The speedometer on my 95 5.2L automatic reads about 10 mph faster than the truck is traveling. It currently has a 40 tooth Speedo gear. Do I need a Speedo gear with more, or fewer teeth to adjust the speedometer down? I should be able to figure this out but my brain quit working.

Also, any idea how many teeth on the output shaft?

 

Is it consistently off by ten miles an hour? Or is it off by a percentage? Two entirely separate problems.

 

It is off consistently by 10 mph.

 

If consistently off (as in "Standing still it shows 10, at 20MPH real it shows 30, and at 50MPH real it shows 60"), it's not the speedo gear, it's the speedo itself.

If, however, you meant "It's consistently showing 50 when I'm doing 60", but it also shows 25 when you're doing 30 - then you need a different speedo gear.

So which is it?

RwP

 

And if it's showing 60 when you're doing 50, but 30 when you're doing 25, then you need one with 30/25th as many teeth - or 6/5 - or, since it's got 40, 48 teeth. You need MORE teeth when it's reading FAST, and FEWER teeth when it's reading SLOW.

But ONLY if it's a fixed percentage off!

A fixed MPH off, OTOH, is a symptom that it's off in calibration to 0 MPH. AN\nd a new speedo gear does ****-all to fix that.

RwP

 

Thanks Ralph.

 

So, does anyone know how to recalibrate the speedometer to zero? Or, do I need to replace the speedometer?

 

I'd consider replacing it.

Yours is a 1994, with the 110MPH speedometer?

What you might TRY is to set up a frequency generator, to peg it at a computed speed; pull the needle and reset it at the proper setting.

I would HIGHLY recommend not trying to do that on the highway at 60MPH ...

RwP

 

Well, final update. I only half followed dearly departed Ralph’s advice. I pulled the speedo needle off and reset it, while driving. I didn’t do it driving at 60 mph, only 40. I synched with the speed from a phone app. It reads almost dead on now. Best news; I didn’t kill myself or any other driver while doing this.

 

Yeah, surviving the experience is always a good thing.