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Currie High-Pinion Diffs: The Ultimate Diff?You never knew it could be so good From the January, 1999 issue of Jp By Rick Péwé Photography by Rick Péwé
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Most hard-core Jeep enthusiasts know about Currie 9-inch rearends for Jeeps and other rigs. In fact, on almost any given trail ride throughout the nation, you can probably find one (or two) of the custom diffs residing under a built-up Jeep. For years, Currie's custom Ford 9-inch differentials have been legendary in Jeeps, hot rods, and other performance applications, with a plethora of aftermarket gear ratios, housings, and lockers that fit them. But regardless of the durability of the 9-incher, the low-pinion placement can cause driveline angle problems for lifted Jeeps and those that require lots of axle travel. One common cure is the popular high-pinion reverse-rotation Dana 44 and 60 axles found in the front of some Ford products. These axles have the pinion placed above the centerline of the axle tube, and the gears are cut backward to rotate in the correct direction. These high-pinion, reverse-rotation axles are great for improving driveline axles and very popular for making custom-axle swaps. But the drawback is that these axles weren't designed to rotate forward when used in the back of a vehicle, and the oiling of the pinion bearings suffer. To solve all these problems, Currie Enterprises has come up with an all-new product, the Currie High-Pinion Differential. Designed to be used as a front or rear end, this specially made diff will accept all the 9-inch traction and axle goodies that make it famous, but uses the company's own brand and manufactured center section. The new nodular iron casting uses the durable 8.8-inch ring-and-pinion set found in the front of late-model Fords. The whole assembly fits right into a standard 9-inch housing, which saves some bucks if your Jeep already sports custom 9-inch units. Currie Enterprises has just expanded again, this time adding a full-service installation and repair facility. That gave us a chance to photograph the Currie High-Pinion Differentials that were installed in John Curries' new TJ. Check out the new high-pinion unit, and see if it's the ultimate diff for your rig.  The difference between the...  The difference between the Currie 9-inch housing on the left and the Currie High-Pinion on the right is startling. The 9-inch has a removable pinion support, but the pinion location is the big difference. The 9-inch unit has the pinion located 2 1/4 inches below the axle centerline, which is lower than a standard Dana 44 or 60. The Currie High-Pinion is 1 1/2 inches above the centerline, 1/4 inch higher than the high-pinion Dana styles. This gives an incredible 3 3/4-inch gain in pinion height from the stock 9-inch rearend.  Both housings are made from...  Both housings are made from high-grade nodular iron instead of the standard, weaker gray iron. The new castings are specifically made for this application and accept all the 9-inch carriers and internals. The Ford 8.8 ring gear has the same bolt pattern as the 9-inch and is virtually as strong. The 8.8 pinion gear doesn't have a pinion support on the end, like a 9-inch, which is why a new casting was needed. The carrier also features chrome-moly bearing caps, bolts, and adjusters, with the same axle spacing as the 9-inch.  The pinion shaft diameter...  The pinion shaft diameter is similar to the Dana 60, but the length is shorter than the Dana styles, which helps in the pinion angle department. The head of the pinion in this 4.56 ratio example is the same as the Dana 60 and bigger than the 44. The bearing journals are about the same size as the 60, but special bearings are used for better load capacity than the stock 8.8 bearings.  Even the ring gear diameter...  Even the ring gear diameter of the 8.8 is larger than the Dana 44, but still smaller than the 60, as shown in this stack. In many high-pinion rear axle applications, the Dana 44 is too small and weak, while the Dana 60 is overkill. To produce the best combo available, Currie designed the Currie High-Pinion differential so that it would be stronger than the 44 yet not as big and heavy as the 60.  When using a reverse rotation...  When using a reverse rotation front axle in the rear, the oil flow is not the same, since the gears are turning backwards. Both the Dana 60 shown and the Dana 44 have oil channels to divert the oil to the pinion bearings, but no way for the oil to come back out except through the bearings. At highway speed this can lead to overheating of the pinion bearings due to the lack of sufficient cooling and lubrication.  The front pinion bearing is...  The front pinion bearing is the one that receives the least amount of oil flow, so this notch was included in the casting (arrow) for oil to flow back out. This channel is precisely sized to keep the rate and volume of flow at an optimum level. This circulation keeps the bearings cool and lubricated at constant highway speed, where the most damage from heat is done.  John Currie designed the first...  John Currie designed the first casting for the High-Pinion housing and then began to test its durability. The oiling system worked well on the first series, but ultimate oiling was the goal. Mocking up a test unit in a giant turret lathe allowed the diff to be spun up to highway speeds, and a cutout in the casting showed how the oil was flowing.  Different types of oil were...  Different types of oil were tested, as shown here, with the hole cut in the top of the casting. Currie specifies a special, extreme-duty oil that they market, which has exceptional properties. The Currie oil has great climbing ability, along with the ability to take extreme pressure and temperature situations. In an emergency, any good-quality hypoid gear oil can be used, but the best oil will make any gearbox last longer. Currie also noted that his diffs require 3 quarts of lube, regardless of the pinion angle or oil fill location and angle.  Further testing revealed that...  Further testing revealed that the pinion bearings could benefit from more oil flow, so a special gate was made to redirect the flow of oil. The gate is welded in place (new castings will have the gate cast in) which directs oil being flung off of the ring gear into the oil cavity. This forces more oil into the bearings for better lubrication.  Another improvement is the...  Another improvement is the baffle on the axlehousing itself. This small sheetmetal baffle is attached to the top stud inside of the case. It functions like the gate on the casting, to further direct the oil flow at all speeds. This is the only modification that's needs to be done on the standard 9-inch housing.  Final testing showed that...  Final testing showed that with the baffle in place (arrow), oil flow was at an optimum at all speeds. In regular rockcrawling, heat isn't generated at sufficient levels to affect cooling, and enough oil is slung around by the components to lube everything. At highway speeds the oiling system nearly pressurizes the pinion bearings with oil, which keeps it all cool.  Installed in a TJ, the Currie...  Installed in a TJ, the Currie High-Pinion looks right at home. Notice the companion flange on the pinion, which allows greater concentricity and the elimination of overtightened U-bolts on the U-joint. While the driveshaft will need to be modified on one end in retrofit applications, the 1310, 1330, and 1350 series of U-joints are available. The current ratios available are 3.55, 3.73, 4.11, and 4.56, with ratios of 4.88 and 5.14 soon to come. Since the standard 9-inch differential is used, all the popular limited slips and locking diffs are available, including the ARB Air Locker. Axle spline counts of 28, 31, and 35 are available, although currently only the Detroit Locker comes in a 35-spline version.
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