Hi folks, I am changing out my rear end gears (dana 60) in my 1977 ford F250, I am looking for better highway and overall gears, I was told that 3:50 were a good choice, what do you folks recommend?

thanks

Bigred

 

What's in there now?

 

Many variables here.

Vehicle weight:

Tire size:

Transmission:

Expected loads:

Type of driving:

There is always a compromise when selecting gears. Engine RPM in the final drive is only one part of the equation. Lowering engine RPM is a nice consideration but not the only one. You have to consider getting such a heavy vehicle motivated, especially if you tow anything. Not having the mechanical advantage to get the heavy truck rolling can really work against you, especially if you have a camper, tow a trailer, or have to pull large hills where you live.

 

Hi folks, I am running LT265 75R 16 tires, C6 trans, I will not be pulling or carrying anything. I am looking for better gears for all around driving including highway and hopefully some better gas economy. I presently have 4:11 gears in the truck.

 

3.54:1 is as low as you can go (numerically) in a Dana 60. If you are not hauling a lot of heavy stuff, they should improve your gas mileage over the 4.10's without a tremedous hit on acceleration.

 

If you are running a 4.10 ratio now, the drop to 3.55 will drop the rpm a bit over 300 rpm. Not too sure how much of an improvement is going to be. I mean its gonna take a few bucks to install a new gear set, and after considering how many miles you might drive a year, this might take a long time to realize a savings in fuel.
Slightly taller tires will do just about the same thing,,,something to think about.

 

Hi guys, I am not an expert in any way but going from 4:10 to 3:54 rear gears should drop the rpm on the highway more than 300 rpm, please correct me if this is not the case. I have talked to people that are more knowledgeable than I am and they say it should drop around 700 RPM.

thanks

Bigred

 

+1 on changing the tires. It would probably be easier and cheaper to go up a size or two and throw in a new speedo gear than to regear. And it would be easier to go back to the smaller size if you didn't like it, than it would be to re gear. Besides who doesn't like an excuse to get new tires? What tire size are you running now?

 

With roughly a 31 inch tire, the difference in math between the 4.10 and the 3.55 is right at 390 Rpm, so we sort of split the difference there, but you wont expect to see a drop of 700 rpm. IN order to obtian this type of drop in Rpm, you would have to run a ratio that does not exist or run a tire that is about 38 inches tall. Neither one of those is going to be reasonable.
With this amount of drop in Rpm, and this tire size, this engine will struggle to accelerate and you will have to be so heavy in the throttle to maintain any speed that you will negate anything you are trying to accomplish. This would be defeating the purpose.
While slight tire changes can make a difference in engine Rpm, it may not be as suitable for thie application, however, I dont really think that you will realize a savings in fuel with a truck shaped like a brick to justify this type of expense. Again there will be some disadvantages, and I am sure that we will hear about the guy with 2.75:1 rear end gears, and how he has more power than he knows what to do with, but this is not quite as suitable for a 3/4 ton truck.
Weight, and overall resistance prevents us from this with our gasser engines, and while we can try to change some stuff around, it might be just as reasonable to air up the tires a little, change our driving style some, and slow down a couple of hundred Rpm or so on the highway.
I mean the difference in Rpm between 70 mph, and 65 or even 60 is considerable, and the real time it takes to travel the same distance is minimal.
A 100 mile trip at 70 can take about an hour and thirty minutes, and the same trip at 65 only takes a few minutes less. Guess which truck will do that with less gas consumption?
Sometimes a driving style change can add up to a more justifiable means of saving fuel.
Again, just thinking out loud............

 

gearing can make a difference. sometimes however, its more of a matter of being at a speed where your motor isnt working as hard to maintain its speed. I.E.: my granddad had a truck with a 300 strait six. he averaged about 11 to 13 on the highway. well one day, he had about a three hour trip ahead of him, and he left around 4 a.m. at that time, there was no worry about po-pos, so he ran the truck between 80 and 90 the whole way. he jumped up to 18 mpg. after doing that math, he bought lower gears for it. go figure. some food for thought...

 

Keeping the 4.10s and putting in an OD trans would be the ticket. Changing tire size isn't going to do a whole lot to bring rpm down unless you put on some big tires. The average 265/75R16 is a little over 31.5" in diameter. If you jump up to a 285/75/R16 you'll be adding around an inch to the tire diameter which will not do much to decrease your rpm. I went from a 265 size to a 285 size on my SD and it didn't affect rpm much at all.(In all gears including 1:1 (3rd) The next step up in diameter is 315/75R16 and they are close to 35" in diameter but are wider and your current rims may be too small. Also remember a decent set of 285s is going to run a minimum of $800 and 315s closer to a grand. If you have a 2wd and you only have to regear one axle you'll be better off regearing than messing with tire diameters IMO. If you can do a regear yourself you can save a lot in labor costs. If you don't do a lot of towing 3.55 gears should give you better highway mpg especially if you have a larger displacement engine with a lot of torque. In around town driving you may not pick up any increase in mpg, may lose a bit. Of course driving 55mph would help your mpg quite a bit. When these dentsides were made the state speed limit in my area was 55mph and these trucks seem to like that speed.

 

Unless you are doing a lot of highway driving I wouldn't bother.