@erik-langhofer-2 Welcome Erik! I'm going to split this off into it's own thread for you.

@erik-langhofer-2 Erik, When you find the cure, let me know. When My Grand Daughter drives my '35 Chevy, I think she is going twice as fast as she really is. I considered a couple of stiff drinks before going out but I don't think that would help your speedometer.

Mike

I would think the problem could be that the magnet that the cable spins inside the metal cup could be touching or the pin in the bearing is dragging. Maybe a good cleaning is needed but I there and some the repair them. I think there is at least one that advertises in the G&D.

Hello Erik Langhofer,

You might check your vehicle speedometer against a GPS groundspeed and a known distance to know what the speed and mileage difference is. Normally wear and binding is a common issue. I'm not familiar with overspeed issues. A cleaning and lubrication and bench check for smooth operation of the speedometer cable eliminates that as a potential part of the problem. Then, inspect the speedometer gear in the transmission for wear and damage. Then the speedometer itself could be malfunctioning internally. A process of elimination as always.

Hi Erik

To help diagnose your problem, a couple of questions need answers.

First, has the speedometer done this as long as you have had the car?  Or is this a recent development?

Second, as you smoothly accelerate, does the indicated speed on the speedometer also smoothly accelerate?  Or is it jumpy and irregular?

Also, when your driven speed is constant, is the speed indicated constant?  Or does it vary?

If it is irregular or varies when it shouldn't, I think Dennis has the answer.

If it is smooth and constant, my guess is the problem is in the spring attached to the rotating dial.

From the pictures I found on Ebay and attached, it appears that this spring "might" be adjustable.

The spring may be broken, but I doubt it as the dial would just rotate up to 80 mph and stay there.

Possibly the adjustment has slipped?

Hope the problem is an easy fix!

Hello Erik, I have my Convertible Landau relocated to Chino Valley so there are now 2 of them in AZ. I am in the process of moving my cars and a lot of my spare parts down to AZ. When I get situated, remind me to look in my spare parts. I may have another '29 speedometer that you could get rebuilt. 

As a side note the '30 speedometer has the same body, just a different shaped bezel.