Trucks Aren’t the only Vehicles with 4-Wheel Drive - Transmission Digest

Trucks Aren’t the only Vehicles with 4-Wheel Drive

In this article we look at the BorgWarner 4476 and 4479 transfer cases, which are all-wheel-drive units. All-wheel drive signifies that the car has the ability to send power to all four wheels all the time with no driver controls. These transfer cases are essentially the same unit with some subtle differences and are found in the Cadillac SRX models. In 2004 all SRX models were equipped with the BW 4476. In 2005 this model was equipped with both the 4476 and 4479, and from 2006 through 2009 all were equipped with 4479 units.

Up to Standards

  • Author: Mike Weinberg, Contributing Editor
  • Subject Matter: Transfer cases
  • Units: BorgWarner 4476 & 4479
  • Vehicle Application: Cadillac SRX
  • Issues: Operation, diagnosis, service

In the never-ending search for market share, the auto manufacturers are now producing many passenger cars equipped with four-wheel drive. This gives these vehicles the ability to perform well in all kinds of weather and increases the safety level for the average driver under bad weather conditions.

In this article we look at the BorgWarner 4476 and 4479 transfer cases, which are all-wheel-drive units. All-wheel drive signifies that the car has the ability to send power to all four wheels all the time with no driver controls. These transfer cases are essentially the same unit with some subtle differences and are found in the Cadillac SRX models. In 2004 all SRX models were equipped with the BW 4476. In 2005 this model was equipped with both the 4476 and 4479, and from 2006 through 2009 all were equipped with 4479 units.

Both the 4476 and 4479 are one-speed transfer cases with no low-range function. These transfer cases supply power to both sets of axles using an internal planetary differential that splits torque to both the front and rear axles full time. The main difference between the two units is that the 4476 has a 50/50 torque split and the 4479 has a 40/60 torque split. The 4479 also has a different drive chain and larger CV joints on the driveshaft.

With both units, both axles are always being driven for four-wheel drive for better traction all the time. These vehicles are also equipped with Vehicle Stability Enhancement System (VSES), which protects the average driver from himself or herself. Through the use of the internal planetary, computer control and speed sensors, the system detects a slipping wheel and applies the brake caliper for that wheel, which sends torque to other wheels that have better traction. These units are found behind the 5L40-E and 5L50-E family of automatic transmissions.

There are several issues to be addressed with what is basically a very simple transfer case. First, as usual, tire sizes are critical to proper operation. Start any diagnosis by measuring tire circumference using a stagger gauge or a measuring tape around each tire at the center of the tread. If the tire sizes on all four wheels are not within 1/4 inch, the computer can interpret the difference in the tire rollout as a slip and begin pinching calipers when it is not needed. Tire pressure also must be within spec on all four wheels.

Next, these units have a lube fill of 0.53 quart. With only slightly more than a half quart of lube, to protect your customer and yourself you should require your customer to have the fluid changed every 15,000 miles.

A vibration damper mounted on the transfer case must be removed when you are servicing one of these units. Make sure to reinstall it when you are reinstalling the unit. The manufacturer never puts anything on a vehicle unless it is needed, so don’t neglect these parts.

When reinstalling the transfer case onto the transmission, line up the front prop shaft at the same time you slide the transfer-case input shaft into the transmission output shaft. Once the transfer case is bolted onto the transmission, the front prop shaft is too long and cannot be installed. You need some play between the transfer case and the transmission to complete the prop-shaft installation.

Another issue that needs to be addressed is towing and dynamic vehicle inspection. If your state requires a dyno test for emissions inspection make sure that all four wheels are turning on the dyno. Towing one of these cars with two wheels in the air or running it on a two-wheel dyno will over-speed the planetary into nuclear meltdown.

Looking at figures 1 and 2 you will see that these units are very simple one-speed transfer cases. There are some internal assembly routines that you need to follow correctly. Before disassembly mark the differential planetary carrier so that you do not reverse it on reassembly.

The input shaft must be installed into the carrier with the raised bosses (1) facing up and the thrust-washer groove facing down (Figure 3). If you reverse the carrier on the 4479 you will reverse the torque split to 60/40 when it should be 40/60.

On the carrier you have two sets of planetary gears and two sun gears. The upper set of planetary gears must be timed to install the upper sun gear. Rotate the upper planet gears so that the dots that are the timing marks are on the outside are lined up with the planet pinions (Figure 4). Unless this gear set is timed the upper sun gear will not go into place.

The addition of more all-wheel-drive transfer cases on passenger cars gives us new sources of revenue and more chances to repair more vehicles. As usual, understanding how they operate will add to your bottom line and prevent wasted labor and comebacks. Remember to look at the whole vehicle before removing the transfer case. These units are prone to stripped axle splines at the front differential, which may lead one to believe the transfer case has a problem when the front axles are really the cause of no four-wheel drive.

Mike Weinberg is president of Rockland Standard Gear.

You May Also Like

Lubricants: Understanding the Mysteries

Lubricating oils or lubricants have been around since the invention of the wheel, and every class or type of machinery uses and needs them. But, how much do we really understand about these products and about the amazing amount of engineering that is found in a can?

Up To Standards

Author: Mike WeinbergSubject Matter: LubricantsIssues: History, additives

Technical Training

Lubricating oils or lubricants have been around since the invention of the wheel, and every class or type of machinery uses and needs them. But, how much do we really understand about these products and about the amazing amount of engineering that is found in a can?

Tires Vastly Improved, but Check the Specs

The advancement of technology in the automotive field is rapid and unrelenting. Forces that shape the marketplace, state and federal regulations, the need to attract new customers, and the need to be different and at the same time profitable are driving the car makers to develop technology at a pace never seen before.

Are We Speaking the Same Language?

If you are repairing transmissions for a living, you will invariably spend some time on the phone ordering parts and speaking with technical hotlines to assist in your diagnosis of problems. Having been on both ends of a tech line for over half a century and an equal amount of time buying parts, I have learned a whole new language. To be successful communicating with those entities, one must understand the language and be speaking about the same correct topic with whoever is on the other end of the conversation.

Electronics In Dual Clutch Units

This article is the final segment of our exploration of the dual-clutch transmission, or direct shift gear box (VW and Audi) or DualTronic in BorgWarner’s brand. We have included several schematics from a VW Touran model, as VW has the largest amount of these transmissions in use. VW using its VAS 5051 diagnostic system provides for, as they say, “guided fault finding,” which means that a test schedule is available for the unit and provides testing for sensors, actuators and the mechatronic (computerized) valve body.

Hydraulic & Fluid Controls in Dual-Clutch Units

To recap, we have looked at how the dual-clutch transmission functions, essentially two gear boxes in one with the input shafts driven by hydraulically applied clutch packs that drive three concentric shafts that are one inside the other. The innermost shaft drives a gerotor-type of fluid pump that provides pressurized fluid to actuate the dual clutches, lubricate and cool the components, and shift the transmission into the selected gear. The next two shafts are driven by the two clutch packs with one shaft shifting the even-number gears and one shifting the odd-numbered gears.

Other Posts

Transmission Tech: 6R80 Harsh Downshift/Drive Apply Condition

Mike Riley is once again on the road, this time looking at a Ford truck with a harsh downshift.

TDTG 061820
Transmission Tech: How Other Components Impact Transmission

Mike Riley covers non-transmission components causing transmission problems.

TDTG 060820
Installation Matters

Zach Harkins, diagnostician, deals with a RE0F09A with a leak.

RnR-installation-matters
Transmission Tech: Subaru TR580 Converter Lockup Diagnosis

Mike Riley walks through the repair process on this Subaru.

TDTG 051920