change rear ratio

[MII]

my 49 F1 is 3:92.1, and I'm thinking of changing to 3:08.1
the transmission is heavy duty 3 speed on the floor
has any one done that and with good results?
it is an 8BA built by Walt

[JSeery]

Depends on what your objectives are for the truck. Trucks are typically geared lower than a car. To me that would be a very high gear, is it going to be mostly a highway vehicle?

[MII]

mostly highway and around town

[estout81]

I have a '48 F=1 with the same gear ratio. I run 235/75 tires on the rear with no undue strain on the engine. I have run interstate highways to Charlotte motor speedway!

[Fordestes]

Expect to stay in the box,(Aphrase used by truckers who constantly have to shift up and down) I tried it here in flat land oklahoma and it resulted in rotten fuel milege and a lot of shifting, mine was a 3:25. you my get better results , the rear diff is still on the shelf collecting dust. I had to run about 65 + mph to keep her from lugging down, also hard on the engine being in a hard pull at lower speeds. Lots of luck!

[estout81]

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I forgot to say, my fuel mileage is 16-18 depending on how hard I drive it. Also, performance is very good. The engine is 276 ci.

[MII]

thanks estout81 and Fordestes now I am totally confused, I have a 239 over .060
my rpm will b 2000 at 55 mph, I am looking at Speedway for the parts, is that the right place?

[MII]

I forgot to add the tire size is P215/75 R16

[estout81]

What parts are you looking for?

[AnthonyG]

Like estout81 I compensated for a 4.11 rear in my '35 by going with a bigger diameter tires on rear, also wen with radials (love them). If your not concerned with a stock look it works well ( & looks cool ). Mine had 600 16's which I believe were approx 26" went to 235X85-16 approx 30 3/8" & believe reduced the 4.11 by 17% or approx to equivelent 3.50 rear. Runs great at highway speeds now.engine doesn't scream like it did at 60 to 70, just purrs now

[MII]

I am new at this, but I think carrier, gears, shims, I assume the bearings will interchange, but new seals the axles should fit they are 19 spline

[expavr]

Originally Posted by MII

I am new at this, but I think carrier, gears, shims, I assume the bearings will interchange, but new seals the axles should fit they are 19 spline

If you’re looking for some input on parts for your differential I’d recommend you contact Chuck at Chucks Trucks. https://www.chuckstrucksllc.com/ He sold me a set of new gears for the tonner and handed out a lot of free advice on how to remove and set them up.

[estout81]

If there is nothing wrong with your rear end other than the ratio, I'd think long and hard about changing the gears. Unless you have experience at rear axle work you best leave it to a professional. Pricey!

[rotorwrench]

Stuff is available for the Dana 44 with the 19-spline axles. If it's a Dana 41, I don't know. They had a different carrier but it might work on the taller ring gears. It depends on the size of the bolt circle.

[slowforty]

You could also swap in a Ford pick up rear end from the late 60s or 70s

[TJ]

The later 9" Ford rear end from '58 up to '72 will fall right in on your springs. You can buy a good used pickup rear a lot cheaper than changing the gears in your existing rear end. I did this swap for a friend and even used the brakes from the '52 rear end on the 9" rear end.

[MII]

thanks TJ I will check on a different rear

[MII]

I wonder which ratios are available, my tire dia. is 29 3/4

[TJ]

In the 9" there are many different ratios. There's usually a tag on them if nobody removed it. With your tire size and 3 speed trans. I would think something in the 3.50 range would give you a good highway cruising speed.

[rick r]

I would look long and hard at replacing the trans with a t5 5 speed. With a 3.90 rear you will be in the rpm range in 5th on the freeways and 4th will be good up to about 50 mph. You will still have the option of playing with rear gears if you feel it is necessary. Am running 5 speeds behind a flathead and a nailhead. Just my 2 cents worth.

[rotorwrench]

The early 48 & 49 F1 pickups had the 3.78 rear (Dana 41). The Dana 44 had the 3.92. Randy's Ring & Pinion has stuff for Dana 44. These old rear axles aren't all that difficult work on. The only special tooling used in them was the pinion depth measuring set up but that can be worked around with the right measuring equipment. I've even seen those old measuring tool sets on flea-pay. The 3.92 gear set was used in the Mercury cars with R10 electric overdrive and it works well with OD.

[Ol' Ron]

I have a 51 merc with 3.3, new brakes,and drums. $250

[rotorwrench]

The Merc Dana 44 axle only needs some spring pad work to be a bolt in. Ron's sounds like one for a Merc-O-Matic trans. The 9-inch axles are good but they are heavy and have a bit of offset.

[MII]

thank you rotorwrench, does 2000 rpm at 55 mph seem like too much of a load for my 239? what would the correct rpm be at that speed?

[Ol' Ron]

Lov you little airplane, looks faster than our old 47 commonwealth.

[rotorwrench]

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Originally Posted by MII

thank you rotorwrench, does 2000 rpm at 55 mph seem like too much of a load for my 239? what would the correct rpm be at that speed?

I don't know how to equate load into it other than starting out in first gear. To me, it's more about engine sound or noise level since I don't run a tach. My old Mercs will go 70 MPH with the engine running at a decent rpm and lower noise level but that's due to the R10 overdrive. If I was running 70 in 3rd gear, it would be winding a bit too much for my taste. With overdrive, the gas mileage is better too. To more or less equal that in 3rd gear (no overdrive) a person would likely need a 3.54 or lower ratio. This could make it lug a bit off the line in 1st gear if the ratio is too low a number.

[Greg58]

I just installed a overdrive in my 50 today, its a world of a difference. At 60 the engine sound is like it used to at 45. If changing to a overdrive is a option you might want to give it a look.

[MII]

thanks to everyone now to make plans

[blucar]

I would opt for a later Ford 9" out of a '57-66 Ford F100. The common gear ratio for '57-66 is 3.73 which is a good average ratio with 28" tires (235/75R 15). The HD trans you have is most likely geared low so an OD would be a good choice.. If you opt for a high speed differential, you will be in the gears (shifting) all the time with the engine out of it's RPM range.
The Ford F100's of the 50'-60's that had OD transmissions had 3.89 gear ratio's with 3 on the tree trans..
My father had a '53 F-1 with the V8, three spd OD which he bought new. I loved that truck. It ran great in town or on the highway. When we had to pull something, we'd disengage the OD which gave us plenty of pulling power. Dad pulled a 35' house trailer with the truck for years.

[MII]

thanks for the info blucar, but I don't understand overdrive is it in the differential or the transmission ?

[rotorwrench]

They can be mounted to transmissions or in the case of the old Columbia set up, it's mounted in the rear axle like a 2-speed axle. There are torque tube drive types like the Mitchell for the older cars & trucks that have that type of drive.

For the late F1 pickups with open drive, there are several transmission possibilities. The old 49 thru early 51 Mercury cars had a column shift type R10 overdrive transmission available. The Ford version is similar but has the smaller 1-inch 10-spline input shaft. The electric operating solenoid can be a problem on the F1s. The T5 transmissions are available and can be made to fit. There are still some of the Ford/Tremec T170 RTS 4-speed overdrive transmissions as used in 84 to early 87 F150 & Bronco trucks but they are getting harder to find. There are others but these are the most common ones used on open drive flathead powered vehicles like the F1.

[Greg58]

Here's one for a 53.

[Greg58]

I was trying to upload the unit I used but it wouldn't load right.

[Greg58]

Here's the governor side.