Transmission Speedometer Gear

[Donald O.]

Re: Transmission Speedometer Gear

Jerry
no need to run the car in gear on jack stands.
with the cable attached to the transmission, see if you can spin the cable in either direction, just make sure you simulate ALL of the bends as it would be wen installed. I’m going to guess and say you can when you shouldn’t be able to. Time for a new correct cable, you did post that your current cable is new didn’t you?
Don

[Gerald C.]

Re: Transmission Speedometer Gear

I installed the correct gear (21 tooth) into the housing and tried to spin it with a tach cable. It did not spin which told me it is engaged. When I did the drill test, the speedo, the odometer and tripometer all moved. I think I'll put the car on jack stands and try that method. Maybe the gears are engaging just enough so that I can't spin the cable by hand. Maybe under power, it won't engage enough to spin the cable.

[Gerald C.]

Re: Transmission Speedometer Gear

Latest Update!

I put the car up on jack stands and installed another speedometer cable outside of the car so that I can watch it spin (hopefully!). Well it did spin with the correct red driven gear. So I think the installed cable itself is too short! So at least it's not in the transmission. I will pull the cluster forward and install a new cable with the correct length, or at least measure the one that's in there.

I'm trying to find out the correct cable length for my 63 with 3:55 Gears. One post I See is 56 1/8".

[Patrick B.]

Re: Transmission Speedometer Gear

As I commented previously, in my Paragon speedo cable for a 67 the inner cable was 4/10's of an inch too short for the cable housing (comparing its projection from the housing with my OE cable assembly). I got a universal speedo cable repair kit and simply cut an inner cable 4/10's longer than the Paragon piece and inserted it in the Paragon housing. That fixed it without having to pull the dash out and replace the whole housing.

[Gerald C.]

Re: Transmission Speedometer Gear

Here's an update: As I mentioned in my previous post, the NAPA cable worked/spun from the transmission while the car was running on the jack stands and the cable end in my hands. Then I tested the installed cable, fitting and driven gear into a drill and ran the drill in reverse and the speedometer worked. Then I re-installed the cable that's in the car and spun the tires and the speedometer didn't work! I don't get while the drive gear runs the NAPA speedo cable and the drill runs the installed cable, but when placed in the fitting with the correct drive gear, the speedo doesn't work. Thoughts on my conundrum??


Okay....my next step will be to replace the inner cable which is probably too short. Thoughts on which vendor sells the correct cable? Dr. Rebuild has been highly recommended. Others???

[Gerald C.]

Re: Transmission Speedometer Gear

Another update! The cable reaches out about 1 1/2" into the driven gear. Still no speedometer. I placed a small screwdriver slightly into the driven gear while it's inside the housing inside the transmission and it didn't turn which tells me its engaged in the drive gear. Also, the drive gear is centered on the hole where the housing goes. I just installed a 22 tooth versus a 21 tooth driven gear tonight to see if that makes and difference. More to follow......I'm running out of options here!

[Joe L.]

Re: Transmission Speedometer Gear

Another update! The cable reaches out about 1 1/2" into the driven gear. Still no speedometer. I placed a small screwdriver slightly into the driven gear while it's inside the housing inside the transmission and it didn't turn which tells me its engaged in the drive gear. Also, the drive gear is centered on the hole where the housing goes. I just installed a 22 tooth versus a 21 tooth driven gear tonight to see if that makes and difference. More to follow......I'm running out of options here!

Gerald------


What color 22 tooth driven gear did you install?

[Gerald C.]

Re: Transmission Speedometer Gear

Green 22 tooth

[Joe L.]

Re: Transmission Speedometer Gear

Gerald———

Assuming that you have a speedometer DRIVE gear that is compatible with the 21 tooth driven gear, it will not be compatible with a green 22 tooth gear.

What was the ORIGINAL driven gear installed in the transmission?

[Gerald C.]

Re: Transmission Speedometer Gear

Joe,

I don't know what the original driven gear was in the car. However, the 21 tooth red gear isn't working. I just don't know where else to look or deal with to get this speedometer to work! I took the car out the other day after restoration and the speedometer was working, then stopped. Come to find out, the cable to the back of the cluster came out. I put it back in and made it tight. Then the speedometer didn't work. The cable is inserted properly as proven by the drill test I did yesterday.

Thanks for your comments and future advice.

Jerry

[Gerald C.]

Re: Transmission Speedometer Gear

Well, the speedometer Gods were good to me. The green 22 tooth gear works and the speedometer is accurate. Hopefully, for good. Go Figure!

Thanks to all for their advice.

[Joe L.]

Re: Transmission Speedometer Gear

Well, the speedometer Gods were good to me. The green 22 tooth gear works and the speedometer is accurate. Hopefully, for good. Go Figure!

Thanks to all for their advice.

Gerald-------


More questions:

Is the transmission original to the car? M-20 or M-21?

Is the differential original to the car and what is its gear ratio?

[Gerald C.]

Re: Transmission Speedometer Gear

Joe,

It is the original (M20) close ratio transmission (340HP) with 3:55 gears.

I took it out yesterday for a 40 miles drive and thankfully the speedo still works appropriately.

Jerry

[Joe L.]

Re: Transmission Speedometer Gear

Joe,

It is the original close ratio transmission (340HP) with 3:55 gears.

I took it out yesterday for a 40 miles drive and thankfully the speedo still works appropriately.

Jerry

Jerry------


Well, it would have to be 3.55:1!

The simple answer would be that your transmission has a GM #3708145 speedometer DRIVE gear (1.74"OD) installed. This gear will mesh only with 22 tooth (green) to 25 tooth DRIVEN gears. If an 18 to 22 tooth (silver) DRIVEN gear is installed, it will not mesh properly with the DRIVE gear and the speedometer will not operate or operate erratically. The 1.74" DRIVE gear requires 22 tooth (green) to 25 tooth DRIVEN gears.

The problem is that GM says that your 1963 3.55:1 application used the GM #3708144 DRIVE gear (1.85" OD) and a 21 tooth DRIVEN gear.

However, some other 3.55:1 applications did use the 3708145 DRIVE gear and 22 tooth (green) DRIVEN gear. The 3.55:1 rear gear is "right-on-the-cusp" as far as required speedometer DRIVEN gear goes and whether a 21 or 22 gear is needed also determines which DRIVE gear is installed (and the 22 tooth silver DRIVEN gear did not exist in 1963).

So, given what you've found, I'd have to surmise that your transmission has the GM #3708145 (1.74"OD) DRIVE gear installed and, thus, can use only 22 tooth (green) through 25 tooth DRIVEN gears.

If you've had this car for awhile and the speedometer did once operate properly, what DRIVEN gear did it have installed then?

Also, I'd be curious as to how accurate the speedometer is now with the 22 tooth (green) DRIVEN gear installed? You can accurately check this with a portable GPS.

[Patrick B.]

Re: Transmission Speedometer Gear

I think the 22 tooth green gear was listed for both the the 3.55 and the 3.70 rears, so great accuracy was not expected and his tires may have the greater influence.