Bilstein B4 OE Replacement 12-15 BMW 640i/650i Front Left Twintube Strut Assembly

We pre-assemble your front shock, coil spring, and top hat (strut mount) into a single, ready-to-install unit—so your lift kit installation is quicker and easier. No spring compressor needed.

• 2× pre-assembled front units (left & right): shock + coil spring + new top hats (included with this service; $190 total value)
  
• Mounting hardware where applicable
  
• Preload/Shock Position set to spec for your selected lift height and load

• Save time: Skip spring assembly and go straight to install (saves 1–2 hours per side).
• Pro build: Assembled by our technicians and torqued to OEM/spec.
• Cost-effective: New top hats included at no extra charge. Save money on installation, shops charge up to $150 per hour

1. Select “Yes — Top Hat included (Free)” on this product.
   
2. Our team assembles your front units.
   
3. We ship them ready to install.

Constant load is the additional weight you carry on your vehicle most of the time, measured per axle (front/rear). It includes all accessories such as: metal bumpers, winch, skid plates, tire carriers, drawer systems, rooftop tent (RTT), full-time water/fuel, etc. It does not include passengers or occasional cargo you remove frequently.

Matching shocks and springs/leaf packs to your constant load keeps your ride height where it should be, preserves up-travel, improves handling, and extends shock/spring life.

These are average weights; some brands may have slightly different weights. Check the specific weight in the product page dropdown option for your desired load

Front Axle

• Standard (0–100 lb): Stock or Aluminum/light bumper, light skid plates.
• Medium (100–250 lb): Steel bumper or winch, partial skid package.
• Heavy (250–400 lb): Steel bumper + winch + full skids / dual battery.

Rear Axle

• Standard (0–200 lb): Light rack, basic gear, empty bed most of the time.
  Medium (200–400 lb): Rear bumper/tire carrier or drawer system + fridge/freezer.
• Heavy (400–700 lb): Rear bumper/tire carrier + drawers + RTT + full-time tools/water/fuel.

UCAs connect the frame to the steering knuckle on independent-front-suspension vehicles. After you lift the front end, factory geometry changes; quality UCAs restore caster/camber range, enhance alignment, and improve clearance so your tires won’t rub against the fender and the vehicle remains more reliable in difficult conditions and heavy loads.

• Stock to 2.0 in lift: Optional. Helpful if you want maximum caster, run wider wheels/tires, or your OE arms are worn.
• 2.0 in lift kits: Recommended to recover alignment range and improve coil bucket/shock-body clearance.
• 2.5 to 3.0 in lift:Strongly recommended (often required) to achieve proper caster/camber and avoid contact at droop.

• Recover alignment range: Adds built-in caster (platform-dependent) for better straight-line stability and return-to-center.
  
• Improve clearance: Reduces risk of coil bucket or spring/shock-body contact at droop; and increases tire-to-arm clearance
  
• Maximize usable travel: A higher-angle joint prevents the UCA from being the limiting factor, allowing the suspension to utilize the full travel available from your coilovers.
  
• Strength & durability: Heavy-duty construction to withstand off-road abuse. great for high travel/harsh use; needs periodic cleaning/lube and a dust boot for road salt; can transmit more NVH.

Ball Joint Type:

• High-Angle Ball Joint (sealed): Lowest maintenance and quiet operation, articulation is usually less than a uniball and strength is excellent for street/trail.
• High-Angle Ball Joint (greasable): Lower articulation than a uniball, but very durable if greased periodically, typically quieter and more affordable.
• Uniball (spherical bearing): Maximum articulation and strength; great for high travel/harsh use; needs periodic cleaning/lube and a dust boot for road salt; can transmit more NVH.

Based on Material:

• Billet Aluminum: Very light with quality alloys and good section thickness. Less impact tolerance. Corrosion-resistant.
• Tubular Steel: A solid balance between aluminum and forged steel, robust and repairable, good impact toughness.
• Forged Steel: Heavier, maximum toughness and fatigue strength, ideal for severe duty and heavy rigs.

Adjustment Capability:

• Fixed (Non-Adjustable): Pre-engineered to add caster/camber in the arm itself. Fewer parts to slip or loosen; consistent results.
• Adjustable: Allows fine-tuning of ball-joint/uniball position for extra caster/camber range

Bushing Type:

• Metal (spherical bearing / heim): More noise/vibration, highest articulation
• Polyurethane: Moderate noise/vibration, better than rubber, not as free as spherical.
• Rubber: The Quietest and most comfortable, great for daily/light trail, lowest articulation.

It’s the extra permanent weight your vehicle carries or will carry from accessories you’ll add to it, both on the front and the rear. 

Front: Bumper, winch, skid plate, etc.

Rear: Roof rack, rear bumper, etc.

Important: Do not consider payload when choosing your constant load. Payload is the capacity to add temporary weight, such as passengers or cargo. Our lift kits will increase your payload capacity as well, but to choose the proper setup, only consider permanent load (constant load).

• Plan Ahead: Consider current and future accessories in order to calculate your constant load.
• Estimate Total Weight: Calculate the combined added weight of all the accessories for the front & rear, respectively.
• Select your loads at Mudify.com: Choose the option that fits your total weight for the front and rear.

• 1" Lift – Mostly for looks. Creates a more leveled stance that sets your vehicle apart from stock, giving it a cleaner, more balanced appearance.
• 2" Lift – More than just looks. A 2-inch lift doesn’t only enhance your vehicle’s stance; it also provides extra clearance that makes a noticeable difference off-road—while still keeping daily comfort.
• 3" Lift – Built for adventure. A 3-inch lift delivers extra ground clearance, making room for larger tires and giving your suspension more range of motion. It’s designed for serious off-road performance and gives your ride a bolder, more aggressive look.

The lift kit height shows how much the front of your vehicle will be lifted compared to its factory height. The rear is usually lifted slightly less, this results in what’s known as “Rake”.

LIFT HEIGHT DETAILS

In the product page whenever you select a lift height or load, this text updates instantly—showing you the exact front and rear lift you'll achieve with that specific lift kit setup.

Not completely. From the factory, trucks sit higher in the rear by about 2”. Our lift kits are designed to reduce that rake to 0.5-1”, leaving a Slight Rake. That way, your truck won't lose stability, the rear won’t sag when loaded, and you will still get a balanced, leveled look. It’s the sweet spot between looks and performance.

A one-click service to receive the best quote from a Mudify-certified shop near you for a professional lift kit installation. Free Quote, White Glove Service, Best Prices and Guaranteed Installation. Just hit “Get a Quote” and we’ll handle the outreach for you.

1. Check the “Get a Quote” checkbox on the product page below Lift Height Details and above Upper Control Arms.
2. Checkout and Pay for your Lift Kit.
3. We’ll match you with handpicked, Mudify-certified installers near the ZIP from your checkout—carefully vetted, truly local.
4. We’ll send you a detailed quote with pricing and shop details.
5. Confirm the quote and we’ll reach out to schedule the date for you.
6. On installation day, don't forget to bring your new parts to the shop.

Note: Parts are always shipped to your home, not to the shop.

• Quality-First Installation: From quote to keys back, we oversee every step with our handpicking Mudify-approved shop so you get pro-level results without the runaround.
• Less hassle: Skip the search—We curate elite, pre-vetted local shops, protecting your time—and your warranty—from shaky work.
• Better Pricing - Zero haggling: We leverage partner rates with elite shops and pass the discount straight to you—with a clean and detailed quote before you book.

1. Choose your lift kit
2. The Alignment Rebate will be added automatically to your order
3. Get your alignment done at your preferred shop and save the receipt.
4. Submit the form & Get your reimbursed

We refund the actual amount spent, up to a maximum of $150 USD.

The Alignment Rebate is available on lift kit orders of $1,500 or more before taxes. You can also combine eligible add-ons — such as UCAs and other suspension components — to help your order reach the minimum amount.

This promotion can be combined with most offers, excluding Big Bundles.

To request your alignment rebate, you’ll need to complete the Mudify rebate form with the following information:

• Mudify order number
• Total amount paid for the alignment
• Name of the shop where the alignment was done
• Shop’s address
• A photo or copy of your alignment invoice/receipt

Make sure all information is accurate so we can process your request without delays.

Once your rebate request is submitted, our team will review and verify your information.

Reimbursements are usually processed within 15 business days after approval, with a maximum of up to 30 days.

We try to keep the process fast and simple so you can receive your reimbursement as quickly as possible.