There are two limited-slip-style differentials available: the Equa Lok and the Traction-Lok. They are similar in design. The Equa Lok is quite rare because it was only used for a few years.
There are internal differences between the two and most parts are not interchangeable. The Equa Lok has four steel and three friction plates that are preloaded by a Belleville washer. The Traction-Lok has five steel and four friction plates. The first steel plate has friction material bonded to one side.
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The assembly steps are very similar, except that you need to add a limited-slip clutch pack if you have a Traction-Lok differential. The clutch pack consists of clutch friction plates, steel reaction plates, and shims. This is very similar to the 8.8-inch assembly process, just with more pinion gears and a different preload spring arrangement.
Step-1: Apply Grease to Pinions
Apply assembly grease to the back of the pinions, to the side gears, and to the washers to help keep them in place.
Step-2: Install Side Gear in Differential Case
Install the same spline tool in the vise as shown in step 6 on page 72 for an open differential. Put the differential case in place and load in the first side gear with its washer in place. This is the side gear with the shoulder on the back surface.
Step-3: Partially Assemble Differential
This part of the assembly follows the procedure for the open differential (see steps 8 and 9 on pages 73 and 74). Make sure that you have all the pinion washers in place.
Step-4: Install Differential Support Block
Install the differential pin support block, which has four small holes in the corners. This block is symmetrical and does not require any special orientation.
Step-5: Install Roll Pins
Install and fully seat the three roll pins (see steps 14 through 17 on pages 76 and 77). Take extra care to not dent or ding the pilot diameter surfaces. Note that this pilot diameter is countersunk, as opposed to being a raised surface as with the open differential.
Step-6: Install Preload Springs
Here you can see that all of the pinion washers are in place. The three roll pins have been tapped in just below the mounting surface. Now you need to install the preload springs for the clutch pack in the bores of the differential pin block. Dip each one in assembly lube before you drop it in place (left). Repeat until you have all four springs in place (right).
Step-7: Grease Pinions
Add another dab of the grease on the visible end of each spring. Add some grease to all four pinions, rotate to feel for smooth motion, and perform a final check to be sure that all springs and washers are in place.
Step-8: Install Spring Plate
Add the spring plate. Orient it so that the arched cutouts line up with the long differential pin. The long pin is the one that has only a single roll pin on the axis (the one in the middle of the three pins).
Step-9: Apply Grease
Fully seat the spring support plate. Add a thin layer of assembly grease on the back of this plate with an acid brush.
Step-10: Install Differential Pins
Install and align the three differential pins, which is just a matter of pushing them in place by hand (see step 12 on page 75). Don’t forget to double-check the alignment of the roll-pin holes.
Clutch Pack Sub-Assembly Step by Step
Step-1: Inspect Clutch Pack Components
The clutch pack components are laid out in order of assembly along with the steel wear plates. I recommend pre-soaking the clutch plates in friction modifier for at least 30 minutes prior to assembly.
Step-2: Pre-Lube Clutch Carrier
The next step in working on the clutch pack sub-assembly is to pre-lube the clutch inner plate carrier. You can use common gear oil for this.
Step-3: Install Reaction Plates
The tabbed outer reaction plate has friction material on a single side (left). Most people refer to this as the composite plate. The four tabs fit into the mating slots in the differential case. Install the first reaction plate with the friction surface down, which is in contact with the inner plate carrier (right).
Step-4: Install Friction Plates
The friction plates have friction material on both sides, so there is no concern as to which side is installed up. These plates have the mating teeth in their inside diameter and line up with the teeth on the inner plate carrier.
Step-5: Install Steel Reaction Plates
The reaction plates are plain steel. Continue to build up the clutch pack alternating between steel reaction plates and friction plates. There are four steel plates, four friction plates, and one unique composite plate, which has friction material on only one side.
Step-6: Finish Clutch Pack Buildup
When you have the entire clutch and reaction plate pack correctly assembled, the sub-assembly should look just like this. The top plate is a steel tabbedstyle reaction plate.
Step-7: Install Four Reaction Plate Wear Caps
These stop the tabbed plates from wearing into the softer cast iron of the original Ford castings that are soft compared to aftermarket units. The five missing teeth on the inner clutch plate carrier are oil transfer holes. This feature allows oil into the clutch pack to help lubricate the pack. More importantly, it transfers heat from the plates to the incoming fresh oil.
Step-8: Apply Grease to Clutch Plate Carrier
The final preparation step of the clutch pack sub-assembly is to apply a small amount of assembly grease to the top surface of the clutch plate carrier. Use an acid brush to apply a thin layer. This grease helps hold the parts in place.
Step-9: Install Inner Plate Carrier Washer
The inner plate carrier washer goes on the top of the assembled clutch pack sub-assembly.
Differential Cover Assembly Step by Step
Step-1: Install Outer Carrier Plate
If your parts are used or have signs of burrs, smooth them out with an emery cloth or a small file, then thoroughly clean the plate. Any of this abrasive material in the oil and clutch pack will surely cause parts to fail prematurely. Apply a small amount of gear oil to the raised surface as shown. This is the surface that the shim rides on.
Step-2: Install Shim
Add a small amount of gear oil in the shim pocket. Just a thin coating is all that is required; too much oil changes the assembled clutch pack height. Set the shim in place. This is the shim that may require adjustment if the clutch pack height is not correct. Unfortunately, to adjust this shim, means disassembling the unit and replacing the shim.
Step-3: Install Clutch Pack and Inner Plate Carrier
Place the clutch pack and inner plate carrier into the differential cover. Note that steel caps on the tabs are not used because the new Currie differential housings are made out of nodular iron, which is much stronger than the original Ford production pieces and therefore do not require the wear caps.
Step-4: Oil Clutch Pack and Inner Plate Carrier
Add some gear oil to the recessed surface. The side gear back face is in contact with this surface during operation.
Step-5: Set Side Gear into Position
Place the side gear in the pre-oiled recess with the toothed side up. The design of this fl at back surface is unique to the Traction-Lok differential. This completes the differential cover assembly process.
Case Halves Assembly Step by Step
Step-1: Gather all Components
I have found that it is best to place the cover assembly on the bench and carefully set the main differential housing on top of it. The grease on the main components side of the differential acts as an assembly aid to keep things together. Pay special attention to the three through holes on the main case because you need them to align with the small threaded holes on the cover. Here, these holes are on the same flange surface as the ring gear bolt holes (but have a larger diameter). You can see them at approximately 2, 7, and 10 o’clock.
Step-2: Bolt Differential Halves Together
Once you have the two halves together and the bolt holes line up, bolt them together. Use three countersunk headstyle bolts for this. Get all of the bolts started and then tighten them snugly in place.
Step-3: Press Case Halves Together
Since the clutch pack is preloaded, use a press to overcome that preload and press the two case halves together. While still in the press, tighten the three bolts securely. Using a press really makes this step simple as it can be easy to strip the Allen-head bolts depending on the amount of clutch pack preload.
Step-4: Check Preload
Check the preload torque and make adjustments to the shim as required. The nominal shim is .050 inch thick. This homemade tool (left) is made from an old socket along with steel straps and bolts. Depending on the application, the preload torque is between 100 and 250 ft-lbs for new plates. This is a wide range but the torque may fluctuate by as much as 40 ft-lbs. The tool is designed to straddle the bearing journal on the differential case (right) and allow you to rotate the differential case through the ring gear bolt holes. Use a torque wrench to check the preload (or break-away torque) of the clutch pack along with the torque required to keep the gear moving steadily. You want a running torque value of 75 ft-lbs for used plates and 155 to 195 ft-lbs for new plates. If it’s too tight, the tires skid during turn events and if it’s too loose, you may have the dreaded single-wheel peel before the gear-separating force comes into play.
Step-5: Align Side Gear and Inner Plate Carrier
Line up the side gear and inner plate carrier because these have separate splines. This photo shows the splines out of position, making it impossible to install the axle shaft later.
Step-6: Index Teeth for Alignment
This photo shows that I have indexed the unit to have the teeth perfectly in alignment. Although this is a very simple step, it’s often overlooked. Of course, if it is forgotten, you can just slightly rotate the axle shaft on the opposite side relative to the ring gear, but you must install the other axle shaft first. It is much easier to do it now. Also, if you forget about this, you may be tempted to draw in the axle shaft with the T-bolts, and that creates a huge problem.
Written by Joe Palazzolo and Republished with Permission of CarTech Inc