Speedometer Drive Gears??

[a69vette]

I have just changed from a 4.11 to a 3.36. Using the toolbox calculator @3500 rpm my speed has went from 70mph to 85 mph. Problem is the speedo is way off. Looking in the parts catalog, I can get drive gears anywhere from 18 to 25 teeth. Which one do I need?? I don't know which one is in there now, but the speedo was acurate with the 4.11. Anyone have any ideas?
Thanks,
Rick

 

[Dad]

a69vette,

No biggie, pull the speedo gear and count the teeth, easy job. Figure the percent of speed/gear change and match it to the tooth number in the new speedo gear. As an example, if you now have a 20 tooth gear you will need a 16 tooth gear to get the speed up to par. You will have to find out which one you have first, 18 sounds kind of large yet. I think I have them all the way down to 13 teeth. Let me know if you can't find one that works.

 

[joevette57]

Dad, (Dad???)
It's been quite a while since I did a speedo recalibrate, but isn't there a relation ship where somewhere along the line you have to change the drive gear as well as the driven? I reset a midyear quite a while back and I remember changing both.
A_69, did you get find out where the trouble is in the speedo yet?

 

[Dad]

joevette57

If you're working in the tach/speedo drive, yes. If you work from the transmission, no. The gear shaft will flex enough to take up the centerline difference.

 

[a69vette]

Dad, Thanks for the advice. I'll try to pull the gear out this weekend and see what it is.

Joevette57, No, I haven't found out why it is hanging up at 45mph and then works again above 60mph. One problem at a time (only enough money for 1 problem at a time).

Thanks alot. I'll let you all know.
Rick