1993-1994 BMW 740i Power Steering Pump: Decoding SLS Tandem vs. Standard Pumps

The Most Important Question: Does Your 740i Have Self-Leveling Suspension (SLS)?

Before buying a replacement power steering pump for a 1993-1994 BMW 740i or 740iL, you must first determine if your vehicle has Self-Leveling Suspension (SLS), also known as LAD. The two systems use completely different pumps that are not interchangeable. Installing the wrong pump will result in failure.

How to Identify if Your Car Has SLS:

• Check the Power Steering Reservoir Cap: The fluid reservoir cap often has a label indicating the required fluid. Systems with SLS typically require Pentosin CHF 11S hydraulic fluid. While not a definitive test on its own, it's a strong clue.
• Inspect the Rear Suspension: Look for hydraulic fluid lines running to the top of the rear shock absorbers. You will also find two spherical pressure accumulators (often called "bombs") mounted near the rear axle. These are clear signs of an SLS system.
• Look at the Pump: The SLS system uses a larger "tandem" pump with more hydraulic lines connected to it compared to the smaller, simpler pump on standard models.
• Perform a Load Test: With the engine running, have a person sit in the back seat or add significant weight to the trunk. After a few moments, you should hear the system engage and see the rear of the car rise to its normal ride height.

Symptoms of a Failing Power Steering Pump

A failing power steering pump will give several distinct warning signs. On SLS-equipped models, these symptoms can affect both steering and suspension.

Common Failure Symptoms (All Models):

• Whining or Groaning Noises: A loud whining or groaning sound, especially when turning the steering wheel, is the most common symptom. This noise often changes pitch with engine RPM. It's caused by air entering the system or the pump's internal components wearing out.
• Stiff or Heavy Steering: The steering wheel becomes difficult to turn, particularly at low speeds or when parking. This indicates a loss of hydraulic assistance.
• Fluid Leaks: Puddles of reddish (ATF) or green (Pentosin) fluid under the front of the car are a sign of leaking seals or hoses. Check the pump body, reservoir, and all connected lines.
• Foamy or Discolored Fluid: Check the fluid in the reservoir. If it appears foamy or bubbly, air is getting into the system. If it's dark brown or black and smells burnt, the fluid has broken down or the pump is failing internally.

SLS-Specific Failure Symptoms:

• Rear Suspension Sagging: If the tandem pump fails, it can no longer supply pressure to the rear suspension, causing the rear of the car to sit low or sag.
• "SLS" or "SELF-LEVEL SUSP INACT" Warning: A message may appear on the instrument cluster's check control display, indicating a fault in the leveling system.
• Bouncy or Harsh Ride: While more commonly caused by failed accumulators, a lack of hydraulic pressure from the pump can also contribute to a poor ride quality in the rear.

Buying a Used PS Pump/Motor: What to Look For

A quality used OEM power steering pump is an excellent value, but careful inspection and verification are key. Given the high cost of a new OEM unit, a reliable recycled part can save hundreds of dollars.

1. Confirm the System Type: This is the most critical step. Verify if you need a standard pump (non-SLS) or a tandem pump (SLS) based on the identification steps above. Do not buy a pump until you are 100% certain which system your car has.
2. Match the Brand (Vickers vs. LUK): BMW used both Vickers and LUK as original equipment suppliers for these pumps. While the BMW part numbers are the same, the physical castings and bracket mounting points can differ slightly. The safest approach is to identify the brand on your old pump and purchase a used one of the same brand to ensure a perfect fit without needing to swap brackets.
3. Physical Inspection: When inspecting a used pump, check the following:
   • Pulley Condition: The pulley should be free of cracks, chips, or deep grooves. Spin it by hand; it should turn smoothly without grinding or excessive resistance.
   • Housing Integrity: Inspect the aluminum pump body for any cracks, corrosion, or signs of heavy impact.
   • Ports and Fittings: Ensure the threaded ports for the hydraulic lines are clean and undamaged. Stripped threads will cause leaks.
   • Signs of Leaks: Look for any residual fluid or heavy grime around the shaft seal (behind the pulley) and where the housing sections meet. A clean, dry pump is a good sign.
4. Mileage vs. Condition: For a part over 30 years old, mileage is less important than its tested, functional condition. These pumps are robust, but they are wear items. Failure is common between 100,000 and 150,000 miles. A low-mileage part is ideal, but a well-maintained, leak-free part from a higher-mileage car is still a good option.

Cost of Replacement

Prices can vary significantly between new, remanufactured, and used OEM parts. The tandem pump for SLS models is considerably more expensive than the standard pump.

Replacement Procedure Overview & Special Tools

Replacing the pump is a moderately difficult job that is feasible for an experienced DIY mechanic. The key challenges are access and properly bleeding the system afterward.

• Fluid Type: This is critical. Check the reservoir cap. If it specifies ATF, use a Dexron III compatible fluid. If it has a green sticker or specifies Pentosin, you must use Pentosin CHF 7.1 or CHF 11S. Never mix ATF and Pentosin.
• Bleeding the System: This is the most important part of the installation. Failure to bleed air from the system will cause a loud whining noise and quickly destroy the new pump.
  1. With the engine OFF and the front wheels lifted off the ground, fill the reservoir with the correct fluid.
  2. Slowly turn the steering wheel from full lock to full lock about 10-15 times. Keep an eye on the fluid level and top it off as it drops.
  3. Once the fluid level is stable, start the engine and let it idle for a moment, then shut it off. Re-check and top off the fluid.
  4. Start the engine again and slowly repeat the lock-to-lock steering turns. Listen for noise and watch the reservoir for bubbles. Continue until the fluid is clear and the pump is quiet.
• Related Parts: Always use new crush washers for the banjo bolt fittings on the high-pressure lines to prevent leaks. It is also wise to inspect all power steering hoses for cracking, brittleness, or swelling and replace them as needed. The reservoir, with its integrated filter, should also be replaced.
• Torque Specs: Specific torque values for the E32 are not readily published. For the high-pressure banjo bolts, the standard procedure is to use new crush washers and tighten them to be snug and leak-free, approximately 30-35 lb-ft. Do not overtighten. The pump mounting bolts should be tightened securely.

Technical Specifications & Part Numbers

Always verify the part number and brand from your original pump before ordering a replacement.

Frequently Asked Questions (FAQ)