VCCA Home Forums GENERAL DISCUSSION General Discussions 1937 truck speedo non drive gear

My speedometer isn't working. I removed it and took it to a shop that did a bench check and it works fine. I reconnected it and traced the cable (replaced the cable). The problem seems to be at the transmission end. The shaft of the non drive gear coming out of the tyranny is not turning when in gear and running. I was told that I should be able to pull on it and it'll come right out. No luck. It turns about a quarter turn either way and then stops. But it won't come just straight out. Any suggestions? Do I need to pull the tyranny apart to remove it?

I don't know the technical term for it but the flexible cable/wire/insert (D: All of the above?) that runs inside the housing and turns the speedo drive does pull straight out. If it doesn't you'll probably have to pull the drive cover off of the transmission to see where it's hanging up. Trace the cable housing back to the transmission. There should be a small housing where it terminates and the drive gear lives so you don't have to pull the transmission to access the drive gear.

Look on the passenger side, opposite where the cable attaches. I think there is a big nut there. Remove that and you should be able to take the speedometer driven gear out.

Mike

Mike, you are my hero. It didn't come out easily. I had to tap it out with a hammer. There is a lot of wear on it. The splines are pretty flattened on one side.
Now the question is where can I find a replacement?

Dennis,
There is the driven gear, which you have removed. There is also a drive (spiral) gear which you can't see very well but it is pressed or keyed onto the output shaft of your transmission. To be safe you must replace both of these. They come in a set, when you find them.
Surgery is required to remove the drive gear from the output shaft.
If you have a 4 speed transmission, you need part number 602526
If you have a 3 speed transmission with the standard axle ratio, you need part number 602519
Speedometer gear sets show up on eBay regularly. You will have to wait for the right one to appear and hope you are the winner. You can also check with the popular vendors of NOS parts to see if they have the set you need. I see them sell from $75-$125.
Do not be tempted to replace only the driven gear. It might have been damaged by the drive gear, which will, no doubt, destroy your new gear also. If your driven gear is the problem, it could have inflicted sufficient damage to the drive gear to make it the new problem even if it was not the original problem.
I hope that by now, this post has become lengthy and convoluted enough that most of you have dozed of at your computers and will awaken with no memory of whatever misinformation I have disseminated here.
Good luck.
If you are not confused already, please feel free to call me at 573 592 1991 (work hours) or 573 864 6539 (mobile)

Mike

To add to what 35Mike said, Chevrolet speedometer gears of this era did not have interchangeable pinions (driven gears) like later cars for different rear axle ratios and tire sizes, that is why they were sold as sets. Even if the drive gear inside the transmission is good, it has to be from the same part number set, or the gears will get torn to bits. Sometimes people who do not know will try to change just the pinion to fix an inaccurate speedometer. After all it is a pretty normal thing to do on much newer Chevrolets. On these early ones, the results are never pretty.