Yukon Gear Trao Loc Spring For Ford 8.8in / 28 Spline

If your Ford 8.8 Traction-Lok has gone soft and spins one tire like an open differential, or you are rebuilding the clutch packs on a 28-spline axle, this is the preload spring the job needs. The Yukon YSPSPR-004 is the Trac Loc spring for 28-spline Ford 8.8 carriers, the kind found in Mustangs, Crown Victorias, Town Cars, Rangers and Mazda B-series pickups. It matters because Ford's own carbon rebuild kit ships with the 31-spline spring only and states that 28-spline axles need a separate 28-spline spring.

What the S-spring does in a Ford 8.8 Traction-Lok

A Traction-Lok is an open differential with a clutch pack behind each side gear. The spring sits in the center of the carrier between the two side gears and pushes them apart, which squeezes both clutch packs against the case before any torque is applied. That standing preload is what keeps the two axle shafts lightly tied together, so when one tire starts to slip the other still gets drive. Under power the spider gears add their own separating force and clamp the packs harder. When the spring fatigues or cracks, that starting preload is gone. The clutches only engage under heavy load, or not at all, and the axle behaves like an open diff in mud, snow or off the line.

Symptoms of a weak or broken Traction-Lok spring

• One-tire burnouts or one wheel spinning on wet pavement or gravel where the axle used to pull both
• Little or no resistance when you turn one raised rear wheel by hand and the other turns the opposite way freely
• A clunk or rattle from the carrier, or spring pieces in the drained oil or on the cover
• Limited slip that stopped working right after a clutch rebuild where the old spring was reused
• Chatter in tight turns is usually the opposite problem, worn plates or missing friction modifier, not a weak spring

How to confirm before you buy

With the rear wheels off the ground and the transmission in neutral, turn one tire. On a healthy Traction-Lok the other tire turns the same direction and you feel real drag; if it spins the opposite way with almost no effort, the preload is gone. Pull the cover and look at the spring through the carrier window for cracks or a flattened shape, and check the clutch plates. If the problem is chatter instead of slipping, read our 8.8 Traction-Lok chatter fix before tearing it down.

Fitment

This spring is for 28-spline Ford 8.8 Traction-Lok carriers. Yukon lists it for 1979-2009 Mustang, 1992-2011 Crown Victoria, 1981-2011 Lincoln Town Car, 1987-1991 LTD Crown Victoria, 1987-1988 Thunderbird, 1984-1992 Mark VII, 1993-1998 Mark VIII, 1990-2011 Ranger, Mazda B3000 and B4000 pickups and the Mazda Navajo. Ford F-150 and Expedition axles from 1997-2008 were also 28-spline, while later F-150s moved to 31 splines and the 2015-up Super 8.8 uses 34-spline shafts and a different carrier.

Spline count is the whole fitment question, so count the splines on an axle shaft or the side gear before you order; a 31-spline carrier needs the 31-spline spring. Our 28 vs 31 spline buyer's guide shows how to tell them apart. If you are unsure, send us the year and VIN or the axle tag code. More parts are in our rebuild kits section.

Install notes

• Drain the axle and pull the cover, remove the pinion shaft lock bolt and pinion shaft, push the axles in and remove the C-clips, then slide the shafts out a few inches.
• The old spring is under load. Pry it out carefully with a bar and keep your hands clear. Rotate the spider gears out of the window, then lift out each side gear with its clutch pack and keep the left and right stacks in order.
• If the plates are glazed or worn, do them now. The Ford 8.8 Traction-Lok clutch kit or the 8.8 Traction-Lok clutch rebuild kit pair with this spring on a 28-spline axle.
• Reassemble the side gears and spiders, then compress the new spring and tap it into place between the side gears with a soft-face hammer. It is a tight fit by design.
• Install the pinion shaft and a new lock bolt with thread locker, refit the C-clips and cover, and fill with 75W-140 or 75W-85 gear oil plus limited-slip friction modifier. Ford's Motorcraft chart calls for the XL-3 modifier added first and not counted in the oil volume.

If the carrier itself is worn or you want a stronger unit, a complete Yukon Dura Grip for 28-spline 8.8 replaces the whole Traction-Lok. For a healthy case with tired preload, a new spring and plates bring it back for far less.

Is this the spring that comes in the Ford M-4700-C carbon rebuild kit?

No. Ford lists the M-4700-C kit with a 31-spline S-spring and says 28-spline applications need a 28-spline spring that is not included. This Yukon spring is the 28-spline version.

How do I know if my 8.8 is 28 or 31 spline?

Count the splines on the end of an axle shaft or on the side gear. Mustang, Crown Victoria, Town Car, Ranger and 1997-2008 F-150 axles are usually 28-spline; later F-150s are 31-spline. When in doubt, send us the year and VIN or axle tag.

Will a new spring stop my Traction-Lok from chattering in turns?

Usually not. Chatter comes from worn or glazed clutch plates or missing friction modifier. A new spring restores preload when the axle slips like an open diff.

Does it fit the 2015 and newer Super 8.8?

No. The Super 8.8 uses 34-spline axles and a different carrier. This spring is for the 28-spline 10-bolt-cover Ford 8.8.

What fluid do I need after installing it?

Fill with 75W-140 or 75W-85 gear oil and add limited-slip friction modifier. Motorcraft says the XL-3 modifier goes in first and is not counted in the oil refill volume.