GM Steering box rebuild
Keeping you on-course and running straight
Story Jim Black / Images Jim Mott - May 17, 2012 10:00 AM
This exploded view shows how all the parts come together.
Here you can see how all the balls interact with the worm shaft within the box.
Here’s our original gearbox (casting number 5679142). After removal from the car, we thoroughly washed the exterior of the box with cleaning solvent to remove all traces of dirt and grease. We began the disassembly by clamping the gearbox in a vise, then removing the lash adjuster lock nut using a wrench and screwdriver.
We also removed the worm bearing adjuster lock nut using a block of wood and hammer.
With a 9/16-inch socket, we removed the three side cover bolts.
Using a screwdriver, we unthreaded the adjuster stud clockwise to remove the side cover.
We carefully loosened the worm bearing adjuster using an adjustable wrench.
Then we unscrewed and removed the worm bearing adjuster.
With the gearbox opened up and accessible, we gave the lash adjuster stud a pull and carefully removed the pitman shaft from the case. A rubber hammer might be necessary to jar it free first.
Next, we removed the worm shaft and ball nut assembly from the housing.
We carefully clamped the worm shaft and ball nut assembly in a vise, and using a screwdriver and wrench, we removed the clamp screw and retainer, and then removed the ball guides and balls.
We also removed both the pitman shaft seal and worm shaft seal using a seal puller, then laid out all the parts prior to cleaning in solvent. This was followed with a careful inspection of all components.
Here’s our new rebuild kit from Paragon Corvette Reproductions (p/n 7518K). It includes a new set of upper and lower worm shaft bearings and races, pitman shaft seal, worm shaft seal (replaced with p/n 480821), lash adjuster locknut and washer, new side cover gasket, and bolts.
Following media blasting of the housing, we can clearly see the markings, casting number 5679142, and the number 67 (casting date), the 67th day of 1965. The stamped number (A1045) found in the machined cover face indicates an assembly date the 104th day of 1965.
Using a suitable sized socket and old extension, we carefully drove out the old upper worm bearing race.
We clamped the worm bearing adjuster in the vise, and using a suitable tool, carefully pried the lower bearing retainer out, followed by the lower worm bearing and bearing race. A puller may be required for this step.
We started to pre-assemble the worm shaft and ball nut by installing cleaned and greased balls back in the ball guides.
Next, we located the ball nut back on the worm shaft. The ball nut must be placed correctly or the pitman shaft will not seat properly. We dropped the remaining balls into each circuit of the ball nut openings, followed by the ball guides, retainer and screw. Rock the steering shaft slightly to aid in installing the balls. Caution: Do not rotate the worm shaft while installing balls, since balls may enter the crossover passage between circuits, causing improper operation of the ball nut.
Prior to assembly we sent out parts to Steve Gregori for plating. We had the housing, cover, and worm bearing adjuster plated in grey phosphate; the adjuster lock nut, lash adjuster screw, and shim plated in silver zinc (clear); and the cover bolts and washers plated in black oxide. Here, our parts are laid out and ready for reassembly.
Using our socket and extension, we carefully pressed in our new worm shaft seal.
We installed a new pitman shaft seal using the same procedure.
Next, we carefully pressed in a new upper worm bearing race. Make sure it’s faced correctly.
We carefully pressed in our new lower worm bearing race into the worm bearing adjuster, followed by the lower ball bearing.
Here’s the bearing race and bearing after installation.
We placed the upper bearing on the worm shaft, centered the ball nut on the worm, and carefully slid the worm shaft, bearing, and nut into the housing. Use caution guiding the worm shaft through the new seal.
Here, the worm shaft assembly is shown properly seated in the housing.
Next, carefully install the pitman shaft into the housing engaging the ball nut teeth. Use caution guiding the pitman shaft through the new seal.
We installed the worm bearing adjuster by carefully threading it in by hand. The adjuster should be installed just tight enough to hold the bearings in place. Note: Adjusting the worm bearing preload should actually be accomplished prior to dropping in the pitman shaft. See adjustment instructions at sidebar.
Next, we slipped the lash adjuster and shim onto the channel of the pitman shaft.
Then we threaded on the housing side cover with new paper gasket and cover bolts. Some sealant applied to the gasket will help prevent leakage. We torque the top two cover bolts to 35 lbs-ft, leaving the third bolt loose.
We threaded on both the worm bearing adjuster and lash adjuster locknuts, leaving them loose for final adjustments. After filling the gearbox with quality chassis grease, we tightened the remaining cover bolt. Our steering gearbox restoration is now complete, only needing final adjustment and installation (see sidebar).
When considering the complete restoration of any prized classic or muscle car, the sum of all parts equals the whole.
That is, each individual component rebuilt and refinished to exacting standards will give the best results when they all come together. You may not think that rebuilding a steering gearbox would give equal consideration but consider this, along with your car’s brakes, your steering is probably the most important component on the car and your life could depend on it.
The recent restoration of a ’65 GTO by Jim Mott Restorations, of Kimberly, Idaho, included many individual components that were rebuilt and restored to their original appearance, including the original steering gearbox. With Jim’s help we’ll give readers a better understanding of the gearbox itself and to provide guidance to those “do-it-yourselfers” who might tackle a rebuild on their own.
The manual steering gearbox in our ’65 GTO is a Saginaw unit (casting number 5679142), which is found in most GM A-body intermediates from 1964-’72, and Corvette models 1963-’67. The steering gear is of the recirculating ball nut type, six turns lock–to-lock, with a 24:1 ratio. The ball nut, mounted on the worm gear, is driven by means of steel balls, which circulate in helical grooves in both the worm and nut. Ball return guides attached to the nut serve to recirculate the two sets of balls in the grooves. As the steering wheel is turned to the right the ball nut moves upward. When the wheel is turned to the left the ball nut moves downward.
The sector teeth on the pinion shaft and the ball nut are designed so that they fit the tightest when the steering wheel is straight ahead. This mesh action is adjusted by an adjusting screw, which moves the pinion shaft endwise until the teeth mesh properly. The worm bearing adjuster provides proper preloading of the upper and lower bearings.
The Saginaw box first appeared on GM cars as far back as 1955 and although dependable and long lasting, time can dry out grease and seals, preventing proper lubrication of components and leading to possible failure. It is probably a good bet that the vast majority of gearboxes rarely received any service whatsoever. Many of these manual units were later replaced with power steering in an effort to ease driver burden, but still many enthusiasts prefer to keep things original. If you fall in this category, then read on.
We’ll use a rebuild kit from Paragon Corvette Reproductions (p/n 7518K) but the worm shaft seal supplied will not work with the A-body cars, so we had to purchase this seal (p/n 480821) from a local parts store. Other kits are complete, but we had this one on hand. There are also many kits available from various sources, so do your homework. No special tools are required with the possible exception of a quality inch-pound torque wrench and seal puller.
The sequence of rebuild will include complete disassembly; cleaning and inspection; bead blasting parts; sending parts out for plating; and final assembly and adjustments. If during inspection some parts appear badly worn or pitted that are not included in your rebuild kit, they should be replaced. Harry’s Steering Gear Repair has a large inventory, so consult them if necessary for any replacements. Please note that all seals, bushings, and bearings should be pre-lubricated prior to assembly.
Refer to the factory illustrations for correct nomenclature and a better understanding of key components prior to attempting a rebuild on your own. The accompanying photos and captions detail the procedure, so follow along.
THE BOTTOM LINE
Following the gearbox rebuild, initial adjustments, and installation on the car, it’s a good idea to re-check fluid level and adjustments once again after putting a few miles on the car. If there are any signs of binding or other problems, consult a professional. Now it’s time to go carve some curves!