speedometer box
- Thread starter Zany28
- Start date
typically (best results) have simply bolted everything together, run it....see how far off speedo is...check how much speedo gear can be had or is needed and adjust accordingly. Those ratio adapters USED to be adjustable (little gear sets) but now I think you gotta order specifically what you need.
^^^^ yes the "swap gears" is what I meant by adjustable. Now I'm pretty sure you can't buy the individual gear sets and they are riveted together instead of bolted making you order ONLY the ratio you need.
More info here:
The GM Wiki:
is confusing but seems to say that they were installed on 3.55 and higher gears with F60 or F70 14 or 15 inch tires. I have personally see them more on 4.10 geared cars but a few 3.73 geared cars with F60-15 tires that i know were original installs. Many were pitched as the grease I think dried up and the gears would quickly break or bind up. I still can't wrap my head around what difference a close ration or wide ratio trans would have made. The speedo runs off the output shaft so it spins at the driveshaft speed which is set by the rear gear and tire combo, not by what gears are in front of it, but the Wiki seems to say it makes a difference on the close or wide ratio trans.
The GM Wiki:
is confusing but seems to say that they were installed on 3.55 and higher gears with F60 or F70 14 or 15 inch tires. I have personally see them more on 4.10 geared cars but a few 3.73 geared cars with F60-15 tires that i know were original installs. Many were pitched as the grease I think dried up and the gears would quickly break or bind up. I still can't wrap my head around what difference a close ration or wide ratio trans would have made. The speedo runs off the output shaft so it spins at the driveshaft speed which is set by the rear gear and tire combo, not by what gears are in front of it, but the Wiki seems to say it makes a difference on the close or wide ratio trans.
The Wiki isn't always right. You are correct, there would be no difference between close ratio and wide ratio as the output shaft is what is measured.
My 70SS with 3.31 gears has a ratio box on the Muncie. They were used wherever needed to make the speedometer correct.
My 70SS with 3.31 gears has a ratio box on the Muncie. They were used wherever needed to make the speedometer correct.
That’s what I thought too. When you say “whenever needed” do you mean based on the tire-gear selection or on a car by car basis? I’m sure they had to know ahead of time which combos would require one and what ratio box to install. Most I’ve seen are the .8241 ratios on 70 Camaros. The F60 tires were new in 70 and I believe they didn’t have the selection of internal gears to set them up right. I think the metal drive gear was only a 9 or 10 tooth. Later they had a better selection of gears and did away with the box, especially when the moved to the T10 in 74
