Speedo Driven Gear

[Ralph E.]

My speedometer needle started bouncing so I checked the speedo driven gear an noticed it was slightly chewed up. When I replaced with a new speedo driven gear I noticed the Speedo driven gear fitting which goes into the side of the transmission has a very slight wobble, even after tightened in place. Is this normal? 67 C2 SB 4 speed

[Joe L.]

Re: Speedo Driven Gear

My speedometer needle started bouncing so I checked the speedo driven gear an noticed it was slightly chewed up. When I replaced with a new speedo driven gear I noticed the Speedo driven gear fitting which goes into the side of the transmission has a very slight wobble, even after tightened in place. Is this normal? 67 C2 SB 4 speed

Ralph-----


Yes, the slight "wobble" is very normal. The fitting retainer does not fit tightly into the slot on the fitting. So, the fitting can move slightly.

What's not normal is a "chewed up" speedometer driven gear. Very likely, whatever caused this to happen to the old gear you removed will cause it to happen to the new gear you installed.

[Wayne M.]

Re: Speedo Driven Gear

..... the Speedo driven gear fitting which goes into the side of the transmission has a very slight wobble, even after tightened in place. Is this normal? 67 C2 SB 4 speed

Allow me to give my opinion on this (define "wobble" ). I took 3 "bullet" fittings that I have, and played around by installing them in various tail housings (one complete trans on my floor, and two other loose "584" bare housings).

I have to (subjectively) conclude that the only time I could detect "wobble" was on the one "bullet" that had NO O-ring. Otherwise, a non-worn O-ring along with the retainer assembly (nut and piece that inserts into slot on side of "bullet" fitting was sufficient to eliminate wobble. There is, however, about a 10 degree rotational movement possible with the retainer installed. In fact, without some additional lubrication, it was quite difficult to insert the "bullet" in the housing hole. Measured the fitting OD and it's 1.875". No visible air gap when inserted in tail housing (see 2nd pic).

Have you recently gone to a small diameter plastic gear from the large ? (the yellow 24-tooth shown is the large dia.) Or, have you changed the drive gear to a smaller diameter ?

[Ralph E.]

Re: Speedo Driven Gear

Allow me to give my opinion on this (define "wobble" ). I took 3 "bullet" fittings that I have, and played around by installing them in various tail housings (one complete trans on my floor, and two other loose "584" bare housings).

I have to (subjectively) conclude that the only time I could detect "wobble" was on the one "bullet" that had NO O-ring. Otherwise, a non-worn O-ring along with the retainer assembly (nut and piece that inserts into slot on side of "bullet" fitting was sufficient to eliminate wobble. There is, however, about a 10 degree rotational movement possible with the retainer installed. In fact, without some additional lubrication, it was quite difficult to insert the "bullet" in the housing hole. Measured the fitting OD and it's 1.875". No visible air gap when inserted in tail housing (see 2nd pic).

Have you recently gone to a small diameter plastic gear from the large ? (the yellow 24-tooth shown is the large dia.) Or, have you changed the drive gear to a smaller diameter ?

Wayne,

The wobble I got was very slight. I would have expected zero wobble. The bullet and O-ring are new. When installing the bullet I did not need to lubricate. It popped right in. Mine is a 22-tooth large green gear. Maybe I should check the end inside the tail housing as shown in pic#2.

[Joe L.]

Re: Speedo Driven Gear

Wayne,

The wobble I got was very slight. I would have expected zero wobble. The bullet and O-ring are new. When installing the bullet I did not need to lubricate. It popped right in. Mine is a 22-tooth large green gear. Maybe I should check the end inside the tail housing as shown in pic#2.

Ralph-----


The 22 tooth green driven gear is only compatible with the smaller drive gear used with most 3.55:1 to 4.11:1 applications. If one uses a 22 tooth driven gear with the larger OD drive gear designed for 11-22(silver) driven gears used with 2.73:1 to 3.36:1 gear ratios just the sort of problem you previously described will usually ensue.

[Steve L.]

Re: Speedo Driven Gear

My '73 chews up this gear every 25K miles. There was a TSB issued for this problem. The fix was to change the 90 deg adapter to a service replacement.

I've posted here before wondering what the difference was between the original and the service replacement 90 deg adapter, but I got no replys which usually means no one knows.

I suspect that the adapter binds up and puts too much load on the plastic gear. Maybe you have that problem or maybe there is too much torque required along the cable.

[Bill C.]

Re: Speedo Driven Gear

Ralph-----


The 22 tooth green driven gear is only compatible with the smaller drive gear used with most 3.55:1 to 4.11:1 applications. If one uses a 22 tooth driven gear with the larger OD drive gear designed for 11-22(silver) driven gears used with 2.73:1 to 3.36:1 gear ratios just the sort of problem you previously described will usually ensue.

Oh boy, seen this a few times. Ralph, bring it over so the local guy can fix it will ya? Wobble?

[Joe L.]

Re: Speedo Driven Gear

My '73 chews up this gear every 25K miles. There was a TSB issued for this problem. The fix was to change the 90 deg adapter to a service replacement.

I've posted here before wondering what the difference was between the original and the service replacement 90 deg adapter, but I got no replys which usually means no one knows.

I suspect that the adapter binds up and puts too much load on the plastic gear. Maybe you have that problem or maybe there is too much torque required along the cable.

Steve-----


1967 Corvettes did not use a speedometer adapter. However, many 71+ did use them. For 1971+ there was only one size drive gear and this was compatible with only the 18-22 (silver) tooth driven gears. Any application that could not achieve proper speedometer calibration with these gears had to use an adapter.

What the difference was between the original 90 degree adapter and the SERVICE piece, I do not know.

[Steve L.]

Re: Speedo Driven Gear

Thanks Joe
When I get to this part of the restoration, I'm going to have a closer look at my original 90 degree adapter. I suspect that there is something in these adapters that are binding, causing the plastic teeth so shear, hence the TSB.

I didn't know about the TSB during those long gone days or I would have taken it in.