Speedo calibration.

[poolballz]

My speedo cable is hooked into a box that is hooked into my tranny. Does anyone know if these go with the original speedo, or is a reducer, or increaser. I don't know my miles per our because i run 4:10's. To me i'd say it is at least 30-40MPH off. When i'm going around 60 IMO it looks like i'm going 100-110. The guy at the tranny shop needs to know that box is a reducer, increaser, or what ratio before he can calibrate it right. Any suggestions on how to tell? Thanks!! I need to get it calibrated SOON. My miles are racking up ALOT quicker with it not...lol

 

[Twisted_Metal]

Sounds like you are a long ways from correct!

You will probably need a "reducer" box with those rear gears.

There is no way of knowing what the gears in your box are doing without finding numbers on it or actually looking at the gears inside.

If you take the box off and connect the speedo cable directly to the tranny and read your speed at a known current RPM, you will be able to get an estimate of the gears in the box and in your speedometer by comparison.

You may have to change the speedo gears in the tranny AND use one of these boxes to get the speedometer calibrated corrrectly. It depends upon the rear gears AND tire size with speedo gears you need.

 

[poolballz]

I know nothing about it...lol But i do know my cable is not long enough to hook up outright to the tranny. The tranny guy told me that, because it would of been easier to calibrate that way. I'll try looking on the box. Any more info. Thanks for the post!!

 

[theflash]

What kind of tranny do you have and what size tire do you have?

 

[purple81]

It's a reducer

http://www.nastyz28.com/forum/showthread.php?t=20601&highlight=speedo+reducer

http://www.nastyz28.com/forum/showthread.php?t=28040&highlight=speedo+reducer

 

[poolballz]

I have a th350 tranny, with 15" tires.

 

[theflash]

I have a th350 tranny, with 15" tires.

I said tire, not wheel. Give me either the height in inches or the metric tire size and I'll look up what speedo gears you need.

 

[poolballz]

my rear wheels are 265-50-15's, if this helps.

 

[theflash]

Wow, that's a short tire. It looks like it's just under 25.5" in diameter. Looks like a 7 tooth drive gear and a 23 tooth driven gear will get you close. An 8/26 combo will get you even closer. These are without that reducer box installed.