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Fixing Your Ford F-150 Power Steering Box

Posted in How To: Transmission Drivetrain on May 4, 2015
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If you've had trouble with your power steering box, whether it is some groaning and moaning, play in the sector shaft, or simply fluid weeping and seeping near the pitman arm, we might have a cure for your ailment. That is, if you want to do your own rebuild. Read on.

We had the occasion to do some repair work on a leaky F-150 power steering box. This particular box was used on '97-'03 models before Ford swapped to rack-and-pinion steering. We picked up a power steering repair kit and set to work rebuilding the Ford steering box. In general, we replaced all the internal seals and O-rings, lubing each liberally with power steering fluid to help slip them in place and help with the initial assembly seal. Our box had no significant shaft play and all the bearings were in good shape, so we kept them. If needed, most of the roller bearings can be replaced as well.

Should you not want to lay out the cash for a fully rebuilt box and want to do the rebuild yourself, follow along as we show you the steps we took. And, if you don't own an F-150, but still have steering box issues, what we show here is applicable to many similar power steering boxes. So, you should get a pretty good idea what's involved in a reseal or rebuild.

We placed the steering box in a vise for support and started the disassembly. First, we centered the steering box movement, and then removed the four bolts securing the sector shaft cover. The lower shaft was tapped with a mallet and the sector shaft assembly pulled from the main housing.

ford-power-steering-box-sector-shaft-components Here's the removed sector shaft and its cover, which can be unthreaded once the locking nut has been removed. We inspected the shaft splines for signs of twisting, the bearing surfaces for damage, and the gear teeth for signs of chipping or other wear. Ours was in good condition.

ford-power-steering-box-valve-housing-piston-removal Next, the four bolts securing the valve housing to the main housing were removed, allowing us to pull the valve housing and the large piston assembly from the box. We were careful not to let the piston rotate and unscrew from the valve housing.

ford-power-steering-box-sector-seal-removal Lastly, we removed the sector shaft dust seal, snap ring, steel spacer, and oil seal from the lower part of the main housing. Here, you want to inspect the roller bearing in the housing for signs of wear or water damage, and replace if necessary. At this point, the box was stripped down. We cleaned and inspected the large piston bore for wear or damage. If you’re simply replacing the sector shaft seals, you could stop the disassembly here.

ford-power-steering-box-valve-housing-piston-assembly Here is the valve housing (left) and the piston (right). They are mated with the worm shaft of the spool valve and ride on each other using steel ball bearings. Dealing with all the loose ball bearings is usually the intimidating part of a steering box rebuild.

We removed the two bolts securing the ball return guide clamp and removed the guide to retrieve the ball bearings inside. We carefully unscrewed the worm shaft from the piston, allowing the remaining ball bearings to drop into the piston. There should be a total of 28 balls for this particular box.

We held the valve housing in a vise and removed the small set screw that retains the adjusting nut that secures the spool valve in the valve housing. There is a special splined tool that fits the slots in the nut, but we were able to loosen and spin the nut with a punch.

Here the spool valve is being pulled from the valve housing. At this point, you want to inspect the worm gear grooves and their compliment grooves in the piston for signs of scarring or wear.

The valve housing uses a dust seal, snap ring, and oil seal. Each of these was pulled for replacement. After cleaning the valve housing, we inspected the roller bearing and the interior cylinder wall where the seals ride.

Here is the complete spool valve. Each of the four Teflon piston seals was removed and replaced with new seals. The seals were dipped in power steering fluid and then carefully stretched over the body into their respective grooves, being careful not to stretch the Teflon seals excessively, nor nick them.

A fresh oil seal, snap ring, and dust seal were installed in the valve housing. The dust seal should be installed with the rubber side facing out.

With new seals installed on the spool valve and it lubricated, it was carefully slid back into the valve housing while rotating it. We were careful to make sure the seals entered the housing smoothly and did not become nicked or twisted. The locking nut and set screw were reinstalled. Recommended torque for the nut is 55 to 90 lb-ft.

We removed the Teflon piston ring and its underlying o-ring, then replaced them with new ones after cleaning and inspecting the piston.

The worm shaft was threaded back into the piston, and it was time to reinsert the ball bearings. This design has an insertion hole in the ball return guide as shown here. We added a little grease and held the ball return guide gently in the piston holes while we fed each of the 28 balls into the assembly. This required a little wiggling and movement of the piston to work each ball down into the worm threads.

Once the balls were all inserted, we bolted the return guide clamp in place to retain the balls and checked for smooth turning movement of the worm shaft in the piston (no more than 3 turns). We installed a new valve housing o-ring.

To prepare the main housing for reassembly, we installed a new sector shaft oil seal, steel spacer, snap ring and dust seal. You can use either a dedicated seal driver or a socket to tap the seals into their bores.

It's easy to forget the small O-ring between the main housing and the valve housing at the fluid passage. We installed it just prior to reinstalling the valve housing.

We slid the lubricated piston and valve housing into the main housing, aligning the piston gear teeth so we could slide the sector shaft in later. We installed the four bolts finger tight.

We installed a new O-ring on the underside of the sector shaft cover. We had also inspected the needle roller bearing in this cover and found it to be in good condition. Then the cover was threaded back onto the sector shaft.

The sector shaft was slid into the main housing and mated to the piston teeth. Once it was slid in place and seated, the four cover bolts were installed. These and the valve housing bolts were all fully tightened.

With the box assembled, the sector shaft preload needs to be adjusted. We centered the steering box movement (high point), then turned the stud in until it was just shy of touching internally. This is good for initial setting, but may need slight readjustment to remove any steering box play after driving a few miles.

Here is our rebuilt box, sealed and ready to serve some more miles.

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