1948 merc truck ,flathead 8 ,3 speed on the floor, Rear end has 373 gears I need more highway friendly gears, I can get 354 for the original but that's it Like to keep original if I can, I do have a 9 inch with 308 gears I can use, Will my flathead carry this... this is my rear end now, I think its a dana 41
3.08 is too tall for a Flathead. I've heard of folks going 3.25 with a 9" rear and a Flathead, but it will hate the hills. 3.50 seems about right. Where are you finding 3.54s for the Dana 41?
Ive used the gears and carriers from international scouts in the ford pickup housing. My 66 GMC has a dana 44 with 336 gears. I bet those could be installed in a early ford housing?
Much cheeper and easier to find than a overdrive would be a granny 4 speed. then you could have taller gears. and have as slow first and reverse. My 66 GMC has the tall 336 gears and 16 inch tall rear tires. 250 six engine. however it has the SM 420 granny 4 speed. don't guzzle gas and still can pull my trailers.
Hey John F., seems you're missing some critical decimal points..! What the hell is a 373 gear, looks like part of a part number to me. Mike
The 3.73 is about perfect for it. I'll explain. My F1 is basically the same truck. It has a 302 but everything else is 1950. It has the standard 3.73 rear gear. I also had a Ford Coupe flathead powered, also with the 3.73. 1... While you hear that these are low revving engines. That's true, but they operate in at the upper end of their range. If in good condition they are fine driving highway speed. 2... Flatheads are a low torque, low hp engine compared to later vehicles. They need a good gear for street driving. What you give it on the Hwy, you take away from the street. 3... How fast do you really want to go? Do you really need to go that fast on the top? (Case in point) The F1 at 110 mph... When I was much younger and a lot dumber..... Unlike the flathead, the 302 has a much higher redline. Cammed, about 1000 more rpm. I had never wound third out. 2nd was a blast in the old truck. In third, there was always plenty more. I had done some work to the F1, replaced tie rod ends serviced the steering. Drove it around the block.....she felt tight. Drove like a million dollars. This was about 2AM in rural Alabama. Drove down to the HWY......where there was a 2 mile straight away.....not a car or car lights in sight. So you know what's next. First, Second when I got to high I stayed in it. She pulled straight as a Saturn 5. " like an arrow shot into the sun.. " until ".... she got to the top. When she got there. The peak, the top.....no more, that's where the ride began. The little hood chase at 50-60mph....Well, it's a lot different in the triples! I knew if the driver's front wheel ever drifted over the center line.....it was over. There was just too much room. If she went that far, she ain't coming back. If the passenger front wheel ever dropped off the pavement....that goes without saying. It was all I could do to hold it in the lane. Most of what I was doing was nothing....I was just trying to hold it. My mind is racing. I am in tune with this dancing, shaking machine. I have to be. This is in milliseconds. The Brake...No no Nooooo! My foot was hovering over the pedal. Nope. She's got to settle down first. I don't name my vehicles but that night, the 50 F1's name was Baby. I talked to it. " Baby, I'm sorry.....Settle down.....settle down. I won't do this again." There was more going on than just a worn out old truck going way way too fast. She was light on the tires. I'm not saying it was "lift" but aerodynamics were let's say, doing unpredictable things, at those speeds. F1s look heavy but as vehicles go, they are relatively light. They have roughly the same curb weight of a 62-65 Fairlane and are lighter than a 70 Mustang. I just let her coast out of it. That 3.73 gear brought her back down fairly quick. She slowed down to normal speeds then I got on the brake and made my turn off the Hwy. My reason for sharing.... 100+ MPH far far exceeds the capabilities of the stock design. In my opinion 70 is really really pushing it. The faster you go, the less margin of error. Interstate speed is really pushing it. Things happen sudden on the interstate......semi....big gust of wind....you are already at the top of controlability. With a stockish F1, my opinion is you need to stay well within it's capability and that men's cruising along in the slow lane. The 3.73 will do that fine and still have that seat of the pants punch redlight to redlight.
Sounds like you're looking to do the speed limit without your engine blowing up.... I have a 9" rear out of a 72 F100 I plan on installing later this year. I've been waffling between 3.25 and 3.50 and decided on 3.50's since I don't think I really want to keep running the flathead and will likely switch to something else down the road and 3.50 is a nice, even keel ratio. I'll check back in and let you know if it makes much difference at all.
I know what you mean about "early" aerodynamics. At 80 mph, my steel Deuce highboy roadster with 2" chopped posts and the top up is all I want to handle with NO crosswind. I-10 between San Antonio and California has decent pavement but crosswinds really play Hell on us at 80 mph. FWIW, an 8" rear from a v-8 Maverick or Comet circa '74 give or take a year will handle ANYTHING that flathead might throw at it plus it's lighter than a 9".
Run a 9” in my 40 Coupe. 3.50 gears with a T5 S10 trans. Flathead V8 motor 150ish bhp. Runs so much better than when it had 3.25 gears
Since the truck is pretty much a cruiser have you considered a Ford 8” ??? Much lighter and at least over where I’m at they have them at most all pic a Parts. Some of them even come with posi trac. Sent from my iPhone using The H.A.M.B. mobile app
Personally I would not change entire axles or even gears to go from 3.73 to 3.55. They are so close together the difference would be marginal and to me not worth the work. Have you confirmed that is indeed a 3.73.? In '51 they went to3.89 as standard. Lower ratios were available in that axle so it might be a lower gear especially if someone changed the axle during it"s life. Changing gears in the original 41-44 case is a big deal. It requires special tools namely the spreader. The manual cautions against springing the housing with the spreader. The case has to be spread to remove the gear. This is best left to a pro if you want to change gear sets. 3.08 is just too tall for a flathead in my opinion. What speed limit? 70? 65? 55? There could be other factors as well and I'all post them later.
A V8 Ford should run the speed limit. It's not a Chevrolet. That's not a joke. Let's start at the fan and work back..... Behind the fan is the 8BA/8RT Loadamatic distributor. This distributor is vacuum advance only. There is no mechanical advance. It must be used with a Ford 94 with the "spark valve". They are a matched pair. If this system is not operating correctly, it will not advance properly. As said the carburetor and distributor are a matched pair. Without a proper working advance, the engine runs poorly and is taxed. It may rev fine without a load.....loaded is a different story. Do a compression check. Next is the clutch. The friction surface is relatively small. If the rear main leaks or the transmission has leaked excessively the friction surface could be well oiled. The flywheel surface could be glazed. This may cause the clutch to slip at speed thus higher rpm than normal. These transmissions are noisy. They were when they were new. They leak especially with 70'years of age. They like to leak out of the cross pins. The transmission may need dope. The bearings may be at the end of their useful life. It may be fine but this is something to check. Universal joints may need replacing and can cause undue vibration. The rear axle may need bearings. Look for leakage. Other things..... Dragging brakes. Wheel bearings too tight. Engine not tuned properly. Go over the truck really well and check these things before you do major work. Lastly.... Driver perception..... We are not used to hearing an engine run and a drive train sing at the higher end of it's operating range.
the stamp on the axle tube says 373, I already have a 9 inch in my barn like new but it has 308 gears ,and yes that's to tall. so that's what I got ,like to use the 9 because if I change things up front I got the rear already covered , this is good guy im learning a lot
My '40 Ford has 3.78 gears from factory and the would run 100 mph stock. How much faster do you need to go? My '51 Fords will do the same with the same gears. Dave
That was my experience with my '50 Coupe with the flathead and 3 speed. Now I did not drive that car at 100 but.....no need. It drove and kept up with traffic as good as any car I owned.
There is a multitude of 9" Ford rears. Very few are bolt on for the 48-52 F1. 1957-1972 Ford F100....There were some Dana F100 rears....those are good too. 1957 Ford car There may be some others but those are the right width. The F100 is the correct 5x5.5 bolt pattern and is a direct bolt on. 1973 up Ford truck rears are wider and 31 spline. Those can be used but really need custom modifications (shortening) to the housing and axles. I would not consider an 8inch for a F 1.
Years ago I had a 49 F-1 with a mostly stock flathead and stock Dana 44 (don't know the ratio), I put an overdrive trans from a car in the truck, and it cruised down the freeway very comfortably at hiway speeds.... LynnW
In addition to all the other comments herein, there's the hp loss at the rear to consider also. I don't have the numbers in front of me but I think that the 9" will cost you more hp than the original rear. Most flatheads don't really have any extra hp to give up to the rear end.
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