Want to change my rear end ratio....

[fijidad]

The '71 F 250 I've got has a 4:11 (or so...where can I find this out, any data plate info on the truck?) and gas mileage is pretty bad. Any suggestion on what ratio to run otherwise? This is going to be a mostly around town truck with perhaps 25% freeway driving.

[Mancar1]

My 68 CS has the Dana rear with 4:10. The highest I can go is 3:54 which will make a cruising difference.
The code for your rear end ratio is on the trucks VIN.
Go to this sites Technical Articles and Tutorials Index and you can decode your VIN.
Hope this helps U.
Keep on Trucking......John

[eggman918]

this is the gear calculator i like/use it will let you test all possibility's
http://www.grimmjeeper.com/gears.html

[HIO Silver]

Install an overdrive transmission!

A 4.11 rear gear coupled with a 0.70 OD gear like on a 4R70W results in a freeway friendly final drive ratio of 2.88.

[fijidad]

My 68 CS has the Dana rear with 4:10. The highest I can go is 3:54 which will make a cruising difference.
The code for your rear end ratio is on the trucks VIN.
Go to this sites Technical Articles and Tutorials Index and you can decode your VIN.
Hope this helps U.
Keep on Trucking......John

Thanks John. I took a look at my tach today doing 70 mph, and it read 3,000 rpm! Yikes! I'll have to decode that VIN and see what's really back there.

[Mancar1]

My 68 CS has the Dana rear with 4:10. The highest I can go is 3:54 which will make a cruising difference.
The code for your rear end ratio is on the trucks VIN.
Go to this sites Technical Articles and Tutorials Index and you can decode your VIN.
Hope this helps U.
Keep on Trucking......John

Thanks John. I took a look at my tach today doing 70 mph, and it read 3,000 rpm! Yikes! I'll have to decode that VIN and see what's really back there.

3,000 at 70 sounds like a prior owner may have put higher gears in. With the 4:10 rear I am at about 4,200 going 70 mph. I turn 3,000 at about 55 mph.
Sounds like U may have something like a 354.

[Mancar1]

Install an overdrive transmission!

A 4.11 rear gear coupled with a 0.70 OD gear like on a 4R70W results in a freeway friendly final drive ratio of 2.88.

True and that sounds great, but it is also a bunch of $$$$.

[6Delta]

With a F250t it is all a bunch of $$$. I have a 360 FE and the 3:73 gears. I waited and picked up a Gear Vendors unit to use behind my C6 before I realized the tail shafts are not even close (at least I can use it in one of my Rancheros. (Remember it is not that easy to pull the transmission only from a F-250 Camper Special). Depending on your engine/transmission you may well be ahead to swap a 429 and 4 speed auto from a later pickup. If you have the factory Dana 60 there are not any "bolt in" third member with a ratio of better that 3:54 - 1 that I have found. I have considered a lift kit and going to 35 inch tires. That would help a lot. Plus with a narrow profile mileage should be improved. However that too is a lot of $$$ since I have 17 inch rims. Also my pickup is high enough already for my taste. I wish there was a cheap 4 speed automatic to bolt behind my FE but the ones out there cost more than I paid for the pickup LOL

Good Luck. Bigger tires may be your best approach depending on your rims. There are several calculators out there regarding bigger tires.

[6Delta]

With a F250 it is all a bunch of $$$. I have a 360 FE and the 3:73 gears. I waited and picked up a Gear Vendors unit to use behind my C6 before I realized the tail shafts are not even close (at least I can use it in one of my Rancheros. (Remember it is not that easy to pull the transmission only from a F-250 Camper Special). Depending on your engine/transmission you may well be ahead to swap a 429 and 4 speed auto from a later pickup. If you have the factory Dana 60 there are not any "bolt in" third member with a ratio of better that 3:54 - 1 that I have found. I have considered a lift kit and going to 35 inch tires. That would help a lot. Plus with a narrow profile mileage should be improved. However that too is a lot of $$$ since I have 17 inch rims. Also my pickup is high enough already for my taste. I wish there was a cheap 4 speed automatic to bolt behind my FE but the ones out there cost more than I paid for the pickup LOL

Good Luck. Bigger tires may be your best approach depending on your rims. There are several calculators out there regarding bigger tires.

[6Delta]

Sorry about the double post.

[fijidad]

My 68 CS has the Dana rear with 4:10. The highest I can go is 3:54 which will make a cruising difference.
The code for your rear end ratio is on the trucks VIN.
Go to this sites Technical Articles and Tutorials Index and you can decode your VIN.
Hope this helps U.
Keep on Trucking......John

Thanks John. I took a look at my tach today doing 70 mph, and it read 3,000 rpm! Yikes! I'll have to decode that VIN and see what's really back there.

3,000 at 70 sounds like a prior owner may have put higher gears in. With the 4:10 rear I am at about 4,200 going 70 mph. I turn 3,000 at about 55 mph.
Sounds like U may have something like a 354.

Good info John, thanks. I'm going to check that VIN today and see what it says.