King Pin & Link Pin Replacement Guide

The steering and suspension system of any vehicle is crucial for safe and comfortable driving. While many modern cars utilise ball joints, older vehicles, particularly classics like the Volkswagen Beetle, rely on king pins and link pins. These components, while robust, are subject to wear and tear over time, leading to steering wander, wheel wobble, and compromised handling. This guide will walk you through the process of adjusting, replacing, and understanding the function of these vital parts.

Understanding King Pins and Link Pins

King pins are essentially pivot points that connect the steering knuckles (which hold the wheel hub) to the suspension arms or axle beams. They allow the wheels to turn for steering. Link pins, often found in conjunction with king pins in certain suspension designs, also play a role in locating and supporting suspension components, and often incorporate an adjustment mechanism to eliminate play.

Link pins, specifically, often feature a helical groove. This groove interacts with pinch bolts, allowing for fine adjustments to take out slack in the suspension linkage. This is a key feature for maintaining precise steering.

Adjusting Link Pins for Play Elimination

Before diving into replacements, it's often possible to rectify minor steering issues by adjusting the link pins. This process is relatively straightforward:

1. Clean and Lubricate: Begin by thoroughly cleaning away any accumulated grease, dirt, or debris from the link pin area. Then, locate the grease nipples and pump fresh grease into them until it visibly oozes from the joints. This ensures proper lubrication and can sometimes help to free up stiff components.
2. Slacken Pinch Bolts: Locate the pinch bolts that secure the torsion arm link assembly to the torsion arms. Slacken these bolts slightly.
3. Tighten Link Pins: Using a spanner on the flats at the end of the link pins, fully tighten them. This will seat the pins.
4. Back Off and Snug: Now, slacken the link pin by about one-eighth of a turn. Gradually tighten it again until all noticeable play is eliminated when rocking the wheel. Crucially, do not overtighten at this stage, as this can cause the suspension to bind, leading to poor handling and premature wear.
5. Secure Pinch Bolts: Once you're satisfied with the adjustment, firmly tighten the pinch bolts.
6. Repeat: Carry out this procedure for all adjustable link pins on the suspension.

Important Note: If, after adjustment, there is still significant movement, or if the shims on either side of the torsion arm link are visibly worn, it may indicate deeper issues. In such cases, replacing the shims or proceeding to king pin replacement might be necessary.

Diagnosing King Pin Wear

Worn king pins are a common, yet often overlooked, cause of steering problems. While owners might focus on steering box adjustments or wheel alignment, worn king pin bushes can be the primary culprit for steering wander and wheel wobble.

Testing for Play:

• Wheel Rock Test: The classic test involves jacking up the front axle. Have an assistant rock the steering wheel back and forth while you observe the connection between the stub axle and the torsion arm link (or steering knuckle). Any noticeable up-and-down or side-to-side movement here indicates wear.
• Combined Wear: It's important to remember that lateral movement felt at the edge of the wheel can be caused by a combination of worn wheel bearings and worn king pins. Focusing solely on one can lead to misdiagnosis.
• Stub Axle Movement: Specifically, look for up-and-down movement of the stub axle within its mounting point. This often points to worn bush flanges. While some up-and-down play might seem minor, it creates gaps that allow dirt and water ingress, accelerating wear and eventually leading to side-to-side play as well.

If movement is detected at the stub axle joint, it's a strong indication that the king pins, and likely their associated bushes, require replacement. In many designs, the link pins also need to be replaced as their bushes are integral to the king pin removal process.

Replacing King Pins and Link Pins: A Step-by-Step Approach

Replacing king pins and link pins is a more involved process than adjustment and requires careful attention to detail. The exact procedure can vary slightly depending on the vehicle model, but the general principles remain the same.

Preparation and Disassembly

1. Remove Wheels and Brakes: Start by removing the road wheels and brake drums. Refer to your vehicle's workshop manual for the specific procedure for wheel bearing removal and brake component disassembly.
2. Disconnect Steering Linkage: Remove the split pin and nut from the outer track rod end. Using a ball joint splitter tool, carefully disconnect the ball joint from the stub axle assembly.
3. Release Torsion Arms: Remove the pinch bolts that secure the link pins to the torsion arms.
4. Remove Brake Backplate: Unbolt the brake backplate from the stub axle. These bolts may be secured with locking wire, so be prepared to cut or unwrap it. Tie the backplate up securely to avoid putting strain on the brake hose or cable.
5. Drive Out Link Pins: With a soft-faced hammer or mallet, strike the torsion arm link to drive out the link pins. Aim to drive them out evenly.

Removing Old Bushes and King Pins

This is often the most challenging part of the process.

• Link Pin Bushes: The bushes within the torsion arm link can be pressed out using a large vice. You'll need a socket that is slightly smaller than the outer diameter of the bush and a piece of pipe that is slightly larger than the bush's inner diameter to support the new bush during installation.
• King Pin Removal: To facilitate king pin removal, the torsion arm link assembly is often heated. An oil bath is recommended for even heating. Aim for a temperature of around 80°C (175°F) for at least 30 minutes. Exercise extreme caution when working with hot oil. Once heated, the king pin can usually be pressed out. If a press is unavailable, a substantial drift, such as a socket extension bar, can be used. Be aware that in some designs, the king pin must be driven from the top due to the angle.
• Stub Axle Separation: With the king pin removed, the stub axle can be separated from the torsion arm link.
• King Pin Bushes: The bronze king pin bushes are then pressed out of the stub axle.

Special Considerations: Some vehicles, like the Austin Seven, have unique designs. For instance, a bottom bush might be in a blind hole, requiring special extractors for both the king pin and the bush. These often involve tapping a thread into the component and using a screw-type extractor.

Installing New Components

1. Press in New Bushes: New bronze king pin bushes are pressed into the stub axle from the inside outwards. Ensure they are seated squarely.
2. Notching for Location: After fitting the upper bush, you'll need to file notches into it to align with the notches in the torsion arm link. This is essential for correctly locating the thrust washer cover plate.
3. Reaming for Precision: This is a critical step. The new king pin bushes must be reamed to the exact diameter of the king pin to eliminate all play without causing binding. This requires an adjustable parallel reamer and guide. The tapered guide is inserted into the opposite bush to act as a guide for the reamer. Ream incrementally, making small adjustments, until the king pin fits snugly with no detectable play. Over-reaming will render the bushes useless.
4. Lubrication Holes: Ensure that the oil holes in the new bushes are correctly aligned with the lubrication points on the stub axle. If the bushes are supplied without holes, fit them first and then drill through from the grease nipple location into the bush. Never assemble without ensuring proper lubrication for both top and bottom bushes.
5. King Pin Installation: Press the new king pin into the reamed bushes.
6. Locking Mechanism: Reinstall the locking pin or cotter pin to secure the king pin in place. Use new pins as old ones are often damaged during removal.
7. Reassembly: Reassemble the stub axle to the torsion arm link, ensuring the thrust bearing and any necessary shims are correctly positioned. Reinstall the end caps, staking them securely.
8. Reassemble Brakes and Wheels: Reinstall the brake backplate, brake components, brake drums, and finally, the wheels.

Reassembly and Final Checks

With the king pins and link pins replaced, reassemble the rest of the suspension and brake components. Ensure all nuts and bolts are torqued to the manufacturer's specifications. Reinstall the wheels and lower the vehicle. Perform a final check of the steering, ensuring it moves freely and without binding. A professional wheel alignment is highly recommended after such work.

King Pin Designs and Variations

Steering head arrangements can vary. Understanding these differences is important:

• Figure 1 Type: The axle ends in a knuckle through which the king pin passes, secured by a tapered cotter. The pin rotates in bushes in the stub axle. Some designs include a thrust washer.
• Figure 2 Type: The axle has bushes, and the king pin is secured in the stub axle. A ball thrust race often takes the load.
• Figure 3 Type: Similar to Figure 1, but the pin is held in the stub axle and rotates in bushes in the axle end. This design allows for the pin to be turned down if wear occurs, a benefit not available in other designs.

The method of bush removal can differ. For bushes in blind holes, specialized extractors are often required, sometimes involving tapping a thread into the old bush to draw it out.

Can a King Pin Be Bent?

While king pins are designed to be robust, they can potentially become bent due to severe impact, such as hitting a large pothole or curb at speed. A bent king pin will cause significant steering pull and uneven tyre wear. If you suspect a bent king pin, it must be replaced. It is not a component that can be straightened or filed down, except in specific designs where the pin itself is designed to be machined (as mentioned in Figure 3). In most cases, filing the pin is incorrect; the bushes are what require reaming or scraping.

Summary Table: King Pin vs. Ball Joint

Frequently Asked Questions (FAQs)

Q1: How often should I check my king pins?

A1: It's advisable to check your king pins during regular suspension inspections, particularly if you experience any steering looseness or uneven tyre wear. For older vehicles, an annual check is a good practice.

Q2: Can I drive with worn king pins?

A2: Driving with significantly worn king pins is dangerous. It compromises steering control, can lead to rapid tyre wear, and increases the risk of component failure.

Q3: Is reaming king pin bushes a job I can do myself?

A3: Reaming requires specialised tools and a degree of skill to achieve the correct tolerance. If you are not experienced with this type of work, it's best to have a professional machine shop or mechanic perform the reaming and fitting.

Q4: What happens if I don't grease the king pins?

A4: Lack of lubrication will significantly accelerate wear on the king pins and their bushes, leading to premature failure and the need for more extensive repairs.

Maintaining your vehicle's suspension system, including the king pins and link pins, is paramount for safety and performance. While the task can seem daunting, understanding the process and taking the necessary precautions will ensure a successful repair and a revitalised driving experience.