Trying to hunt for that magic spot between speed and RPM of the engine and the OD on the highway. Seems the Overdrive unit hums more at 70 but the engine (312 Y block) is still lowish revs. First time with the 3 speed overdrive so im hoping to learn a bit.
You need to know your rear axle ratio, tire diameter and the % overdrive. There are many online calculators that will give you rpm and speed based upon that info. Ideally about 2000-2200 rpm makes a good cruising rpm. Sent from my iPhone using The H.A.M.B. mobile app
The key to a successful early OD install is the correct rear axle ratio. Ford used 3.89 or 4.10 rear gears typically, with the 70% OD that translates into either a 2.72 or 2.87 final drive ratio in OD. This gives a great balance between performance and economy. Taller axle ratios give you a too-tall final ratio that the Y-block will have difficulty pulling. Also remember that if OD is engaged (OD cable pushed in), the car will coast away in any forward gear when parked. You have to use the parking brake, shift into reverse, or manually disengage the OD to prevent that. Probably the best 'cruising' manual transmission ever built. Just don't beat on it...
Got rid of my 'hum' in OD by adjusting the drive line/rear end inclination after the transmission change. Made a BIG difference....remember, the engine is going slower but the driveline is spinning as fast as it would be at 70 with a 3 speed non OD in 3rd..... you don't have the engine noise to cancel the 'hum'
Along with the above items, it would be nice to know what car it's in. 312's from the factory came with the T-85 R-11 trans. 292's and down typically the T-86 R-10. There's a big difference in what they'll handle. Wagons and police cars used the Dana rear end until the 9" came out in 57 and the ratios and changing them are different. If it's in a factory car the data plate will tell you what was original. Not that a lot hasn't been swapped around over the years. Mummert's site will give you some info on casting numbers etc. to see what's really there. http://www.ford-y-block.com/ Properly matched those old o/do's are a great combination.
Mine was a little different than your car, mine was a 1960 Van with a 200 cubic inch six , T-86 R-10 and 4:11 rear gears with 14 inch radial tires ( do remember how tall). That was the perfect combo for that vehicle. Excellent cruise at 75 plus and no noise. Bones
I had the T-86 R-10 in my '56 Ford convert, 292 'warmed-over'... Chevy guys would ask me to 'roll start', (25 MPH) and they'd shift to 2nd, I'd pretend to also...but I'd actually push in the overdrive lever, let off, and shift into low gear/overdrive. We'd get to the 'start' line, I'd kick down on the accelerator lever and hit 'passing gear', 'low gear natural. 292 revved quite high, easy 6,000 + RPM. 65 in low gear, very quickly. 95 in 2nd, Chevy in rearview mirror was a familiar sight. Rear end 4.11, rear tires 8.20 X 15. Howard M-8 cam, Isky springs, matched ports. Teapot carb...
In my avatar picture I'm running one in my 29 Roadster. 354 in 1957 Pontiac motor Ford 3-speed Overdrive with a 9in Outback with 4:11 gears with a posi. Running 750 - 16 tires I can cruise at 70 at 22- 2300 RPM
I am running one in my '61 Ford with 223 a hopped-up inliner 6. Love it. Far easier to install than a T5, and much more interesting to drive.
Had one years ago in a 49 F-1 behind a stockish 239 flathead with (I think) 411 gears.... Was a very good hiway cruiser.... LynnW
The Jalopy Journal
