Project F Word: Strange Engineering

Project F Word: Strange Engineering’s Bolt-In, Full-Floater 9-Inch

Things continue to move quickly on our Project F Word ’69 F100 muscle truck. Resurrected from a life of rotting in a field, the patina truck is moving swiftly toward becoming a corner-carving contender. If you’ve been keeping tabs, owner Ivan Korda started at the bottom and is working his way up. 

He commenced taking it entirely apart shortly after working with Silver Sport Transmission to fit a T-56 between the framerails. His goal was to strip the frame bare, then strengthen and powdercoat it to ensure the bolt-in QA1 suspension would have a solid foundation. If you were paying close attention during our previous article focusing on installing the Baer Brakes, we hinted that this article would cover the new Ford 9-inch from Strange Engineering.

Out with the old, in with the new! Project F Word is moving right along, but the old factory rearend isn’t going to cut it with the changes we’re making!

Introducing The Strange HD 9-Inch Ford Housing For ’65 to ’72 F100

Strange Engineering used Project F Word’s factory housing to design an entirely new, direct-bolt-in rearend developed expressly for those looking to lower their ’65 to ’72 F100 — the Strange HD 9-Inch Ford Housing (P/N HF9FT65F100ME). This is not a bare-bones, off-the-shelf rearend where you have to locate everything and weld in your own shock mounts and spring perches. Instead, it uses heavy-duty leaf and shock mounts in the OEM locations but is a significant upgrade from stock. Strange improved the geometry for lowered trucks by moving the shock mounts down 1.25 inches and forward 2.75 inches. But, Strange Sales Manager J.C. Cascio, tells us the shock locations still function just fine if the vehicle is not lowered.

After 52 years of service, Project F Word’s tired old 9-inch sacrificed itself for R&D at Strange Engineering to develop a new bolt-in solution for other F100 owners.

The center housing is constructed from .141-inch mild steel with a heavy-duty .282-inch-thick faceplate. Internal gussets provide rigidity while also better supporting the 3-inch OD by .250-inch-wall axle tubes. The housing ends are forged steel. Strange also makes it easier on the owner by including brake line tabs, fill and drain plugs, and a vent to prevent internal pressure buildup. Everything is welded utilizing a jig to ensure proper alignment and exceptional weld quality. 

This housing is a perfect base for building a fresh new rearend under your daily street-driven truck or something a bit more race-oriented like the Pro Touring full-floater that Ivan decided on for Project F Word. In the next section, we will discuss the additional options he chose to suit his plans.

The all-new Strange HD 9-inch Ford Housing for '65 to '72 F100 pickup trucks is a true bolt-in piece that improves the geometry for lowered trucks but can be used in stock-height trucks as well.

The Robust Rearend In Project F Word

With the center housing as a starting point, you have many options, so it is good to call Strange (as Ivan did) to build a rear that suits your needs. Ivan expects big horsepower out of the Gen 3 Coyote Aluminator that will be installed shortly, and plans to thrash this truck. For that reason, he wanted some beefy upgrades. The first was the 9-inch HD Pro Aluminum Case Assembly Aluminum Support with Differential Standard Gear and 1350 Series Yoke (P/N PRF180). 

(L): The Strange 9-Inch HD Pro Aluminum Case With Differential Standard Gear. (R): The 1350 Series Yoke. On the inside of that case is a set of 4.11:1 ratio Motive Performance Gear ring and pinion!

The Pro HD assembly for F Word includes the 3.250-inch bore HD Pro Aluminum Case Kit for 35 spline axles, which features billet aluminum main caps and solid steel adjuster nuts. It comes standard with a forged aluminum tapered bearing pinion support with oversized Timken bearings and races. Ivan chose the black-oxide finished, extra-stout 4140 chromoly 1350-series Yoke. Meanwhile, Project F Word will utilize a 4.11:1 ratio Motive Performance Gear ring-and-pinion set (P/N RS07890411) machined from 8620 forged steel to get off the corners quickly.

For the differential unit, Ivan upgraded to the 9-Inch 35-Spline Axle Strange Forged S-Trac (P/N N1980). The S-Trac is a clutchless helical-gear differential offering a smoother and more progressive power transfer over OEM and clutch-style units, ideal for the thrashing F Word will give it on the street and track. The forged steel case halves are fully machined and heat-treated to make the S-Trac a lightweight, durable, and rigid unit. Internal gear pocket geometry minimizes stress risers. It utilizes made-in-the-USA, heat-treated 9310 steel gears (chromoly pinion) with aggressive gear helix angles to provide superior torque bias, perfect for unequal traction situations. All gears have a dry-film-lubricant coating on the thrust surfaces to minimize wear.

Here is the new Strange Engineering HD 9-inch for Project F Word as shipped, in raw metal as Ivan ordered. Seeing as Strange had the brakes already to design the floater housings, they installed them for him as well.

We think the S-Trac is worth the upgrade! “The S-Trac differential was designed to withstand the abuse of street, drag, autocross, and road racing, “Cascio confirms. “Simply put, it is the best all-around differential on the market. This premium unit even carries a limited lifetime warranty to the original purchaser.”

The huge diameter 28-1/8 to 32-inch 35-Spline Floater Axles (P/N A1040H32) are machined from solid Hy-Tuf material. The involuted splines are hobbed before heat treating, have a 30-percent pressure angle, and use a Spirolux retaining ring. They are low-carbon, high-manganese, high-nickel, and high-molybdenum steel that is sure to handle whatever Project F Word can throw at them. 

With the growing popularity of multi-purpose vehicles, the Strange street floater provides great all-around performance and reliability. — J.C. Cascio, Strange Engineering

The last choice was vital for competition on the track. Ivan opted to use the Strange Pro Touring Floater Kit (P/N F5010) for the housing ends. The spindles are 2-inch OD 4130-steel designed to fit the 3-inch housing tubing. Ivan chose to go with Ford’s 4.5-inch spacing on the machined hubs with 1/2-inch studs.

“With the growing popularity of multi-purpose vehicles, the Strange street floater provides great all-around performance and reliability,” Cascio states. “Strange has been expanding its bolt-in housing applications that are capable of handling tremendous amounts of power, and the street floater takes things to the next level. Regardless of the purpose of your build, Strange will have the right combination of parts to keep you going.”

Strange worked directly with Baer Brakes to make a floater housing and bracket to fit the giant new 6P brakes. They look killer.

Strange worked directly with Baer to develop this particular floater kit on Project F Word, specifically fitting the big rotors and calipers, and the option is now available to the public. “Baer Brakes is one of the most respected names in aftermarket brake systems,” Cascio says. “The collaboration between Strange and Baer was an obvious choice. The communication and development of the brake kit were smooth and ensures a great fit with flawless function.”

So, What Is A Floater Anyway?

Floaters are not a new concept, but you rarely saw them on a street vehicle until recently. With the rise in performance-based touring machines designed to compete on the track, the floater has become a must-have, but why? The underlying reason is safety, but performance is the name of the game. 

For vehicles spending a lot of time cornering, they exert mega-Gs of sideloading, creating problems ranging from a small nuisance to a catastrophic failure. The most extreme issue is the loss of a wheel when an axle breaks, while the most common is brake-caliper piston knockback. A floater addresses both of these concerns.

In a traditional flanged rearend, the axle performs more functions than just holding the wheel on the truck. It supports the vehicle’s weight, transfers the torque from the chunk, and drives it forward. You may not think a hardened solid-steel axle supported by a bearing at the housing end can flex, but it most certainly can and will. With the brake rotor mounted on the axle flange and the brake caliper solid-mounted to the housing, when the axle flexes, the flange (and therefore, the rotor) is no longer straight up and down (essentially wobbling). 

The wobbly rotor knocks the brake pad against the piston, tapping it back into the cylinder. The next time you go for the brakes, you’ll have to pump the brakes to get pressure before really hammering them. Not only is it frightening, but it is also dangerous when you are on the razor’s edge where milliseconds count.

However, a floater fixes this problem by incorporating a spindle in place of the traditional flange end. A floater hub installed over the spindle supports the weight of the truck on two large tapered bearings (one outside, one inside). The axle slides in through the spindle and attaches to a drive plate that mounts over the wheel studs on the floater hub. The axle only drives the wheel and doesn’t carry any of the car’s load. This technology ensures two things: 1) there is no brake rotor deflection, and 2) should an axle break, you won’t lose the wheel.  

One added benefit of a full-floater rearend is when it comes to maintenance. On a traditional rearend housing, if you need to do anything with the center section like changing the gear ratio, you have to remove the brake calipers, rotors, and caliper brackets before you can remove the axle. With a full-floater, all of this can be left undisturbed, not only saving you time but also saving you the possibility of messing something up when putting it back together.

Here is the rearend ready to go into Project F Word. Ivan brought out the elbow grease and an Emery cloth to shine it up, then clear coated it instead of painting it. You’ll also notice the lower shock mounts have been removed to accommodate the QA1 rear sway bar.

A True Bolt-In!

The best part about Strange using Project F Word’s original rearend to locate the bracketry and fixtures was that it came back to us fully assembled and ready to bolt-in. If you’ve been following the build, you will remember our articles on the QA1 suspension, part 1 here and part 2 here. Because the QA1 suspension uses the factory mounting points, all we had to do was connect everything back to where we mounted it with the factory 9-inch. 

Here is the rearend mounted in the truck. For Ivan, it was just a matter of bolting everything back up seeing he already mocked it up with the old 9-inch before sending it off to Strange.

Now, if you are using the QA1 rear sway bar, there is one thing to note for the installation. Because the Strange rearend is designed as a direct bolt-in for the ’65 to ’72 F100, you will need to remove the stock-location lower shock mounts to make room for the sway bar. You won’t need them if you are using the entire QA1 setup as we did. Beyond that, the installation is straightforward — even more so if you are doing a stock swap.

This front shot gives you a good view of why we had to cut off the stock-location shock mounts in order to mount the QA1 anti-sway bar.

Shortened and Strengthened Driveshaft

If you remember, back in our transmission install article, we already put a driveshaft in F Word, but at the time, we were working with the stock 360 FE engine. Adding the Coyote meant we’d need a beefier option. Also, with the truck lowered between five to seven inches, the driveshaft needed shortening, so it doesn’t damage the transmission. Strange stepped up to the plate in this department as well. Strange offers custom-made driveshafts to fit any application balanced to within .008-inch runout. 

Having a lift really helps when mounting a driveshaft. Ivan started by pulling the plug from the transmission output shaft and installing the front yoke so no gear lube would come out. Then, he worked on lining up the pinion yoke. Look at those welds!!

Since the Coyote is a high-revving engine, and Ivan plans to drive this truck hard, we needed a driveshaft that was precisely balanced to manage the 8,000 rpm rev limit. Once we installed the rearend, we needed to take a few measurements to give to Strange. They took those measurements, along with our power output expectations, and made the driveshaft using 3-inch OD by .083-inch seamless, heat-treated 4130 chromoly tubing (P/N U1699).

As they say, driveline integrity is limited to the weakest component’s strength, so Strange uses Spicer HD 1350 forged weld ends both front and rear. Because the transmission yoke is needed for balancing, they attached the stout black-oxide finished Ford 31-spline Severe Duty 4340 chromoly T56 yoke (P/N U1669) to match the differential yoke.

Recognizing that the driveshaft is one of the final assembly steps, Strange works a quick turnaround to ship the driveshaft once they receive the measurements. We got ours within a week! All we had to do was slip the yoke in the transmission, line up the U-joints, and bolt them in.

Here is the new Strange Engineering 3-inch chromoly Driveshaft mounted in the truck.

Fill ‘er Up!

The final check box on our to-do list was to fill the rearend with gear oil, but what kind? We talked to JC at Strange, who recommended 80w-140 gear oil. So, we picked up three quarts of VP Racing Lubricants Hi-Performance API GL-5 80w-140LS Gear Oil

Ivan chose VP Lubricants Hi-Performance API GL-5 80w-140LS Gear Oil for the rearend. Strange recommends 2.5 quarts.

This gear oil is a semi-mineral-based GL-5 extreme pressure gear oil with anti-scuff, anti-wear properties, providing outstanding protection against low-speed/high-torque wear, limited-slip, and high-speed scoring applications. VP adds a balance of multiple wear chemistries beyond ZDDP that adhere to metal surfaces creating a protective layer. Its low odor formula will keep our Strange Engineering 9-inch happy and lubricated when thrashing around on the street and track.

We attached a length of clear hose to the cap to reach the fill hole easier and added the 2.5 quarts recommended by Strange. A word to the wise — this lube is thick — so if it’s cold outside when you fill the rearend, you might want to warm the fluid slightly before wearing out your forearms squeezing the bottle.

Ivan found some clear tubing to fit over the opening of the cap. This stuff is thick, so we'd recommend warming it slightly or using a pump — Ivan didn't need to go to the gym afterward!


With the Strange Engineering rearend filled with VP gear oil and driveshaft installed, we were able to step back and look at the final product. Overall, we love the look of the rearend with the QA1 suspension and big Baer brakes installed. You can tell just by looking at it how stout this rearend is with the full-floater option. 

Down on the ground, the stance is killer, with the drop afforded by the changes Strange Engineering made to make this a viable performance-oriented rearend along with the QA1 suspension. We can’t wait to get Project F Word fired up and on the road so we can put everything through its paces. It won’t be long now! 

Be sure to bookmark the Project F Word build page for the next installment coming soon!

The new Strange Engineering HD 9-inch Ford Full-Floater looks awesome under the chassis. Now it’s on to the next phase of construction!

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About the author

Shawn Brereton

Shawn is a lifelong car enthusiast who appreciates all things automotive. He is the proud owner of a blown '55 Chevy, a daily-driven '66 Fairlane with an '09 GT500 drivetrain, and a '96 Miata track car.
Read My Articles

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