Behemoth Helix IS Independent Suspension EV Gearbox

The Behemoth Drivetrain Helix IS is a limited-slip differential gearbox for electric vehicles with independent suspension. The motor bolts straight to the back of it on a splined input, and half-shafts run from each side to the wheels, so one unit replaces both the transmission and the rear end. It's the heart of an IRS EV conversion or a fully independent custom chassis, and it can be run at the front or the rear of the vehicle.

Choose from two sizes. The E30 is built around Dana 30 differential geometry: compact and light, for sports cars, rear-IRS Porsches and Volkswagens, restomods, buggies and other lightweight to mid-size EVs. The E40 is based on Dana 44 geometry: heavy-duty, with more load capacity for heavier vehicles, bigger tires, off-road, commercial and motorsport use.

Both are engineered from the ground up for the instant torque, sustained RPM and heat of an electric motor, on differential designs with decades of proven durability and easy-to-find service parts. They're self-contained like any conventional differential, so there's no external cooler or pump to plumb. Housings and components are precision-machined, and every unit is built and assembled in the USA.

Gearing: the Helix IS uses standard Dana ring-and-pinion sets, so you pick the final drive that suits your motor, tire size and use. On the E30, common choices run from 3.73 for higher top speed up to 4.88 or 5.13 for more launch torque and bigger tires. Ring-and-pinion sets are off-the-shelf, so changing the ratio later is a normal diff job, not a custom part. Tell us your motor, tire size and target top speed and we'll recommend a ratio.

Behemoth designed the Helix IS family with axial flux motors in mind and lists Cascadia, Turntide, HyPer 9 and YASA as compatible. In our catalog that includes the Turntide AF300 and AF400 axial flux motors.

If your build keeps a solid rear axle, the Behemoth Helix IL inline gearbox is the simpler choice.

Typical lead time is 6–8 weeks, and the gearbox ships by pallet freight, quoted separately.

Notes from the Current EV team

Everything we sell is a part we use in our own builds. Here's what we think of this one and what we've learned putting it in cars.

Why we like it: the E30 is small and strong. It packages into tight spaces where a bigger diff won't fit, and still handles serious motor torque. It works really well in rear-IRS cars like Porsches and Volkswagens, and we like that you can run it at the front too, which opens up dual-motor and all-wheel-drive builds with the same hardware front and rear. When the vehicle is heavier or the tires get bigger, the E40 gives you the same layout with Dana 44 strength.

Picking a ratio: because it uses standard Dana ring-and-pinion sets, we choose the ratio around the motor's speed range and the tire size rather than the other way round. Send us your motor, tire size and the top speed you want and we'll suggest one.

Motor mounting: the motor bolts to the rear of the housing on the splined input, so the motor and gearbox act as one unit. Mount that assembly to the subframe or chassis so the torque reaction goes into the structure, not through the motor's flange alone.

Half-shafts: size your CVs and axles for the motor's torque multiplied by your ring-and-pinion ratio, not for the original engine. Check plunge and operating angles through full suspension travel.

Service: it's self-contained like any diff, so there's no cooler or pump to plumb. Fill with the correct limited-slip gear oil, and check the level after the first few drives.

Tell us your vehicle and motor before you order and we'll confirm the model, fitment and ratio.