Underbody

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Brake Conversion and Upgrades  |  Exhaust Kits  |  Free Whell Hubs

Upgrade what’s under your 4WD with brake conversion and upgrade kits, stainless steel exhaust kits and free wheel hubs, matched to your make and model.

About Hulk 4x4 Underbody Upgrades

The Underbody range covers the parts underneath your 4WD that see the most strain from touring and towing: brakes, exhaust and front hubs. Every kit is listed for a specific make, model and series, so you can match parts to your vehicle before you order.

  • Brake Conversion Kits: Rear drum to disc brake conversion kits, big front brake upgrade kits and front disc upgrades for vehicles carrying more weight or towing more often.
  • Stainless Steel Exhaust Kits: Over 70 stainless steel exhaust kits, including DPF-back and muffler delete options, matched to engine size, body style and build date.
  • Free Wheel Hubs: Replacement free wheel hubs for part-time 4WDs, from HiLux and LandCruiser to Patrol, Pajero, Jimny and Jeep.

Find the Right Underbody Upgrade for Your 4WD

Start with what your vehicle is asking for. If it’s heavier than stock with bar work, a canopy, drawers or bigger tyres, look at a brake conversion kit or brake upgrade first. If you’re replacing a rusted or tired factory system, a stainless steel exhaust kit is the next step. If your front hubs are slipping, grinding or not locking in, a replacement free wheel hub will get your 4WD engaging properly again.

Brake Conversion Kits

Our brake conversion kits replace factory rear drum brakes with discs, using rotors, calipers and brackets. Several kits also include new wheel bearings. Kits are listed for:

You’ll also find big front brake upgrade kits for Ranger, BT-50, D-MAX and RG Colorado, plus replacement parts such as Kevlar ceramic pads, slotted rotors, braided brake hoses, calipers and handbrake shoes.

Stainless Steel Exhaust Kits

Our stainless steel exhaust kits replace factory systems on popular utes and wagons, including:

DPF-back kits keep your diesel particulate filter in place and replace everything after it. Muffler delete kits suit owners who want a stronger exhaust note. Some kits are specific to automatic or manual gearboxes, so check the listing for your build.

Free Wheel Hubs

Free wheel hubs let your front wheels turn freely when you’re in 2WD and lock them to the front axle when you need 4WD. Our free wheel hubs suit a wide range of part-time 4WDs:

The range includes a heavy-duty manual locking hub upgrade for D-MAX, Rodeo, Colorado and Jackaroo.

Upgrade Your 4WD from the Ground Up

Whether you’re building a tourer, setting up for towing or replacing worn factory parts, the Hulk 4x4 underbody range helps your 4WD stop, breathe and engage the way it should. Browse brake conversion kits, stainless steel exhaust kits and free wheel hubs above, or explore our recovery gear to finish your setup.

Underbody Upgrade FAQs

What does a brake conversion kit do?

A rear drum to disc brake conversion kit swaps your factory drum brakes for disc rotors and calipers. Discs shed heat better than drums, which helps braking stay consistent on long descents and when towing or carrying a load. See our brake conversion kits for vehicle-specific kits and contents.

Are stainless steel exhaust kits better than factory exhausts?

Stainless steel resists rust and corrosion better than the mild steel used in many factory systems, which matters for 4WDs that see water crossings, mud and salt. Our stainless steel exhaust kits are made to replace the factory system on the specific vehicle each kit is listed for.

What’s the difference between a DPF-back and a muffler delete exhaust?

A DPF-back exhaust replaces the system from the diesel particulate filter rearward and keeps the DPF in place. A muffler delete replaces the muffler with straight pipe, which makes the exhaust louder. Check your state’s vehicle noise rules before fitting a muffler delete.

What are free wheel hubs and why do they matter?

On part-time 4WDs, free wheel hubs disconnect the front wheels from the front axle when you’re in 2WD. This reduces wear on front driveline parts and can reduce fuel use on the highway. When you need 4WD, you lock the hubs so drive reaches the front wheels.

How do I know if my free wheel hubs need replacing?

Common signs are hubs that won’t lock or unlock, slipping or clicking in 4WD, and grinding noises from the front wheels. Worn hubs can stop 4WD from engaging when you need it, so it’s worth replacing them before your next off-road trip.

How do I check if a part fits my vehicle?

Each product lists the make, model, series and build date range it suits. Some exhaust kits are also specific to engine size, body style or gearbox type. Check these details against your vehicle before ordering, and contact us if you’re unsure.

Can I install underbody upgrades myself?

Some parts, like brake pads, braided hoses and free wheel hubs, suit confident DIY installers. We recommend professional installation for brake conversion kits and exhaust systems, because correct fitting is critical for safety and performance.

When should I receive my order?

An in-stock item usually ships within two business days. Depending on the item and where it’s going, delivery takes 2–7 business days.