Packard Forum Index » Pre-War (1899-1942)

My 39 120 speedometer was acting up, not spinning at the right speed. One of our members swapped speedometers with me and I installed it. It had the same symptoms - no movement until about 40 mph, when it read 20. Replaced the cable, thinking it was bad. No change. I got a spare speedometer for my 51 and hooked it up, holding it up under the dash. It read just fine, and appears to be relatively accurate.

Question - is there a possibility that the routing of the cable under the dash could be messing up the stock speedometer? I took the unit to our local shop here, and he wanted $120 just to open it up and check it out. I didn't test the swapped unit out in the car, holding it under the dash, but it did read fine when hooked up to an electric drill.

Any suggestions as to what to check next?

Usually a sharp bend in the cable will exhibit a scraping noise and jerking action but if the bind is severe and cable end is worn it could be slipping at the transmission gear socket. Some cables have a crimp type fit into a receiver like piece that actually fits into the gear so that could also be causing a problem if there is a bind and the crimp loosened. You can check the cable condition by twisting the end of the exposed cable at speedo end. You should not be able to rotate it more than a few degrees to take the twist slop out of the cable. If you can rotate more than a few degrees then something is slipping.

A common problem is lack of lube so I would check for a dry bushing on the speedo input shaft. Anything that slows the spinning magnet down will affect the readout & dry lube has been a problem on many speedos to the point some have seized. You can check for this by inserting a small screwdriver or something similar in the receiver socket that can engage the square and then turning the input shaft. It should turn quite easily with no undue effort or friction. The cup and needle shaft is typically supported in two spots and has not been as much a problem. If the hair spring is able to return the needle to 0 freely then it should be OK but a tiny drop of light or clock oil wouldn't hurt.

Some units need oil directly on the edge of bushing where it enters the case but most units have a small felt filled oil hole in a protruding section of the case near threaded cable connection. The hole periodically needs a few drops of oil. On some speedos the grease on the worms and spur gear train between input shaft and odometer has dried which also causes a lot of drag.

David, I thought of something else it could possibly be, but it doesn't line up with all of the symptoms. If there is any chance the driving gear in the transmission is slipping, what you see would be the symptoms.

However, The only way this could happen on the Packard transmission is that if the output you joint joke not is not fully tight on the shaft. If this is the case the speedometer driving gear, which is normally compressed between the output bearing and the U joint yolk, would be free to spend. I recently had thishappen on my Hudson.

If you suspect there is any issue with the speedometer, we can swap back again.

Pat