Meet the Oids

Amboid and Hypoid… If you’ve ever heard these words, I bet you never gave them much more consideration. In actuality, they are impacting truck design and understanding what you have, and when you can expect one versus the other may be to your benefit. The terms refer to how the driveshaft is oriented for entry into the drive axle.

Amboid is considered high entry, or above the centerline of the axle. This position is least robust, but most efficient. So, when you chose an over-the-road suspension and desire an axle such as the Meritor MT40-14XHE or Dana D40-145, you will receive an amboid rear drive axle. This provides for High Efficiency Bearings on Meritor, which minimize driveline vibration. The flip side of the coin is that you cannot get differential (side-to-side) axles locks in the amboid axle. The position of the pinion it too high to accommodate the geometry of the gears. You could still have lockers in the forward drive axle, which is always hypoid.

Hypoid is defined as the pinion meeting the ring gear on the drive axle at a position below the centerline of the axle. This position is considered more robust, and is used for all vocational applications, as well as when differential locks are specified. This configuration will always be hypoid on both axles, so allows for full lockers (side-to-side on both forward and read drive axles).

Should your customer desire full lockers in the future, they are not available with an amboid axle. Knowing whether your truck will receive an amboid rear drive axle can be difficult, unless the spec is vocational. In over-the-road applications, typically defined by rear suspension selection, amboid is prevalent. In these cases, if there is any chance the vehicle may need a locking axle, a best practice may be to order a locker in the rearmost drive axle.