[Wifes66]

Hi guys,

Well, like a dummy when I had the rear end apart for new seals and gaskets I failed to count my ring rear and pinion teeth. The rear end is a ford 8". I made a little sharpie mark on the yoke and the housing and another pair on the drum and backing plate. I tied off the oposite brake drum so it would'nt turn. I turned the pinion until all 4 marks re-aligned. Here are the results.

I turned the pinion 7 revolutions and the drum turned 5 revolutions before all 4 makes came back into alignment. I am math challanged and don't know exactly how to calculate the ratio like this. I assume it would be 7 divided by 5 which would be a 1.4:1 ratio. Could this be possible? That seems like extreemly tall gears. Did this car originally have a 6 cyl engine?

I need to know this so I can calculate with my new 15" tires for my speedo calibration. I will post on that when I get ready to do it. I don't yet know what speedo gears I have.

Help!

Steve

[jay67fast]

Pop's
From your explanation, I think the problem is too many marks!!!
The way to get a close approximation of the rear end ratio is to mark the driveshaft and the tire (or drum, if the tire is not mounted). Yes, you're correct, do not allow the other wheel to rotate. Make sure both marks are even. Then turn the wheel (drum) while counting pinion revolutions and wheel (drum) revolutions till they are back even . Then divide the pinion revolutions by the wheel (drum) revolutions. The result will be a close approximatiion of the rear end ratio.
Hope that helps.
Jay67fast

[Wifes66]

Thanks jay. The extra marks were so I could tell exactly where I started from. I did the math as you described and came up with a 1.4:1 ratio. That just does'nt see right though. Was that ratio even an option in 1966?

Steve

[snaranjo]

Sounds like you are off by two. 2.8:1 was a common ratio in 66s with a C4

[andrewmp6]

Look on the diff for a metal tag or the door tag.

[Wifes66]

andrewmp6:
There were no tags on the rear end when we pulled it and the drivers door has been replaced. Unfortunatly the only valid numbers I have on the car are on the left front fender apron.

snaranjo:
That has got to be right. I doubt they even run 1.4:1 at the salt flats. 2.8:1 is 1.4:1 times 2. I wonder if it has to do with the planatary (spider) gears. There is some mathematical or mechanical relationship here that I have failed to recognize or consider. Thank you for the info.

Anybody have any info or a link to a speedo gear calculator? Lord knows I can't trust my math skills. But I knew that going in.

Thanks again,

Steve

[paul289]

This is because you're keeping one wheel stationary. If you let both wheels spin freely, you'll get 2.8:1, which was the standard ratio for 289 2v w/ a C4 auto.

[Wifes66]

Thanks paul289. 2.8:1 sounds a lot better. I should be able to claibrate the speedo from there.

Steve