Yukon Gear 05-08 Ford F250/F350 Super Duty Power Steering Gear Box (Input - Splined Single...

A 2005-2008 Ford F-250 or F-350 Super Duty that feels loose on center, darts over pavement seams, or leaves a drip of fluid under the driver-side frame rail often has a tired steering gear. Plenty of these trucks are past 150,000 miles on the original box, and many have pulled heavy trailers the whole time. The Yukon Gear & Axle ZSG7621 is a new replacement gear box from Yukon's USA Standard Gear line with the 29-spline, single-flat input shaft used on this generation, so your existing steering shaft slides straight on. It is new rather than a rebuilt core, so there is no core deposit to chase.

What the steering box does on a 2005-2008 Super Duty

The box is the link between the steering column and the front axle linkage. Turning the wheel rotates the input shaft; a recirculating-ball worm gear moves a ball nut that rocks the sector shaft, and the pitman arm bolted to that shaft pushes the drag link and tie rods. Hydraulic pressure from the belt-driven pump is metered by a valve on the input side, so the box both steers and boosts. Across years of potholes, plowing and towing, the seals harden and the gear mesh wears, so the box develops lash at center and starts leaking. Per the manufacturer, this unit gives 4.25 turns lock-to-lock.

Signs the steering gear is worn

• Wheel play you can feel before the truck changes direction, especially between 50 and 70 mph
• The truck follows ruts and crowned roads and needs both hands to hold a lane
• Steering that will not return to center on its own after a turn, or a tight spot partway through the turn
• Wet, oily residue on the box housing, the sector shaft seal or the frame rail beneath it
• A knock felt in the wheel over bumps once the suspension and linkage have been checked and are tight

How to confirm it is the box

Lift the hood and put a light on the box while someone moves the steering wheel side to side with the engine running and the tires on the ground. Watch the input shaft and the pitman arm at the same time. Any rotation at the input shaft that does not move the pitman arm is lash inside the gear. Then check the parts that commonly get blamed on the box: the intermediate shaft U-joints, drag link ends, tie rod ends, ball joints and track bar. Also confirm the reservoir is full and the fluid is clean, because aerated or low fluid makes steering heavy and noisy. If your noise shows up when you get on and off the throttle rather than when you steer, it is more likely driveline; see our 5R110W noise diagnosis guide before you buy.

Fitment

This box is listed for 2005-2008 Ford F-250 and F-350 Super Duty pickups with the 29-spline single-flat input shaft. During the 2008 model year Ford moved to a double-flat input, and those trucks, plus 2009-2010 models, take the 2008-2010 Super Duty steering box (ZSG7631). If you own a 2008, pull the coupler or look closely at the input shaft before ordering. Match the bolt pattern, port locations and input shaft to the photos, or send us your year and VIN and we will confirm fitment. Parts for the automatic in these trucks are in our 5R110W parts collection.

Install notes

• Set the wheels straight ahead and lock the steering wheel centered before separating the shaft, so the clockspring and wheel stay in sync.
• Scribe a mark across the coupler and input shaft. On the splined input, the coupler only slides on easily when the flat lines up with the pinch-bolt side.
• Disconnect the pressure and return lines, catch the fluid and plug the ports. Use a pitman arm puller to remove the arm, and reinstall it on the new box on its master splines.
• Tighten the frame mounting bolts, pitman arm nut and coupler pinch bolt to factory torque.
• Drain or flush the system so the new box starts with clean fluid. Adding a Magnefine magnetic inline filter to the return hose traps metal from the old gear.
• Refill with the fluid named on your reservoir cap or in the owner's manual, then bleed by turning slowly lock-to-lock with the front tires off the ground. Never hold the wheel at full lock.
• Recheck toe and steering wheel center, then inspect the line fittings for leaks after the first drive.

Rear axle work on the same trucks? The Yukon chromoly 10.5 in. rear axle shaft fits 2005-up Super Duty. For long-term care of the transmission behind this truck, read our 5R110W common problems and fixes.

What input shaft does this box have?

A 29-spline input with a single flat, used on 2005-2008 Super Duty trucks. Trucks with a double-flat input need the 2008-2010 ZSG7631 box.

I have a 2008 F-350. How do I know which box I need?

2008 is listed for both boxes. Look at the input shaft on your current box: a single flat on a splined shaft means this ZSG7621; a double flat means the ZSG7631. You can also send us your VIN.

Is there a core charge?

No. This is a new box, not a remanufactured core, so nothing has to be returned.

Why does my truck still wander after a new steering box?

Usually because play remains in the linkage or front axle: tie rod ends, drag link, ball joints, track bar bushings or the steering shaft U-joints. Check all of them during the job so the new box can do its work.

What fluid do I use?

Use the power steering fluid printed on the reservoir cap or listed in your owner's manual, and do not mix types. Flush the old fluid out when you install the new box.

Do I need to adjust the new box?

No. It comes set from the factory. Install it, bleed the system, and check toe and steering wheel center.

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