Odometer Accurate but Speedometer Not Accurate

[toolmanmike]

@Dibbons You get it, I get it, many don't.

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

Possibly it was cleaned and lubricated and the face and needle were restored but the unit was not calibrated.

 

[pnora]

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.

Then send it back. Plain and simple.

 

[#41]

So no matter what other forums members may like to contribute, the fact remains: odometer accurate and speedo inaccurate as it currently stands

Not to beat a dead horse, but I did not see that you have responded to the comments that it would be advised to check the odo over a longer distance than 2 miles. In my experience of measuring actual placement of mile markers for road race timing, I found that accurate placement between individual markers is hit and miss. Sometimes they are close, and sometimes off by a hundred yards. Just 100 yards in one mile is a 5-1/2% error. You can reduce that to a negligible amount by extending your measurement to 10 miles.

 

[YY1]

Use your GPS on a long trip vs the car's odo.

Nice, round 100 miles is a good place to start.

Maybe 50 miles out and 50 miles back.

 

[khryslerkid]

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.

View attachment 1722440

Most do here also. One time I saw the sign read "slow down" and after that it said "Police on Patrol".

 

[kiwigtx]

Most do here also. One time I saw the sign read "slow down" and after that it said "Police on Patrol".

I think that is so that some motorists don't treat it as a challenge to see how high a number they can achieve.

Cops taking all the fun out of things again.

 

[khryslerkid]

I think that is so that some motorists don't treat it as a challenge to see how high a number they can achieve.

Cops taking all the fun out of things again.

There's a better one out there with a high score theme...

 

[ynst]

Magnetizing & Degaussing.

Mechanically, everything is totally accurate. You've already proved that.

All that's left to calibrate is the magnet force that "drags" the needle across the face of the speedometer. Either the return spring is set wrong or the overall magnetism is off.

In any event, the speedometer head needs to come apart and get calibrated.

Leave the gears and odometer alone. They're working correctly.

 

[toolmanmike]

Mechanically, everything is totally accurate. You've already proved that.

All that's left to calibrate is the magnet force that "drags" the needle across the face of the speedometer. Either the return spring is set wrong or the overall magnetism is off.

In any event, the speedometer head needs to come apart and get calibrated.

Leave the gears and odometer alone. They're working correctly.

Another fellow that gets it.

 

[Quintin]

I would assume you talked to the place that did the restoration. What do they have to say?

 

[ynst]

Another fellow that gets it.

Thanks.

The needle on my Stewart Warner speedo in my hot rod is spot on but the odometer is off by 5%. It's been that way for decades and I just add 5% to my recorded mileage for my record-keeping and I know that I'm not going to get pulled over for speeding because I elected to swap out the gearing in my trans.

My '48 Chrysler, on the other hand, is WAY off on the speedo but the odometer is spot on. TWO trips back to the speedo shop didn't correct the issue so I use my GPS most of the time and set my cruise control accordingly.

For all you folks who don't understand this, try driving your cars cross country every summer instead of just hauling them to the local cruise night in your enclosed trailers.

 

[cudamark]

If the odometer is accurate and the speedometer is not, it's the tension spring for the needle that needs adjusting.

 

[ynst]

If the odometer is accurate and the speedometer is not, it's the tension spring for the needle that needs adjusting.

Not necessarily true.

That's what the speedo shop that restored my '48 Chrysler speedo told me, too. After two tries subsequent to the initial "restoration" I just put it in and printed a chart for my dashboard with the correct speed printed beside the indicated speed. It's off by almost 10 mph on the low speed end and gradually gets closer to being accurate as the speed approaches 60 mph. I gave up and I just deal with it. Ive been using that chart since 1988.

The ONLY point in time that the needle is spot on is when i'm doing 60 mph. The rest of the time, it's either reading too high (below 60 mph) or too low (over 60 mph).

On the interstate I just set the cruise control (it's got a Rostra unit in it) and I don't have to worry about being nailed for speeding. Even around town, I use the cruise control. I live in a rural area so it works out very well. Set it and forget it.

 

[Jam72]

Mechanically, everything is totally accurate. You've already proved that.

All that's left to calibrate is the magnet force that "drags" the needle across the face of the speedometer. Either the return spring is set wrong or the overall magnetism is off.

In any event, the speedometer head needs to come apart and get calibrated.

Leave the gears and odometer alone. They're working correctly.

I totally agree. You could take it up with the outfit that did the work.

 

[threewood]

The speedo needle needs a better calibration. Finding the right pinion is easy with simple math. I know, because my GTX has the correct pinion, odometer is accurate, but the gauge shows fast.

 

[Sam69sat]

The speedo needle needs a better calibration. Finding the right pinion is easy with simple math. I know, because my GTX has the correct pinion, odometer is accurate, but the gauge shows fast.

Haha.. you tricked my ***! I was about to make a snide comment until i read the caption on your avatar and figured out you weren't one of the usual suspects.

 

[threewood]

Haha.. you tricked my ***! I was about to make a snide comment until i read the caption on your avatar and figured out you weren't one of the usual suspects.