Got a bit of a problem. I am looking at going with Broader Performance to build me a C6 transmission for my '82 F150 and I will swap it in when the time comes.

I don't know what year C6`s he uses as he doesn't require a core charge I will be asking him this how ever. But the thing I am dwelling on right now is which output shaft should I ask him to install in this transmission?

From what I know C6 Ford transmissions had either a 6, 8, or 9 tooth drive gear cut into the output shaft. I cant find the related information on my Ford parts and illustration guide but online all I could find for a driven gear for a C6 is either 16, 19, 20, or 21 teeth.

Doing the math with my 31x10.50-15 tires (they are listed as 30.5" diameter) and either 3.00:1 or 3.25:1 axle ratio which is one of the two I will be going with. With this in mind it looks like the 6 tooth drive gear output shaft would be useless for me as with a 3.00:1 or 3.25:1 I will need either a 12-tooth or 13-tooth driven gear. Which I cant find a listing for online. Trying the 8 tooth drive gear output shaft with a 3.00:1 axle it is showing I will need a 16-Tooth driven gear which is available but for a 3.25:1 axle it is showing 17-tooth driven gear which is not available for a C6 from what I have found. Trying a 9 tooth drive gear output shaft with a 3.00:1 axle it is showing I will need a 18-tooth driven gear which is not available but with a 3.25:1 axle it is showing a 19-tooth driven gear which is available.

My goal is I am shooting for a 3.25:1 axle ratio to be swapped in later on but the transmission is being done first and with the limited number of driven gears I don't see a drive gear available that will cover both ratios. I just cant stand the thought of requesting a 9 tooth drive gear only to find out the C6 has more slip than I planned and I will have to run the 3.00:1 and now I have no driven gear available for it. Like wise I hate to bank on the 3.00:1 then find out I need the 3.25:1 instead.

Does anyone know of other driven gear tooth count available for the C6 transmission? Cause I am at a loss on this and I want my speedometer to read correctly once I am done with everything.

~Update~
Did some more digging in the parts and illustration guide. I found for a L78x15C tire with a C6 which is very close to the 30.5" diameter size my tire is with a 3.00 Axle ratio. C7SZ-17271-A, a green driven gear for a C6 that is 17-Tooth which is not listed on any website online that sells gears, but I found a bunch of NOS units online.

Seems like I can request the correct OE 8 tooth output shaft which is correct for C6 equipped trucks with a 2.73:1 through 3.08:1 axle ratios. Based off the TCI calculators which seem to be the same as others I have tried, 8 tooth drive with 3.00:1 with 30.5" tires is 15.85 tooth or 16 tooth, and 3.25:1 with 30.5" tires is 17.17 tooth or 17 tooth. Only down side is speedometer will read a bit fast with a 3.00:1 axle ratio and a bit slow with a 3.25:1 axle ratio but at least its close enough that it should be with in a mph or two. Not sure how to calculate how far off the speedometer will be running a 16 tooth driven gear when it needs a 15.85 tooth. But it should be close enough.

 

Contact Bob’s speedometer in Howell Michigan. They should be able to help.

 

I will do that cause I am second guessing even my own math and reasoning skills.

From my math I am seeing with a 8-tooth output shaft which is what ford put in C6`s with a 2.73:1 - 3.08:1 axle ratio I should be able to run a 16-Tooth or 17-Tooth gear with a 3.00:1 or 3.25:1 axle ratio with 30 1/2" tires and be with in 1mph on my speedometer reading. Im just still concerned just like I am concerned that there might be differences in C6`s that could cause me un seen problems bolting up to my 306. I know I will be reusing my old block plate as well as the same flex plate. I also will be reusing my OE kick down rod with the Holley extender to make it fit my 4V carb.

For me doing this in stages is whats concerning me cause engine is what I am trying to finish up now, then its transmission then after I figure out the percentage of slippage in the transmission its then either a 3.00:1 or 3.25:1 axle ratio change I will do to off set my taller than stock tires. Just want to plan it out properly so I don't create a unnecessary headache for me requiring something as big as pulling my C6 back out to have the output shaft changed.