Building a Three-Link and Converting Two-Wheel Drive to Four-Wheel Drive
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If you have a two-wheel drive and youre fed up with getting stuck, or your buddies with four-bys just plain leave you in the dust, then its probably time to sell the pegleg, step up to the plate, and buy a 4x4. Or is it?
Two-bys can be lots of fun for high-speed use, and our 79 Ford F-150 was no exception. It certainly wasnt a slouch with 35-inch tires and 17 inches of travel in the front, accompanied by 14 inches in the rear. Jumps from 5 feet were no problem, and dips and bumps were easily absorbed. However, dune and mud runs had left us stranded and wanting a 4x4. In some situations low range would have been nice too. We have a lot of time and money wrapped up in our truck, including a new engine, tranny, and rearend. It didnt make much sense to sell it and start over, so we decided to convert it to a 4x4. It is possible to buy a 4x4 of the same make and bolt on all of the good parts and sell the leftover truck, but we just couldnt part with our 79.
Now that we decided to keep the truck, we needed to decide how to go about the conversion. Bolting on factory 73-79 Ford 4x4 components (tranny, transfer case, axle, and suspension) might seem like the easiest method, and it is for many models. It turns out that the 66-79 Ford two-wheel-drive frames are different from the four-wheel-drive frames. The main difference is the engine crossmember. The 4x4 crossmember is made from square tube and is positioned in front of the engine, away from the axle assembly. The two-wheel-drive piece provides a mounting location for the I-beams and hangs below the engine. It needs to be removed or modified unless a huge lift is planned. We were lifting our truck 6-7 inches over stock.
Another complication is that the transmission in your two-wheel drive is probably fine. This was the case for our truck, so it seemed wasteful to swap it out for a 4x4 trans mated to a transfer case. A divorce-mounted transfer case was the perfect solution. Divorced Dana 24s and NP205s are somewhat common in wrecking yards and can be found relatively cheap since they hardly ever break. A divorce mounted case would also help with weight distribution by moving a good portion of bulk to the rear of the vehicle. The third advantage that came to mind was that we could clock the transfer case for more ground clearance. We didnt need an expensive adapter, just a third driveshaft. We decided on a divorced Dodge NP205 to provide splitting duties.
The Dodge transfer case has the front output on the passenger side. This offers us plenty of options for a front axle but we have our limitations too. Custom units were too expensive and we wanted to be able to buy spare parts from wrecking yards if need be. Ford axles have the differentials on the wrong side, and the high-pinion design would have caused major clearance problems with the factory two-wheel-drive crossmember. Chevy axles have the diff on the same side as the Dodge transfer case and are more common than Dodge axles with 5-on-5 ½ lug patterns. So Chevy it was.
We thought that a bombproof Dana 60 would be nice, but we doubted that its size and weight were really needed. In fact, it was too heavy and probably way overkill for our high-speed, nimble truck with 35-inch tires. It was also an expensive option that would need to be converted to a five-lug or we would have to swap out the rear axle to match the eight-lug front. A Dana 44 from a 73-76 Chevy was deemed to be the best option. It has ½-inch-thick, 2 ¾-inch-diameter axletubes, the diff is on the correct side, lots of them exist in wrecking yards, and the six-lug pattern could be easily changed to 5-on-5 ½. It turned out that the width was only slightly wider than the factory Ford 9-inch in the back of our truck. A call to Boyce Equipment netted us a rebuilt Dana 44 with 4.10 gears to match the back. If your project or budget calls for a 10-bolt, a Dana 60, or even a 2 ½- or a 5-ton axle, Boyce has them all.
The truck was originally built as a high-speed desert runner, and we didnt want to lose that capability with the integration of four-wheel drive. Leaf springs would have been simple to install since the perches on our axle were about the same width as our framerails. Coils could have been mounted in the original (aftermarket in our case) coil buckets, but installing Ford radius arms on our Chevy axle posed its own set of problems. Neither of these designs would look or perform any different than a normal straight-axle Ford 4x4. Also, if long travel is built into the factory radius arm suspension there will be significant caster change throughout the travel. Articulation would also be limited by the presence of the C-bushings. We knew it would be difficult to keep the 17 inches of suspension we originally had and still maintain safe steering linkages, but we were willing to settle for a little less travel in exchange for four-wheel drive.
We chose to build a three-link suspension with a Panhard rod. Coilover shocks will compactly and economically perform damping and rebound chores. The links are attached to the axle and frame with Aurora rod ends on 1 ½-inch DOM tubing. The tubing has a wall thickness of almost 3/8 inch so it can handle rocks and just about anything we hit it with. All three arms are the same length, and the upper and lower arms are parallel to each other. This ensures that there is no caster change throughout the travel and we only need to carry one spare arm. The axle is kept inline by a 11/8-inch-diameter, heavy wall DOM Panhard rod with Aurora rod ends. The drag link is made of the same material. Both components use the same rod ends and both are the same length, so again, only one spare is needed.
Staying true to the find-it- anywhere motif, we ditched the behind-the-engine steering and chose a 70-78 Camaro Saginaw power steering box that has 2 ½ turns lock-to-lock. The box is a 76 GM 800 unit with the larger bearings and stronger casting. This box has the same bolt pattern as many American cars, so a field replacement should be a snap if it should ever fail. The box is connected to our factory column with a Flaming River collapsible steering shaft. We built our own steering-box mount using DOM tubing that pierces the freshly reinforced framerail. This month well cover the axle installation, steering, and the three-link suspension design. Next month well cover the transfer case, driveshafts, the shocks, how to build the shock hoops, and any leftover details.
Common hand tools
Assorted drill bits and hole saws
Welder (preferably MIG or TIG) with at least ¼-inch single-pass capability
Sawzall, torch, or plasma cutter
Tube bender: can be used to make cool shock hoops and brackets
Tubing notcher: copes tubing for easy fit-up and welding
¾-inch fine thread tap
3/16-inch mild plate steel: size and amount will depend on bracket design
1 ½-inch 0.120 wall mild steel tubing: 15-30 feet
1 1/8-inch DOM tubing with 5/8-inch inside diameter: 4 feet
1 ½-inch heavy-wall DOM or chrome moly tubing: amount depends on the length of the links
11/8-inch heavy-wall DOM with 11/16-inch inside diameter: length will depend on drag link and Panhard rod design
Wrangler shackle bushings (two pair)
PFTE- (Teflon) lined Aurora rod ends (size and type will depend on use)
King Prerunner coilover and standard shocks and hardware
Divorced Dodge NP205
72-76 ½-ton GM Dana 44 front axle
73-79 F-150 hubs and rotors
Skyjacker stainless braided lines
Warn locking hubs
Miscellaneous Grade 8 hardware
Autofab 4 ½-inch bumpstops
Flaming River steering shaft
GM 800 steering box with Camaro pitman arm
Transfer case shift linkage
Wheels and tires
Lift for rear
To read "Project Two-By Four, Part 2: Shocks and Hoops," click here
. For Project Two-By Four, Part 3: Driveline and Airtime, click here .