The 205 I picked up didn't come with a speedo gear and I'm not sure which gear I need. I am running 4.10 gears.

 

Are you talking about the "drive" gear in the 205 or the "driven" gear for the speedo cable?

 

The gear for the speedo cable. I figured there were different tooth counts for rear end ratios. I see bronco graveyard has color coded gears but they don't say what ratio they are for.

 

There are but tire rolling distance is also key. I can look them up but my Ford slides are going to list them according to the original tire sizes. Before the current P and LT metric sizes. T/C's took Ford's manual transmission driven gears. Not the ones meant for automatic trannys. You can bolt it all together with what you have (count the number of teeth on it 1st) and take it for a cruise with either a GPS on hand or a know correct reading vehicle driving in front of you doing 60 MPH. Find out how far off your speedo is. Do the math to figure the percentage. Then do the math to figure out how many teeth less or more you need. More teeth on the driven gear slows the speedo down. Less teeth speeds the speedo up.

 

Ok maybe I'm confused. I have the adapter to use my existing speedo cable but I need a gear that goes on the adapter to be able to put into the tcase. I can't use my existing gear as it was for a Dana 24.

 

Is this adapter you mention one that takes a long steel driven gear? Dentsides came with a 435 4 speed and 205 T/C. Looking up a driven gear for a Dent there are only plastic gears listed.

4:11 gears:
435 trans...4X4...7.X 15, L78/15 tires...C1DD17271A...replaced by C1DZ17271A 20 tooth gear.
435 trans...4X4...LR78 x 15 tires..........C40Z17271A 21 tooth gear.
...."............"......10 X 15 tires............C0DD17271C...replaced by C0DZ17271B 19 tooth gear.

So, depending on your current tire size, one of these may work. Taller tires require less teeth on the driven gear. Go from here. I believe all these are still available from Ford.

 

Look up 4.10 ratio for 1968/69 & 1970/72 F250 4WD (section 172, pages 19 & 20), you'll see both nylon and steel gears listed.

Pic: Nylon DRIVEN gears are TYPE 1 - 2 - 2A / 01T Steel DRIVEN gears are TYPE 5.

 

Nylon is merely a thermoPLASTIC.

...."Nylon is a thermoplastic,[5] silky material, first used commercially in a nylon-bristled toothbrush (1938), followed more famously by women's stockings ("nylons"; 1940)"....

Nylon is to plastic as aluminum is to metal.

 

Hey Bill. I went to the Dents to look up the Op's driven gear because he installed a 205 T/C. Bumps did not get a 205 so looking up a gear in the 68/69 and 70/72 section would not apply. In the 73/79 slide it makes no difference 4:10 or 4:11. Still all commonly called plastic gears listed.

So I go back to the OP. This adapter you mentioned, does it take a plastic gear or the long Metal one? Ford is not the only one to use the N/P 205. That adapter may be out of something else.

 

Here is my adapter I bought to be able to run my older speedo cable. I just need a "nylon" gear to put on the adapter to slide into the t case but I'm just not sure how many teeth I need on the gear. I am running 33" tires.

 

Ford Speedometer Calculator

 

That adapter does take the commonly called plastic gear. Don't forget it uses part number C1DD17292A clip to hold the gear on. I believe the gears and this clip are still available from Ford. Ford's speedo gears range from 16-21 teeth.

 

Thank you fellas! Ultraranger, on that calculator when I type in my specs what do I put in the bar that says 'Speedo Drive Gear" ? Its already set at 7. If I leave it at 7 I get a call for an 18 tooth.

 

...205 in a Bump...must have been a rare factory, pre-production prototype that got listed?.

 

As Jeff mentioned, the Ford Driven plastic gears come in 16-21 tooth counts. The Drive gears can be 6, 7 or 8 tooth counts. Some Drive gears are metal, some are plastic and some are machined into the output shaft itself (at least on some Ford transmissions).

I don't have a 4-wheel drive so, I'm not familiar with the internals of a transfer case or how the Drive gear is configured on it --whether it's plastic, metal or if it's actually machined into the shaft (?). If the Drive gear isn't machined into the shaft itself, the Drive gear can be (fairly easily) swapped, if it had to be.

In the older Fords, as it relates to the transmissions anyway, 7 tooth counts were pretty common. Later transmissions commonly have 8 tooth count Drive gears machined into the output shaft of the transmission --again, not sure how the Trans Case is configured in this regard. In order to change Drive gear tooth counts on a transmission that has the Drive gears machined into the output shaft, you would have to totally disassemble the transmission to swap the output shaft for one with a different Drive gear tooth count machined into the shaft.

As a default, I would go with the 7 tooth Drive gear tooth count. If the speedometer still is inaccurate after you change the Driven gear, you'll have to bump up in Driven gear tooth count until your speedometer is more closely correct.

Just as an FYI ....There is a plastic 23 tooth Driven gear available from the aftermarket. However, the teeth on the plastic gear are pretty thin and this Driven gear usually only lasts for about 25,000 to 30,000 miles before the teeth wear away on it and it has to be replaced.