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

I went to the mechanics today to pick up my car, it had the rear end upgraded from a 4.69 to a 4.06 so it can be driven a bit faster without damaging the engine. Thing is it changes the ratio of the gear drive for the speedo. When the speedo says 50 my car is actually going 60. Is there a way to change the speedo drive to fix the indicated speed new gears, recalibrated instrument?

If there was a factory option for the new axle ratio you might be able to find the proper Packard cable pinion gear from one of the vendors. I believe the number of pinion teeth needed for an axle ratio is listed in the parts manual.

If nothing is available you will probably need to have a conversion box custom made at one of the speedo shops. Do a search for speedometer ratio conversion box and several sites will come up that offer various options including some where they will put together a gear train with different teeth in the set of gears to get a proper speed change and keep the correct cable rotation direction. I don't know if the threaded nut Packard used in 35 at the cable ends will be the same as anything modern but since the conversion box will go inline in the cable that might be a sticking point..

One of the sites that came up was Bob's Speedometer which I believe is the company owned by one of our frequent posters. If it is he is a Packard owner and should be able to give you a definitive answer as to what is available.

Just check page 182 of the 1933-1936 Parts List for identification of all the speedo cable pinion gears required for each rear axle ratio. The gear change is done at the transmission end of the speedo drive cable.