69 350/300 hp. 4 speed speedometer drive gear

[gary van meter]

Speedometer is 15mph slower than actual speed. I have a neutral color driven gear and there is only one driven gear left to try; it would bring the difference to within 10 mph difference.

Where can I find a driven gear that will solve the problem and is it difficult to replace?

[Joe L.]

Re: 69 350/300 hp. 4 speed speedometer drive gear

Gary-----

1969 Corvettes with 300/350 and 4 speed were originally equipped with only 2 rear gear ratios: 3.08:1 and 3.36:1. The 19 tooth "natural" gear should work with the 3.08 and a 20 tooth blue gear should work with the 3.36:1 to give you reasonable speedometer accuracy.

The above assumes that the rear gear ratio has not been changed AND that tire diameter is close to the original size.

As far off as you, apparently, are, I'd say that one or both of the above factors is not as it needs to be. As such, there is NO driven gear available that's going to work with your existing DRIVE gear. Therefore, you have 2 options:

1) Change the DRIVE gear which will allow you the option of using other DRIVEN gear tooth counts. This requires removal of the transmission from the car and, at least, partial disassembly of the transmission to change the DRIVE gear, or;

2) Use an appropriate ratio speedometer adapter to correct the reading. For this, your best bet is to take the car to a speedometer shop.

[gary van meter]

Re: 69 350/300 hp. 4 speed speedometer drive gear

Hello Joe, Thanks for the quick reply. The rear-end is 3:08 so my best bet is your second suggestion to find a speedometer shop. The prospect of lowering the steering shaft (tilt/telescope) and removing the dash is not enticing; maybe will continue to watch the mile posts and tackle this in the winter. Are speedometer shops an easy thing to find? Any suggestions out there?
Regards,
gary

[Joe L.]

Re: 69 350/300 hp. 4 speed speedometer drive gear

Gary-----

No lowering of the steering column should be required. Even if there is a problem with the speedometer head, you can usually remove the dash panel without lowering the column if you're careful. If you can't get it out, usually all you have to do is to remove the 2 bolts under the column and SLIGHTLY lower the column.

Anyway, the speedo gears, both DRIVE and DRIVEN are in the transmission. The DRIVEN gear is easily removed and it sounds like you've already done that. Installing an adapter is easy, too. It installs right at the speedo fitting on the transmission. Figuring out the gear ratio necessary and setting up a proper adapter ratio is the hard part. That's where the speedo shop comes in. Installing the adpater is just a few minute job for them. Most big cities have a speedometer service. I know where there's a GREAT ONE in the San Francisco Bay Area, but I don't know of them elsewhere.

One other thing. If the rear gear ratio is 3.08:1 and if your tires are stock OD or near stock OD, then 18 tooth brown gear or the 19 tooth natural gear should give you acceptable speedo calibration. What sires tires do you have?