1939 ford gear ratio 3.78 or 3.54

[bluesman]

Hey guys,listen I need some advise...I have stock 221 39 ford 2-door sedan.The gear ratio i think is 3.78 with 6.50x16 tires!Speeds between 55-60 mph the motor is really turning some rpms how much I dont know? I dont have a tach.The car running at 60mph is about top speed on the highway.My question is would 3.54 be a great improvment for highway speeds? Where is a good place to buy good quality rearend parts, ring and pinion seals,bearings ect....would like to get some of yall thoughts on this matter.......Thanks Randy

[Tim]

3:54 and 7:50-16's will/should give you 2000 RPM at about 65-68 MPH. At least that's what it does in my A. It's happy like that and that's fast enough for cruising.


Tim

[41ford1]

Get or borrow a tach. Then findout what the revs are at 60. I suspect you are running 4.11:1s by your description. At 60 you will see about 3200RPM. 3.78:1 will give about 2900RPM. 3.54:1 about 2730RPM. Those numbers assume a 29" diam tire.

Clean off the bottom of the differential housing. The gear teeth counts were stamped near the pinion.

[bluesman]

Originally Posted by 41ford1

Get or borrow a tach. Then findout what the revs are at 60. I suspect you are running 4.11:1s by your description. At 60 you will see about 3200RPM. 3.78:1 will give about 2900RPM. 3.54:1 about 2730RPM. Those numbers assume a 29" diam tire.

Clean off the bottom of the differential housing. The gear teeth counts were stamped near the pinion.

Yeah your right 2900 sound about right! I will check the housing to be for sure. So it sounds like from 3.78 to 3.54 should drop about 2000 rpm not too bad..So that should put me about 68-70mph?

[JM 35 Sedan]

You can't always go by the numbers on the bottom of the banjo housing. In that cars 72 years someone could have changed the rear gears and not changed the numbers. It does sound like you have 4:11 gears now. 3.54's will make that '39 and it's engine happy when driving at 55-65 or higher. Speedway has a good price on gear sets. Last time I looked they were selling for about $350.00. Joblot had a package deal/kit for rebuilding a Ford V8 rear. It had all the seals, bearings, races, and maybe the gaskets that are required to rebuild the rear.

[Walt Dupont--Me.]

Sponsored Links (Register now to hide all advertisements)

With a 221 stock engine, if you live in hilly country, you'll always gearing down on hills with 3:54, but if you do alot of turnpike cruising 3:54 is the way to go. Walt

[41ford1]

I guess the question is: Are 3.78s really that hard on the engine? I've ridden in and driven a couple of 39 & 40 221s with that ratio. They seem quite happy at 60 to 65MPH. Give some thought to what Walt says. You may sacrifice all around driveability by going to a taller ratio.

[Planojc]

Speedway has the gears. My 35 with 3.54 and a 59ab works great, even in hill country.

[Marv]

Speedway even has 3:25 gears if you would want them. All of their gears for the old Fords are $350. Marv

[blucar]

The 3.54 gearing will work well with a stock 85 hp 221 CID engine for average city/hiway driving with a stock 600x16 (29") tires. As you increase the tire size you will over gear the car causing it to fall flat on it's face from a stop and/or hilly areas.
If you are running the stock fan, by removing the fan blade from the generator you will find that most of the noise is caused by the fan. Of course it is not practical to run without a fan in traffic and/or summer driving.
In the days gone bye, the early V8 Fords were called "Screaming Eights" because of the fan noise.... I think that is where the Germans in WWII got the idea to scare people with the screaming sound of their dive bombers.
An electric fan is a cheap fix to reduce the engine noise.
Of course the best solution to the gearing problems is to install an over-drive in the car... The cost per mile would be high, but then, if you take into consideration the cost to re-gear a differential, which is only a "Band-Aid" to solve the problem, the over-drive becomes more attractive.
Several years ago I calculated the cost per mile to install a $3,000. OD. It figured out that I would have to drive the vehicle 60k miles to break even... From that point of view the whole idea did not make much sense.
However, I would venture the guess that an OD equipped vehicle would sell faster and at a much higher price, which would allow a person to recoup some of the expense.

[bluesman]

Originally Posted by JM 35 Sedan

You can't always go by the numbers on the bottom of the banjo housing. In that cars 72 years someone could have changed the rear gears and not changed the numbers. It does sound like you have 4:11 gears now. 3.54's will make that '39 and it's engine happy when driving at 55-65 or higher. Speedway has a good price on gear sets. Last time I looked they were selling for about $350.00. Joblot had a package deal/kit for rebuilding a Ford V8 rear. It had all the seals, bearings, races, and maybe the gaskets that are required to rebuild the rear.

Thanks John

[bluesman]

Originally Posted by blucar

The 3.54 gearing will work well with a stock 85 hp 221 CID engine for average city/hiway driving with a stock 600x16 (29") tires. As you increase the tire size you will over gear the car causing it to fall flat on it's face from a stop and/or hilly areas.
If you are running the stock fan, by removing the fan blade from the generator you will find that most of the noise is caused by the fan. Of course it is not practical to run without a fan in traffic and/or summer driving.
In the days gone bye, the early V8 Fords were called "Screaming Eights" because of the fan noise.... I think that is where the Germans in WWII got the idea to scare people with the screaming sound of their dive bombers.
An electric fan is a cheap fix to reduce the engine noise.
Of course the best solution to the gearing problems is to install an over-drive in the car... The cost per mile would be high, but then, if you take into consideration the cost to re-gear a differential, which is only a "Band-Aid" to solve the problem, the over-drive becomes more attractive.
Several years ago I calculated the cost per mile to install a $3,000. OD. It figured out that I would have to drive the vehicle 60k miles to break even... From that point of view the whole idea did not make much sense.
However, I would venture the guess that an OD equipped vehicle would sell faster and at a much higher price, which would allow a person to recoup some of the expense.

Good point

[bluesman]

Well guys thanks for all your posts. l checked my housing! looks like have 934 stamped on it.
Would this be 411 gears?

[Kens 36]

That would indicate 3.78 (34 divided by 9).

Ken

[fordy_nine]

[Hey guys,listen I need some advise...I have stock 221 39 ford 2-door sedan.The gear ratio i think is 3.78 with 6.50x16 tires!Speeds between 55-60 mph the motor is really turning some rpms ]

If you have 6.50X16 tires, your actual speed is higher than indicated - use a GPS to get accurate speed reasding. You probably don't need to make any changes except to the fan..........Bob L

[HOTROD_WILLIE]

I have 3.54 gear that I am interesting in selling if there is interest please email me.

[Ross in East Texas]

I have owned my '39 since I was in college in 1965. I drove it weekly on the Interstate at 70+ MPH for 2 years. It has the stock 3.78 gears and never complained. I normally got 15 MPG and it took 5 gallons to get take me the 150 miles home. I knew that the car was old but that never kept me from running it. As far as top end, with the original 3 ring cast iron pistons it would top out at 95 MPH indicated on Henry's speedometer. After I overhauled it and put in 4 ring aluminum pistons, I never could get over 90 MPH out of her.
My advise, leave the 3.78 gears in and enjoy your car, I do not believe that you will ever have any problems even at Interstate speeds if you have a good solid engine.

[Ernie]

I have 39 ford 221 that has been turn into a strocker runs very well,But the rear end is low I have 750x16 on rear at 70 mph i am doing 3000rpm need to bring the rpm down, what should i do.
thanks
Ernie

[flatford8]

If you go to www.thirdgen.org/calculations there is several formulas for figuring your rpm-trans ratio-rear end ratio-tire size-mph. You need to know some of your numbers and it calculates the rest. Tire radius is from center to ground so your air pressure should be right. It's a brand X website but I just use the formulas. Happy Motoring!!!

[flatford8]

But you should still listen to Walt.....We all have to !!!!!