Change to higher speed differential gears

[67 StylesLide]

My '67 has 3.71 gears which are too low for my taste (and engine rpm). I have the 240 and 3 spd transmission.
I'd like opinions on changing to 3.25 gears.
For instance,, Is my engine too underpowered to support this ratio?
Other input please and thank you.

[ultraranger]

My '69 F100 Ranger has a 240 with a C-4 automatic. It came with a 3.50 rear end ratio.

Going from a 3.70 up to a 3.25 is a pretty good jump. A 240 has a good deal less power than a 300 so, it's probably going to be more noticeable that you won't have as much low end oomph with the higher (lower numerically) 3.25 gears.

I suppose the only way to see if it's satisfactory to you is to swap out 3rd members and try it. If you don't like it, you can always switch back.

You will have to change the driven gear, on the transmission end of the speedometer cable, to make the speedometer read correctly.

[eggman918]

This site might help you "think"
http://www.grimmjeeper.com/gears.html

[Red Mercury]

I have done that exact experiment. My stock 67 F100 has a 240 with a 3 speed manual transmission. It originally had 3.70 gears. In an effort to gain some fuel economy I changed to a 3.00 gear set and then to a 3.25 gear set which is still in it today. I am going back to the 3.70 gears. The 240 just doesn't have have enough power to move the truck properly with higher speed gears. I find that I have to ride the clutch quite a bit to get it rolling from a dead stop and at highway speeds it just doesn't have enough power to pass other vehicles safely--its a real dog. As for fuel economy there was a slight increase with the higher gears--maybe 2-3 MPG. Basically the little engine has to work a lot harder to move that truck on the highway with high speed differential gears. Any 240-3 speed manual bumps that I have seen have 3.70 gears from the factory. I think Ford installed those gears for a reason. I would consider using 3.50 gears--they would drop your RPM's slightly without sucking all of the power out of your 240 and you might see a slight fuel economy improvement.

[67 StylesLide]

Thanks Red Merc. Small world! Yes I figured that 3.25 is too high for the little 6. Yup now I'm sure I'd wear out a clutch quickly.
I do have a 9" with 3.50 ratio but it's in a 4" narrower width. I hate to try to change the gears.
I will live with it for now. At least while I concentrate on lowering / ride quality / making it handle nice.
Perhaps I'll just "aquire" the 3.25 in case I change the engine.

[Red Mercury]

Good plan to "acquire" the 3.25 gears. I think they would be well suited to a 300 or any V8. My father had a 1969 F100 with a 302, C4 automatic with 3.25 gears--all stock as well. It was a wonderful truck and the power train was well matched to the 3.25 gears. Fuel economy was near 20 MPG (Canadian gallon). It was a better set up than my 67 with the 240/3 speed manual and I wish I could have acquired that truck instead of the one I presently have. Unfortunately my father fell on hard times and gave it to an employee for wages that were owed. The employee was happy with this I was glad to see the truck fall into good hands considering the circumstances.

[takehikes]

I have a 68 with 240 and 3 speed and 3.50 gears and I was happy to read this thread as I was considering dropping to a 3.25. Think I'll stay right where I am.
I think the real answer is to put in a 5 speed but I do not wish to hack up the truck at all so I'll stick with the 3 speed on the tree.