Check this out. 1978 Ford F 150 | Gateway Classic Cars | 279-PHY I bet this would make for a decent fuel mileage cruiser. Is overdrive factory? Must have been pretty rare. Wonder if its just a car trans.

 

Why bother. A 2.70 rear end with a non synchronized first gear isn't that tough to operate.

 

RUG SR-OD Single Rail 4 Speed Overdrive: 1978/83 F100/150 2WD 300/302 & E100/250 300/302/351W / 1977/80 Granada 200/250/302; 1978 Mustang II 302; 1979/83 Mustang/Capri/Fairmont/Zephyr 200/302.

FoMoCo installed this trans in these cars, trucks and vans in an effort to improve MPG after the first Arab Oil Embargo (1973/74) occurred. Another Arab Oil Embargo occurred in 1979.

 

Thats cool. Any idea on ratio?

 

 

RTS TS-OD Top Shift 4 Speed Overdrive: 1984/89 F150 2WD/4WD & Bronco 300/302/351W

The last year for a 3 speed manual trans with overdrive (Warner T-85N w/a column shift) was 1971 and it was only available in F100's.

 

I seen a old brochure online somewhere where ford claim over 20mpg with a dentside. Think it was like 23 or 24mpg? Crazy mileage for a truck. The 300 and overdrive must have been what they was using.

 

Most of the mileage claims Ford made in the 70s and 80s were grossly unrealistic.
Also, Ford did refer to the 4 speed overdrives as 3+OD so technically it isn;t wrong to call them a 3 speed with overdrive if Ford did.

 

I think they hit a wall when the smog regulations started tightening, with the existing tech at the time. "Lean burn" strategies for highway cruise modes were showing promise in terms of mileage but, raised NOX (responsible for the brown haze seen over cities) emissions significantly. So engineers detuned the big V8 - lowered compression ratios, buggered with camshafts and other strategies that actually degraded engine efficiency. You can tune the old cars with V8 to get 20 to 25 mpg hwy no problem if the gearing is right, but they won't pass smog and any catalyst would be nuked in short order.

Also back then the gasoline was probably good for an extra mpg or two, especially the stuff used for testing. No corn squeezins or "oxygenates".

 

I owned one of those 4spd overdrives in a Granada with a 302. Really nice 2 door, light blue with white vinyl top, Crager mags and W/L tires.

The transmission has the typical 4spd shift pattern, but the first three gear ratios are exactly like a 3 speed. The 4th overdrive gear has a ratio that is very close to third gear. A very disappointing transmission for any fun or for that real 4 speed experience.

 

I had an SROD in my old '82 Mustang GT. Broke it. I replaced it with a T5 5 speed.

The problem with the SROD/3+ODs and the NP-435/T-19 4-speeds is the same problem 3-speeds have: That horrendous jump from 2nd to 3rd gear. 3-speeds usually have a good 1st and 2nd gear, but the jump to direct is too much. The NP-435 and T-19 just move the jump to between 3rd and 4th, but they give you that granny gear for 1st which enables you to get away with something like a 2.70:1 gear. The T5 in my Stang eliminated the huge jump, but I liked the 2nd gear pull from the old SROD better. They really should've not bothered with a 1:1/direct gear in the SRODs, and made 3rd gear something less than 1:1, with the only large jump between 3rd and 4th/OD.

With the SRODs you want at least a 3.25-3.50:1 without the granny 1st gear, but the overdrive would probably net you a lower highway RPM than the 2.70:1 rearend with a 1:1/direct top gear.

My understanding is that the truck 5-speeds like the M5OD still incorporate that damned wide jump somewhere in the 1st-4th ranges.

Honestly, I'd like to stick a T-5 in my rig. I done some math and seen that I could run the T5 and a 4.11:1 gear, and still have a lower highway RPM! The nice reasonably rationed 1st-4th ratios would really benefit my truck's driveability, allowing it to accelerate quicker and way more consistently. Then I could get rid of my 2.70 or whatever's back there, (it has play in it anyway...) and go with something better like a 3.50-3.70:1. My 240 engine would like that...

 

My dad ordered an '80 E-150 Super Van (the extra long one) with a 302 and this manual OD tranny. For a big van, it actually did pretty good at 16 mpg. Several years later, they had to replace the engine, and stepped it up to a 351. Seems I recall it was the Windsor version. Had a noticeable amount of increased power, and still got 16 mpg. My mom hated the stiff clutch in this van.

Later, in 1985, they ordered a new van (same size)... this one having a 351-4 bbl and 3 speed automatic. Best it ever got was 13 mpg, and usually just barely got that. But for a van, it hauled ***!

So having the manual OD over an automatic could save you a few MPG's. If that big van could get 16, I'm sure a short bed Dent with a 6 cyl and the OD could easily get 20.

 

I'll bet my truck will pull down 20 MPGs at 45-55, maaaybe 60 MPH. I've got what I believe to be a 240, with a 3-speed manual, and what I believe to be 2.70-or-so gears. It sucks taking off from a stop on certain grades, so I'd like to change at least my rearend gear ratio.
I think that my rearend came from a 4-speed truck - plus the cab that was on it when I got it was a 4-speed/4WD cab, with a 4-speed transmission cover with its shifter hole welded shut...

 

240 I-6 cancelled at the end of the 1974 model run. No 4WD truck came w/a 2.70 ratio.

 

No 4WD anywhere near my truck, but I think there are 4-speed parts on it - except for the transmission. I think my transmission cover and rearend came from a 4-speed truck. And I used a mirror and saw my head's number, and it's a 240 head. But I doubt that it's sitting on a 300 short block.