[tom s]

OK,probably simple.My speedometer in my 62 GP is 21% off.Will that mean my odometer is 21% off.I feel it should be.Tom

[Chris65LeMans]

Yes

[tom s]

Thanks!Tom

[LPete]

I’m not sure that’s necessarily true. It could be, though. The odometer is strictly a mechanical connection, so it is what it is, but the speedometer needle is driven magnetically, with no mechanical link, and the two wouldn’t have to match. Just my 2 cents.

[Half-Inch Stud]

speedo is magnetically coupled and the needle reading fights a return spring. That copper spring could have corrosion and read high.

[tom s]

I know the speedo is off because of a trans and rear end change.I have that handled just was wondering about the odometer.Tom

[Radman]

With a trans and axle change everything will be off by the same amount. You can correct both by changing the speedometer gear in the transmission.

[tom s]

The only way to correct my trans is to make a change on the internal gear on the main shaft.I have learned to live with it.Tom

[johnta1]

I think you can get an adapter to go between the cable and the tranny.

But otherwise just remember to change the mileage for MPG calculations by 21% up/down.

[sdbob]

When I had 4.10s,L60 15s in my SD I got the external adapter. It worked. GM had at least 2 that I remember. I also changed the gear on the trans adapter to get the speedometer close. Since I put everything back to stk.

[tom s]

It happened when I put the 2.68 in the back.Tom

[PontiacJim1959]

Originally Posted by tom s

OK,probably simple.My speedometer in my 62 GP is 21% off.Will that mean my odometer is 21% off.I feel it should be.Tom

Don't know how close you live to any major interstates, but on the sides of the interstate are mile markers. These can be used to confirm you odometer as being off or not. They are typically broken down in 1/10ths, so you can sorta get an idea how much the odometers is off. I have used this to gauge mine in the past and if you don't have a GPS/MPH app on your phone, 60 miles an hour is 1 mile a minute and with your watch you can figure if your speedo is off.

[400 4spd.]

Plenty of interstate access in SoCal, but I don't remember mile markers during my driving experience there in '05. The 5, the 101, etc.

[4zpeed]

Easy enough to run with someone's, 'correct speedo' for 5 - 10 miles and check it.

If it is 21% off, 5 miles should give you approximately a mile difference right?



Frank

[Formulabruce]

2.68 ! You are ready to go cross country now!

[Jeff Hamlin]

I have and use a Speedo app on my phone.
No guessing...

[Torqued]

Rather than changing the drive gear in my transmission,I bought this https://www.cpttransmission.com/.I called and told him the percentage is was off,and when it showed up it was dead on vs a GPS

[tom s]

that site can not be found?I have the speedo diff down pat,im not sure about the odometer yet.I have a couple gps apps.Tom

[misterp266]

https://www.cpttransmission.com

Try this Tom.

[tom s]

Thanks,I have found a few sites that sell them,found a 20% unit.For me to use it I need to also install a 45 degree as my ST-10 has the speedo cable going in the pass side of the trans.Not sure if they retain the same direction yet or reverses it.Tom