rear dif. swap

K

kingskid

Member
wondering what would be the best rear dif. swap for my 47 business coupe original banjo dif. original gears. Would like a good cruising gear.
 
We really need more information. If you are planning on running a flathead and stock transmission, you'll get one answer. If you are planning a change to some super-duper high HP engine, you'll get another. If the latter case, this is probably not the best place to ask this particular question.

Also, driving habits and local terrain make a difference.
 
There is also the matter of, can you do the work yourself or must you pay for it. Swapping out the gears, isn't that complicated, but you just have to know how.. Going to a different brand can be expensive.
Gramps
 
Like others have said, more information would be useful. In general, it's easiest to swap out a complete rear for yours. I don't know what ratios were available '47, but I believe 3.54's was the highest gear Ford offered. 3.78's offer the best of both worlds between 3.54's & 4.11's.

Just swapping out for an aftermarket ring & pinion will cost you approx. $400-500 for the parts. Will be higher if you need to change the pinion bearings.
 
kingskid said:
59AB Engine. Offy Heads, 2 97's, 400 Isky cam. Purchased the car in this config. stock rear & trans. no overdrive.
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So, what gear do you have NOW, and what is wrong with it? If the rear end is original to the car, there will be two numbers stamped on the very bottom of the "BANJO" shaped center section of the rear end, like "11/39" for instance. Clean that spot real well when looking. This would signify a 3.54 ratio. 3.78 and 4.11 ratios were also common. DD
.
 
If you live in a hilly terrain, I doubt if you would want a 3:54 rear gear.
Might be best to stick with 3:78.
 
Better yet a Columbia 2 speed axle would be the best. I almost wouldn’t have one these days without it. Yes they are expensive but they are out there. If you are changing gears or doing the Columbia I would redo the rear end anyway. Most of the time they need it. Rebuilding the Columbia properly and Bullet proofing is a must.
You must know what your doing. Find someone in your area that is schooled at it. If no one in the v8 group near you try the Model A guys. It’s the same principal and those who are schooled have done v8’s as well. I’ve done hundreds of Flathead A &V8 axles. Not brain surgery but there is a process. Having the right tools and knowledge is key. Don’t cheap out either.
 
my buddy had a '46, flatty, with 3:00's or so in a ford 9". unless he got a good head start he would have to shift into 2nd. on most inclines.
 
larrys40 said:
Better yet a Columbia 2 speed axle would be the best. I almost wouldn’t have one these days without it. Yes they are expensive but they are out there. If you are changing gears or doing the Columbia I would redo the rear end anyway. Most of the time they need it. Rebuilding the Columbia properly and Bullet proofing is a must.
You must know what your doing. Find someone in your area that is schooled at it. If no one in the v8 group near you try the Model A guys. It’s the same principal and those who are schooled have done v8’s as well. I’ve done hundreds of Flathead A &V8 axles. Not brain surgery but there is a process. Having the right tools and knowledge is key. Don’t cheap out either.
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The advise that 'Larry' shared with you about a Columbia 2 speed rear end is spot on if you are considering improving the gear ratio and drivability of your car.
My 36, which I have owned since 1952 came with a Columbia. I re-powered the car with a well built 59AB engine in 1954. Changed the trans to a column shift trans and up graded the Columbia to a '47-48, with several suspension improvements in '54-55. My Columbia has 3.78 gears which work great for street racing, the car had no difficulty hitting 100 mph in second OD. Cruising the highway at 70 plus was pure pleasure.
I have not raced the car in years, however, I can't help myself sometimes from not putting the peddle to the metal.:cool:
 
I had a 46 coupe with 3.54s and a loaded flathead. Went uphill with no problems and on flat ground it cruised at 65.
 
The Isky 400 cam is not a lot of fun in traffic, and a lower rear end gear ration will make it even less so, particularly in a heavier car, like your coupe. If you have the 3.78 rear end, maybe best bet is to keep the cam and put in a Mitchell overdrive to get you a more comfortable cruise RPM. That said, if you want to cruise over 55, you would be well advised to put Lincoln/Bendix self energizing brakes on the front.
 
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