|
|
 We marked the specific components...  We marked the specific components of an axle assembly to clarify the terms well use throughout this article. The parts are as follows: (1) ring gear, (2) pinion gear, (3) inspection cover, (4) axle, (5) hub, (6) axle retainer, (7) spring perch, (8) axle tube, (9) centersection (also called the pumpkin), (10) yoke, (11) axle splines, (12) differential (also called the carrier), and (13) axlehousing.  The axleshaft for a 20 (bottom)...  The axleshaft for a 20 (bottom) has a visibly smaller diameter than the shaft for a 44 (top); another reason the Model 20 is inferior in stock trim. The bearing assemblies are weaker because theyre smaller in diameter and width than the bearings in a 44, which means theres less bearing surface and, therefore, more friction and heat.  Probably the most common upgrade...  Probably the most common upgrade for a 20 is to swap in aftermarket one-piece axles. The one-piece axles eliminate the outer splines, thereby removing the weakest point of the axles. Available from 4 Wheel Parts Wholesalers and others, the axles are made by Durablue, Genuine Gear, Moser, Summers Brothers, and other companies. The kits usually come with new retainers, seals, bearings, and shims.  The Model 20 has two-piece...  The Model 20 has two-piece axles, which are probably the weakest points of the whole assembly. Each axle consists of a shaft, which attaches to the differential and runs the length of the tube, and a hub, which is the flange that the wheel bolts to. The hub is pressed on the tapered end of the shaft. Often the shaft spins inside the hub, ruining the splined-portion of both pieces. Some 44s came with two-piece assemblies too, so check the axleshafts to see if theyre one- or two-piece assemblies.  On the carrier side, the axles...  On the carrier side, the axles for a Model 20 (bottom) all have 29 splines, while the axles for the 44 came with four different splines10, 19, 27, and 30depending on the year they were produced and the type of vehicle they came under. The 72-75 CJ Danas had 30 splines, which is considered the strongest.  The axle tubes are another...  The axle tubes are another weak point on the Model 20 because theyre known to separate from the centersection when subjected to excessive abuse, such as jumping. This weakness is remedied by welding the tubes to the pumpkin, but it should be done by a professional. The pumpkin on a 44 has longer flanges to hold the tubes in place, so separation isnt a problem.  The 20 (right, with a Trac-Lok...  The 20 (right, with a Trac-Lok diff) has a larger-diameter ring gear than the Dana 44 (left, with an open diff). But the main-journal bearings are smaller and weaker in a 20, making them more prone to breakage. Having a larger ring gear adds strength to the ring-and-pinion set because power from the engine is distributed over a larger surface area, reducing strain on the teeth.  Most people swap in an aftermarket...  Most people swap in an aftermarket differential for added strength and traction. Shown here are three locking differentials available for the Model 20. The Detroit Locker (upper left) is a mechanical locking differential that replaces the original carrier. The ARB Air Locker (upper right) also replaces the original carrier, but it acts like an open differential until its actuated by compressed air, at which point it becomes completely locked. The Detroit E-Z Locker (bottom) replaces only the spider gears in the stock open carrier and essentially makes the stock carrier act like a locker without adding any strength, but its a much cheaper alternative to the other two.  The ring-and-pinion sets shown...  The ring-and-pinion sets shown for both the Model 20 (left) and the Dana 44 (middle) are 4.56snotice that the Model 20 pinion gear is massive compared to the 44 pinion gear. The ring gear for the 20 is also much thicker than the ring gear for the 44. As the gear ratios get numerically higher, the pinion gears get smaller. Compare the middle Dana 44 gearset with the 3.07 Dana set (right). Once the ratios for a 44 get into the 4.56:1 range, the pinion becomes a weak point in the differential assembly.  You can bolt certain Dana...  You can bolt certain Dana 44s from Jeepster Commandos (upper axle assembly) directly under a 76-86 CJ without even relocating the spring perches. As you can tell by the photo, the tubes on the Jeepster 44 are shorter than the tubes on the 20. But the backing plates, which arent attached in this photo, stick out farther than the backing plates on a 20, so the overall difference is minimal.  Rody Jarve at the Drivetrain...  Rody Jarve at the Drivetrain Service Center at 4 Wheel Parts Wholesalers told us that in addition to relocating the spring perches, its necessary to alter the brake lines and parking-brake cables after swapping in a Dana 44. The brake-line junction on a 44 is in a different location, and in most cases, the rubber hose that runs from the frame to the axle will need to be lengthened.  The Model 20 came with 11x2-inch...  The Model 20 came with 11x2-inch drum brakes from 76 to 78 1/2, when the brakes were changed to 10x2 inches. The Dana 44s on 72-75 CJs came with 11x2-inch brakes, but earlier ones came with 10x2-inch and even 9x13/4-inch brakes. You want the larger brakes, especially if bigger tires are part of your plans. Disc-brake conversions are also available for both axlehousings. Frame cracks around a Chevys steering box. Closed-knuckle front-axle assemblies on early-70s Fords. Model 20 axles on Jeeps. Flaws. Every vehicle has at least one weakness, while others have quite a few. Some problems are easily fixed and dont cost an arm and a leg, but unfortunately most arent easily remedied and require a sizable investment in order to go away. The Model 20 was used for 10 years under the back of all CJs and is infamous for its weaknesses. Regular on-roadonly use with stock-sized tires doesnt usually aggravate these weaknesses and the diff works just fine. But once you put bigger tires on a Jeep, rocky terrain underneath it, and some extra ponies under the hood, serious breakage soon follows. A common fix and upgrade is to swap in another axlehousing, most often a Dana 44, and throw away the Model 20. But finding a Dana 44 in good shape is getting more and more difficult, and the cost of a completely rebuilt Dana can be enough to turn people away. As a result, some enthusiasts go with the enormous amount of aftermarket parts available for strengthening the Model 20. In this article, well examine exactly what it takes to upgrade a typical Model 20 versus swapping in a Dana 44. Were keeping a budget in mind and will do a cost comparison to show you how the numbers add up. To find the pros and cons of both axles, we went to Tri-County Gear in Pomona, California. The company has been rebuilding axle assemblies for more than 10 years and can customize one to fit most applications. The staff was able to give us some straight answers, and they had several axlehousings in various stages of assembly so we could compare internal parts. of them wap out there. But theres a catchthere are countless versions. Some are narrow, some are wide, some have tapered (two-piece) axles, and most have different widths and spring-perch locations. The ideal Dana 44 for this swap is one from a 72-75 CJ, because its the correct width and has 30-spline one-piece axles. The spring perches, however, will have to be relocated to fit under a 76-86 CJ, a task that requires a skilled drivetrain shop like Tri-County. Also, some 76-79 CJ-7s came with a Quadra-Trac T-case and offset centersections. These will accept a Dana 44 from a 70½-71 CJ-5 or CJ-6 with the T18 transfer case. Other Danas can be used, but they usually have to be narrowed or otherwise altered, which adds considerable expense. Postal Jeeps came with Dana 44s and can be picked up cheap, but there are additional difficulties with swapping one of these Danas under a CJ. The main problem is that the centersection is offset by a few inches. Weve been told a CJ at stock height will accommodate a Postal Dana, but once the Jeep is lifted, the driveline angle gets severe and the U-joints start failing. Postal Danas are also narrower, but this can be corrected with wheel backspacing. We would stick with a Dana 44 out of a CJ. The Bottom Line As always, the bottom line for upgrades is the cost. Please keep in mind that the prices listed were accurate at the time this article was written and can change at any time. We didnt include labor costs, with the exception of welding a 20, because they vary greatly from shop to shop. We went to 4 Wheel Parts Wholesalers for prices on the parts to upgrade a Model 20, and the company can ship the parts to you. The approximate price for a complete Dana 44 ready to bolt in a CJ with an open differential came from Tri-County Gear, but specific prices depend on what year Jeep you want to use and any special modifications you may need. The company can customize any axlehousing to fit your application, and it can ship complete assemblies. The opinion youll get on which axle is strongeran upgraded 20 or a stock 44depends on who you talk to. We think a beefed Model 20 is every bit as strong as a Dana 44perhaps even a little stronger because of the larger ring-and-pinion gears. The main difference is the price: Upgrading a Model 20 is about $350 cheaper than swapping in a Dana 44 (we didnt include any extra swap costs, like new brake lines or parking-brake cables, because some applications dont need these). In addition, you get a locker with the upgraded Model 20 we spec out in the chart, which would have to be added to the Dana at extra cost. Dana 44 loyalists may disagree, but we think youd be surprised at the amount of strength provided by an upgraded Model 20, and you certainly cant dispute the price. Model 20
Genuine Gear axles $329.95
Detroit Locker $469.95
Welding $50
Total $849.90 Dana 44
Total approx. $1200
|