Hot Rods Rear End - Gear Ratio??

Missed that. Yeah, toss the C4 and run an AOD.

More gears is alway more better.

 

With those numbers and a 26 inch tire you would have to have a 4.20 gear

 

Or a 4.00:1 gear, and slippage.

An AOD would fix both issues.

 

That would take some serious trans tunnel mods, they aren't roomy on those cars....

 

This is a rod and custom site.

I have a T56 in my 1st generation Falcon.

 

Sounds like it ain’t going into hi gear to me if it’s a 3:20 gear

 

Check your shifter set up. Confirm the year of your transmission. If it's a Cruisomatic C4, through '65 and not a Selectomatic 1965 up, you may not be in drive.
Cruisomatic Green Dot
Un***led by Travis Brown, on Flickr
If you put on the Green Dot, You'll be in 2nd on a Selectomatic with a Cruisomatic shifter.
Selectomatic C4
P-R-N-D-2-1
Cruisomatic
P - Park
R - Reverse
N - Neutral
White Dot - Starts in 2nd, automatically shifts to 3rd
Green Dot - Starts in 1st, automatically shifts to 2nd and 3rd
L - holds first or second gear, whichever you happen to be in when you pull the shifter to this location. Will not automatically upshift, but can downshift.
Green Dot is regular drive.

 

I never had a car with an AOD, so dont beat me up too bad. Are they controlled by vacuum and a governor, or do you have to have a controller or internal mods done to make them shift?

 

In the 1980s they were controlled by a cable to the throttle linkage, no electronics.

The later ones are computer controlled, but they also have different names, involving letters and numbers that I don't know anything about.

 

RedNeckYoga.....I just sent a PM to you.

Lynn

 

Rearend ratio in my 260 / Fordomatic 1964 Fairlane was 3.00 to 1.
Three speed manual trans in same year, same engine car had a 3.25.
All the I6 and V8 Fairlanes and Meteors from '62 to '65 had 8" differentials and five bolt wheel pattern.

 

Yep...looks like I have the 4 to 1

 

I'm almost always 100% behind going to an AOD trans for situations like this, and still am. But the early Ford AOD trans introduced in 1980 was and is a piece of **** unless someone tosses a lot of money at them to build them up. They have numerous issues with clutch pack failures, and something as simple as shifting them into 4th OD under open throttle will destroy the clutches.
In this case I'd consider going OD, but getting the later improved electronic version that came out around 1993 called the 4R70W that's a huge improvement. It's easily controlled without expensive electronics to make it work in an earlier car like yours.

 

The mercomatic is not an OD transmission so final drive is 1:1. The C4 is also not an OD transmission so the final drive is also 1:1. It stands to reason that if it would run on the highway with the 260 it would run on the highway with the 289. How accurate is your tach? Have you changed to low profile tires?

 

If that thing has a 4.10:1 gear in it I’d definitely change it for a 3.25 or so before I’d put an AOD in it. AOD’s can bet tough to get right with the throttle cable. If it’s not right it’s smoked before you get around the block. Just my opinion though.

 

I'm late to the party but this is probably the easiest to use plug in three and find the fourth speed, rpm, tire size, gear rato calculator I have found (don't get your undies in a knot because it is from an electric vehicle conversion site, it is simple to use) Tire Size, RPM, Speed, and Differential Ratio Calculator (advanced-ev.com)

Plug in any three and you can get the fourth. If you want to see what RPM is with an overdrive multiply the rear axle ratio by the overdrive ratio and put that as the rear axle ratio meaning that a 4.11 with a .79 overdrive would be a 3.26 ratio when you round 3.2469 off.
Reading back though the posts, I would reread the one that asks "are you sure you are in third gear" I swapped a 425 and turbo 400 into a later cad that had come with an overdrive trans and the first time my wife and daughter took it on trip to town they blew the engine up because they were driving it in second rather than third. Not only was the shiftter off, it had 3.7 gears.
This is what the calculator I posted for 55 mph at 3000 rpm with a 26 inch tall (which may be too tall for what's on that car) tire= 4.22 or around there rear axle ratio.