62 spedo driven gear/transmission

[Steve]

I've discussed this issue with a few people off ther main discussion board, and thought before I attack the problem and buy any parts I should post to get any more feedback.

I have a 62 vette w/ 4 speed, 3.08 rear end, with a Hurst shifter. The issue at hand is the speedometer has stopped working. If it does work, it may when I am in 2nd gear, or have done a quick shift at a higher speed from 3rd to 4th (I've seen this twice). Sometimes if I am in 2nd gear, if I pull back on the shifter, I might be able to get the driven gear engaged.

I took the driven gear out once (about a month after I had the car). I remember the gear was grey/natural color, but did not get a count of the teeth. I did spin the cable and the speedometer does read. The driven gear did not look chewed up, but this was the first one that I had ever seen.

I have not taken the gear back out yet because it was the old 5 minutes out, 1.5 hours back in jobs. (that is a tough spot to reach!)

After consulting a few people, a 3.08 rear 4 speed should have a 20 tooth blue driven gear. But the "only in second gear" syndrome is throwing everyone.

Short of dropping the tranny, the plan of attack is to take the gear out hope it is the wrong tooth/color match, order a new one, and give it a try.

Anything else I should be concerned with checking once I take the driven gear out again? What about the gear that spins the driven gear? is this nylon or metal? Maybe adjustment of the linkage on the shifter? I am not really in a position to be able to drop the transmission out now, but any other insight would be greatly appreciated.

Steve

[Bill Clupper]

Re: 62 spedo driven gear/transmission

According to the parts book, with 6.70 tires and a 3.08 rear end, you will need a brown 18 tooth gear to drive the cable, mated to an 8 tooth 1 27/32 od steel gear in the trans. From your description, it sounds like you may have the drive gear used with lower (higher numerically) rear axles, which measure only 1 3/4 inch in diameter. Your car uses a smaller diameter gear than that used by the other rear axles on the speedo output, and the small gear will work only sporadically when mated to the 1 3/4 inch dia gear on the mainshaft. Original part numbers for the brown 18 tooth gear was 3770083 and the drive gear was 3708144. My latest part numbers for these gears are 18T-3987918 and 6261794. for the 8 tooth drive gear. I don't know for sure if the 6261794 is plastic or metal, but used metal ones are relatively plentiful if you know a trans rebuilder.

[Bill Clupper]

Re: 62 spedo driven gear/transmission

According to the parts book, with 6.70 tires and a 3.08 rear end, you will need a brown 18 tooth gear to drive the cable, mated to an 8 tooth 1 27/32 od steel gear in the trans. From your description, it sounds like you may have the drive gear used with lower (higher numerically) rear axles, which measure only 1 3/4 inch in diameter. Your car uses a smaller diameter gear than that used by the other rear axles on the speedo output, and the small gear will work only sporadically when mated to the 1 3/4 inch dia gear on the mainshaft. Original part numbers for the brown 18 tooth gear was 3770083 and the drive gear was 3708144. My latest part numbers for these gears are 18T-3987918 and 6261794. for the 8 tooth drive gear. I don't know for sure if the 6261794 is plastic or metal, but used metal ones are relatively plentiful if you know a trans rebuilder.

[Doug Flaten]

Re: 62 spedo driven gear/transmission

...(famous words from my Dad) A word of caution, I have managed to drop the plastic speedo gear into the tail housing on my '61 necessitating removal of the transmission. I think it may have been a Muncie unit on the car at the time as well as the incorrect axle, and wheels. Luckily I have not done it on the Borg unit......Yet! Therefore I cannot definitely tell you whether it is possible.

[Doug Flaten]

Re: 62 spedo driven gear/transmission

...(famous words from my Dad) A word of caution, I have managed to drop the plastic speedo gear into the tail housing on my '61 necessitating removal of the transmission. I think it may have been a Muncie unit on the car at the time as well as the incorrect axle, and wheels. Luckily I have not done it on the Borg unit......Yet! Therefore I cannot definitely tell you whether it is possible.

[Joe L.]

Re: 62 spedo driven gear/transmission

Bill----

I think that you may very well have figured this one out. The slight differences in the diameters of the gears may be Steve's problem. Also, the 3708144 steel gear has been discontinued. It is roughly comparable to gear GM #6261795, which is a plastic gear and has also been discontinued. Plastic gear GM #6261794 is roughly equivalent to metal gear GM #3708145, both of which are still available. These gears have always been far more common than the 3708144 or 6261795 gears. The plastic drive gears, GM #6261794 and 6261795 cannot be used on pre-1968 cars since the main shafts in these transmissions lack the groove for the retaining clip, GM #1373122, which is necessary to use this type of gear.

[Joe L.]

Re: 62 spedo driven gear/transmission

Bill----

I think that you may very well have figured this one out. The slight differences in the diameters of the gears may be Steve's problem. Also, the 3708144 steel gear has been discontinued. It is roughly comparable to gear GM #6261795, which is a plastic gear and has also been discontinued. Plastic gear GM #6261794 is roughly equivalent to metal gear GM #3708145, both of which are still available. These gears have always been far more common than the 3708144 or 6261795 gears. The plastic drive gears, GM #6261794 and 6261795 cannot be used on pre-1968 cars since the main shafts in these transmissions lack the groove for the retaining clip, GM #1373122, which is necessary to use this type of gear.