHD the speedo is not too easy to see.

I have now had a better chance to check the speedo. I think that it is not just a question of calibration. Doing 50 mph on the motorway ( confirmed by GPS), the speedo swings between 60 & 80. This would appear to me to be worn 'gears' from the transmission/ speedo cable.
Good design would suggest that the speedo cable, as the most easily replacable part, should be the bit to wear. Has anyone any experience of such a problem?

Swings between 60 and 80....I would say it is in the head. I assume you lubricated the cable.

It is possible that your problem is in the head of the speedometer. However, I have seen several drum type speedometers do the same thing as you are experiencing and lubricating the speedometer cable cured the problem.

First thing to do is lubricate the bottom 1/2 of the speedometer cable. It will be necessary to remove the housing and cable from the speedometer. Then just pull out the inside cable. Use a light grease to coat the bottom end (toward the transmission). A light to moderate coating is all that is required. When you slide the cable back into the housing some of the grease will wipe off. If there is any significant buildup at the top of the housing wipe is off. Grease should not get transferred to the speedometer head from the cable or housing. Put back together and test run. That should cure the drum osculations.

Thanks guys for all the helpful suggestions. Will hope that they cure the problem