Gearing Up for the Road - Diesel World

Axle Maintenance and Gear Swaps on a 1996 Power Stroke

If you’ve been following along with advancements in trucks coming from the OEM’s you’ve obviously noticed the current horsepower wars we seem to be experiencing between Ram, GM, and Ford in their diesel trucks. The peak torque and horsepower ratings of their respective engines has been the headline of just about every piece of marketing material you’ve seen from the big three releases for a few years now. You may have noticed how they continue to add gears to their automatic transmissions. First it was a 4-speed, then 5-speeds, and for a while they’d settled on six. The latest 2020 models are now coming equipped with as many as 10-speeds and man are they nice to drive. Something most buyers wouldn’t have noticed is what all the extra power and the extra gears mean for the rest of the drivetrain.

With those changes in trucks, manufacturers have also been able to run much taller axle ratios, which means lower RPM’s while cruising without sacrificing torque multiplication and towing performance. It’s all about the gearing and ratios available to give you the right amount of torque to the ground. When 4.10’s and 3.73 gear sets were common in trucks 15-20 years ago, now the 3.55 and 3.31 gear sets have replaced them. Todays trucks just make the kind of torque and have the transmission ratios to get away with the taller gear ratios.

So, what does all this mean for you guys still driving older trucks? Take this 1996 7.3L Power Stroke owned by Nate Brekken of Phoenix, AZ. This F350 came equipped with 4.10 gears from the factory and with just 215hp and 450ft-lbs of torque when produced, that gearing was almost a necessity for towing heavy loads. But as the years have passed since it’s production, the aftermarket has really made some large strides in the power potential of that older 73L engine platform. With the addition of an intercooler system, performance tuning, maybe an electric fuel system, larger injectors, and a healthier turbocharger, 400-450 horsepower isn’t out of the question for these trucks. Like this truck, it’s making power and torque like a new truck would, but that 4.10 gearing seems to really limit the drivability and it affects its highway performance, with the engine RPM’s screaming at 70+ mph.

This is where Yukon Gears comes into the picture. As a manufacturer of axle parts, like ring and pinion gears and differential carriers for decades now, Yukon has made a name for themselves for producing the highest quality axle parts in the business. For a daily driver like this big Ford, the 4.10 gears really limit its highway usage and create a lot of extra shifting around town, which can wear a left leg out running a clutch from stop light to stop light. Swapping the truck over to a 3.73 ratio offers a few advantages here. One, it’s got over 200,000 miles on the clock, so you know the factory stuff is worn out. Two, the gear ratio change will bring down the RPM’s on the freeway, meaning better mileage and less abuse on the engine running 75-80mph. Lastly, the truck just simply makes the power to pull through the taller gear set without affecting its towing ability much if any.

Along with the change in ring and pinion gears from Yukon, they offer complete axle overhaul kits with all the bearings, seals, and hardware you’ll need to complete the gear swap tasks. Their Dura Grip posi-traction carrier is also a nice upgrade for an excellent lock-up feel with great street manners and durability. The Dura Grip design isn’t a new one, as it basically builds on a posi-traction GM was using in their muscle cars back in the 60’s and 70’s. It’s obviously a much improved version of those old setups, however. With composite clutches and Net Form Forging technology in the spider gears the Dura Grip offers increased strength and resistance to fatigue under heavy load. This setup offers better traction and longevity than most limited slip carriers.

While the axles are torn apart for the ring and pinion swap, it’s also a great time to look into some braking upgrades and even your ball joints. Since this truck runs a much larger than stock tire, a full 35” all-terrain, there is some added wear and tear created on the axle assembly, so upgrading to a more durable ball joint, like the heavy duty units from Dynatrac is never a bad idea. The heat treated billet ball joint body offers a chromoly stem and precision ground stainless steel ball that meets military specs for strength and durability. Dynatrac also coats their ball joint with a Teflon coating that ensures a long life, plus they could be rebuilt should they ever need to be. The joint design resists wear so they’ll stay tight regardless of the abuse you put them under.

While Diesel World likes to spotlight projects the average weekend mechanic could tackle in their own garage, a ring and pinion swap is a job you’ll want to look at having professionally done. The knowledge of how to properly setup the differentials only come with years of experience. Setting up the proper shims for the perfect wear pattern on the gear sets will also require some specific tools, that can be expensive. While you may take pride in doing your work yourself, this is a job better of done by a qualified shop. Not to mention it’s rather labor intensive. Once completed, the 4.10 to 3.73 gear change dropped the engine rpm’s almost a full 300 revolutions per minute. Meaning this bug truck is much happier at 75mph and that 7.3L Power Stroke actually has a shot at pulling down some decent fuel mileage.

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The first par to this process will be updating and modifying the front axle. While the main goal is to change the factory gear ratio from the 4.10 gearing to a more daily driver friendly 3.73 ratio, there will be some other upgrades made like all new bearings and seals provided by Yukon and heavy duty ball joints from Dynatrac.

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This truck had already had the suspension overhauled, so the axle updates were the natural next step to putting new life into the old Ford. Disassembly starts at the hubs and brake system. The early body style Fords used an internal rotor system that requires the hub assembly be removed to replace brake rotors, so if your pads and rotors show some abuse, no is a great time to upgrade them as well.

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With the outer hub switch removed you expose the internal workings of the four wheel drive hub assembly. The large spiral lock ring will need to be removed first to start pulling the inner gears and seals off.

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With the locking hub assembly removed, you’ll find these three spacers/locking rings. The outer ring locks everything in place. While the inner spacer will lock into the dowel locater of the inner ring. This is what holds the hub/rotor assembly on to the axle.

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Here you can see what the axle shaft looks like once the hub assembly, brakes, and the spindle are removed.

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With the front differential drained and the pan removed it’s time to disassemble the differential for the ring gear and pinion gear swap. You’ll notice on this Dana axle, the ‘V’ shaped markings were already on the axle and bearing caps from the factory. It’s important to take note of the marking, so the pieces all go back together in the same place and orientation.

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Here you can see the old races, shims and oil slingers that were removed from the front axle. These will all replaced with new pieces included in the overhaul kit from Yukon Gear.

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This picture shows the hub assembly going back together with the brand new races and shims.

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This is a rather labor intensive job and will require some specialty tools not likely found in most weekender’s garages. Here, a large press and bearing tool are being used to remove the old bearing from the original pinion gear.

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Again, with the help of a specialty bearing tool, the original bearing is being removed from the original differential carrier so the ring gear can be replaced with the new 3.73 gear set.

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This specific tool from Ford makes reinstalling the new inner axles seals a breeze. The tool allows for perfect pressing pressure to ensure a proper seat into the axle without damaging the seals. You can also see the new 3.73 pinion gear has been installed.

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Here, the new ring gear is being installed onto the original carrier section. You’ll get all sorts of answers on how to professionally install this, some will say to press it on then install the bolts. Some will tell you to just pull the gear on with the bolts. Jury is still out on which is ‘correct’.

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Again, more specialty tools for the job. These ball joint tools are used to press the old ball joints out of the knuckle. It will also be needed when it comes time to install the new heavy duty ball joints from Dynatrac.

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On the rear axle of the Ford, not only will the ring and pinion set be swapped out. The worn out, tired limited slip different will also be upgraded with Yukon’s Dura Grip posi-traction unit. The Dura Grip offers excellent lock-up characteristics on the street and while towing, with improved durability over stock units.

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The Dynatrac ball joint was developed to be far superior over your average part stores OEM replacement units. Featuring heat-treated high-strength billet bodies with chromoly stems, the ball joints actually meet military standards for heavy abuse and longevity.

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Since the factory rear axle on our 1996 F350 is a full float design, removal of the axle shafts is quite simple by just removing the eight bolts located on the end of the hub.

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Inside the rear cover you’ll find that factory limited slip carrier that has definitely seen some miles. While the 4.10 gear is good for towing and was needed for a 175-225hp Power Stroke, with the power potential available in the aftermarket now, this older truck will have no issues pulling with a 3.73 gear. This swap will help with fuel mileage too.

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When the new Dura Grip carrier and 3.73 gear sets have been assembled and installed into the axle, it’s extremely important to check your back lash and wear pattern. Adjusting shims on both the pinion and carrier may be needed to make sure you’re getting as much contact on the gear faces as possible.

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The factory 4.10 pinion next the new Yukon 3.73 pinion shows just how precise Yukon builds these pieces. This is a direct swap unit that will require no changes or modification to your axle pieces, outside of being sure to install new bearings of course.

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This photo is simply to show you the notch on the factory exciter ring that will need to be lined up on the carrier/ring gear assembly. The exciter ring is used by the abs/speedo to collect the accurate data on how quickly your axles are turning.

SOURCES

Yukon Gear
www.yukongear.com

Dynatrac
www.dynatrac.com

Strictly Diesel
www.strictlydiesel.com

 

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