The Oldsmobile Connection

phaZe · Joined: 22 Jul 2008 Posts: 9 Location: Western Washington

I'll cut the chase, my speedometer is off by around 5 mph, maybe more and of course it's not the same at all speeds. The tires are stock size (checked the plaque on the driver side door) and it has a TH350 in it. At one point the rear tires were slightly bigger than stock, but that was years ago. The differential has never been changed so it probably isn't the problem.

...Got any ideas?

(Kinda off topic, but from my knowledge both rear tires aren't suppose to spin in loose gravel right away at the same time, correct? Only asking because maybe that could be a problem, maybe not.) :D

88 Coupe · Posted: Sat Jul 26, 2008 2:37 pm Post subject: Re: Speedometer Off

phaZe wrote: ........ my speedometer is off by around 5 mph ........
Fast or slow = 65 at an actual 60 MPH, or 55 at an actual 60 MPH?

Is the odometer accurate?

phaZe wrote: ........ tires are stock size ........ At one point the rear tires were slightly bigger than stock ........
Not a factor, unless the head was recalibrated, at that time, to compensate for the increased circumference.

phaZe wrote: ........ both rear tires aren't suppose to spin in loose gravel right away at the same time ........
Depends on a lot of factors. Biggest is whether, or not, it has an Anti-Spin differential.

phaZe wrote: ........ maybe that could be a problem ........

Not a problem, and not related to the speedometer.

Norm

phaZe · Joined: 22 Jul 2008 Posts: 9 Location: Western Washington

It's fast, the odometer is probably off. I believe it reads over 450,000 when it hasn't been driven that much.

88 Coupe · Posted: Sat Jul 26, 2008 3:43 pm Post subject: Re: Speedometer Off

phaZe wrote: It's fast ........
Might be from age, might be from a previous recalibration.

If you remove the cable housing, from the trans, and spin the cable at 3600 RPM with a drill motor, you should see 60 MPH on the meter.

phaZe wrote: ........ the odometer is probably off ........
Probably?

phaZe wrote: ........ it reads over 450,000 when it hasn't been driven that much.
450K or 45K?

Need the miles registered vs actual miles traveled, in order to verify its accuracy.

Norm

phaZe · Joined: 22 Jul 2008 Posts: 9 Location: Western Washington

I'm assuming most drills spin at 3,600 RPM? I will definitely have to try it.

Quote: Might be from age, might be from a previous recalibration.
I know at one time it had bigger rear wheels and I believe it was off then as well. We threw all stock size tires on and it's still off. I'm not sure that would help you out, but I might as well throw out somethings I know.

Quote: 450K or 45K?
Around 450K.

88 Coupe · Posted: Tue Aug 12, 2008 2:49 pm Post subject: Re: Speedometer Off

phaZe wrote: I'm assuming most drills spin at 3,600 RPM? ........
110/120 VAC, at the outlet = 60 Hz. 60Hz x 60 seconds = 3600 cycles per minute = 3600 RPM. Or one minute, if a clock is plugged into the same outlet.

If you spin the cable at 3600 RPM (60 MPH) for 1 minute, exactly 1 mile should be added to the odometer reading.

Speedometer and odometer are only related in that they are driven off the same cable. Odometer is gear driven and the speedo uses a magnetic coupling that works against a spring.

Once the the accuracy of the gear ratio is established, the speedo head can be easily adjusted.

Norm

phaZe · Joined: 22 Jul 2008 Posts: 9 Location: Western Washington

Alright, I will try that out.

If the speedo cable ends up reading correctly, what else could be the problem?

88 Coupe · Posted: Wed Aug 13, 2008 6:59 am Post subject: Re: Speedometer Off

Final drive ratio and/or tire size.

Norm

andrewk · Joined: 18 May 2005 Posts: 1263 Location: Ames, IA

88 Coupe wrote: phaZe wrote: I'm assuming most drills spin at 3,600 RPM? ........
110/120 VAC, at the outlet = 60 Hz. 60Hz x 60 seconds = 3600 cycles per minute = 3600 RPM. Or one minute, if a clock is plugged into the same outlet.

Depending on your drill, it might not spin at 3600. It will give you no load RPM on the ID plate.

I have 3 electric drills, and only my el-cheapo model runs at 3600rpm. My other two drills both have gear reduction drives and run at about 900 rpm, full bore.

I see a lot of cheaper drills that run 2600 rpm too, but I don't know what sort of internal components they use.

On any given drill, there is a motor ID plate on the side, that tells you what RPM the drill runs.

Regards,
Andrew

88 Coupe · Posted: Thu Aug 14, 2008 9:02 pm Post subject: Re: Speedometer Off

andrewk wrote: ........ Depending on your drill, it might not spin at 3600 ........
My stuff is not as new as yours.

Thanks for the help.

Norm

phaZe · Joined: 22 Jul 2008 Posts: 9 Location: Western Washington

Sorry guys, I didn't even realize what I said. I meant to say the speedometer is slow, not fast.

I'll have to try out the drill test, my dad has an older drill that I'm sure has the plate with how fast it can spin. All the others we have are cordless drills.

Thanks for the help, btw. 8-)

phaZe wrote: 450,000
Another mistake of mine, the new engine in it was put in around 7 years ago and has 45k to 50k on it. I know it doesn't matter, but I felt stupid for saying that when it actually doesn't even go past 100,000 on the odometer. :D