Been searching the forums and can't seem to figure this out correctly....my stock setup is 195/75/15 with a 3.55 gear ratio with a 19 tooth gear. Trying to figure out which speedometer gear will correct my speedometer with 275/45/20's on the truck? Any help would be much appreciated

 

What is the OD of the tires? I could figure it myself, just don't have the time.
What transmission do you have?
With these 2 items, I can assist in finding the right tooth count gear and part number to get the speedo close. The speedo unit itself has a fine adjustment that may need tweaked to finish the correction.

You mention 3.55 gears, so I'm guessing it's an 83-86 with an 8.8 rear axle.

 

Didn't I answer this question in another post here?

I pretty much spoon fed you the answer there....

 

OD of the tires in 30.4 and the transmission is AOD yes it's a 83 with a 8.8

 

Wow. Really? Is it that you don't want to work to get the answer your looking for and want RW to do all of it for you or that you are just intentionally ignoring me to be a jerk.

 

Wow, sorry that wasn't the case at all....I'm reading this from my phone and when I pulled it up I didn't see your post....thank you for posting the link I will take a look at it

 

Sorry. It just seemed like you ignored both posts where I put the link and you wanted the information given to you. I have a problem with someone not willing to put in the research or work when the answer is given to them. Now, if you had questions about how to fill out the calculator I would understand that.

 

Those are a bit taller than the typical 235/75-15 (28.5-29) offered on 2wd trucks, but very close to the typical 31x10.50-15 (30-31.5") that was available on 4wd.
With this info, perhaps one of our members who has access to the Master parts catalog (or your local ford dealer) could look up what the factory calls for with this combo. If you have a 2wd, you may still have to try adding or subtracting a tooth from the factory spec gear for the 235/75-15, since I don't think a 31" tire was offered for a 2wd AOD/3.55 combo, if so, it would have likely been in an F250 and I don't know what the equivilent 16"/16.5" tire would be.
If it's 4wd, then whatever gear the chart shows for a 31x10.50-15 should be well within the adjustment range of the speedo head.

 

I looked at that calculator, and it asked for info that I don't know on my own trucks. Yes, there are a few things I don't know about my trucks, so I find it very reasonable that this could be the case for most others as well.

 

What information is it looking for that you don't know?

 

Drive gear teeth, and speedo RPM. I know these are pretty standard numbers, since the C6 uses a cast gear that is a permenant part of the the output shaft, I just don't know how many teeth it has, and I dern sure ain't tearing it apart to count........
Especially since I knew there was a chart in the MPC that listed speedo gears by application (trans/tire size/axle ratio). Of course, it's dependant upon a factory standard spec.

 

I figured the OP had counted the teeth when he had the truck tore apart. He had the transmission and engine out. That would be real easy to count the teeth then.

From the old post:

As for the RPM's. I think the most common is 1000 RPMs at 60mph. You should be able to ask a transmission shop for confirmation on that or get a method to test it.

 

It's a two wheel drive....I'm in the process of swapping the motor and trans.....not to mention the older cars is all new ground for me.....so needless to say I'm doing a lot of searching on here and learning a lot....sometimes using the net on the phone isn't the best way...when I try to get the calculator to submit it doesn't do anything for me I think it's not responding on my phone

 

I don't know if I said it wrong or maybe I got a little lost in this, but if we are talking about the speedometer gear going into the trans it is a 19 tooth, it's in the first post, I should have separated it better

 

OK. Assuming that you have a 7 tooth drive gear and the speedo needs 1000RPMs to get to 60mph the number of teeth on the driven gear is 16.5. I would probably go to a 16. That way you'll be running a bit fast but you won't get a speeding ticket.