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Inside the Original Jeep Quadra-TracWhat It's In, Maintenance Tips, and a Look at Whats Going On Inside From the February, 2009 issue of Jp
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 The only transmission used...  The only transmission used with the Quadra-Trac was the General Motors TH400 three-speed automatic with a bellhousing pattern unique to the AMC engines. The tailshaft is the only other nonstandard GM partits a 10-spline shaft that sticks out a good foot from the rear of the housing. This shaft drives the sun gear in the reduction housing, or the drive coupler in the units without low range. The coarse nature of the 10-spline shaft wears on itself and the sun gear, causing a loud bang when its shifted into Reverse.  The aluminum adapter between...  The aluminum adapter between the transmission and the transfer case is also a transmission mount and a tailshaft support. Notice the large ball-type bearing in the adapter, which is much stronger than the current offerings of bushings or small needle bearings. The transmission pattern is standard TH400, which means a Chevy or a Buick/Olds/Pontiac TH400 can be adapted to the case using factory parts; only the output shaft of the transmission needs to be switched to the Quadra-Trac style.  Lack of maintenance is what...  Lack of maintenance is what gives the Quadra-Trac its undeserved reputation. The aluminum case is plenty strong until a bad chain or other debris gets lodged between the case and the drive sprocket, which will cause the unit to literally explode.  The chain is the only item,...  The chain is the only item, other than the fluid, normally replaced during service. As the chain wears from use, it stretches to the point of actually jumping over the sprockets during heavy acceleration. To check the tension of the chain, insert a screwdriver in the chain-inspection hole at the bottom of the case after the fluid is drained. Push up on the bottom of the chain to see how loose it is; if theres more than a half inch of slop, the chain should be replaced.  The low-range sun gear and...  The low-range sun gear and mainshaft suffer from the same 10-spline blues as the transmission output shaft. In this view, the trans shaft enters the sun gear from the left. It wears out the sun gear, which in turn wears out the mainshaft sticking out to the right. At this point, things can get expensive. At press time, the mainshaft (PN J8122705) goes for $138 at your local Jeep dealer, and the sun gear (PN J81227708) has been discontinued.  The optional reduction unit...  The optional reduction unit offers a 2.57:1 ratio for low range and bolts onto the back of the case in place of the cover plate, drive hub, and sleeve. This photo shows two reduction units and the different styles of shifters. The unit on the right is actuated by a cable that ran from under the dash in fullsize Jeeps from 1973 to 1975. The lever and solid-linkage design shown on the left was used in all low-range-equipped vehicles from 1976 to 1979. The lever sticks up from the floor in front of the driver seat to the left of the transmission hump.  The vacuum shifter (A) receives...  The vacuum shifter (A) receives engine vacuum from a glovebox-mounted vacuum switch labeled Emergency Drive. Rotating the switch applies vacuum to one of two nipples on the shifter, causing the rod to move in or out. The attached fork (B) slides a collar on the output shaft, which locks the center differential. The control diaphragm is no longer available from Jeep, but both Crown Automotive and MileMarker stock them.  Inside the reduction unit...  Inside the reduction unit is a simple four-pinion planetary reduction setup, very similar to many late-model transfer cases. A few Torrington bearings and a large ball bearing in the rear are all that will wear out, and proper maintenance can keep those parts in good working order. Disassembly is straightforward and consists mainly of removing snap rings and a few bolts. The reduction housing has its own oil supply and needs to be filled and drained separately from the rest of the case.  When the shift cover is off,...  When the shift cover is off, you can extract the small spring that secures the vacuum shifter in the case. Note the square rubber ring that seals the cover. The same sealing method is used to seal the two case halves together. A complete gasket and seal kit is available from Crown Automotive through your local Jeep shop. Many mechanics prefer to use RTV instead of the rubber sealing rings, but either method is acceptable.  The small E-clips that hold...  The small E-clips that hold the aluminum shift fork on the shaft must be taken out prior to removal of the aluminum shift fork. Without the vacuum control, the differential cant be locked, or if the case hasnt been converted to part-time, it cant be shifted into four-wheel drive. A broken vacuum control is a common problem on the trail, but first it must be determined if vacuum is even getting to the control. A hand vacuum pump is handy for applying vacuum to the control, but the vehicle usually needs to be moving a bit so the gear teeth can be lined up for the shifter to function.  If you need to replace your...  If you need to replace your vacuum shifter, you need to watch out for spring-loaded detent balls that could sail through the air. Here, the spring has been reinserted and the ball is about to be put back. A small screwdriver can be used to depress the ball and the spring as the rod is slid over to retain them. Its a good idea to have a small magnet handy in case you drop the ball into the shift-fork cavity.  If the transfer case is going...  If the transfer case is going to be removed from the vehicle, the driveshafts, speedometer cable, vacuum lines, exhaust bracket, and transmission mounts must be removed. For a chain replacement or a part-time kit installation, only the rear half needs to be taken off. You can separate the case halves by removing the case bolts. Unfortunately, this shift indicator switch is in the way of one of the bolts and must also be removed.  Rugged simplicity is evident...  Rugged simplicity is evident when the case is apart. The drive hub on the right is one piece, and the differential unit on the left is a bolt-together unit. The drivechain rides between the sprockets, which are supported on large, caged, needle bearings. If youre replacing the chain, simply clean the parts, put on a new chain, and bolt it back together. A ratcheting sound during acceleration is often the chain hopping over the sprockets, but the differential should be inspected before the chain is condemned.  When the differential is taken...  When the differential is taken apart, you can see the side gears nestled into the cone gear with the clutch plates on the backside. The preloaded plates force the tapered cone into the taper on the diff housing (much like an Auburn axle differential), creating the limited-slip bias. These pieces were never available separately from any manufacturer, including Jeep, because the differential had to be purchased as an assembly. Good used differentials still command a premium price.  A common yet often overlooked...  A common yet often overlooked Quadra-Trac malady is the inner splines stripping inside the differential. Here, the side gear shows splines in good condition, but all the cone gear splines have been worn away by the front output shaft (arrow). The output shaft is harder and never wears, but the stripped splines cause a ratcheting sound on acceleration and will eventually keep the vehicle from moving unless the Quadra-Tracs differential is locked.  If the differential is in...  If the differential is in good shape, simply clean and lube the clutches and cones with TCL-1 fluid and reassemble it. Note that the case holes are offset to ensure proper assembly. The roll pin (arrow) holds the spider gear cross-shaft in place and must not be left out, which is what almost happened here. The differential clutches can get sticky due to old or improper lube, and also from lack of operation. You can usually eliminate this slip-stick condition by driving in a few figure eights or by changing the fluid.  The Quadra-Trac system needs...  The Quadra-Trac system needs a special formulation of oil to allow proper friction between the cones and plates of the differential. TCL-1 from Crown Automotive is a duplicate of the factory formula and comes in quart bottles. Two bottles are more than enough to fill a Quadra-Trac that has the reduction unit installed. Also remember that there are two separate fill plugs for the case and the reduction unit, and each must be filled separately. The fluid is very susceptible to water contamination and should always be changed after water running or once a year in humid environs.  If the differential is trashed...  If the differential is trashed or a part-time conversion is for you, MileMarker makes a kit that replaces the differential assembly. A direct-replacement sprocket and a new rear output shaft come in kit form with simple instructions. The kit is also available with a smaller sprocket (right), which, when coupled with a different chain, equates to a 16 percent overdrive for rigs with low axle gears that need better mileage. The rear of the case also needs to be taken apart for the new output shaft installation, but simple handtools are all thats needed. After the conversion kit is installed, regular ATF can be used instead of the TCL-1.  The stern Emergency...  The stern Emergency Drive label has kept quite a few drivers from using the unfamiliar glovebox switch. If you convert the Quadra-Trac to part-time, the kit includes a sticker to put over this label. The sticker states two-wheel drive on the left side and four-wheel drive on the right. In addition to the vacuum switch, the locking hubs must be engaged for four-wheel drive to work.  Even though most of the hard...  Even though most of the hard parts are discontinued, most Quadra-Trac service items are available. Crown Automotive sent us a new Morse chain (not a cheap import), front and rear output ball bearings, all four caged needle bearings for the sprockets, a plastic thrust washer, and a new vacuum-control diaphragm. The company also supplies the complete gasket and seal kit, the shift position indicator switch, and the important TCL-1 fluid. Jeep still services the indicator switch, the drivechain, the vacuum-control switch in the glovebox, the knob, and the plastic wear pads on the shift fork.  When you replace the chain,...  When you replace the chain, align the sprockets precisely in their bores for it all to slip together. If you have three hands, it makes for an easier time, especially if youre under the rig putting the sprockets and chain in the front half of the case.  After the case is clean and...  After the case is clean and has a new gasket (or RTV silicone), slap the halves back together and tighten the bolts. Because the case is aluminum, be careful not to cross-thread the fasteners, and torque them with a torque wrench to spec. The reduction unit can be installed along with all the other peripherals, then filled with the correct fluid for your application. Preventative maintenance will keep your Quadra-Trac functioning for many more years to come. The early 70s were the years of full-time four-wheel drivea time before gas crises and performance reductions caused by emissions-control mandates. Dodge, GM, and Ford trucks were fitted with the New Process 203 full-time unit that used an open-center differential and a heavy cast-iron case. But American Motors had a different solution for full-time 4x4s: a lightweight aluminum transfer case from Borg-Warner. Unlike the NP203, AMCs Borg-Warner 1339 Quadra-Trac transfer case included a clutch-pack limited-slip center differential for superior full-time performance, yet like the 203, the differential could be locked to provide equal power output to the front and rear for true four-wheel-drive performance. However, the Quadra-Trac was available without low-range gearingthe gear-reduction unit was an option that was bolted onto the backside of the case. The Quadra-Trac was an option for 73-79 Wagoneers, Cherokees, and J-series pickups, and it was available in the CJ-7 from 1976 to 1979. In 1980, a new NP207 case was introduced. The 207 was nothing like the Borg-Warner 1339, but fullsize Jeeps still carried the name Quadra-Trac on the body, and the sales literature and owners manual called it Quadra-Trac as well. Newer Grand Cherokees also use the Quadra-Trac name, even though todays transfer case is not even related to the original design. However, many of the 73-79 versions are still on (and off) the road. And many uninformed people continue to denigrate the original Quadra-Trac because they dont know how it works. Even though its a chaindriven, vacuum-actuated case with an optional low range, it has been used successfully by racers for years. Rich Severson of Flamingo Racing ran a stock Quadra-Trac in a CJ-7 for five winning seasons without a single failure. Severson notes that maintenance included only a thorough cleaning and replacement of the special fluid and occasional replacement of the chain. For on-road drivers and trail riders, the Quadra-Trac can even be converted to part-time operation with a kit from MileMarker. Only four areas of the Quadra-Trac case usually cause problems: the low-range reduction unit mainshaft and sun gear, the vacuum-operated shifting mechanism, the limited-slip differential, and the normal wear of the drivechain. Most repairs can be accomplished without removing the entire casesimply remove the reduction unit, then separate the main case halves, leaving the front half in the vehicle. This allows you to access everything but the adapter bearing and seals and the front output bearing and seals, which only occasionally present problems, and dont forget that only a special fluid is to be used in the Quadra-Trac for proper operation of the differential.
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Chrysler-Jeep
See your local dealer
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MileMarker Inc.
1450 SW 13th Ct
Pompano Beach
FL
33069
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Crown Automotive Sales
See your local four-wheel-drive store
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