I was able to buy what I was told is a '51 Ford tranny with OD. It has the same bellhousing as early Ford truck so I can use the same clutch set up as the one in my '48 Ford panel truck. I also have a Ford 9" out of a pre-'73 Ford F-100. My '48 panel has basically a stock flattie. I was thinking of using the OD transmission with the 9" behind the flattie. Is this a good combination? The person I bought the tranny from thinks using the 9" behind the OD tranny is overdoing it and will not work. What are the thoughts of the drive train experts? Anyone have a set up like this in their '48-52 Ford truck?
Honestly it all kinda depends on you rearend ratio and tire diameter. Thats what makes gearing work. Or not work. Are you highway driving or just scooting around town?
The plus with the 9", is the center sections drop out and can be easily switched if your not happy with the gear ratio.
Sorry, forgot that very important information: 9" ratio is 3.25, 600X16 tires. Mostly around town but I'd like to be able to take it on longer trips on the highway and keep up with traffic. My main concern is that this combo isn't over the top and make for a bad situation.
Bob, you don't have to engage the OD unless it is needed.....I only use 5th gear in my truck on the highway at 60+ mph. Sure is nice to have that extra gear when you want it though.....
Now I can see the advantage of installing the 9" and only using the OD when on the highway. Sounds like it should work out pretty good. It'd be nice to keep up with modern traffic.
you may want to opt for a higher gear set as Ford 's highest was a 3.54, I believe, with a flathead. You'll probably find you have to grab 2nd. gear a lot with a 3.25 especially with those tall tires.
That would make a drive to say Kentucky? quite enjoyable! Does your panel already have column shift or would you just do an aftermarket floor shifter to use the side shift od trans? Later Josh
A 3.25:1 is a really tall gear to run an over drive, and those tires will make it even taller in a final drive ratio. If you were running Bonneville I'd say go for it, but I don't think your stock flatty is going to have enough torque to run in OD even at highway speeds on glat ground. Sorry man, even if it DOES have the grunt to pull it along at 70 mph you'll be so low in the rpm range I don't think you'll be moving enough coolant to keep it cool. Consider this: I have a '50 Ford Tudor. It was a V8 car, manual non-OD trans. This car came with a 3.89:1 ring and pinion. The same car with an over drive would have come with a 4.11:1 r&p. These cars would hit 100 mph if ya gave them time, but even at that they wouldn't pull a steep grade in OD. (I found an OD for mine and need to put it in.) Now cut that final ratio by 20% (your 3.25:1). You'll be feathering the clutch every time you start, PLUS you want an OD on top? I think you will be sorely disappointed in the end result. Either run the OD with a shorter gear or run the 9" as is, not both. In my case I'm hoping I can run (and sustain) 75-80 on the flats without running my mildly built 8BA too hard. Any slower and I'll get run over on these roads!
X2 for me. Since you have a diff that can provide plenty of ratio choices better hand down lower at 3:54 or closer to 4:11 since you have the luxury of an O/D to handle the top end. If you balance things out right you should end up with the best of both worlds.
The pics show a 49-51 Merc overdrive tranny. For 1951 Ford actually used this style for just part of the model year....they changed to the 4 bolt gearbox midway thru the model year.
If you run 3.25 with that o/d you are gonna be disappointed. With an o/d trans you will want 3.70 gears with that tire. You'll get good acceleration and still cut highway revs substantially.
The stock '51 Merc rear for OD was 4.27. I think your 3.25 with the 16" tires is going to be disappointing for accelleration but a low RPM cruiser on the interstate.
There is a 3.89 gear set available for a nine inch. I have used that ratio with a combination similar to yours, it worked out great. A 3.25 may make you unhappy.
I agree with the gearing comments but just a quick qun : why do you want to run a 9" with a stock flathead ??? Lhey are large, heavy, add unsprung weight, suck power from your FH which you need to turn the wheels - esp with a stock engine. An 8" is plenty strong for a FH, has plenty of ratios available, the centres/axles drop out like a 9" and they suck less power and weigh less. Just a thought? I run a Borg Warner with 3.7s behind a blown flathead without an issue. Lighter, less unsprung weight, gears are available and imo way more efficient than a 9" in this particular application. Just food for thought.... Rat
What rear end is in the truck now? It's likely much lower than the 9", and more suitable for the OD. That flathead won't power an OD with that tall ratio, it will be somewhere around 2.2 in OD. As stated above, that's Bonneville ratios!
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