I was wondering what changing my stock rear axle gearing from 3.08 to something like 3.77 would do. I know i would get much better acceleration(which I need desperetly), but how bad would it hurt my mileage and cruising RPM's? Is it worth the money?

 

It depends on what tranny and tires size is using your truck, EFI or carby???

 

i have a 5 speed manual tranny and 31 in tires.

 

and it is a '95 EFI, i have pulled out the second cat and put on a glasspack muffler, and also modified the airbox to be like a cold air intake.

 

I have a 95 flareside 4x4 with the m5od, 31x10.50 tires and I have 3.55 gears, I would like to have some 3.73's for towing (and a zf tranny for that matter) but I'd have to swap out both differentials. I'm sure you can find the 3.55's fairly easy. It's a very popular rearend. Even my dad's 87 2wd f150 3 speed w/ overdrive has the same gears. Any 8.8 rearend from 87-96 is a direct swap (the 87+ have the abs ring)

 

do ya think that will give me some more pick up? and will it kill my gas mileage?

 

You shouldn't get that much of a change in mileage, pending your driving habbits. I Currently run 33's with the 3.08 and I was looking into the 3.73 or even 4.10. When I did my math (which could be way off) the change from 3.08 to 3.73 would make about 600 rpm difference at 70 mph running the truck at about 2700 rpm's in overdrive. As a test I ran in 4th for my comute which varies from 55-70mph and at 70 mph the rpm's were about 2600 with the 3.08. I lost about 1 mpg (tested over several tanks) but pulled itself allot better.

I do intend on changing mine out this winter, the 3.08 are just to high, especially because I want to run 35's

 

well i think im gonna look into getting 3.73's installed, i'd just like to not lose speed every time i go up a hill at over 55mph in overdrive.

 

well overdrive is made for flat ground going 55+, if you try to climb too much of a hill in od (other than a slight grade), it's really hard on the transmission especially since it's a m5od. You need to baby them things to get any kind of life out of them. They're not the greatest by any means. Mine has 102,000 miles and the shifter is starting to whine a little bit (only when I tow with it though), I heard that if you keep your hand on it all the time it will wear the synchronizers out, when it's making that noise I hold the **** a little bit one way and it doesn't do it.Tranny also has the famous leaks and whatnot and I just added some today before I towed.

Forgot to add something... at 60mph I tach 2,000 w/ the 31x10.50 tires and I get 15-16 mpg my driving around town, some highway and I shift around 2,000 or so the tach drops to 1,500 run her up again and so forth... 2,000 rpm's is right in the sweet spot of the 300, it makes it's most power from 2,000-3,500 after 3,500 is a waste. Oh and ford didn't use a 3.73 gear, you could buy some from summit they carry richmond gears which IMHO are the best gears on the market.

 

so do you think it would be wise to purchase the 3.73's, or would the power not be all that noticeable?

 

With the 31" tires I'd at least reccommend 3.55's, also it would depend on how much of a hill you want to climb, even with 3.73's it really wouldn't be that much better, you still might have to downshift. IMO 3.55's are perfect for the 300. Now if your going to go with a set of new gears since you'd be buying what you wanted anyways 3.73 probabally would be the way to go, if your gonna get a rearend from a junkyard 3.55 is very common. I was thinking about upgrading just because sometimes I do some heavy towing (I mean around 9,000 pounds) I said 3.55's cause they are readily availible because ford used it soo much. Now to me my truck feels like it has more power and is a lot faster than my dad's 87 2wd, his has 300, 3 speed w/ overdrive and 3.55 gears. I'm just comparing going in 4th gear for me which is 1:1 and his third is 1:1, my truck has plenty of power, now if I can just get rid of this pos tranny.

 

yea i mean my truck is 2wd (even tho i'd kill for a 4x4, i love offroadin, i couldnt afford one) but i was just looken for some more on roadin power. it sucks taken like 30secs. to get to 60 but i guess thats what i get from an engine made for pullin.

 

I changed my air filter and crankcase breather this past saturday, they was both pretty filthy, I put a k&n replacement filter and a purolator crankcase filter and the truck has a little bit more get up and go, most people say they don't notice any difference with the k&n and my filter was actually pretty dirty so that may have been it. But anyways the engine does respond a lot better especially when I take off and go through the gears. I cleaned the throttle body real good but that was sunday when I did that, it wasn't really that dirty but I did get it a little bit of stuff out. I bought a new pcv valve but I don't like how they fit compared to the oem one (they have two ports and you have to plug the upper one off and the hose is too loose and you'd have to use a hose clamp to hold it on there) so I soaked mine in the same cleaner I used, for my dad's truck I thought I could get an oem one but there's is just like all the rest I've seen, his has popped out of the grommet a few times because the hose isn't really long enough and it's putting pressure and it's sucking it out of there.

 

yea i cut the bottom off of my stock air box so its gets alot more air to it, and i cut off one of my cats and put a glasspack with a turn down on it, that stuff gave me noticibly more power, but i guess i just thought that my overdrive was like a 5speed, im looken at gettin some 3.55's from a junkyard now tho.

 

If you get those gears I think you'll be very satisfied. Some people say that you can actually increase mpg by using a lower (numerically higher) gear, especially since you have od. Right now I'm gonna save up for tires so I can get them on before winter, and hopefully an exhaust. I'm also gonna try to save up enough money to have in the bank for a zf tranny for when the m5od craps out on me.