Speedo drive gear question

SuperDave

I have checked the 48-54 Parts book and it confuses me.. If I change from a 4:58 rear to a 4:10, can I just change the driven gear on the cable end without having to change the driving gear in the tranny?



I checked the Hollanders Interchange book on ring and pinions and the pinion gear I have has 9 teeth and the ring gear has 41 teeth. That comes out to 4.5555555. Closer to 4:56than the 4:58 some sources reference..???

Dave W.

Hudsy Wudsy

I've always heard them refered to as 4:56.

Park_W

Dave, there's a chart in the parts book that shows all the drive and driven (pinion) gears. I believe there's a pinion gear listed for cars with OD and 4.11 axle ratio instead of 4.56. Al Saffrahn is generally a good place to start for these gears, but his stock is diminishing.

Fred

yes, you just change the driven gear at the end of the cable. That is what I did and the speedometer is dead on @ 60 mph.

Fred

Geoff

Fred, you are lucky to have got away with this, as the gears are usually a matched pair, and should be changed accordingly, as the ratios and pitches are different. The worm drive inside the transmission has a different angle to match the different number of teeth on the pinion. Obvioulsy there is enough leeway for it to work in this instance, but it could induce wear on the mismached gears. The parts books list the worms and gears in ratios. Good luck,

Geoff.

SuperDave

Geoff C., N.Z. wrote:

Fred, you are lucky to have got away with this, as the gears are usually a matched pair, and should be changed accordingly, as the ratios and pitches are different. The worm drive inside the transmission has a different angle to match the different number of teeth on the pinion. Obvioulsy there is enough leeway for it to work in this instance, but it could induce wear on the mismached gears. The parts books list the worms and gears in ratios. Good luck,

Geoff.

Geoff,

Prezactly.. That explains why I said I was confused (by the chart).

I saw that some gears had the same tooth count, but had a differenty part number.The pitch may well be different..Add in the HDM, OD,Non OD, Automatics etc. Sheesh!



It gets a bit more complex when you start considering tire size. I wish they had referenced tire circumference rather than tire size. I'm sure they figured tire sizes would remain standard.

Fun for sure..

Dave W.;)

junkcarfann

You can go to a speedometer shop and get a "speedometer transmission" that has internal gears that change the ratio. These are available so that they connect to the transmission and mate with it like a speedometer cable, and the other end connects to the speedo cable in the normal fashion.

I do not know if these are available for Hudson, but I know they exist because we used one on a Ford with a Borg-Warner Transmission. In that case, we had to reverse the rotation of the speedo so it would work, in addition to changing the ratio to match the new rear axle.

If you research this and find an answer for Hudson, Please post it. Thanks, Paul.