Differential Basics
As a vehicle goes around corners, the outside wheels have to travel a greater distance than the inside wheels. While the difference seems minor, a vehicle is a precision machine, and small variances could do a lot of damage over the long run if not compensated for. The Differential is responsible for this compensation in the driven wheels of a vehicle. It does so through a set of “spider” gears that mechanically transfer the torque from one wheel to the other. When one wheel needs to travel a smaller distance, it transfers some of its torque to the opposite wheel, which needs to travel the greater distance. This automated torque balancing action keeps the overall load on the engine and transmission steady, regardless of how sharp the vehicle is turning. In doing so, the gears in the differential experience heavy and varying loads, which leads to heat and wear on all the mechanical components. To ensure smooth operation, the gears need to mesh perfectly and stay well lubricated. That’s why they are bathed in thick, dense, gear oil that requires changing regularly to maintain its viscosity, friction reducing, and heat dissipation properties.
Differential Design
Differentials are normally designed for one of three types of operation: Open, Locked, or Limited Slip. A locking differential is designed to overcome the chief limitation of a standard open differential by essentially “locking” both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually. There are numerous variations such as manual and automatic locking designs, and several limited slip designs.
Open Differentials
An open (or unlocked) differential always provides the same torque (rotational force) to both wheels on the same axle. So although the wheels can rotate at different speeds, they apply the same rotational force, even if one is entirely stationary, and the other spinning.
Locked Differentials
By contrast, a locked differential forces both left and right wheels on the same axle to rotate at the same speed under nearly all circumstances, regardless of traction differences. Therefore, each wheel can apply as much rotational force as the traction under it will allow, but the torques on each side-shaft can be unequal.
A locked differential can provide a significant traction advantage over an open differential, but only when the traction under each wheel differs significantly.
All the above comments apply to central differentials as well as to those in each axle: full-time four-wheel-drive (often called “All Wheel Drive”) vehicles have three differentials, one in each axle, and a central one incorporated into the transfer case.
Limited Slip
Limited Slip differentials are considered a compromise between a standard differential and a locking differential because they operate more smoothly, and they do direct some extra torque to the wheel with the most traction compared to a standard differential, but they are not capable of 100% lockup.
Traction Control
Traction Control systems are also used in many modern vehicles either in addition to, or as a replacement of, a locking differential. This is not in fact a differential lock, but operates at each wheel. Sensors monitor wheel speeds, and if one is rotating significantly faster than the other the traction control system momentarily applies braking to the slipping wheel. This transfers more power to the wheel with traction by employing the open differential. If all drive wheels lose traction, then throttle control may be automatically applied. Electronic traction control systems are usually integrated with anti-lock braking systems, which have a similar braking action and use many of the same components.
Differential Service Recommendations
Most vehicle manufacturers recommend that the differential fluid be changed every 50,000 Km to 70,000 Km. We recommend even more frequently if the vehicle is used for towing or other heavy workloads. It is a messy job, and should be done by a licensed mechanic. The fluid will have to be disposed of properly, you may need new gaskets or seals, and the parts inside the differential housing will need to be wiped down so that any contaminants from the old fluid aren’t transferred to the new. Plus, the differential is underneath the vehicle so it will need to be lifted on a hoist for clear access.
During a differential service, our experienced technicians will diagnose any potential problems before they become significant. They can measure the float, run a gear pattern, set the preload, and inspect the axle and pinion bearings and seals. They’ll also inspect and make adjustments to any positive traction mechanisms to ensure they are optimized throughout the life of the vehicle. They can also repair any leaks that could lead to fluid loss and catastrophic failure of the differential.
You’ve had the Ring and Pinion Gear Set in your Differential Replaced – Now What?
When you’ve had a new ring and pinion gear set installed in your differential, we highly recommend that you follow these break-in procedures to ensure the best performance and longevity from your vehicle.
After driving the first 20 to 30 Km, stop and let the differential cool down. Keep the vehicle at speeds below 100 KPH for the first 150 Km. We also recommend putting at least 750 Km on the new gear set before heavy usage such as towing. During the first 60 Km of heavy usage it helps to go about 20 Km at a time, then stopping to let the differential cool for 15 minutes before continuing. This is necessary because not all of the gear tooth surface is making contact until it’s heavily loaded. When loaded, the teeth flex to make more complete contact and cause the previously unloaded portion of the teeth to touch and become work-hardened. All of this may seem paranoid but it is very easy to damage new ring and pinion gears through overloading before the teeth are broken in. If you take it easy on a new gear set and keep the differential full of clean, high quality oil, it will last a lot longer.
Bob’s Driveline Specializes in the Following Differential Services:
- Maintenance & Adjustments
- Repair Damage
- Change Gear Ratios
- Upgrade Torque Capacity
- Align Drive Angles
- Custom Design and Build
Visit Bob’s Driveline for all of your Differential Repairs, Service & Maintenance. Serving clients from Aldergrove, Langley, Abbotsford, and throughout the Lower Mainland. Call (604) 856-8816 to schedule an appointment, or book your appointment online HERE.
