The Stovebolt Site Forums The Shop Area Driveline 1952 3100 Standard trans speedo drive gear

Hi, I have a new 1952 Chevy 3100 with standard 3 speed transmission. My speedometer is not working. Have new speedometer, cable and I have eliminated those and the driven gear. I found that the drive gear in the trans is spinning on the shaft. Can anybody tell me what holds this in place and how to get it out? Also can it be done with the transmission in place? I know the torque tube has to be dropped out of the way. Any help or pictures would be helpful.

thanks, Gary

I had trouble with mine too, on a 4 speed. I tapped mine back and off the shaft if I recall correctly. I think it is a press fit. I did not need to take out my transmission.

The gear is held on the shaft by the u-joint. You will need to lower the torque tube and the u-joint to gain access.The tranny side of the u-joint is held in place by a bolt going onto the shaft. Maybe you’ll get lucky and just have to tighten the bolt. There is an excellent video on YouTube by Jayhawker on the SM318 rebuild. Its in two parts. Look up “Part 2: 1937-1954 Chevrolet 3 Speed Transmission Rebuild - Reassembly” and between 30:33 and 32:15 shows the gears being installed.

Hope this helps!

I saw that video but he never explained the press fit. Is the drive gear made on the tube he slides over the shaft? Is there a washer that goes on before the u-joint? I am willing to tear into this if it is not too hard or expensive.

thanks, Gary

Also he has the trans out and says he shifts into two gears at once. With the trans in the truck I can only shift into one gear. will this work to tight the yoke?

As long as the the clutch is released and the transmission is in gear, you can loosen/tighten the bolt holding on the u-joint. In the video he didn’t have the engine to keep the tranny from turning.

The speedo gear on the tranny tail shaft is a slip fit. It is held in place by the u-joint when its tightened to the tail shaft. There is a spacer that goes on before the speedo gear.

The hardest part is getting the torque tube dropped enough to get the u-joint removed. Changing the gear if required is easy.

Here is the tranny breakdown from the Chevrolet Truck Shop Manual.

Okay, thanks for the info. I will be getting to it soon.

Do you know how much torque is on the bolt that holds the yoke in place? I tightened pretty good but the speedo gear was still slipping. I didn't want to break the bolt.

15-20 ft-lb per the shop manual. Sounds like you need a slightly thicker spacer or shim so the speedo gear will tighten up.

If the spacer tube is worn on then ends from not being pinched tight between the yoke, and the speedo gear, it may not be able to pinch tight now without a shim.
Sometimes flipping over the washer on the yoke helps, if it has become concave.

Got the drive shaft all back together and speedometer drive gear is working but speedometer still has issues. When I took it for a test drive using my gps speedometer to gauge my progress at 30 speedo showed 10 at around 45 it jumped quickly to 70 and would not come down till I was back around 30. I think the speedometer head is now the problem. Someone replace it with a new one but I think it is defective. Going to pull it out of the dash and inspect. Any suggestions or have you seen this before. I check the cable and it is new and the speedometer is not bouncing, just not registering. Thank you all for the help.

Hi. When you say it is a slip fit, do you mean that it should spin freely on the main shaft? It doesn't seem right that mine spins freely. Wouldn't that make it really inaccurate? I've been considering peening in some divots to make it "catch" onto the main shaft. Stop me before I damage a possibly irreplaceable part!

It's a slip fit in order that it can be assembled easily, along with the spacer. There should be no need to peen anything. The above posts should give you all the info you need to make it work. Most likely possibility is the washer getting dished - just flip it over. If the speedo gear still spins with the u-joint bolt torqued properly, then you may have a spacer that's too short (having worn down from the speedo gear spinning). You could put a few center punch marks around the face of the u-joint yoke to upset some metal and make it effectively longer.

Were still talking about the transmission where the speedometer gear slips on the tail-shaft, correct? If so, as Kevin has already said, the gear is a slip fit on the tail shaft until the yoke is installed and torqued. This should tighten the gear so it won’t slip. If it does, as”Pre ‘68 Dave” has said, either flip the washer or install a shim to tighten the gear.

I think I get it now...

When I torque the U-joint it will put pressure on the u-joint spacer(#17) which is in contact with the speedo gear (#16) which is in contact with the speedo gear spacer (#15) which is in contact with the inner race of the main shaft rear bearing (#13). The speedo gear becomes "sandwiched" and therefor remains locked to the main shaft.

Do I have that right?

Thanks to klhansen and Phak1!