Hey Guys, I have a 302 in my 56 with a C4 tranny. I got a 9" rear end out of a 59 F100, I am guessing the ratio in it is around 3.73. With my motor and tranny combo what gear ratio would you guys recommend? I will not be racing it, just want to be able to cruise the interstate every now and then. Thanks in advance for your suggestions.
Dave

 

In mine I`m thinking of a 3.00 or lower would work fine. It`s a bummer without the overdrive transmission. Maybe some day....

 

I would say a 2:73 to 3:08 would work.

 

I have a 56 with a 302 and a C4. I believe it has the stock gears, a 3.92 and 55-60 is about all that seems comfortable to run it.

 

Since you won't be doing a lot of highway cruising and mostly short runs I'd say a 3.25 to 3.50 would do nicely. If you were doing mostly interstate driving then I'd go with a 3.00.

Vern

 

Dave, if you are using a 'normal' size wheel & tire a rear gear ratio
around 3.00 to 3.25 should be fine around town . I'm using the 302/C4
with 3.25 gears with 205/75R15 tires.

 

It depends on your tires, but llike NorthWoods and truckbuff relate, a 3.25 would be good, and if your tire diameter is not more than 29", you can pull a 3.00 with an automatic, because under load it will slip 7-10%, at at cruise it will slip 2-3%, so the 3.00 as compared to a stick will be 3.09 to 3.30, depending on load. (climbing, towing, accelerating) In general I go one ratio size higher than I would use with a stick. Standard ratios were: 2.79, 3.00, 3.25, 3.50, 3.73, 4.11. There are third party ratios made for racing and since it is hard to find 9" pumpkins in the wrecking yards anymore, you may have to buy a ring and pinion to change the ratio. If you go to a very large tire size where the tire diameter goes to 31" then you have to go a ratio change lower.

Alanco

 

I'm running a 3.25 Currie w/ 26in. tires and it works fine

John

 

The 3.7x ratio (there should be a tag on the rear end telling you the exact ratio, or else you can jack it up and count the pinion turns per tire revolution.) would be fine for mostly around town driving without embarassing yourself in an occasional stoplight contest without being a problem on the interstate up to legal speeds.
There are plenty of calculators on the web that will tell you the RPM at any given speed or vice versa if you know the outside diameter or circumferance of the tire you are going to be using.

 

FWIW, most 2wd 70's f100's have the 9 inch rear with a 3.25:1 in the third member. They would be 28 spline, and these trucks should be common in the junkyards. Check the axle tag to be sure though. My 2 cents.

 

I have 56 with 289 and C4. I'm running 2:75 gear with 235/70/15 tires. Going 70 miles per hour, I'm turning about 2800 RPM, getting about 18 or 19 miles to a gallon.

Nick

 

Thanks alot for all the help guys. I ended up buying a nice used set of ring and pinion gears off ebay for $20, ratio is 3:00. A buddy of mine at work is into drag racing and will do the swap for me. You guys are the best!
Dave

 

I hate to be the one to tell you this...but buying used rear end gears is about like buying used bearings or used brakes. Maybe you will come out okay since they were cheap and you have someone to set them up for you but only new ring and pinion gears should be considered...

Vern

 

I have to agree with GNW, once a ring and pinion is installed and run it develops a specific wear pattern and even removing and reinstalling them in the same carrier or readjusting the lash later will move that contact patch/pattern likely resulting in increased wear and and noise. Drag racers seldom care if the rear end howls for the few seconds they are driving it, and likely won't hear it anyhow. Circle track and road racers will have extra carriers set up with different ratio gears and change out the whole thing. Unless you are doing a lot of long distance over the speed limit expressway driving I'd still recommend sticking with the 3.7 gear set you already have, it will only cost you a mile or two per gal and be a lot peppier around town with that little 302 pulling around 2 ton. You won't be embarassed by 18 wheelers and kids on tricycles beating you away from the traffic lights! You can always change it later if you don't like it, but my money says you will.

 

Don't let anyone scare you. Setting up a used ring and pinion is all about patience, confidence, and trial and error. It is harder with a Ford hypoid style as the pinion is below the ring centerline and the teeth are curved and much longer. You need to set up some preload on the carrier to get a low backlash, have a brush and white lithium grease so you can see the contact pattern, and work with the ring depth until you have a good pattern. Moving the ring will change the ring/carrier preload. It may take a while but you can get it.

This is something I do a lot of and it becomes easy after a while, and in my experience I have taken howling gearsets and fixed them. What wears out in most rear ends is the carrier bearings. When they wear, the tooth contact is lessened and moves out to the edge of the teeth causing the howling. I feel that ued sets need to look good, that is, no excessive wear on the teeth, no edge contact, etc., but there is no reason to think that a good set wil never work right. Also, there is no reason to fear a used bearing if, upon inspection, there is no overheating, no pitting, no cone wear. I would not reuse carrier bearings or pinion bearings unless they looked new, with no obvious wear anywhere. It is easier to set up a rear end with used bearings, because they will seat better than a new bearing at the same preload. They have worn in where a new bearing hasn't. This is the reason for all the bearing preload, so you do not end up with a loose pinion later, and more backlash from the carrier bearings later. If you don't now have a bunch of 9" parts, be sure to buy a pinion shim set. If you race, do not use a compressible sleeve on the pinion, use a solid spacer and shims. It is more work, but it gains you two things: The pinion preload won't change, and you can remove the companion flange to change a seal without worrying if the sleeve will compress when you retighten the pinion nut. Also, with the differential off, be sure to use new spider gears and shafts if there is any wear at all, and shim the spiders, and side gears tightly. This will make the differential more locking.

Oh, and I have to disagree strongly with AX Racer. You can get the same tooth contact back on a used set. After all, both cast "pumpkins" are machined the same, and the parts are in the same relative position as they were in the other casting.

Also, the way to get gas mileage with a gas engine is to load it more with the throttle open more. Having a "low" rear end for racing does not consider that it reduces engine load and keeps the throttle closed more, creating more vacuum, which creates pumping losses. Ideally, with a vacuum gauge, you chould cruise at 10.5-13" relative to 18" at idle. Make sure your power valve does not open until about 8.5 inches. You will maximize your mileage this way.

Good Luck!

Regards,

Alanco