Speedometer Calibration

[tkeiser1]

I'm looking for help on calibrating the speedometer on my '63 Riviera. Is it even possible? I can't find anything in the service manual to indicate that it's adjustable.

 

Tom

[ply33]

I believe that all old American cars with mechanical speedometers are adjustable. At least adjustable by someone with proper tools and knowledge.

 

Way back in the 1970s when I got my old car the speedometer was way off. After breaking it attempting to fix it I took the pieces to a local automotive instrument shop (there were such things then). The fellow put it back together and calibrated it for me. But I was surprised that he did not calibrate it on the car and asked about that. His response was that all American speedometers are built so the cable turns 1000 times per mile. (Old memory, the 1000 might not be correct, but the concept that all American cars were the same stuck.)

[Bloo]

My speedometer guy said the same thing, 1000turns per mile. Despite his protestations I don't think it is always true before the war. It certainly should be true on a 63 Riviera.

 

I would like to clarify though that speedometers are calibrated to the odometer, not actual vehicle speed.

 

A speed error on a car with a correct odometer is indeed a calibration error in the speedometer. When both the speedometer and odometer are off, that is a gearing error. Gearing errors are corrected with the little speedometer drive gears in the transmission. On something as new as 1963 it is likely only the outer gear (the easy one) would need to be changed although I am not 100% sure. Speedometer shops offer little external gearboxes to correct the gearing in instances where it would be inconvenient or impossible to change what is in the transmission.

 

The first step is to drive 10 miles or so, better yet 20, watching the odometer closely as you pass the mile markers. Determine if there is an error, and how low or how high. Typically you should be within 5% or less, and that is about what the calibration step (next gear option) is on many cars.

 

A 5% error would result in a 5mph error at 100mph, or 2.5mph at 50mph, so not a big deal and most cars only have marks on the speedometer face every 5 miles per hour (I can't remember offhand what the Riviera has).

 

If the odometer is OK, send the speedometer head out to a speedometer shop.

 

.

 

 

[Turbinator]

I had the speedometer on my 63 Riviera calibrated with an onboard calibrator. The company is in Texas makes the interface between your Speedo cable and drive gear.

They asked me to note the mileage on my odometer and drive a measured mile on an interstate. I was to report the mileage on the odometer after the measured mile. The company made the adapter for around $130.00. Easy to install and fixed the problem.

Of course, your Speedo has to work. The company just calibrates the speedo for the right speed.

Turbinator

[RivNut]

If the magnets in the speedometer cup and the drive are in goog shape in a first generation Riviera, you can get the correct speedometer readout by changing the combination of gears in the transmission and speedometer cable end.

 

It's easy to check your speedometer at any speed. Time yourself over a measured mile (mile markers on an interstate will work) in seconds and divide those seconds into 3600. The answer is your speed in mph.  Or simply use your GPS. 

 

Your original speedometer is geared to work with the original sized tire; any other tire will have a different circumference so it will throw your speedometer off.

[Barney Eaton]

I have never heard the 1000RPM story.    Even on a given model year of a car (lets say Buick)  The speedometer would be the same on a Special or Roadmaster but they used different size tires. 

So there needs to be a way to compensate for the difference in tire size... most common is a gear in the transmission where the speedometer cable attaches.  There is a hex screw and a retainer plate and out comes 

the gear... they were color coded to quickly identify the number of teeth on the plastic gear.   By changing to a gear with less teeth the speedometer will read faster...more teeth will read slower.

Because there is no fine adjustment (without opening the speedometer) you can get the speedometer to read pretty close.

On my old cars, I use my Garmin to determine if the speedometer is fast or slow. 

Another calibration adjustment method, used more on trucks, again because the wide options on tires (also final drive ratios) is a small gear box that attaches to the output on the transmission

and there are a varity of gears in them.

I am attaching a picture of some of the colored plastic gears and a gearbox.

[Turbinator]

5 hours ago, Barney Eaton said:

am attaching a picture of some of the colored plastic gears and a gearbox.

Sir, I used the 19 tooth white plastic drive gear for my 63. I was told to find the gear ratio stamped on the rear end then cross reference.

Evrrything worked except the speed was off more than I could live with. I was then told about the calibrating interface I had made up. Your way is the most interesting solution. I like the idea of a fix for $130.00. Had I got into the speedo and transmission it’s hard to tell where I would end up!

Thank you for your post.

Turbinator

Edited December 26, 2020 by Turbinator (see edit history)

[Zimm63]

I had my speedometer rebuilt by D&M Restoration in Greenville SC.  It bounced so much, I never could tell what the reading was.  Works fine now, and appears to be accurate.  

 

www.dandmrestoration.com

 

Not cheap, but good work.

[Bloo]

Correction of the odometer for tire size or axle ratio is done with the gears . The speedometer itself should be calibrated to match the odometer, period. If it is calibrated correctly, the speed will be right when the gears are right. The chances of a speedometer made in 1963 needing work are very high, just due to dried out lubricant in inaccessible areas even if the speedometer is not worn out. I have had good results with Commercial Speedometer of Sacramento, CA. The proprietor has been doing this since 1958.

[ply33]

Adding to the comment by @Bloo the speedometer works by spinning a magnet inside an conductive non-magnetic cup (the ones I have looked at are aluminum). The spinning magnets create an eddy current in the cup which tries to rotate the cup with the magnet. The shaft the cup is on has a spring to resist that motion. And at the end of the shaft is a needle with which you read the amount the cup has rotated as the speed.

 

So a few things can go wrong.

• The first as @Bloo mentioned is dirt getting into the mechanism.
• Another one for a old speedometer is the magnet losing some of its magnetism. The incredibly strong rare earth magnets we have nowadays did not exist back then and the permanent magnets of that day were not as permanent as one might like.
• If it was abused, then something might have gotten bent binding up the works.
• Finally, the return spring could need adjustment.

 

A good instrument repair shop will make sure all of the above is in order.

[telriv]

Just get the speedo adapter that screws into the trans. I'm sure Bob (Turbinater) mentioned I gave him the info so he should still have it.  Unscrew/remove cable from trans, screw on/insert adapter into trans. Screw speedo cable back on.  Over & done in minutes.

 

Tom T.

[RivNut]

12 hours ago, Turbinator said:

Sir, I used the 19 tooth white plastic drive gear for my 63. I was told to find the gear ratio stamped on the rear end then cross reference.

Evrrything worked except the speed was off more than I could live with. I was then told about the calibrating interface I had made up. Your way is the most interesting solution. I like the idea of a fix for $130.00. Had I got into the speedo and transmission it’s hard to tell where I would end up!

Thank you for your post.

Turbinator

Bob,

Before you installed the adapter were the speedometer AND the odometer off or just the speedometer?  If the odometer was correct wouldn't it be off since the speedometer was corrected?

 

When I bought my 63, it had like 97K on it and about 45K of that with a 3.91 rear gear the owner installed for towing a big Airstream.  He had made a lexan speedometer face that just lay in the bezel and told him his true speed. At that time, I wondered what the real mileage on the odometer was.  The speed indicated on the actual speedometer was a lot faster than was indicated on the lexan face.  So I tried but could never really calculate the true mileage on the car.  After about a year, I found a different pumpkin to replace the 3.91, but it was not the 3.07 that was original, it was (and still is) a 3.23. So I still add more miles to the odometer than actual miles driven. Plus the radial tires have a smaller diameter than the old bias tires.  So when it's time to sell it, do I try to figure out the actual mileage and reset the odometer to what I think it should be or do I sell it with a long history of what I think the actual mileage should be?

[tkeiser1]

3 hours ago, ply33 said:

So a few things can go wrong.

• The first as @Bloo mentioned is dirt getting into the mechanism.
• Another one for a old speedometer is the magnet losing some of its magnetism. The incredibly strong rare earth magnets we have nowadays did not exist back then and the permanent magnets of that day were not as permanent as one might like.
• If it was abused, then something might have gotten bent binding up the works.
• Finally, the return spring could need adjustment.

 

My guess is the problem is with the speedometer itself. The odometer seems to be working find. The speedometer works fine as well, just reads faster than it should. (Tires are the right size.)

 

Although I'm not a mechanic. I just like to figure things out and fix them myself. Gives me a sense of satisfaction not to mention a break from my academia responsibilities.  Anyway, my question is . . . is this something I could do or is it beyond the scope of a do-it-yourselfer?

Edited December 27, 2020 by tkeiser1 (see edit history)

[ply33]

1 minute ago, tkeiser1 said:

 

Although I'm not a mechanic. I just like to figure things out and fix them myself. Gives me a sense of satisfaction not to mention a break from my academia responsibilities.  Anyway, my question is . . . is this something I could do or is it beyond the scope of a do-it-yourselfer?

I don’t know your skill level. . . And the only speedometer I have looked very closely at is the one on my old car, there may be a number of design differences.

 

That said, there are a number of delicate and fragile parts that are easily broken. And, I suspect, a number of specialty tools (perhaps the same or similar to those used for clock repair).

 

So I will say it is beyond my skill set with the tools I have.

 

 

[tkeiser1]

4 minutes ago, ply33 said:

That said, there are a number of delicate and fragile parts that are easily broken. And, I suspect, a number of specialty tools (perhaps the same or similar to those used for clock repair).

 

Specialty tools, and breaking parts I can't replace are my biggest concern.

Thanks for the  input.

[Bloo]

21 minutes ago, tkeiser1 said:

Anyway, my question is . . . is this something I could do or is it beyond the scope of a do-it-yourselfer?

 

If it wouldn't bother you to work on a relatively small mechanical clock it might be ok.

 

[RivNut]

I would imagine that's why watch repairmen and speedometer repairmen work in specialty shops. 

[Turbinator]

13 hours ago, RivNut said:

So when it's time to sell it, do I try to figure out the actual mileage and reset the odometer to what I think it should be or do I sell it with a long history of what I think the actual mileage should be?

Ed, I would leave the odometer alone. I had an acquaintance that was found guilty of odometer tampering on his used car lot. He went away to a federal penitentiary for a year.

 

Now, a pro sales guy would answer you with a number of questions. First, find out what is important to the customer in valuing the car. So, let’s agree the buyer wants to know the true mileage. You can honestly give him your best based estimate on your well founded assumptions. Mix in what your insurance company insured the annual mileage on the car and factor in your estimates. Some fellows are not going to follow the math in the least. What you want is an agreement with the buyer your information regarding mileage is acceptable. I keep a journal of all the torment the Red Riviera and I have gone through to make the car road worthy. Mileage is included. I try to ask questions to see what the buyer likes about the car. If you have the intestinal fortitude you can ask what the buyer sees as an area of concern. Now you have information you ask for the sale. When I have knowledge of my product and it is priced fair the sale usually comes through providing buyer is motivated and has the do-re-me.

[Turbinator]

13 hours ago, RivNut said:

Before you installed the adapter were the speedometer AND the odometer off or just the speedometer?  If the odometer was correct wouldn't it be off since the speedometer was corrected?

 

Ed, second answer. Unbeknownst to me the odometer was off. The company that made the adapter told me to drive the car a government measured mile on the interstate. I was to note the mileage on the odometer at  THE BEGINNING and END of the  measured mile. I do remember writing the beginning and ending mileage at least 2-3 times on the same measured mile. I sent the data the company requested. I got the adapter and surprisingly I got on it easy enough. I have a cell phone app “88” that measures the cars speed. Both the speedo and the phone app match. Additionally, I check measured speed with government speed checks signs with my speedo. I’m happy. 
Again, Tom Telesco had the knowledge and passed it on to me.  (I’m the Turbine hub cap guy)

[Turbinator]

14 hours ago, telriv said:

Over & done in minutes.

 

Tom, besides putting air in the tires this is the easiest thing I’ve done to the car.

bob

[Turbinator]

On 12/26/2020 at 8:49 PM, RivNut said:

Bob,

Before you installed the adapter were the speedometer AND the odometer off or just the speedometer?  If the odometer was correct wouldn't it be off since the speedometer was corrected?

 

Ed, once the speedometer was accurate I stopped the project. Now, that you bring it up I’ll test the car’s odometer on a government measured highway mile marker. I’ll report my findings. 
im not sure how many many things work. The adapter is another item I have no clue how it works. I would speculate the people at the company that made my adapter have a math formula that works. I did not consider the variables in the problem that needed attention. It is true I’m sure I wouldn’t know how to set up the equation. My guess is simultaneous equation?

Turbinator

[RivNut]

If I understand speedometers and odometers correctly, if one is correct, the other doesn't necessarily have to be correct.  The odometer and speedometer both are driven by the same cable coming from the transmission via a gear setup. The number of teeth on the gear in the transmission is determined by the rear end ratio and tire size.  That is not a variable.  On the other end, the spinning cable turns a worm gear in the odometer via a solid drive - nothing variable.  That is not adjustable without tearing into it.  The speedometer is a two piece affair.  A cup is connected to the speedometer needle.  Inside the cup, but not touching it, is a disc with magnets on it.  As the magnetic disk spins, it attracts the cup and spins it. The faster the magnets spin, the faster the cup/needle "tries" to spin and keep up, but there is resistance built in which means the cup and needle don't spin, they just move to a different position.  What can happen is that the magnets lose some of their magnetism so they don't exert the force on the cup and your speedometer reads slow.  Or the resistance against the cup wears and it spins too fast meaning that your speedometer reads too fast.  Dirt can cause things to slow down or speed up.  

 

In other words, the odometer is gear driven and is normally correct, the speedometer is magnetically driven and is subject to all sorts of issues that can throw it off.  So, if install an adapter to compensate for wear in the speedometer, chances are it will mess up your odometer.  Direct drive vs magnetic drive. Remember as a kid in elementary school you were given a battery a piece of wire and a nail to make an electromagnet?  The more wire you wrapped around the nail, the stronger your magnet was.  Nothing mechanical changed. Same nail, same battery. But the dynamics of the magnetic field changed.  

 

A friend of mine put an aftermarket set of gauges in his 65.  The new speedometer works off GPS just like a Garmin and your phone.  It's always accurate.  Sadly, I don't think there's a retrofit for converting 55 year old speedometers to GPS. 

[Bloo]

It is most likely the gearing that is incorrect. A lot can change over the decades, but tire size is a biggie. Junkyard transmissions with the wrong gear are another. Rear axle gears could have been changed. The factory not getting the speedometer gearing right in the first place is more common than you probably think. You fix the gearing because that is how the system is designed to work. If it is already correct there is nothing to do.

 

If the speedometer itself is wrong when the odometer is right, then the speedometer needs work. You could try to compensate for bad gearing by backyard recalibrating the speedometer spring tension... I guess. Or you could try to compensate for a bad speedometer head by changing the gearing. It sounds like a fools errand to me, since the speedometer was not designed or built to operate that way, and most likely has something wrong with it.

 

I have yet to run into a bad magnets issue. Admittedly I have not worked on a speedometer head for a long time, but it seems like it was always shot bushings causing one drum to drag on another, or swelling pot metal causing too much drag and constantly twisting off cables, or lack of lubrication in the wick, or someone "oiled" the speedometer and the oil got out on the drum or....

 

It's pretty simple. You drive by some mile markers and check the gearing against the odometer. If it is right (spoiler: it won't be), then the speed should be right too. If the gearing is wrong, the speedometer should be off by the same amount. If not, it is time to send the speedometer head out.

 

P.S. 60s speedometers are not precision devices. Even when factory correct, the speed won't be perfect across the scale.

 

 

 

[60FlatTop]

You can have it both ways with this: https://www.autometer.com/hall-effect-speedometer-sender.html?gclid=EAIaIQobChMIl7Pkq_7w7QIVylPVCh2EuQYAEAYYBCABEgIN_vD_BwE&gclsrc=aw.ds

 

Speeder motors for the speedometer and gauges have been common for about 20 years. The round white things are the motors that are on my '05 Silverado.

 

Pretty reliable and accurate although I didn't know I had them until I noticed it was showing 19 volts on the voltmeter one day.

Boards are available for most analog outputs. Nice winter project. Fifty bucks worth of stepper motors and a handful of LED's, you could have a crowd around your car as big as the MoPar guys looking a a radio delete plate.

[Turbinator]

On 12/27/2020 at 10:43 PM, Bloo said:

It is most likely the gearing that is incorrect. A lot can change over the decades, but tire size is a biggie. Junkyard transmissions with the wrong gear are another. Rear axle gears could have been changed. The factory not getting the speedometer gearing right in the first place is more common than you probably think. You fix the gearing because that is how the system is designed to work. If it is already correct there is nothing to do.

 

If the speedometer itself is wrong when the odometer is right, then the speedometer needs work. You could try to compensate for bad gearing by backyard recalibrating the speedometer spring tension... I guess. Or you could try to compensate for a bad speedometer head by changing the gearing. It sounds like a fools errand to me, since the speedometer was not designed or built to operate that way, and most likely has something wrong with it.

 

I have yet to run into a bad magnets issue. Admittedly I have not worked on a speedometer head for a long time, but it seems like it was always shot bushings causing one drum to drag on another, or swelling pot metal causing too much drag and constantly twisting off cables, or lack of lubrication in the wick, or someone "oiled" the speedometer and the oil got out on the drum or....

 

It's pretty simple. You drive by some mile markers and check the gearing against the odometer. If it is right (spoiler: it won't be), then the speed should be right too. If the gearing is wrong, the speedometer should be off by the same amount. If not, it is time to send the speedometer head out.

 

P.S. 60s speedometers are not precision devices. Even when factory correct, the speed won't be perfect across the scale.

 

 

 

The app I have on this phone is known as “Speed Limit”. Speed Limit measure speed of a moving object with the app on board of the moving object. The adapter I put on my speedo and transmission allows my speedometer match up with the app I have on my cell phone. I don’t know how the app works or the how speedometer works. I can tell you without hesitation both the app and the speedometer are show the same speed as I go down the highway.

As a musician I studied and still study music theory; however, I don’t let it ever get in the way of how I play the instrument.

Edited January 4, 2021 by Turbinator
Addition (see edit history)

[Turbinator]

23 hours ago, RivNut said:

It's always accurate.

An F6 and Dm when voiced the same absolutely have the same sound.

 

The app on my cell phone shows the same speed that is on my speedometer. I have no clue how the phone app works or the adapter. Maybe the adapter manufacturer reinvented the wheel?

[RivNut]

34 minutes ago, Turbinator said:

An F6 and Dm when voiced the same absolutely have the same sound.

 

The app on my cell phone shows the same speed that is on my speedometer. 

Sounds like some old hippy caught another hippy tripping on acid.

[Turbinator]

12 hours ago, RivNut said:

Sounds like some old hippy caught another hippy tripping on acid.

Ed, I knew your insight was right on!

All your basis for assumptions I’m sure are solid. Mechanical stuff does not have much , if any flexibility, in gears.

So, I’ll check my Speedo yet again to see what is up or down. 
I have a long measuring tape I can use to stake out a mile along the interstate to make sure I have 5280 ft for a constant. Should be fun!

Turbinator

[RivNut]

So I take it that you know as much about trigonometry as I know about music?

[Turbinator]

7 hours ago, RivNut said:

So I take it that you know as much about trigonometry as I know about music?

Ed, I did ok in Trig and Geometry. Algebra was just barely passing and that was a gift because I worked so hard. If you like music then you know a lot. Music is fun to learn. Each note on the staff has a time value. The standard notation can be read all over the world for those trained in Western music. Hindi music is in another realm as is throat singing from Tuva. Oh, James Brown music cannot be written. James changes whenever he wants and gives no attention to standard practice.

[RivNut]

some old hippy caught another hippy tripping on acid.  So you remember this then?  

[Turbinator]

16 hours ago, RivNut said:

some old hippy caught another hippy tripping on acid.  So you remember this then?  

SOHCAHTOA an Indian Princess here.

[RivNut]

Sin=0pposite/Hypotenuse. Cosin=Adjacent/Hypotenuse. Tangent=Opposite/Adjacent 

[J3Studio]

A very instructive thread—in many ways.