I have been tinkering with the speedo gear housing in my 67 Impala. The speedometer has been cleaned and calibrated and a new speedo cable was installed. Speedo no worky. So, I jacked up the car, unbolted the speedo gear housing and observed the large gear as I turned the tire. It was turning. So I re-installed the speedo gear housing and observed the gear as I turn the tire again. Nothing. I then rotated the housing 90 degrees and observed while I turned the tire. It was turning also. Figuring I fixed the prob, I bolted the clamp back on and took it for a test drive. Voila, the speedo worked, albeit incorrectly, but it worked nonetheless. I then parked the car and started it the other day. As I pulled out, I noticed a puddle of tranny fluid on the floor. I surmised that with the housing rotated like it was, the clamp wasn't getting a good enough grip on it. So, I put it back to the way it was, the speedo returned to it's non-working status and there have been no further leaks. Can someone give me some help in determining what I need to do in order for the speedo gears to work? I have already figured out the correct sizes, being that I have a 27 inch tire and a 4.11 rear gear. I can't understand why they worked with the housing rotated 90 degrees, but didn't when it was installed correctly. Can you help a brotha out?

 

If I remember correctly, there are 2 different holders for the speedo gear....one covers up to 37 or so teeth, the other up to 41 or more teeth (the exact numbers are imprinted on the housing).Though they both fit in the trans,they are not interchangeable- the correct gear must be sized with the correct housing to reach the tranny gear properly, and it must be turned (oriented) the right way when installed. (guess how I found this out)..... don't know if this solves your problem, but worth checking out......good luck.

 

The speedo gear has 38 teeth on it. The housing has the number 40 through 43 on it. You are correct sir! I need to get a speedo gear with 40 teeth on it and a trans gear with 13 and my speedo should work. Thank you for the help!

 

It would be easier to buy the correct holder, I think they are still available from Chevy. Joe

 

There was a site that had a formula on how to correct your speedometer if you changed gears/tires. Basically, you multiply your rear end ratio by 20.2, then divide the answer by the rear tire diameter. The value that you come up with, cross-reference it on a chart and you find your speedo gear and trans gear teeth. Both large and small gear teeth are displayed on the chart.

 

As Joe says, easier to replace the holder.....the small gear in the trans requires removal of the trans tail housing to exchange. You can see it through the hole when you remove the housing with the speedo gear......count the number of teeth it has, and then size your speedo gear accordingly with the correct housing.