I have this belief that since modern freeways were changed to 70mph, that vehicles prior to that just aren't geared to run their best at those speeds in terms of RPMs and thus milage.
I'm not on the freeway often but when I am with my 4spd auto 92 4.9 F150, I can practically see the gauge drop(minor exaggeration) and even without a tach can sense my engine running too high and working too hard compared to newer vehicles.
My basic question is, are there any ways to change the gearing or transmission swaps, or something to make these older trucks more adapted to freeways.

 

Each vehicle is different but I in most cases this vintage truck doesn't have enough gearing to operate appropriately at highway speeds and the I6 trucks were often crippled particularly bad with super high(numerically low) axle ratios. Couple that with the relatively low engine power output the motors of this era generated and you have a perfect recipe for a vehicle that is a complete slug on the highway. If the tires are stock or close then many will tell you that 3.55 gears are probably about perfect for an I6 truck but it also depends how you use it and how fast you drive. The I6 can get around allright with 3.08 or 3.31 gears but you'll find it's unresponsive on the highway in OD and also unable to maintain speed up hills without dropping out of OD.

 

Your best bet is a rear end gear change to something taller. I'm not sure what is in your year though.

 

As said above it all depends on your rearend gear ratio. I run a 300ci 5 speed, and I have a 2.72 gear in my rearend. That is the tallest gear they had in these trucks. And due to that I get about 18-19 mpg on the interstate going 65. And I am at a comfortable 2,500 rpms. But at the same time with that tall of a gear mine lacks the towing power that say, one with a 3.55 or 4.10 gearSo if your wanting better mpg, and less stress on the engine on the interstate, I would find me a rearend in a junkyard that has maybe a 3.08 gear or so in it. There are charts to find out what gears you currently have in your truck. You will find the code for the rearend on your door sticker. Hope its helpfull.

 

Bingo...Conanski, you NAILED it....(As always)...
Personally....I've driven my dads' 1992 F-150 302/5speed/3.55LS/4x2....

And in all honesty....I can't tell much difference from 0-50mph....From his truck, and my 1992 F-150 300/5speed/3.08Open/4x2....

Both trucks are on factory sized tires, and are standard cab/longbeds....

As to the rear end gearing...
I personally think that the 3.55/3.73's would suit the 300's very well.....Given you aren't trying to make it perform beyond its limit...
<TABLE style="BORDER-BOTTOM: rgb(221,221,221) 1px solid; BORDER-LEFT: rgb(221,221,221) 1px solid; BORDER-TOP: rgb(221,221,221) 1px solid; BORDER-RIGHT: rgb(221,221,221) 1px solid" border=0 width="96%"><TBODY><TR><TD width="33%">MG Part #

</TD><TD width="34%">OEM #

</TD><TD width="13%">Teeth

</TD><TD width="20%">Ratio

</TD></TR><TR><TD width="33%">F8.8-308 </TD><TD width="34%">E7TZ4209A

</TD><TD width="13%">40-13

</TD><TD width="20%">3.08

</TD></TR><TR><TD width="33%">F8.8-327 </TD><TD width="34%">E7TZ4209B

</TD><TD width="13%">36-11

</TD><TD width="20%">3.27

</TD></TR><TR><TD height=13 width="33%">F8.8-331 </TD><TD height=13 width="34%">F3UZ4209A

</TD><TD height=13 width="13%">43-13

</TD><TD height=13 width="20%">3.31

</TD></TR><TR><TD width="33%">F8.8-355 </TD><TD width="34%">E3TZ4209J

</TD><TD width="13%">39-11

</TD><TD width="20%">3.55

</TD></TR><TR><TD width="33%">F8.8-373 </TD><TD width="34%">E4TZ4209A

</TD><TD width="13%">41-11

</TD><TD width="20%">3.73

</TD></TR><TR><TD width="33%">F8.8-410 </TD><TD width="34%">E9TZ4209B

</TD><TD width="13%">41-10

</TD><TD width="20%">4.10

</TD></TR></TBODY></TABLE>

 

Actually I have a stock 4.10 rear on my 95 300 straight six. I wish it was geared alot lower because i dont tow that much and im on the highway everyday.

 

What I think you need to do is figure what speed you'll be driving at most often, what size tires you're running, and calculate a gear ratio that will keep the engine running around peak torque.

For example, I drove 590 miles of almost all interstate driving this past weekend in the truck in my sig. Normally, I get 11-12 mpg highway on long trips. However, my average highway speed is only around 60 mph (2 lane blacktop with a stop every 10-20 miles). This trip, I drove mostly between 70-80 mph on the interstates through Minnesota and North Dakota and got 13.6 mpg. While I did have a slight (5-10 mph) tailwind, I believe the biggest difference was that I was running between 2000-2200 RPM and the 460 makes peak torque around 2200 RPM. This is quite a difference from my cruising RPM of 1600-1700 RPM on two lane blacktop.

 

I wish I could meet you in the middle. my 2.72 gear makes my behemoth a sloth.

 

Are you sure you have 2.72's? Which trans do you have? My truck runs 110kph/68mph @2100-2200rpm with the ZF5 and 355's. Speed is taken with gps and the tires are close to the stock size.

Scott

 

Not being a know-it-all...But you should have 2.73's......

 

Something else I forgot to mention above is that the transmission plays a big part in how good or bad a truck will perform with any particular axle gearing on the highway, and that's mainly because there is a pretty big difference in overdrive ratios between the manuals and automatics. The M5 and ZF manuals have 0.76-0.80 OD ratios while the 4R70w and E4OD have a deeper 0.67-0.70 ratios, and that means the auto trucks are turning 300-500rpm less at 70mph depending on axle gearing.

 

Yeah im pretty sure. I checked the axle code on the door, and it said it was a 2.73. And Im not positive, but I think I have the mazda 5 speed in mine. And my tires are also stock size.

 

Oops. Thanks for the correction.

 

Something wrong there, either your tach is WAY off, your clutch is slipping badly, or your truck does not have the axle gearing it's supposed to. At 65mph in OD you should only be turning about 1700rpm.

 

I had forgotten, my trucks rear end was replaced when it was sideswiped before I owned it. I'll have to put in a tach to know how much it's revving. It dropped out of OD just trying to get up a slight incline on the freeway doing 65.

Rather than start a new thread. I can't find struts on oriellys' website or eBay. I think my driver side is weak, given I get shuddering when hitting a bump, uneven suspension bounce. Can't really feel it in the wheel but the frame.
Loose steering that's mildly dangerous when getting thrown off track by good sized bumps. What steering components wear out most?