Odometer Accurate but Speedometer Not Accurate

[Dibbons]

Re: 1972 Satellite Sebring Plus. I sent off my instruments to have the ammeter gauge converted to voltmeter (and general gauge restoration). Now I find the speedometer is nice and steady but reads too fast. The odometer evidently is right on the money, so changing the speedo pinion gear won't correct things (anyway, the drivetrain is all original so no reason to have to mess with the speedo pinion). Must be a fix out there somewhere, right? Thank you.

 

[70chall440]

You might have to change out your speedometer gear in the trans.

 

[Cranky]

The pinion gear in the trans controls the speedometer and odometer....

 

[hunt2elk]

How do you know the odometer is right on?

 

[pnora]

How do you know the odometer is right on?

That was my thought also.

 

[Sam69sat]

Magnetizing & Degaussing.

 

[Dibbons]

How do you know the odometer is right on?

Using highway mile markers i drove exactly 2 kilometers. Odometer began at 7.7 miles and ended at 8.95 miles so 8.95 minus 7.7 equals 1.25 miles. 1.25 miles equals 2.01 kilometers. That tells me the speedo pinion in the transmission is correct, which it should be since the drivetrain is all factory original.

Next I will go out with my Android phone which has GPS speed function and compare that with the dash speedometer.

 

[pnora]

That tells me the speedo pinion in the transmission is correct, which it should be since the drivetrain is all factory original.

So your tire size is also the exact size the car was built with to?

 

[khryslerkid]

I wonder if whoever did the restoration didn't use the correct gearing in the speedometer head. You would think the speedometer part is sinked with the odometer.

 

[toolmanmike]

I wonder if whoever did the restoration didn't use the correct gearing in the speedometer head. You would think the speedometer part is sinked with the odometer.

If the odometer is correct according to distance travelled the speedometer head needs repair and calibration.If you have the wrong gear in the transmission,the speedo and odometer will both be off.

 

[wahya]

First, I don’t see how you can say that the odometer is right on only driving 2 km. Some years ago, I checked my odometer on my truck over a fairly long distance on the Interstate. I noticed that there was a difference. If I remember correctly, it was off something like 1 mile after driving about fifty miles. Also, that is assuming that the mile markers were perfect (which they are not).
Also, how did you discover that the speedometer was off.
Well, at least if it is fast, you shouldn’t get a ticket for speeding.
On Edit. You could put a larger diameter tires on the rear.

 

[Dibbons]

Speedometer is off when driving by the Caltrans portable radar signs along the highway. I'm not going to screw up the accurate odometer by installing larger/smaller tires (I'm on Social Security dang it and afford to replace new tires with other new tires). And the odometer is accurate like I've already stated: same engine, same transmission, same rear axle, same speedo pinion that the factory installed verified by roadside check. No reason the odometer would be off, nothing changed since 1972. The speedo reads too fast.

 

[kiwigtx]

Speedometer is off when driving by the Caltrans portable radar signs along the highway. I'm not going to screw up the accurate odometer by installing larger/smaller tires (I'm on Social Security dang it and afford to replace new tires with other new tires). And the odometer is accurate like I've already stated: same engine, same transmission, same rear axle, same speedo pinion that the factory installed verified by roadside check. No reason the odometer would be off, nothing changed since 1972. The speedo reads too fast.

View attachment 1722417

That's a high-score .... over here when you exceed the speed limit posted on those signs it just says "SLOW DOWN" with no speed readout shown.

 

[Nacho-RT74]

I never have played with the magnet, but with the return spring tension to get a more accurate reading after repair the speedo needle shaft bushing.

I used a drill, a piece of old speedo wire and a chronometer to check for both (odo and speedo). 1000 rpms on drill (on reverse) should give 60 mph on speedo… and if you run the drill for 5 minutes should give you 5 miles on odo, right?

The more time running, the more accurate, but will overheat the drill, so will depend on that.


I didn’t have a 1000 rpms drill with reverse speed, but 600, so made the maths.

 

[pnora]

Speedometer is off when driving by the Caltrans portable radar signs along the highway. I'm not going to screw up the accurate odometer by installing larger/smaller tires (I'm on Social Security dang it and afford to replace new tires with other new tires). And the odometer is accurate like I've already stated: same engine, same transmission, same rear axle, same speedo pinion that the factory installed verified by roadside check. No reason the odometer would be off, nothing changed since 1972. The speedo reads too fast.

View attachment 1722417

So you have the exact size style tire as it left the factory with? You still have not said how much faster it is reading????????

 

[wahya]

Speedometer is off when driving by the Caltrans portable radar signs along the highway. I'm not going to screw up the accurate odometer by installing larger/smaller tires (I'm on Social Security dang it and afford to replace new tires with other new tires). And the odometer is accurate like I've already stated: same engine, same transmission, same rear axle, same speedo pinion that the factory installed verified by roadside check. No reason the odometer would be off, nothing changed since 1972. The speedo reads too fast.

View attachment 1722417

Interesting, was there other traffic on the road when you checked. Coincidentally, the day before yesterday my wife was driving her car and I was a passenger. We approached one of those signs and it read 68. We were actually going 62. I looked at the outside rear view mirror and noticed a car behind us and getting closer. We stayed at the same speed and after we passed the sign, that car passed us.
Btw, if the speedometer is off by a percentage and say it reads one mph fast at say 30mph, would it not read a different number of mph off at 60 mph.
All my cars only register in increments of 1/10 mile, not .05 miles on odometer. I think you need to do a longer measure on the Highway. I have noticed on some roads that the mileposts actually include miles down to tenths.

 

[YY1]

Speedo is 1% off in 2KM

Add that up over the miles on the car?

 

[pnora]

Speedo is 1% off in 2KM

Add that up over the miles on the car?

Back in the day when we had customers complaining about speedometer accuracy we were told a certain percentage like 3 to maybe 5 was considered normal. A certified speedometer was finely tuned and has a smaller percent of in-accuracy. People were always concerned about speed accuracy. I do not think there was ever a complaint on odometer accuracy. Right now the poster is basing the speedometer accuracy of the odometer which is impossible. The slow turning analog will not give the relevant results needed. If it was digital than thats a different story. Speedometer gear change is his only way. Forget about what came from the factory. Those charts just put you in the ball park.

 

[Dibbons]

Update: GPS results in this form: GPS MPH/Speedo MPH
7/11, 11/15, 16/20, 20/25, 23/30, 33/40, 42/50, 47/55, 52/60, 62/70

And I am not going to repeat myself again, before I sent the gauges away for restoration, the speedo was accurate. I drove the Satellite a couple of thousand miles before the gauges were sent out.

I also have checked the NUMEROUS Caltrans radar setups. In fact, I was driving by one of them every day with no other traffic around.

I also drove a NEW 1971 Road Runner to high school as a junior and senior (class of 1973) so I know the ins and outs of the gauges and the factory accuracy of such.

So no matter what other forums members may like to contribute, the fact remains: odometer accurate and speedo inaccurate as it currently stands. I would rather have the odometer accurate than the speedo because that way I can keep accurate records and make accurate gas mileage calculations. It's important driving from La Paz, Baja California. Sur, Mexico to San Diego to know where to find gasoline and how far I can make it between stops.

It would be nice to have the speedo accurate as well (more so for other family members than for myself) but nothing is going to be perfect on these classic cars. It's just I paid a good sum of cash to have something come back that far off.

I have another 71-74 BBody instrument cluster in storage I could restore myself that may very well bring things back to normal. The only reason I sent the original out for restoration was to have someone convert the ammeter to voltmeter.

 

[Sam69sat]

Update: GPS results in this form: GPS MPH/Speedo MPH
7/11, 11/15, 16/20, 20/25, 23/30, 33/40, 42/50, 47/55, 52/60, 62/70

And I am not going to repeat myself again, before I sent the gauges away for restoration, the speedo was accurate. I drove the Satellite a couple of thousand miles before the gauges were sent out.

I also have checked the NUMEROUS Caltrans radar setups. In fact, I was driving by one of them every day with no other traffic around.

I also drove a NEW 1971 Road Runner to high school as a junior and senior (class of 1973) so I know the ins and outs of the gauges and the factory accuracy of such.

So no matter what other forums members may like to contribute, the fact remains: odometer accurate and speedo inaccurate as it currently stands. I would rather have the odometer accurate than the speedo because that way I can keep accurate records and make accurate gas mileage calculations. It's important driving from La Paz, Baja California. Sur, Mexico to San Diego to know where to find gasoline and how far I can make it between stops.

It would be nice to have the speedo accurate as well (more so for other family members than for myself) but nothing is going to be perfect on these classic cars. It's just I paid a good sum of cash to have something come back that far off.

I have another 71-74 BBody instrument cluster in storage I could restore myself that may very well bring things back to normal. The only reason I sent the original out for restoration was to have someone convert the ammeter to voltmeter.

Maybe the person who restored gave you a different set of guages. Did they do any repairs on the speedometer needle?