speedometer gear

[Doug Ward]

I have found a nice diff. with a 3:08 gear set. The speedometer drive gear is toast & I need to find a good one, new or used. Anyone have a lead on one ? Please reply to Doug Ward, 714-six two four-9044, or 17dougward39@gmail.com, or here on the forum. Thanks.

[66vairguy]

I have found a nice diff. with a 3:08 gear set. The speedometer drive gear is toast & I need to find a good one, new or used. Anyone have a lead on one ? Please reply to Doug Ward, 714-six two four-9044, or 17dougward39@gmail.com, or here on the forum. Thanks.

As you probably know, Clark's does not list a speedometer drive gear for the 3.08. Decades ago a local speedometer shop would make up little gear boxes that went between the cable and speedometer to make different "hot rod" setups work. He would put your car on the "rollers" and check cars speedometer against the accurate unit on his "rollers".

The other way is to have a shop calibrate your speedometer to the drive ratio. Most U.S. 1960 cars used 1001 cable rotations per mile. Tire size, weak speedometer magnets, and in your case axle ratio all affect this. You can put in a plastic gear that is close, then measure the cable rotations per mile. Covering a measured mile may not be practical, but the greater distance the more accurate your number will be. A good old time speedometer shop can change the needle spring tension AND magnetic field strength to read correctly over the FULL scale. BOTH must be adjusted or the speedometer won't be linear (read accurately at low and higher speeds). Keep in mind it is difficult to find folks that have the equipment and skills to do this now.

Today most speedometer shops only do "electronic" repairs. But you might go online and see what is available. There are a few places that specialize in the old gauges. Good luck.

[vairchet]

Which gear is actually damaged? I may have a replacement if you could give me a photo of damaged gear.

Speedometer Gears

[cnicol]

Here's what I posted over on Corvair Center:

"Speedometer gears for 3.08 are listed in my 1967-printed parts manual. Unfortunately there's a first and second design listed. First design '63/3.08 calls for 3781324 green 20-tooth. Second design '63/3.08 calls for 3783087 Orange 21-tooth. This second one is also listed for 3.27 axles and a couple of other odd things"

Why were there two "designs"? I can think of two reasons: Different diameter drive gears on the pinion shaft. I recall this being a real thing. FCs and cars had different diameter drive gears so there were different diameter driven (plastic) gears. The other possibility is an error correction with a revised specification (tooth count change). BOTH the green-20 and the Orange-21 are CORRECT 3.08 gears.

I suggest looking at the date code on your ring and pinion and judging if it's early production. I'd also compare the speedometer drive gear on your 3.08 gearset vs a car 3.27 or 3.55 drive gear for diameter and tooth count.

[RexJohnson]

I believe that the drive gears have the same tooth count. I think the the different diameter might have to do with the number of teeth on the driven gear. The parts book is vague on this since the ring and pinion sets always had the pinion shaft installed so there is no breakdown for the different sizes of the drive gears.

[Doug Ward]

Hi vairchet, The gear I need is the driven one as your center picture shows. ( not the worm gears that are part if the pinion shaft.) Its about 7/8" diameter & I believe 21 teeth. Its nylon but I can not determine the color. Please let me know if you have one . 714-six two four-9044 Doug

[davemotohead]

I found these in my stash, NOS and 21 teeth? Not sure if this is correct or not for Doug's application?

[vairchet]

This is what I have, 21 tooth speedometer gear:

21 Tooth Speedometer Gear

[Doug Ward]

Hi Dave and vairchat, I don't think the one Dave has will work, but vairchat's looks good to me. What would you be asking for it ? Please let me know. Doug Ward 714-six two four-9044 ( California 92868)

[junkman]

The green speedometer gear is for full-size cars like Biscane, BelAir, and Impala. My 1962 BelAir has a 308 posi differential, and I don't remember the color of the gear that I installed into the Powerglide tail shaft. The one thing that I do remember is that the speedometer isn't accurate according to my dash-mounted GPS. If the green gear is still available, I would like to purchase it for my car. Thanks Junkman