Finesse 1-2-3: Ford Heavies - Drivetrain

Story & Photos by Jim Allen
Ford Heavies: 1980-86 F-250/F-350 4x4

In this final installment on the ‘80-86 Ford 3/4 and 1-tons, we cover the drivetrain. These trucks are reasonably well endowed in this area, with improvements relatively easy.

Stock Transmissions

There are only four options. The Warner T-18 four-speed is the most common manual trans for gas engines, 6.6L and smaller. With the 460 gas and the 6.9L diesel, the close ratio T-19 is most common. The ratios on the T-19 varied between the 460 and the 6.9L but there is nothing constant and both types are found attached to either engine. When stocks of Warner trannies ran low, or for special fleet orders, the NP435 sometimes replaced the T-18. As to automatics, there was only one during this era, the venerable and legendary C-6. There were several variations of the C-6, with the diesel having some unique internal parts as well as a unique bellhousing shape. For ‘85-86, the light duty (LD) regular cab F-250 with the fuel injected 5.0L V8 could come with the AOD overdrive automatic, a 4-speed unit based loosely on the FMX.

Transmission Upgrades

With the exception of the AOD, all the above mentioned transmissions are good for heavy duty use. There is not much you can do to “mod” the manuals, though a switch to a top quality synthetic lubricant will reduce friction and heat. The first thing to do to any workin’ auto tranny is to install a trans temp gauge. The sender can be mounted in several places, the pan, the line out to the cooler or the return line from the cooler. The out line will read the highest temperature. Most people think the return line or the pan provides the most useful info.The next step is a cooler. Its size is dictated by observing tranny temps during different situations or based on the GVW loads you normally carry. Coolers are usually marked according to GVW. In most cases, you want to install the air-to-oil cooler in series with the existing radiator cooler, usually after it. In consistently cool or cold climates, it may be advantageous to install the auxiliary cooler before the radiator cooler, so as to help keep the tranny fluid warm and free of condensation. Some owners in hot climates bypass the radiator cooler altogether. This will reduce the heat load on the radiator, but be sure to go 2-3 sizes larger on the auxiliary cooler so you have adequate tranny cooling.

A tranny temp gauge (center unit) is the workin’ truck’s best friend. This trio of gauges has been working for 20 years in this location on an ’86 F-250HD. The goal is to keep tranny temp at no more than 200 degrees continuous and never over 250 degrees for anything more than short spurts. ATF breaks down very quickly at 250-plus. Many ’80-86 F-series heavies are still working. More are probably seen in harness than used as ‘wheeling rigs. With a few mods, they can still make the new trucks work up a sweat... and for a fraction of the money. The existing automatics can be built with varying degrees of success.

The AOD is pretty weak as a truck tranny, though it’s upgradable into satisfactory territory for all venues except heavy towing. The C6 is very buildable and can handle some serious engine torque and towing duties. A shift kit is the first level and this can be done without any major disassembly. From there, it’s teardown time. High performance clutch linings, valve body mods, larger servos, lower first and second gear planetary gear sets and high performance converters are all part and parcel of building an automatic from the inside out. Take care not to go too high on stall speed with these old-time, nonlockup converters unless you have a specific need, otherwise mpg will suffer. Broader Performance, in Weatherford, Texas, is well known for their expertise on the C6 and can build you a super stout tranny.

The downside to most of the early transmissions, auto and manual alike, Many ’80-86 F-series heavies are still working. More are probably seen in harness than used as ‘wheeling rigs. With a few mods, they can still make the new trucks work up a sweat... and for a fraction of the money. A tranny temp gauge (center unit) is the workin’ truck’s best friend. This trio of gauges has been working for 20 years in this location on an ’86 F-250HD. The goal is to keep tranny temp at no more than 200 degrees continuous and never over 250 degrees for anything more than short spurts. ATF breaks down very quickly at 250-plus. is the lack of an overdrive gear.

These older trucks can pick up 2-6 mpg by just swapping in an OD trans. The later ZF-five speed, which appeared in ’87- 97 trucks is a potential swapper where the bellhousing pattern and transfer case is compatible. The ZF is a little fragile for the “wild & crazy” crowd, but it makes a good day to day manual. The NV-4500 is also a popular swap and a kit is offered by at least one company, High Impact Gear, for fitment into the trucks we are discussing.

The 4-speed E4OD (’89-98) is the main automatic swapper. It was based on the C6 and adapted to electronic controls. If you are not buying a built tranny, get one that fits the application... i.e. don’t put a unit from a LD F-250 into an F-350 and starting towing 12,000 pounds. You must buy a programmable electronic controller (called a TCS) to operate this unit, such as the “Baumannator” from Bauman Engineering. The E4OD can run out of beef in the heavy towing realm, so buying a “built” unit puts you into stronger territory.

The ZF five speed that appeared in the ’87-97 3/4 and 1-ton trucks is a potential swapper into the earlier 4-speed trucks. The bellhousings and flywheels must match the engines, diesel to diesel, 460 to 460, and 5.8L/5.0L and 4.9L to the same. This tranny has nice ratios, the gassers with a 5.72:1 first and the diesels a 4.14:1 first gear and a 0.76 or 0.77 overdrive.

Manual Trans Clutch Upgrades

The stock clutches ranged from 10 inches diameter in the trucks under 8,500 GVW to 11 or 12 inchers for the trucks over 8,500. There were many other details within each of these categories, but the bottom line is that the stock clutch was adequate for a stock truck. If you have upgraded engine power, work the truck hard or have installed big tires and ‘wheel a lot, a swap to a performance clutch is a very wise move.

There are lots of performance clutches on the market and we covered some tips on clutch choices in the July 2007 issue of ORA. To recap, a full face performance clutch, like the Centerforce II, will offer the best combination of torque capacity and driveability for most of you. If you have a mondo-powerful engine that puts a big strain on clutch capacity, and you can live with some grabby tendencies, you might try a dual faced clutch that has a full face on one side and pucks on the other. A full puck style clutch is very grabby for street use, but it’s your case of whiplash. You might also consider a dual disc clutch (if one exists for your truck), which used two clutch discs for more holding power and generally good drivability.

Don’t stop at the clutch parts either. Many flywheels are simple grey iron. A step up from that are nodular iron flywheels, which withstand abuse much better. Even better are steel billet flywheels. Avoid aluminum flywheels since trucks need the low end inertia that comes from a heavy flywheel.

The Borg-Warner 1345 is a keeper most of the time. The generally similar 1356 replaced it in ’87 but has a slip yoke rather than a fixed rear output. If you look in the area of the arrow, the model number is cast into the case. The 1356 also had a slightly taller lower range, 2.69:1.

Transfer Case

The selection of transfer cases comes down to a common one, the Borg Warner 1345 from ’82-86 and beyond, and a couple of oddballs in the early years. In 1980 and possibly into 1981, you could find the NP-208 in the LD F-250. The higher GVW trucks in ’80-81 generally had the Ford (left drop) NP-205.

The aluminum, chain drive BW-1345 is an able unit, with a good 2.74:1 low-range. There’s little reason for a swap unless you need a lot more beef. A Ford (left side front output) NP 205 is a worthwhile swap from that standpoint, but the 2:1 low range is marginal. The Advance Adapters Atlas transfer case comes in two or four-speed units that will fit into your Ford, allowing for low range ratios from 2.0:1 to 6.0:1.

A splitter, such as a Klune-V underdrive, is also possible. By mounting a Klune- V unit between the trans and transfer case, you can have a wider range of lower ratios available. The units come with 2.7 or 4.0:1 ratios and are reputed to be nearly bulletproof.

If you need overdrive capability, the alternative to a tranny swap is the addition of an overdrive. Gear Vendors makes such a unit, which bolts onto the back of the transfer case (replacing the case half). It can only be used in 2wd, obviously, but the unit has a overdrive ratio of 0.78:1.

Axle Modifications, General We’ll cover specific axles below, but there are some common elements to all axle buildups. The first most obvious element is gearing, which will be dictated by tire size and general use. The sidebars will round up some formulas to use and a chart that generally covers the gear ratios needed to accommodate a range of tire diameters and driving situations. The other obvious common element would be traction aids. There are many good choices from the aftermarket. For a mostly street driven truck, a low bias limited slip (like a factory Trac-Lok, Powr-Lok, Eaton Posi, Auburn HP Series or Detroit Trutrac) or on-demand locker (like an ARB Air Locker, Eaton E-Locker, Ox Locker (which will not fit the TTB front) or Auburn ECTED) are your best bets for transparent or nearly transparent operation.. Your choices here are dictated by need. If you ever use 4-wheel drive on the street (snow/ice), you will want to avoid an automatic locker or a high bias limited slip up front. If your truck is mostly a trail machine, then an automatic locker may be appropriate.

The Dana 44 TTB is adequate for stock or near stock trucks. Max tire size is 35 inches. With the exception of traction aids, there’s not a lot available to make this unit a whole lot stouter.

Stock Front Axles

There are three possibilities, the Dana 44IFS for the F-250 and F-250HD from ’80-86, the Dana 50IFS, standard under the ’80-85 F-350 4x4 (optional under the F-250HD) and the Dana 60 beam axle under the ’85-up F-350.

The Dana 44IFS (a.k.a. the Dana 44TTB, see sidebar for specs) has a high pinion center section and uses 297 size u-joints and 30-spline axles. The outer axles, spindles and hubs are similar or identical to what you might find on any other D44, On the long side shaft, there is an extra u-joint on the axle pivot, just outboard of the diff. For the most part, you can regard this axle as the equivalent of a standard Dana 44. It’s good for all but the hardest ‘wheeling drivers and can handle tires up to about 35 inches.

The Dana 50 IFS (a.k.a. the Dana 50TTB, see sidebar for specs) is a stouter high pinion unit with a 9-inch ring gear. It uses larger u-joints than the D44TTB, stronger outer shafts and stronger 30-spline hubs. Side gear splines are still 30 but overall the axle is up to 30 percent stronger than a D44IFS. This axle is good in stock form to about 37 inch tires.

The Dana 60 beam axle appeared on F-350s in the early part of 1985, though some F-350s retained the D50 TTB that year. It was a high pinion unit with 35 spline inner shafts, big 332 series u-joints and 30 spline outer shafts. It’s the strongest and most desirable factory front axle. You are safe to 39-40 inch tires with this axle and more with only a few mods.

Front Axle Modifications

The factory hubs are relatively weak pieces. A set of premium hubs from Warn, for example, are approximately 20 percent stronger than the stock units and this may hold true for other premium brands as well. Alloy shafts (such as 4340 Chrome-Moly) can be a great asset to axle strength but, unfortunately, no readymade units are available for the TTBs. The outer shafts for the beam D44 are the same as for the TTB, but there would be no benefit to this huge strength disparity. Ditto for the super strength u-joints out there, which are grossly stronger than the stock shafts. Unless alloy shafts for TTB axles are made available, use the new cold forged Spicer u-joints for the best service and a little extra beef. One general TTB tip is to make sure your center pivot bushing doesn’t get too soft or worn. Especially when lifted, the complex geometry that occurs on the inner passenger side u-joint makes for increased breakage there.

Dana 44 IFS: Spicer 760 cold-forged u-joints are a good upgrade, as are the aforementioned premium hubs. The inner u-joint on the passenger side is prone to breakage and some TTB owners will substitute parts from the Dana 50, to include the stub axle that comes out of the diff and the matching yoke on the passenger axle shaft, inboard of the slip-yoke.

Dana 50 IFS: Premium hubs and top quality u-joints are about all that’s available for this axle.

Dana 60: The first level upgrade is to install 35- spline outer shafts and the matching locking hub. Some people say the pre-’92 kingpin axles housings are better than the later ball joint types. Premium hubs and cold forged u-joints (Spicer 5-806X) are suitable for stock shafts. Alloy USA offers 4340 inner alloy shafts to fit ’85-91 Ford D60s and also 35 spline outer stud axles. Couple these axles with a super-strength ujoint of your choice.

Bottom line, a swap to a Dana 60 is the best money spent for front axle beef. The swap from a Dana 44TTB to a Dana 50 TTB is hardly worth the effort. The solid D60 swap is a bolt-in using an F-350 axle from ’85-96. You need the axle, tie rod and linkage, track bar and chassis bracket, u-bolts, u-bolt bracket and possibly the driveshaft.

Stock Rear Axles

Through ’84 and into ’85, you will find Dana 60, 61 or 70U rear axles under your F-250 or F-350. Early in ‘85, the Sterling 10.25 axle debuted in semi and full-float forms. The semi-floats appeared in the lower GVW realms and weren’t offered with the big engines. The few F-350 duallys used a Sterling 10.25. See the Axle sidebar for detailed info on the axles available.In general, any of the full float axles are very serviceable. The Dana 70U is one of the troublesome versions of the Dana 70 because of it’s undersized pinion bearings. The 10.25 Sterling is considered a much better axle than either the full-float D60HD or the D70U. The D60 and 10.25 Sterling semi-floats in the LD F-250s are so-so, the main issues not so much torque capacity as load capacity. With frequent heavy loads, the wheel bearings tend to go away quickly.

The Dana axles were offered with the Trac-Lok, which was a low bias, plate type limited slip. It’s an acceptable unit for mild use and is rebuildable, but there are much, much better aftermarket choices. The factory installed Ford Traction-Lock is a fairly useless low bias unit that just gets weaker with age and miles. Don’t go out of your way to install or rebuild one.

The Dana 50 TTB is a couple of steps up in beef from the Dana 44 and opens your tire size options up a bit, but it’s no super-hero.


Rear Axle Modifications

Heat buildup when towing is the number one killer of rear axles. With towing in mind, a high capacity diff cover like the Mag-Hytec will increase the lubricant capacity and significantly reduce oil temps. The lubricant used will have the same effect. A top quality synthetic gear oil, such as Royal Purple, will both reduce friction and withstand more heat than most conventional oils. A high capacity cover and a synthetic lubricant is a one-two punch against heat.

Though not especially common, an axle oil temp gauge is useful for tow rigs. Auto Meter builds one, but any oil temp gauge/sender can be made to work. A bung can be welded into the cover for the sender and some covers, the Mag-Hytec for one, has a spot built in. The ideal is to keep the oil under 200 degrees continuously. That’s not always possible, but no more than 250 continuous for a good synthetic is acceptable. Ordinary gear oil will break down quickly under these temps, so more frequent oil changes are needed.

You’ll have more trouble finding alloy axle shafts for the “big-boy” axles than the smaller ones. That’s because they are less in need. The Ford axles, in fact, use a better SAE 1050 high carbon steel alloy which makes them a bit stronger than the average 1040 medium carbon steel used by Dana.

The Dana 44 and Dana 50 TTB units can be hard to tell apart. Here’s a quick way to tell them apart. On the left is a D50 u-joint with its external snap ring. On the right, the D44 has an internal snap ring.

The Dana 60 is the best swap into any ‘80-86 TTB truck. It matches the rear axle for strength very well. The conversion shown belongs to Ford IDI diesel guru Dave Sponaugle, who regularly snowplows. The stock D44IFS wouldn’t stay in one piece and this D60 beam axle was the solution to that problem. The arrow points out the track bar, which makes street driving much better and can be transferred from the donor truck. It does tend to restrict articulation a bit on the trail. Most F-250HD trucks have the holes already drilled in the chassis for the bracket.


4 Wheel Parts

Advance Adapters


Auburn Gear

Auto Meter

Baumann Engineering

Broader Performance


Eaton/Detroit Locker

Gear Vendors

Genuine Gear

High Impact Gear & Transmission 



Royal Purple


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