Can I change the rear end ratio on my sons truck. It is a F250 with the 460 engine, and he is only getting 10 miles to a gallon. The tag on the axle say's 10 10 2 3 F15 and I am not sure what that means.
The tag in both cases is a 4.10 (the 4 is behind a bolt), 10.25" Sterling.... you can swap the gear or the whole axle for another Sterling or a DANA 60. As a rule, a 460 isn't designed to get great mileage regardless of ratio.
may i ask a followup? i have since yesterday found the following table:
12 2.73 3800 FORD REG
18 3.08 3800 FORD REG
19 3.55 3800 FORD REG
25 4.10 5300 FORD REG
29 3.55 5300 FORD REG
35 4.10 6250 FORD REG
39 3.55 6250 FORD REG
45 4.10 7400 FORD REG
49 3.55 7400 FORD REG
65 4.10 8250 FORD REG
69 3.55 8250 FORD REG
72 4.63 11000 DANA REG
73 5.13 11000 DANA REG
H5 4.10 3800 FORD LIMITED SLIP
H9 3.55 3800 FORD LIMITED SLIP
H8 3.08 3800 FORD LIMITED SLIP
B5 4.10 5300 FORD LIMITED SLIP
B9 3.55 5300 FORD LIMITED SLIP
C5 4.10 6250 FORD LIMITED SLIP
C9 3.55 6250 FORD LIMITED SLIP
D5 4.10 7400 FORD LIMITED SLIP
F5 4.10 8250 FORD LIMITED SLIP
i do not know the original source of this data.
my axle code is a 45, so i assume "FORD" = Sterling. I also assume that this is a "full float" axle.......?
my goal is to lower my ratio and increase my hiway speed. this truck id driven on the hiway almost exclusively, and the revs are really high. i have no illusions about fuel mileage increasing.
my guess that the ideal swap would be for me to get a code "49", which appears to be the same setup with a different ratio? is there a resource that will help me know what years i might find vehicles with that code?
also, i have found for sale a rear end that looks like mine, but the axle code for the vechicle it came in was a "39". it was an f350, but a SRW. so is it safe to say that a "39" axle code vehicle is the same rear end, but not set up for DRW? and since i have all that stuff, i could make it work?
The 3800, 5300, 6250, 7500, etc are the Axle Weight Ratings for those axles. The 7400 is likely a Ford 10.25" Sterling axle found in 3/4 and 1 ton single rear wheels. I think the 10.25" Sterling was also used in some duallys but Im not sure. Judging by the numbers you provided for your axle, I guess the answer is yes. The 8250 axle is likely a Dana 70 in a one ton dually. The 6250 could be a Ford 9.75" semi float axle in a late model lightweight 3/4 ton or a Dana 60 in an early 3/4 ton.
The '39' axle is not the same axle as your '45' axle. You are right, you would be looking for a '49' axle, same as yours but with a 3.55 ratio.
Going from 4.10 to 3.55 you will be lowering your engine rpms for any given vehicle speed and probably save some gas on the freeway when unloaded. Your mileage may actually suffer when towing or driving around town depending on what size your engine is. I'm assuming you dont have overdrive and that is why you are wanting to switch to the higher (numerically lower) axle ratio? If you use the truck for towing, you will likely experience a performance decrease going with the higher axle ratio (3.55). This also depends on your tire size.
3.55 isn't that great of a ratio for a dually that is used for it's intended purpose (hauling weight). My old Chevy dually had 4.10's in it with stock tires and no ovedrive. I know what you mean about turning high rpm's at fast freeway speeds. I just drove slower. My current F350 has 4.56's with 33" tires and no overdrive, which works out to the same thing as having stock tires and a 4.30 axle ratio. I do drive slower on the freeway now. Before I had 3.55's in it and could drive quite fast but it had no power at lower speeds and was a total dog on hills and towing was a very slooowww process as I spent alot of time in 2nd gear with it.
If your tires are stock, 3.73 would be a compromise between mileage/lower rpms and pulling power. 3.73 is not available in a whole axle swap, but can be had with a gear change. You may find the price is not too much different between the two, but that all depends on how cheaply you can acquire the other axle and if you have to put any money into rebuilding it.
An inexpensive alternative to swapping axles or changing gears is simply to go to the next larger size tire, which will have the same effect as raising your gear ratio. An approximate 2" difference in tire hieght equals approximately a 0.25 increase in gearing, meaning that your 4.10 axle will act similar to a 3.85 axle as far as engine rpms and power/mileage are concerned. A 3" increase in tire size would put you at approximately 3.73, and so on.
Unfortunatley, an increase in tire hieght usually means an increase in width as well and that is a consideration with dual rears. I have seen duallys with wide tires and spacers between the rear wheels so the tires don't rub, so that could be an answer.
Last edited by SoCalDesertRider; 03-13-2004 at 01:24 AM.
Originally posted by SoCalDesertRider Unfortunatley, an increase in tire hieght usually means an increase in width as well and that is a consideration with dual rears. I have seen duallys with wide tires and spacers between the rear wheels so the tires don't rub, so that could be an answer.
This also increases rolling resistance and angular momentum which can lead to reduced mileage and increased brake wear... just some feed back.
Actually SoCal's got the good info, I'd try a 3.73 into the existing housing. The MPG will only increase by gallon if that, but you won't sacrifice the trucks intended purpose. If you're looking at an all out cruising vehicle then the 3.55 will work, but again don't look for an awesome improvement in mpg. If you increase the tire height by more than a few inches think about leaving the rear intact at a 4.10 and giving a couple inches of body lift to compensate for the height, as well as back spacing the tire for rub. Also think about the larger tires and changing the ratio like this...The mileage you'll gain on the hiway may be wasted trying to get the truck to move with a hiway geared rear and tall tires.