3.25 rear

Unless it is an overdrive they are all 1:1. All you need to know is the rear axle ratio. If it is an OD you just add the OD ratio to the top line of the formula as a multiplier. On the rear axle ratios it is best to check them, they could have been changed. You could start by checking the ratio numbers on the center section, but still need to check them to be sure.
 
Thanks JSeery, that tells me what I need to know. I just replaced my 3.78 gears with 3.54 but it still doesn't have an interior yet so I have only driven it a small bit, sitting on a milk crate at that. does any one know what gear in the turtle I would need with 3.54 gears?
 
Ford Parts book, I can post a photo later. Do an online rearch for Green Book, there are free downloads, believe the V8 Club has it, indispensable information.
 
edhd58 said:
I was hoping someone reading this post would know the trans gear ratios to know if mine was close or the same as 42 Merc/Ma. Merc what trans do you have in yours so I can look up the final drive ratios. Thanks
Click to expand...

I'm not expert, but 3rd should be 1 to 1 ratio.
 
I have one on file. Here you go. No 3.25 of course.
The Green book is nice to have too.
 

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All early fords are 1:1 in top gear in the trans. Rule of thumb for tyre diameter is twice the width plus the wheel diameter. 6.5x2 = 13. 13+16=29 inches. a 7.50 is 31". I'd agree that a good guess at the rpm difference for the difference between 6.50s and 7.50s is about 200rpm.

Edit I found a calculator.
3.25 gears. 6.50 16s, 60mph. 2115 rpm.
3.25 gears. 7.50 16s, 60mph. 2261 rpm.

So about 150 rpm.

Not much really.

Just for giggles, same with 3.54 (7.50 then 6.50)
2463.
2304

3.78
2630
2460

4.11
2860
2675





Mart.
 
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That's why I don't understand killing the low end stop and go driving by installing high ratio gearing! You have to do a lot of high speed driving to justify it. Between the cost and the loss of performance I fail to see the appeal. If you truly what to drive that fast that often I would highly recommend an overdrive.
 
Mart said:
All early fords are 1:1 in top gear in the trans. Rule of thumb for tyre diameter is twice the width plus the wheel diameter. 6.5x2 = 13. 13+16=29 inches. a 7.50 is 31". I'd agree that a good guess at the rpm difference for the difference between 6.50s and 7.50s is about 200rpm.

Edit I found a calculator.
3.25 gears. 6.50 16s, 60mph. 2115 rpm.
3.25 gears. 7.50 16s, 60mph. 2261 rpm.

So about 150 rpm.

Not much really.

Just for giggles, same with 3.54 (7.50 then 6.50)
2463.
2304

3.78
2630
2460

4.11
2860
2675





Mart.
Click to expand...


Should the rpms be lower with the taller tire?
 
You divide by the tire diameter, so the larger the diameter (larger number) the smaller the answer (RPM) will be. (MPH X Axle Ratio X 336) / Tire Dia = RPM
 
Yeah, I put them the wrong way round. Doh!

All the right numbers are there, just the wrong way round!

Mart.
 
you guys are awesome, Thanks very very much.
JSeery, the reason I went with taller gears is I live out in the country, nearly all my driving will be open road. Even the towns aren't very big, so I'll be at 60 and 65 a lot of the time. It's 23 miles one way to my work and I hit one stop light going to and coming home from, the rest of the time I am cruising, unless its spring and then I follow a tractor a lot in the evening, lol. I replaced the gears in mine because the pinion stripped a few teeth one afternoon when I was showing off the new motor and chirped the tires in second gear.
 
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I was just pointing out you are talking 150 - 200 RPM. If that difference is important to you I would do it also. To me most of the time the money and effort expended are not justified by the gains achieved. Part of the difference is to some these cars are daily transportation, to me they are a fun item to play around with and I like performance!:D I run a 4:11!!
 
Just for reference, here are some nominal tire diameters (different brands will be slightly different, but it gives you an idea of relative sizes)

7.50 x 16 = 31"
7.00 x 16 = 30.4"
6.50 x 16 = 29.25"
6.00 x 16 = 27.9"

I'm a big fan of 7.00x16 in the rear with 6.00x16 up front. It's a nice rubber rake and the 7.00 are normally a wee bit wider than the 7.50 tires, believe it or not. Here's an example

New-Shoes-1.jpg
 
I'm also a fan of the 4.11:1 rear ratio. That, along with an Overdrive, makes a really great combination. Really, the best of both worlds
 
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