Speedometer adjustment

Assuming that this is a generic question, so not posting in the make specific forum.

Is it possible to adjust the speedometer of my 1951 Olds 88. Right now, it is reading very high, e.g. at 45 mph on a GPS it reads 55 mph, at 65 mph on the GPS it reads 80mph. Also at speedometer readings above 65 mph, it is very unstable, with the needle swing left to right with a range of 10-15 mph. Can I fix either of these issues, or are they something that I will just have to live with?

Thanks in advance to all the wise men reading and contributing to this forum

Stefan

Check the speedometer drive gear in the transmission. It sounds like you need a drive gear with one more tooth on it to make the speedometer cable turn at a slower speed. It is easy to check. There is usually just one bolt holding the speedometer cable in on the drivers side at the back of the transmission. Pull the cable out of the transmission and count the number of teeth on the drive gear on the end of the cable.

The fluctuating speedometer needle indicates that the speedometer cable needs lubricating. Reach up under the dash and unscrew the cable from the back of the speedometer. Pull the cable out of the cable housing, clean it, lubricate it with a light grease and reinstall, making sure that the cable housing isn't kinked or bent sharply somewhere. Doing this while you have the cable out of the transmission at the other end makes reinstalling it easier.

There may also be a small hole in the back of the speedometer into which a couple of drops of a light oil (3 in 1 or sewing machine oil) could be put. You will have to get your head up under the dash for this job, so you may need to be a bit of a contortionist to do it!

Remove any rings, metal wrist watch straps before you put your hand up behind the dash board. Shorting out something with a ring etc., isn't fun.

Terry

Quite right about adjusting the speedo by changing the drive gear and also about greasing the speedo cable. This needs to be done every 10 or 20 years. All you do is pull the inner cable out from the bottom end, wipe it clean, grease it and put it back.You can buy a tube of speedo cable grease at any good auto parts store. One tube will last a lifetime.

Do not grease the first 6" to 12" at the speedo end of the cable. You do not want the grease to work its way into the speedo or it can gum things up.

You should also check that the cable is in gentle curves, not bent or kinked.

Thanks guys, once again the wise men of the forum come through with an answer. And to Terry, I have to get used to being a contortionist, I am about to replace my wiring harness and I have been warned about the the fun I will have behind the dashboard.

Regards and thanks to both of you

Stefan

NOTE: Does the car register the correct miles (not speed) driving down the road? If it reads the correct mileage the speedometer gear does not need to be replaced. It is the correct gear for the vehicle. It is a dry system that needs to be lubed.

If you have a cable that has a stiff spot in it, you can buy just a cable without casing and install it. Sometimes a cable would get a stiff spot in it and it will cause the speedo needle to jump. Look here for a replacement cable: http://www.motoparthub.com/01_0107_Motion_Pro_Speedo_Cable_Kit?src=Google&gclid=CPnwrYv8uMECFXEQ7Aod5i4AcA

You cut the new cable to length and attach the new end that goes into the transmission. This should be able to be completed from the bottom of the car where the speedo cable attaches to the transmission.

I would do this and lube the speedometer head.

There are also points inside the speedometer that could need to be lubed and the lower speed would indicate that the bearings for the needle are dry. Be careful not to move the arm that the clock spring is attached to as it is the adjustment to the speedometer needle for correct speed. Use a good light oil as noted above.

This is very much a TIME & materials (minimal amount) experience.

Something else to consider. Are the tires the correct size? Undersize tires will cause the speedo to read high.

Terry

NOTE: Does the car register the correct miles (not speed) driving down the road? If it reads the correct mileage the speedometer gear does not need to be replaced. It is the correct gear for the vehicle.

Coincidentally I made a run on Friday with a precise route and I have the start and stop mileage from the speedo. Based on that we drove 46 miles, while Google maps shows 40 miles for the same route. So the gearing does indeed need changing, and to something that will change the speed/mileage reading by about 15%. The car is about to be laid up for other repairs, so I will have plenty of time to find the right way to disconnect, replace the gear wheel and lubricate the cable. Only problem is that it will be a few weeks before I can find out if the changes worked.

Something else to consider. Are the tires the correct size? Undersize tires will cause the speedo to read high.

Terry

Ta for the good idea mate, AFAIK the tires are correct, but I will check carefully. There could be some impact from the difference between cross-ply (originally installed) and radial (currently installed).

Thnaks again

Stefan

P.S. Which part of Surrey do you live in? I spent a year in Cobham before we finally came to the States for good.

Ta for the good idea mate, AFAIK the tires are correct, but I will check carefully. There could be some impact from the difference between cross-ply (originally installed) and radial (currently installed).

Thnaks again

Stefan

P.S. Which part of Surrey do you live in? I spent a year in Cobham before we finally came to the States for good.

Take a closer look at my address, Stefan. I live in the city of Surrey, in an area called Guildford, in a subdivision called Somerset in British Columbia, Canada.

Terry

Duh, reading too quickly :redface:

And actually Cobham is quite near "the original" Guildford, while I was there my office was in Guildford. And I am sure your Surrey is as beautiful a place to visit as the other Surrey

We check speedos and odometers easily using a GPS. If the vehicle is 6 volt it's simple to just carry along a 12 V battery to power the GPS. In my daily driver I now find myself looking at the GPS to check my speed more than the speedo.

We check speedos and odometers easily using a GPS. If the vehicle is 6 volt it's simple to just carry along a 12 V battery to power the GPS. In my daily driver I now find myself looking at the GPS to check my speed more than the speedo.

I checked my speedometer using a speed app on my smartphone, no need to carry a 12V battery.

Stefan

Check the speedometer drive gear in the transmission. It sounds like you need a drive gear with one more tooth on it to make the speedometer cable turn at a slower speed. It is easy to check. There is usually just one bolt holding the speedometer cable in on the drivers side at the back of the transmission. Pull the cable out of the transmission and count the number of teeth on the drive gear on the end of the cable.

I found the speedometer gear chart in the shop manual for my car. Currently it should have a 19 tooth driven gear connected to an 8 tooth drive gear. The list shows that other cars (axles) had either a 20 or 22 tooth drive gear and if I did my calculations correctly the 22 tooth will give me the 15% change that I need. Now to see if I can find that gear, at least I have the original part number.

Stefan