Speedo Running ''Slow''
 

So I still have the original speedometer in my '68 C/10 Stepside, a truck I bought at 23, and now I'm 75. It's got 407,000 showing on the odometer. [I bought it at about 80,000. It was a 5 year old truck.]
Just lately it's been indicating ~40-45 MPH when GPS says I'm doing 50-55.
I checked the cable connections: Underdash was secure. The cable to the correction box was secure. Corrector was secure, with a little swing to it -- which I think is normal.
Next step will be to pull the little speed corrector box -- maybe it's turned to jelly inside after a number of years -- IDK.
A few years ago, I pulled the inside speedo cable out and dusted it with graphite powder as I inserted it back in. That took out the jumpiness. Not jumping now, but it won't go over 40 or 50 indicated.
Long time ago, because I went to taller tires, it consistantly read slow. I took it to a shop. They mounted me on a dyno, and they called out what speed my wheels were turning, and I noted what number was indicated. I made a Correction Scale and it's still dymo-taped to my dash above the ash tray.
If, after I pull the Correction Box, I get the old correction numbers, then we'll know that's what it is. Otherwise it's in the clockwork of the OEM Speedo -- and after only 407,000 miles. Shocking!

Re: Speedo Running ''Slow''
 

It could be that the magnet in your speedometer is tired. I have seen that in most of the gauge clusters I have rebuilt. The magnet can be remagnetized, but it does require complete disassembly of the speedometer.

It will be interesting to see what happens when you remove the correction box.

Re: Speedo Running ''Slow''
 

Re: Speedo Running ''Slow''
 

you can try flipping the box. On edit: I meant the spedo adapter.

j

Re: Speedo Running ''Slow''
 

I pulled it. My indicasted speeds were waaay low. Like 35 indicated for GPS 50 MPH.
40 was 57.8.
Box was pretty greasy.
Must be Patrick's tired magnets.

Re: Speedo Running ''Slow''
 

If you send your speedometer to me, I can calibrate it.

Re: Speedo Running ''Slow''
 

Deal.
Working tomorrow thru Wednesday.
I might have another Dash core on the property, I can put that Speedo in the hole in my dash if I send it.
Odometer is collaterally affected. Showing less miles than actually travelled.
:chevy:

Re: Speedo Running ''Slow''
 

Or you could send your extra speedo if in decent shape, and I could adjust the odo to match the currently installed one while calibrating it.

Re: Speedo Running ''Slow''
 

That's a thought. But it might be from a '70 with a round Red Dot for Brights On, instead of the Red Hyphen for '67/'68. Not that it matters.
I will have to root around for the extra Speedo. Not gonna cannibalize White Fang. ['67 K/10 Sub.]
Be cool if you coud add a 4 in the hundred thousands column.

Would you like to inspect the Correction Box too? It's pretty greasy. Gets motor oil off the bottom of the block, then all that graphite I poured down the cable shaft accumulated in the Box.

Can't ground #919 until next Friday 3/06, as I like to have a spare rig ready to get to work if the Tahoe won't start.

Re: Speedo Running ''Slow''
 

I'd be happy to look at the correction box, too. I get it about the rectangular vs. circular high beam indicator. I care about details like that.

Re: Speedo Running ''Slow''
 

I call the three periods of the '67 thru '72 Chevy Truck Run, Phase I 1967/68, Phase II 1969/70 and Phase III 1971/72.
I like to keep my Phase I Orange Stepside period correct. Although a 1969 Thunderbird bucket-back bench seat [electrically adjustable] is pure fantasy hotrod. But for the rest, it's still a simple fleet truck.

On the '71 GMC Jimmy, I have long plotted to make some of the interior more First Phase like. Primarily so I don't have to think about which year truck it is while dealing with traffic. Last year, I pulled the '68's Wiper knob off in my hand trying to turn on the headlights. [Thinking it was the '71] So moving the '71's Wiper over to the left, and lowering the Headlight swiitch is planned. A retrofitted Manual Choke is already on the right. Adding Manual Throttle will be difficult. I have the Knob and Cable but getting it to actuate is beyond my technical expertise.
I have a spare 3-Spoke 1st Phase Steering Wheel and GMC horn cap, so that would drop in place.
The gullible may deduce I have a '68 MY Jimmy when that all comes about. Not sure how I'll handle that. Case-by-case is best. An expert will know it's modified.
I don't mind being thought of as a Smart A$$, but don't want to be a Liar, either.
I guess like Johnny Cash would say,
''It's Sixty-Seven, Sixty-Eight, Seventy, Seventy-One General Motors Automobile...''