2 speed rear axle

94f350

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So I just wanted to know if it was possible (feasible) to do a 2 speed rear axle swap in an obs f350 with a zf5 to make it a 10 speed. I had the idea the other day and I wanted to know if anyone has any experience with anything like that.
 

Nero

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Anything is possible with enough welding. But why?
 

94f350

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Anything is possible with enough welding. But why?
Well I just thought it would help a lot with towing as 7.3s are a little slow in that aspect and I know there are remedies for that but I was just wondering if anyone had done it before
 

chillman88

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I certainly wouldn't expect anything to be faster by adding a two speed rear axle. From what I've heard most of them the high speed is still significantly lower than the stock gearing in one of these trucks. Might end up topping out at 45mph LOL

What you want is an overdrive/underdrive unit. I'd like one as well but they're not cheap to find a good one, and it's a bunch of work to put in. That would allow you to keep your rear ratio and run it in underdrive when you need more gearing, or run in overdrive when running around empty. I don't know if they're synchronized so I don't know if you could split your gears or not under normal driving.
 

DrCharles

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I put a Spicer 5831B brownie in my '65 F-350 (caution: not an IDI) ;) because it was the only suitable one I found at a reasonable price. Trans is an NP435 with 6.67, 3.34, 1.66 and direct. The brownie has 2.35, direct, 0.85 gears and the rear is the stock 4.88 dually with 235/85-16 tires.

In 4th direct, 60 mph is 3000 rpm. With the OD engaged that drops to about 2500 which is much more doable for highway use. The gear splits aren't even but you learn them pretty quick. There are other 5831 gearsets - the 0.73 OD would be desirable but it doesn't have the super-low underdrive.

The 2.35 UD is primarily useful when backing up, or going slow on rough ground. Reverse is the lowest NP435 gear at a deep 8.2, so you can really crawl at an idle with the clutch engaged in UD.

That particular auxiliary trans is not synchronized, but it isn't hard to shift once you know what the revs should be, and double-clutch the downshifts. With a really heavy load in the flatbed, it's more work driving with both sticks, but the huge splits in the NP435 (2:1 except for 3rd-4th) make it hard to get up to speed on any kind of rolling road without splitting some gears.

Another possibility is the old Advance Adapters "Ranger Two-Speed" (either OD or UD but not both). But that goes between the bellhousing and the transmission, and moves everything back seven inches. Not sure if there is one to fit an IDI or not.

Most end up with a Gear Vendors behind the trans, but you're looking at $3K or more...
 
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IDIBRONCO

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I certainly wouldn't expect anything to be faster by adding a two speed rear axle. From what I've heard most of them the high speed is still significantly lower than the stock gearing in one of these trucks. Might end up topping out at 45mph
To add a little bit more here, not only that, now you're talking about tire sizes and wheel styles too. I doubt very much that your could get any rims that looked somewhat close to the front ones if you used a two speed rear end. Not to mention the differences in tire sizes. All two speeds that I've seen used larger (20"+) rims. I'm sure that there were some that used smaller diameter rims than that, I just don't remember seeing them. then you'd have the "fun" of attaching your driveshaft to the rear end. Light duty trucks and medium/heavy duty trucks (that had two speeds in them) use WAY different sized U joints. I'm really afraid that this would be trying to reinvent the wheel, and a not very successful attempt at that.
On the other hand though...the guy who used to be my shop foreman and then manager at the diesel shop I worked at was in the Navy during the end of the Vietnam war. He finished out his enlistment in San Diego. He said that the State Troopers (I think) had two speed rear ends in their cars and they could out run anyone on the highways (at that time). So maybe there is something out there that's custom made and would fit in our truck somewhat easily. Of course that would lead to one of my most hated words: expensive. That would probably be a deal breaker for most of us.
It also impresses bystanders when you upshift while going backwards LOL
On this note, my dad told me that he used to gave a 1952 Buick of some kind with an automatic transmission. That was a real strong runner of a car. He swore that it had a "passing gear" in reverse. That never did and still doesn't make any sense to me. Just the reasoning and mechanics of it just don't seem even possible. I think that it's more than likely that his transmission was slipping in reverse and would grab solidly when he used a lot of input on the gas pedal. Since he died in 2006 and probably had that car quite a while before I was born, there's no way to confirm those wild claims.
 

Old Goat

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I have driven a lot of trucks with a 2 spd rear end. They are great as you can split the gears. Don`t have to split each gear, all depends on the load.
First truck I drove was a 67 F600 4-spd with the 330 V8 Industrial engine, with electric 2-spd.

last one when I retired was a 95 International 4900 466 DT, and 2 spd air shift.
This truck had the 22inch 24.5 tubeless tires or something like that, with the 10 hole lug nuts.

I too always thought to have one for a 3/4 or 1 ton would be nifty.
But no way you could adapt those big differentials in a F-250.

I have a 1 1/2 ton 67 International Harvester B1500, or 1500B forget which end the "B" is on. 14K GVW.
Those trucks came with a RA20 Diff and I think the RA28 was a 2-spd. Don`t remember the gear ratio of the Diff.
But that one could with enough money, could, maybe be modified to fit a 250 350?
But it came with the 5 Budd hole split rims.
7.50 17" tire. Good luck finding that size tire.

I also stuck a 3 spd brownie in it years ago, but has been sitting since 79.

I do have a small 3 spd Brownie that came out of a 89 F-350, picked it up for $275 several years ago.

Goat
 

MadMac

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Forgoing the stories about head-ons with drunks in Cadillacs (dude: Chose the corn field 30 ft down on the left, or the river 20ft down on the right, ‘cuz your caddie isn’t going to move the bumper of this rig…), I spent a couple of years delivering Ice mostly on crowned levee river roads - requiring a bobtail - which was often (always?) some 10K or more per axle overweight, so - not by a little.

The Splitter on a five speed manual was required to get out of the yard. For that application - the right implementation without any doubt. Even the beastly Dodge we used to tow the party trailer had one…

Not trying to be judgmental here… I can see the usefulness of a splitter in a non-turbo IDI rig, but is it the right application for a turbo F-250/350 - can’t really see it from a practical perspective. That said - it is always useful to be able to find the perfect rev range. For similar money - put a turbo in… And by all means, don’t run as overweight as I somehow managed to do…
 

FrozenMerc

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I run an Advanced Adaptor Ranger Gear Splitter in my '85 F350. For me it was a cheaper option than a ZF swap or Gear Vendors to get overdrive into the truck. All in, it was about $1700 (2016 money), including shortening the driveshaft and new carpet. For me, it functions as a twin stick 5 speed. Start out in low range, 1,2,3,4, Up shift into 4th-Over at highway speeds. The only time I split any other gears is if I have a big trailer hanging off the bumper with a ton of weight, then it can be nice to split the big gap between 2 and 3. 3rd-Over is essentially the same ratio as 4-low with my 4.11 rear axle. The only difference I have noticed since switching from the stock 6.9 to a 7.3 Turbo is I can run in OD while towing much, much more consistently and don't need to down shift for every little hill.

Shame that Advance Adaptors has discontinued production. They are good units, bit noisy, but stout.

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XOLATEM

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On this note, my dad told me that he used to gave a 1952 Buick of some kind with an automatic transmission. That was a real strong runner of a car. He swore that it had a "passing gear" in reverse. That never did and still doesn't make any sense to me. Just the reasoning and mechanics of it just don't seem even possible. I think that it's more than likely that his transmission was slipping in reverse and would grab solidly when he used a lot of input on the gas pedal. Since he died in 2006 and probably had that car quite a while before I was born, there's no way to confirm those wild claims.
Hey IDIBRONCO... older transmission mechanic here with some experience on 50's units...

If that Buick had a unit called a Dynaflow...the torque convertor had a planetary in it...they were bolted together and you could disassemble them to clean and rebuild and shim the end clearance.

So... what your Dad was feeling was the torque convertor changing pitch whille he was pulling a J-turn to outrun the revenooers while hauling whaht laht'nin...or some such...

By the way...I think that John Delorean is the engineer that drew up and designed the valve body for the Dynaflow.

If it wasn't a Dynaflow then it could have been some other older unit that had the same idea. Back in the 50's the manufacturers were going hog wild with torque convertors because they could do all sorts of things with them and they did not need so many forward speeds.

Caddy had the first lock up torque convertor back then.

F-85 Olds just had forward and reverse and the convertor changed pitch.

Later on...the Turbo-hydramatic 400 in the early years of its production had a variable pitch convertor...activated by a kickdown switch and a simple solenoid. Mid 60's...and then years later the high-performance and drag racing transmission companies offered a 'switch-pitch' conversion for turbo 400's

There was all sorts of stuff to figure out back then...and later...the manufacturers decided to use something more simple and stick with it for a couple decades.

Until...1978 when Chrysler re-introduced the lock up convertor and GM followed suit in 1982
Ford at first just ran the direct drum drive shaft (3rd gear) directly into the convertor with a spring loaded damper plate. You could tell when it went into 3rd because the rpm drop was drastic.

So...your Dad was telling the honest truth about his WOT reverse driving...it probably felt like a gear change to him.
 

IDIBRONCO

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All I know is that the car was LOOOONG gone before I was around. He also said that it would run so fast that it scared him so he got rid of it. Dad was something else in his stories or maybe he just scared easier than I do. maybe that's because I've cheated death two times already. I guess you may be able to call it three times if you count my time in Iraq as a civilian contractor. Anyway, I'd bet any amount of money that I've been faster on two wheels than he ever went with four. On the other hand, that bike was probably safer than his Buick was even at 85MPH.
 

XOLATEM

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I agree...tires, brakes, suspension, ride height, profile in the aerodynamics, rate of acceleration, being strapped in the seat as opposed to just hanging on to the wheel, modern cars are a lot more nimble and sure-footed than back then.

If I was to get a classic car as a restored cruiser...just one to be 'stylin' and 'profilin'...I would want a 1969 Ford Galaxie XL with a 427, C-6, and a 9 inch rear with 3.50 gears.

I had a 1990 T-bird super coupe for a while and it handled well and was pretty quick but it weighed 1000 lbs more than I wanted.
 

Black dawg

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In my pickup, I have an old us gear overdrive unit. Use it all the time even unloaded, splitting gears and for overdrive. After having it, I dont think I could deal with the way manual transmissions are geared without it....
My truck currently is 3.55 geared with a close ratio 4 speed (4.14 first gear)
unloaded is 1st over, 2nd over, 3rd then over, 4th then over.
Loaded is 1st, 2nd, then over, 3rd, then over, 4th, then over.

Makes for pretty smooth quiet acceleration, and easily keeping the engine in a good spot.
 
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