The Stovebolt Site Forums The Shop Area Driveline Need different speedometer gear

Message edited by adding the following paragraph:
The message I posted below was in response to BillyDon's message of 8/27/24. Unfortunately, I posted before reading subsequent posts that show that he did as JoeH suggested and found that the odometer was off by 38%. Sorry that I pulled the trigger too soon. I'll try to do better.



BillyDon:

My reply to your question "can someone confirm that Bill Hanlon is correct and my thinking is bass ackwards" got lost in the problems our forum has been having the last few days. I'll re-post.

Your thinking was correct. I was the bass ackwards one. You do need a speedo gear with less teeth. MAYBE.

I still recommend checking the speedo at various speeds, not just at the 35 mph indicated was actually 48 mph. If the problem is strictly linear, the proper ratio adapter will fix it. But if the problem is not linear, the ratio adapter will only fix it at one speed. The speedo on my '57 GMC read low at 30 mph, gradually got "right" at about 58-60 and then read low again at 75. An old-time speedometer shop in Houston did a clean-up and adjust on the speedo and had it within 2 mph from 30 to 80.

There were two suggestions made in this thread that you didn't follow up on. Either one will tell you if a ratio adapter will solve your problem.

My suggestion was to check the speedo at other speeds. If a ratio adapter will fix your problem, your speedo should read like this:

Indicated Actual
35 .........48 This is the only error you reported
25 .........34 Does your
30 .........41 speedo read
40 .........55 like this?

Or do like JoeH suggested and check the odometer for a proper reading. Start at a milepost on an Interstate highway. Record your odometer. Drive to and stop at the 10 miles away milepost. Subtract starting odometer reading from ending reading. Each 1/10th of a mile off of 10 miles is a one percent error in the gearing.

Or, buy a ratio adapter first and hope for the best.