700r4 speedo gears..
Thread Starter
Racer
Joined: Sep 2005
Posts: 453
Likes: 1
From: Austin TX
700r4 speedo gears..
I just viewed some recent posts here on what gears a 700r4 with a 26" tire should use (255 60R 15). It appears I need a gray 15T drive gear and maybe a blue 43T driven gear? The good news is I have the 15T drive gear.
I've used a couple of calculators this morning and I got stuff ranging from 15T drive gear to 17T drive gear (BTO's calculator) and 35T driven to 39T driven. Which is the correct ones to use? I sure don't want to take this housing off anymore. My car is a 78 with a converted 700r4 and 3.08 axle. I would like confirmation from people that have a specific set of gears in the car working and actually accurate, if possible.
I've used a couple of calculators this morning and I got stuff ranging from 15T drive gear to 17T drive gear (BTO's calculator) and 35T driven to 39T driven. Which is the correct ones to use? I sure don't want to take this housing off anymore. My car is a 78 with a converted 700r4 and 3.08 axle. I would like confirmation from people that have a specific set of gears in the car working and actually accurate, if possible.
Melting Slicks
Joined: Dec 2005
Posts: 2,441
Likes: 0
When using the calculators be sure you know the exact tire diameter, the speed calculator from Keisler says a 255-60/15 tire has a rolling diameter of 27".
http://www.keislerauto.com/tools/gm_analyzer_5sp.html
http://www.keislerauto.com/tools/gm_analyzer_5sp.html
Thread Starter
Racer
Joined: Sep 2005
Posts: 453
Likes: 1
From: Austin TX
Ok, so using this calc http://www.700r4.com/speedoCalc/speedocalc.shtml with overall tire diameter set to 27 inches and 3.08 axle, it says I need a 17 tooth drive and a 39 tooth driven.
I googled 700r4 speedo gears and came up with this page http://www.transmissioncenter.net/sp...n_______va.htm
A little ways down they have a formula where you do the arithmetic by hand. Here it requires a drive tooth number, which I already have in the transmission and is 15. So with a 15 tooth drive the outcome says I need a 34 tooth driven. The 34 tooth is light green and currently what I have installed, but my speedo is reading at least 10mph slow at 60 so I assume this data is wrong. This same site has a calculator by it requires a calibration number on the back of the speedo which I don't know.
I'm guessing the BTO calculator it probably more along the lines of being correct but I would like to be 100% sure before I waste money on a set of plastic gears.
I googled 700r4 speedo gears and came up with this page http://www.transmissioncenter.net/sp...n_______va.htm
A little ways down they have a formula where you do the arithmetic by hand. Here it requires a drive tooth number, which I already have in the transmission and is 15. So with a 15 tooth drive the outcome says I need a 34 tooth driven. The 34 tooth is light green and currently what I have installed, but my speedo is reading at least 10mph slow at 60 so I assume this data is wrong. This same site has a calculator by it requires a calibration number on the back of the speedo which I don't know.
I'm guessing the BTO calculator it probably more along the lines of being correct but I would like to be 100% sure before I waste money on a set of plastic gears.
