How do i fix my Speedo

[true blue]

Just changed from a 2.73 to a 3.36 gears and

my speedo is out of wack. What do i need to

get it back in sync again. Its a 350 Turbo

tranny.

 

Thanks TrueBlue

[Guest]

probably just a new speedo cable.

check out bowtie overdrives at 700r4.com to find the correct speedo cable. it has the calculator for finding the right one.

 

justin

[72 LS5]

Unscrew speedo cable from the tranny, remove the speedo gear housing cover, and replace the plastic speedo gear with the correct one from your local Chevy dealer or favorite online store. Put a pan under the tranny as you may loose some fluid.

[Heckeng]

When you take the old gears apart so you can see them, count the teeth and note the color. If you do that and post the results, we can tell you what gears you probably need to go with on the forum, or you can figure stuff out on the web. TCI has a good informational page at

 

http://www.tciauto.com/tech_info/speedo_gears.htm

and

http://www.tciauto.com/components/speedometer_gears.htm

 

Some of the gears are hard to find, but if you do some searching you can probably find what you need. Skoggin Dickey was very helpful for me. You can get their number from their website SDPC2000.com

[lastss]

I can't fiqure this out. My 71 ss turbo 400 has a 11 drive teeth 44 speedo with stock 3.31 gears with the on line calulators don't add up. GM parts catalog list all 71 have 18 drive teeth?? Anybody know if you change gears to 3.73 with turbo 400 in stock 71 ss what the sppedo gear would be??? Thanks Bob

[Heckeng]

what size tires are you using in the rear?

 

If you are using a 28" tall tire (like a 275-60-R15),and 3.73 gears, you should use a 15 tooth drive gear, and a 40 tooth driven gear.

 

It sounds like somebody had changed some of your stuff at some point or as far as the stock gears go. Interesting. Maybe a rebuilt transmission? I wouldn't think the speedo would be reading right for you now, have you ever verified it with anybody?

 

TrueBlue, did you figure out what you needed?

[true blue]

Hav'nt figured it out yet, will take out the

plastic gear tomorrow and count the teeth and

note the color.

 

Thanks TrueBlue

[Heckeng]

Anybody have any results yet?

[kc8oye]

verifying your speedo is really quite simple

 

pick a speed that's legal.. 70 mph is the speedlimit around here..

 

maintain exactly that speed from one mile marker to the next.. record the time with a stop watch

 

now take 3600 (60mph * 60 seconds) and divide by the time you recorded..

 

say you came up with 53 seconds.

 

3600 / 53 = 67.9245mph so you'd be reading about 2mph fast. (speedo says 70, you are doing 68)

 

 

it's more then acurate enough given that speedos have somthing like +/- 5% error. maybe more in our case.

 

this is how I learned that with my trans (no idea what gears it's geared for) and my really tall tires, 235-75-15's I'm 7 reading 7mph slow. so when I show 70mph, I'm actully dong 77... this is important to keep in mind so I usally do about "65" on the hwy.. (72mph) hehe.