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EFV-8 Club Forum / General Ford Discussion / "40 Ford rear end

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Posted By Discussion Topic: "40 Ford rear end     '40Tudor 06-02-2014 @ 3:57 PM reply profile send p.m. Member Posts: 8 Joined: Jan 2013 Can anyone tell mw what gear ratio is most likely found in the '40 ford passenger cars, and is there a way to tell if that is in fact the rear end in a particular car? Thanks. transbytip 06-02-2014 @ 4:30 PM reply profile send p.m. Member Posts: 19 Joined: Dec 2011 Most 40s were 3.78 on the bottom rib of r.e. should be stamped into rib two sets of no,s divide the small no.into big no. will give you your ratio ex. 3.78 is 9-34 with reguards Cliff. Tipton '40Tudor 06-09-2014 @ 7:53 AM reply profile send p.m. Member Posts: 8 Joined: Jan 2013 Thank you for your help. I purchases a mostly (aprox. 95% restored '40 Ford Tudor. The car has a 47 Mercury block with edelbrock heads, dual strombergs and a cam. That much I know. I do not know what else may have been done to modify the engine but assume more mods were performed during the rebuild. The previous owner hass passed away and I am unable to find out where and by whom the engine wok was done. My dilemma is that the engine seems to top out around 3700 rpm on the tac and I'm going only 50 mph. I need to get up to 60 to be able to drive on the highway but I'm reluctant to push it that far since the engine seems to be screaming. Any thoughts? JM 06-09-2014 @ 9:31 AM reply profile send p.m. Senior Posts: 822 Joined: Oct 2009 I am not trying to be critical when I say this, but this car sounds like a resto rod or hotrod, rather than what we would call a restored car. That's not necessarily a bad thing.....just saying. If your engine is at 4k rpm at the speed you mention, I don't think you have 3.78:1 gears, maybe 4.11:1. It would be better to have engine rpm at about 2500 at the highway speeds you would like to travel. John This message was edited by JM on 6-9-14 @ 7:28 PM CharlieStephens 06-09-2014 @ 9:40 AM reply profile send p.m. Senior Posts: 888 Joined: Oct 2009 Mark the crank pulley and mark the tires. Push the car forward and see how many times the tires rotate for one revolution of the crank in high gear. With the engine modifications my guess would be that someone may have put a lower ratio in the rear end. If there is a number on the rear end it was probably not updated when the rear end was changed. If your speedometer and odometer are accurate you can check the number on the speedometer drive gear ((the turtle on the front end of the torque tube where the speedometer cable enters) to get the rear end ratio. You might want to actually count the teeth on the speedometer drive gear in case someone replaced the gear within the housing. Post what you find and what tires you are running and someone will tell you the ratio. Charlie Stephens This message was edited by CharlieStephens on 6-9-14 @ 9:43 AM 4dFordSC 06-09-2014 @ 1:11 PM reply profile send p.m. Member Posts: 266 Joined: Oct 2009 Like JM says, sounds like a previous owner has installed a lower ratio rear end, e.g., 4.11. If so, your options are to switch a higher ratio rear end, (e.g., 3.78 or 3.54), or install an overdrive unit. The original Ford OD back in the day was the Columbia Two-Speed Axle. They can still be found, but are a bit pricey in good condition with all the controls. Another alternative is the modern-day Mitch*ll Model 1000 Overdrive kit (Mitch*ll Manufacturing, 1-800-859-2088, mitchmanfc@frontiernet.net). WARNING: Once you've driven a flathead with overdrive, you'll never want to go back:-) (* = e in Mitch*ll) '40Tudor 06-23-2014 @ 1:57 PM reply profile send p.m. Member Posts: 8 Joined: Jan 2013 II guess you're right although I am unable to find a definition for retro rod. Most of what I see on the internet are car that have stock appearance on the outside with innards that are usually modern engines and drive trains. The dealer from whom I purchased the car bought from the previous owners widow so I'm in the dark about a lot of things although I was told that the drive train, clutch, transmission and rear end were stock. So, if you have a definition that includes my car please let me know. Thanks for your help.. supereal 06-23-2014 @ 3:36 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 The usual term is "Resto-rod", indicating a car that appears to be stock, but has modified engine and drive train. It is usually difficult to determine what is stock, and what was replaced. If you are hitting the 3700 rpm mark at 50 mph, that is a 50% increase from the expected amount with a 3:78 rear. I'd be sure that your tach is accurate. At 3,700 rpm, your engine is in danger of flying apart. The Ford flathead reaches the "sweet spot", where horsepower and torque curves meet. With 600x16 wheels and tires, that rpm is usually reached st about 50 mph. My '47 has a 3:78 rear, and with my 33% overdrice, I can run at highway speeds of 65-70 mph. As the others have suggested, find out what rear end gearing you actually have. Ford made gears of 4:55, but that still wouldn't explain 3,700 rpm at 50 mph. My bet is that the tach isn't correct. BrianCT 06-25-2014 @ 6:37 PM reply profile send p.m. Member Posts: 95 Joined: Oct 2009 Sounds like the tach is switched to 6 cylinder mode. 3700 -1200 = 2500 which is in the ballpark..

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