Speedometer Off

[bmnk]

Ok, so I just got the 52' back on the road after putting it back together the past couple years..... one slight problem.

My speedometer is off about 10mph at 55mph. It's a new speedometer out of the box from Dolphin Gauges. Its a mechanical gauge, that just hooked up to my 350 turbo with the speedometer cable. I didn't notice any adjustments on the back of the gauge when I had installed it last summer.

Before I run it over to the local speedometer shop, is there anything I could be missing to try first?

Thought I would add a photo of the almost completed truck.....

[jimig1]

I'd guess it is the spedo gear in the trans

here is a calculator http://www.tciauto.com/Products/Tech...eedo_gears.asp

[Wheelie]

Need to add a tooth or drop a tooth on the speedo drive gear in the trans depending on if its 10MPH up or down. should get you in the 2-4 legal MPH range deviation.

[raycow]

You will need to replace one or both of the speedo drive gears in the transmission. In order to get the correct gears, you will need to know your tire diameter and rear axle ratio.

Ray

[entourageguy]

change your rear tire size .....

[Wrenchbender Ret]

Most 350's use the large speedo gear. Pull it out of the trans. & the number of teeth will be on it or count them. If the speedo is too fast put in a gear with about 2 teeth more. If it is slow put one in about 2 teeth less. They are available from a parts store in the Motor Mite line. You can compare the odometer with the mile markers on the freeway. As you pass one note the 10'ths reading. Go to about 2 more markers & note it again. If you have gained tenth's it is too fast & vice versa. You can juggle gears till you get it real close.

[mr48chev]

If you have access to a handheld gps take the truck out and figure out exactly how far it is off. probably at 60 mph on the speedo. Then figure out what percentage you are off and after counting the teeth on the driven gear and matching the color of the drive gear you can figure out what gear set will give you the right speed. You can get them at a local transmission shop, your GM parts counter or online. This outfit has a lot of good info on their website. It will pretty well walk you through without any real guesswork http://www.transmissioncenter.net/sp...FQEziQod3SGNeQ

You have to scroll down not quite half way down the page for turbo 350 info and pieces.