Hey guys, Just picked up a '39 Deluxe tudor sedan with original trans, 3.78 rearend, and '47 Flathead. I really want to keep the flathead and I am considering keeping the 3spd trans as well as long as I can drive the thing at a reasonable speed. Rear tire will most likely end up a 7.00, possibly a 7.50. Will I be able to cruise this thing 60-70 mph comfortably? I read some limited info here that with that gear and tire size it should be just right. Thanks Nick
I had a '32 pickup with the same combo. It felt more "natural" at 60 than 70. A 3;54 gear and you would probably like it a lot more. Tim
Tim is correct, but with a 7.50 rear tire at 65 mph, your engine will be right at 2800 rpm. Not too bad at all. 3.54 would be a bit better, tho
Bear in mind that this car was built when the national speed limit was 50 mph, and most roads were dirt. It was not intended to be a freeway flyer nor a on a dime stopper. That's why we HotRod them.
With 3.78. Gears and 750x16 tyres you should pull 2677rpm at 60mph With 3.54 gears and 750x16 tyres you should pull 2507 rpm at 60 mph Formula desired speed (60mph)x rear end ratio(3.78) x366 (a constant) divided by tyre height (750 x16 =31") =2677 rpm.
That's what I was thinking. My 38 (mechanical brakes) will run 60+ but you better have a clear 40 acres to stop it.
I have a '51 with a stock drivetrain (no overdrive) with 3.55 gears. I drove it from the twin cities to Chicago for a car show about 20 years ago. I was in a hurry to get home, so I took the interstate back and had no problem keeping up with traffic. I agree with the guys recommending 3.54's.
Mitchell Manufacturing makes a bolt in unit that gets high marks from users: 1-800-859-2088. Another option is a Columbia Two-Speed Axle from back in the day. They're still out there, but a little pricey, and finding all the controls can be a challenge. Mine with 3.78 rear end will happily cruise all day at 70+.
Wasn't there a thread on Ford Barn about grafting a Volvo OD unit in to a Model A torque tube? Would something like this work for a V8?
If you plan on adding an overdrive you could also consider a T-5. My 37 is running an 8BA with the original 3 speed and highway gears. Its happy all day at 65 mph. Ran a 1000 mile trip last year in two days. Why would you need more speed for the highway in an old ford?
Thanks for the replies guys. I just want to be able to cruise comfortably at highway speeds when needed, without beating the engine. I have considered the t5 conversion and the overdrive is a possibility. The car is quite low and I would be a bit concerned about clearance for the overdrive though. Too be honest if she'll run 65 or so as is (which is sounds like it will) I prefer not to pull the drivetrain apart.
I've been driving a '32 tudor with a flathead and '39 trans for eight years now. It has 3.78 rear gears and 7.00x16 rear tires. This engine really purrs at 2600 RPM, but it will cruise down the road just fine at 2700-2800 to keep up with interstate traffic. I did buy a 3.54 gear set a couple years ago that I will put in some day. It seems to have enough low end torque that I don't think it will suffer around town when I put the higher gears in.
My '48 has always had 3.78 and the standard 600-16's. In college, I put on lots of miles covering my known universe (New Orleans to Vt-Canada border area) and documented the car's cruising zone with stacks of 75-85 MPH speeding tickets (Outta the car, long hair!!) long before the 55 limit days. Cruising in the '60's was not a strain on the combo. Once, a cop about to fill in my ticket asked "Will this thing GO that fast?" I proudly replied that it could touch 100, but that wasn't the right answer apparently... Speedo was quite accurate at highway speeds, according to officer radar and his many friends, but I doubt the 100 area was accurate...
Our 51 Merc runs a flattie and a stock 3 speed. Swapped in a 62 Econline rear with its stock gear I think the gear is in the high 2's. It will run 75mph all day long and pull 14 inches of vacumm doing it Ave mpg will be about 16-17mpg with 2 Holley 94's running syncronized linkage.