1948 ford pick up

[tomrobson]

I have the above 48 pick up it has a 4speed trans . The gas milage is bad. Im trying to figure out how to reduce the RPM.In looking at manuals I see the std 3speed trans is supposed to have a 3.73 rear end. The question is mine being a 4speed does this change therear end and make this truck an F2. the rear end does have some numbers on it they are a pat #1868618 and on the other side 18423 can any one out there help me identify this rear end ? And perhaps suggest how I can chang something to reduce the RPM? Thank You

[Bob C]

The F1 is a 1/2 ton and the F2 is a 3/4 ton the trans has nothing to do with it. I think the easiest swap
would be a 49-50 Mercury overdrive transmission. If you have an F1 you can also bolt in a later Ford
P/U rear axle.

Bob

[TJ]

There is usually a plate on the inside of the glove box door that will give you the rear end ratio.

[GreenMonster48]

Swapping in a 9" rear from a 57-72 Ford F100 is usually the preferred first step as it is more or less a bolt in, others have swapped in an S10 five speed transmission, some have done both. To my knowledge, the only two rear end gear options in 48 was 3.91 or 4.27 for the F-1s.

[Barry-ct]

There are aftermarket 3.73 ring and pinions, but they were not stock in a F-1, The 4 speed crash box tranny you have was an option. The measiest way is to swap the rear as suggested above. If you do the tranny swap, you'll have to swap driveshafts, tranny, and possibly the crossmember. I vote for the rear swap. Remember, these trucks were not built for speed, but to work.

[Mountaindoc]

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Yes, 3.73's were indeed stock in the Dana 41's that were in the 48-50 F-1's. My 49 F-1 has a Dana 41 with a 3.73. Climb under your truck and see if the metal tag is still attached to one of the cover bolts on the back. It will probably be at about the 4:00 position. If it's a 3.73, it should say something like "W 41/11".

Edit: The confusion about the 3.73's in the 48-50 often comes from a chart in the red shop manual. On page 366, it only lists a 3.92 and 4.27 as the two options for an F-1. That's right IF you're talking about a 1951-52 F-1, but page 166 shows the correct 3.73 and 4.27 options for the 48-51's.

[GreenMonster48]

Interesting, Doc. I'll have to re-check my shop manual.

[tomrobson]

thank you gentleman for your info. I guess I will start looking for a newer resr end.

[Bob C]

I would still think you would want to replace the stump pulling 4 speed crash box,
would make driving more enjoyable.

Bob

[Mountaindoc]

Originally Posted by Bob C

I would still think you would want to replace the stump pulling 4 speed crash box,
would make driving more enjoyable.

Bob

Agreed. With my LD 3-speed and 3.73 rear end, I can run about 50-55 mph before it really starts feeling unstable. If you go for a 9 inch rear, I have a good friend over on FTE who would definitely promote about a 3.50. He just made the swap and seems to be happy with it. As far as the gas mileage concern in the OP, I'm gonna think the improvement would be minimal at best. I wouldn't do a swap personally aimed at improving MPG in this situation, but rather to increase comfort and driveability.