Speedo is way off !?!

[dirty slut]

ok, thanks for makin it easy for me!! I feel better now that you guys think I have 3.73s, I felt like the previous owner had bamboozled me for a little bit there. I will count the driveshaft revolutions as soon as I get to the lift to do the tranny fluid. Thanks, you guys are awsome!!!!!!!!

 

[TRWXXA]

- If you hold the number of teeth on the DRIVE gear constant, when you increase the number of teeth on the DRIVEN gear, you speed the speedo up. When you decrease the number of teeth on the DRIVEN gear, you slow the speedo down. So, dropping from 23 to 21 is only gonna make it worse. Remember - it probably had a 17 or 18 tooth on their to start with.

I think you may have said that backwards, Michael. If your speedo is reading too fast, you need more teeth on the DRIVEN gear to slow it down. If the speedo is reading too slow, fewer teeth on the DRIVEN gear will speed it up. Easy to get it backwards.

One revolution of the DRIVE gear will move X number of teeth on the DRIVEN gear. If the DRIVEN gear has more teeth on it, it will turn slower than one with fewer teeth. If, for example, one turn of the DRIVE gear can move 6 teeth on the DRIVEN gear, then three rotations of the DRIVEN gear will rotate an 18-tooth DRIVEN gear one full turn, while a 23-tooth gear would only make a little more than 3/4 of a turn.

 

[Michael Yount]

Chris - thanks for slowing me down (no pun); it flew out of my hands bass-ackwards.

Increasing driven gear teeth slows the speedo down. Increasing DRIVE gear teeth speeds the speedo up. How the speedo gets impacted when both are being changed is a function of the ratio of the number of teeth driven/drive before and after the swap.

Can't tell you how many calculations I went through trying to get speedo on Volvo accurate. And there's no fancy links that spell it all out for you....

 

[TRWXXA]

Chris - thanks for slowing me down (no pun); it flew out of my hands bass-ackwards.

I know you know your tech stuff. There's so many variables in the speedo gear department, it's easy to make a mistake. Even the speedo gear calculators out there aren't always right. I did all the calculations for my SSP's 3.27 gears, and STILL got the wrong speedo gear for it. In the end, it may come down to a little trial and error to get it just right.

 

[Michael Yount]

"...it may come down to a little trial and error to get it just right."

True for just about every element of working on cars...