Model A speedo question.

Bassman/NZ

Bassman/NZ

Well-known member
I've got a 28-29 oval SW speedo that I would like to disassemble and clean/lubricate. Before I attack it with a 3lb BFH :D does anyone have a diagram or can anyone state the sequence of disassembly?
Thanks, Marty.
 
Disassembly is really quite simple.

First, remove the front cover. It can be carefully pried off using the two attaching "lugs" for leverage. The face plate will probably remain attached to the speedometer as you pull the cover including the glass away from the case. There should be a small felt washer around the trip odometer stem which should be removed. The face plate will then easily come off of its three index pins. Turn the case over and remove the lead seal if it is still in place. Then remove the one slotted screw that retains the stamped case to the internal cast cage. The bushings needing lubrication are obvious.

The spot that will need to be cleaned and greased is where the bevel gears mesh at the bottom of the unit. I find it best to address this area when the metal stamped case is installed which protects the mechanism as you are working. Remove the oval plate at the bottom of the speedometer and clean the internal gears. I find it worthwhile to squirt penatrating oil in that area while I have the speedometer held upside down in a fixture. With the cavity filled with oil, I run the speedometer with a SW test machine. A portable electric drill hooked up to a cable assembly would work well. After some running time, I drain the oil and pack the area with Shell 22, a grease that I am very comfortable with using. I retain the oval cover with model airplane "CA" glue. Gar Williams
 
Are the bevel gears the only part you "can" clean?

Is it possible to withdraw the main shaft?
 
Speedometer.jpg


I have never removed the main shaft for the speedometer, as it would take special tools, which I don't have. I use a stack of rare earth magnets and an Exacto knife to remove the thin oval cover over the bevel gears. I always find old hard yellow grease, which I clean out and put in fresh Mystik JT-6 high temp grease. I put a drop of heavy gear oil on all the other gears and bushings.

Make sure the small steel bushings are snug in their pockets. I bought an oval speedometer that looked good, but when I took it apart I found a steel bushing fell out of place and was caught by the rotating magnet, and it snaped the end off the main shaft. It's the one in this picture.

After much oiling and spinning of the main shaft, if it still is tight, I have used a punch that just fits inside the pocket at the top end of the main shaft. I give the punch a couple of light taps and have freed some speedometers this way. You must use caution when doing this as the threaded top end of the main shaft is very thin and easily broken by a hard tap.
 
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