Building A Chain Drive Differential From Junkyard Parts

A differential is a very useful thing for a vehicle. It allows two driven wheels to rotate at different speeds, such as when going around a corner. [Workshop From Scratch] needed a chain driven differential, so set about building one from a salvaged automotive unit.

The differential itself was taken from a BMW E46 3-Series, specifically a 2.0-liter diesel model. The work began by removing the differential’s center gears from its big, hefty iron housing. Disassembly then ensued, with the spider gears removed from their carrier and the other components discarded. The differential gears themselves were installed instead in a new compact housing, fabricated with much welding and lathery. The housing was fitted with a large chain sprocket to deliver drive, in place of the original differential’s ring gear and pinion.

The video’s description states it would be an ideal differential for a go-kart, buggy, or other such small vehicle. Given the differential gears were originally built to handle a full-sized car, they should be more than capable of dealing with such applications.

If you’re a little unfamiliar with how differentials work, check out this primer from the early 20th century. It’s widely considered to be the best education on the topic. Video after the break.

24 thoughts on “Building A Chain Drive Differential From Junkyard Parts

        1. I feel your pain, btw:
          -Look up youtube DIY tutorial on fabrication
          -“Okay, so all you gotta do is fire up your $30,000 1930s lathe and $5,000,000 Japanese 12-axis CNC mill…”
          -Go outside and make filthy Mad Max kludges instead

      1. I’d say the best way to accomplish this is a pair of independent, freewheeling chain drives – inexpensive, off-the-shelf bike parts.

        I’m a turn, the outer wheel runs a little faster and freewheels – unless you push it hard enough to overload the inner wheel, then it just acts like a locked diff.

        If I’m not mistaken, early motor vehicles, like WWI era trucks, were set up like this.

        No reverse gear, but it’s not needed for a light vehicle like a cycle.

        1. That method would be simpler just using one way bearings on the shaft to wheel hub setup then you can drive the main shaft with a single sprocket. Don’t forget brakes on each wheel.

        2. Main problems with that setup are how hard you have to push on really right (near zero radius) turns since you’re powering the inside wheel at all times. Also, depending on where they are in there system, you may have to completely reconfigure braking

    1. Pedal-generator-motor-wheel can work at surprisingly high efficiencies (at least, comparable to chains), and it’s trivial to stick a motor per wheel and just let them run at slightly different speeds if needed.

      1. You reckon? Chains are generally considered 90-95% efficient in low load scenarios. Motors are generally 80-90 across their operating range. Batteries 85. Converters 95 each way…..

  1. Inboard brakes are rarely preferable for anything due to the huge increase in half-shaft mass required to resist the high braking torque (usually a lot more than the torque available from the engine).

    1. The brake rotors are larger than the chain ring driving it and the stub axles are from a far more massive vehicle. Maybe if he puts CV axles in from an ATV there could be issues moving them inboard but I assume he’s making a tradeoff in favor of reduced mass at the wheel. If this had been shaft driven, a traditional diff could use a single brake rotor at the pinion. Then we could have hoped for a video of machining a Torsen LSD on the lathe for brake biasing…

      1. One legging on acceleration isn’t great, but one wheel brakes?
        The LSD wouldn’t have been optional, unless he plans on dying on the thing. Even 4×4’s that use pinion mounted brakes only use them as e-brakes. Because brake cables are a huge pain when combined with big lifts and tires.
        Electronic e-brakes are just a money maker for stealership service departments, like self closing doors, for suckers only.

        GP’s point on half shafts was the un-sprung weight you save by moving the brakes inboard is offset by the un-sprung weight you lose to bigger half shafts. Even Jag came to their senses, no amount of service department revenue made those a good idea.

        As you say, he’s using stupid big half shafts (to match the diff components off a diesel), as the project sits. Even ATV parts would be huge overkill. Human legs make about 1 pony for very short bursts.

    2. Unless this vehicle is going to be FWD, the brake torque on this end just isn’t going to be that huge.

      There’s also the possibility that there is a desire to avoid flexible brake lines/linkages.

  2. The reasons a go-kart is able to experience 4gs of forces in turning is specifically because of the design it uses without a diff. The chassis flexes to lift the inside rear tire so a diff is not required. If I had to guess, the use of a diff would only be slower then the current system in place but I could potentially be mistaken. I’d have to see some evidence to believe it would be a better system. The greatness of a go-kart is the performance to simplicity, which results in a lower price/ enjoyment ratio (in relation to other race at sports that is, racing is always expensive)

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.