speedometer gear
 

Could someone tell me which speedometer gear goes in a 66 gmc 305e with a 3 speed Saginaw manual transmission? Thanks

Re: speedometer gear
 

Frost:
Not quite that simple. Depends on what rear end you have and what "drive gear" you have inside your transmission along with the height of your tires. I just fiddled with mine. First step is to find out how far off your current set up is. You need to either use a GPS or a speedometer app on a smart phone to find your actual speed compared to the readout on your speedometer. Then you can see how far off your speedometer is. Next step is to pull out the "driven gear" that is inside where the speedo cable hooks to the tranny and count the number of teeth on the gear you have. Finally, you can order a new "driven gear" with more or less teeth to correct the speedo readout. The info I read says that more teeth on "driven gear" slow down speedo and less teeth increase speedo. Change of one tooth adjusts the speedo by 5%.

For example, I found that my speedo was 15% too slow. So I pulled out my gear and found that it was green in color and had 22 teeth. I ordered a new 19 tooth gear to replace it. Three less teeth should increase speedo by 15%. I haven't put the new one in yet, but that is my plan.

Gears are available online at speedo shops, Summit Racing, Ebay, etc.

Hope that helps.
Regards,
Steve
New Orleans

Re: speedometer gear
 

So you think a 19 teeth gear would work. It had a 25 teeth gear in it. The Speedo never worked it just jump up and down. Thanks

Re: speedometer gear
 

Frost:
First step would be to diagnose and repair the reason it is jumping around. That is most likely caused by a lack of lubrication in the cable and/or lack of lubrication in the speedo itself. Start off with lubricating both and get the speedo to stop jumping. The gear is not the source of your problem.
regards,
Steve

Re: speedometer gear
 

I'll try that. I took the gear out and it turned the cable fine. Now it has stopped turning the cable at all when I put it back in. Maybe I put the gear in wrong. Seems like it would go in one way. What do I know.

Re: speedometer gear
 

Frost:
Disconnect from the top by the speedo and try sliding out the inner cable. You may find that it has broken, thus why the speedo is no longer moving. If not, lubricate and slip back in and retry.
Regards
Steve
New Orleans

Re: speedometer gear
 

Thanks, will do....