Identifying drivetrain components: Front wheel drive

When an automobile is involved in a collision, it is important to not overlook damage to drivetrain components that are attributed to the collision. Not only is it in the best interest of the vehicle owner to get their vehicle made whole, a collision shop opens up a whole new revenue source when they perform repairs beyond the sheet metal.

This month we will cover typical FWD components and what to look for when assessing a vehicle post collision. For the past ten to fifteen years, FWD is the most common of the drive train you will find in most cars, mini vans and small SUVs. Most 1500 series and up trucks and vans still use Rear Wheel Drive (RWD), but cars typically utilize FWD.

Using the front tires to pull the rest of the car forward, you won’t find much going on in the back of a FWD car. Just normal suspension of various types with the only spinning components in the back being the tires and related wheel bearings. Most of what comprises a FWD drivetrain is going to be located forward of the passenger compartment.

Typical FWD powertrain configuration: 2004 Chrysler Town and Country

Transaxle
Transaxle is a fancy name to describe a FWD transmission. A transaxle combines 2 major components into one, the transmission and the differential. Transaxles are designed in three basic flavors: Manual, Automatic and Constant Variable Transmission (CVT). From a collision aspect, the different types do not matter much as most share similar dimensions and external components that are easily damaged during a significant impact.

In all types of transaxles, the transmission part connects directly to the engine and harnesses the power from the crankshaft to the torque converter or mechanical clutch depending on which transmission type you have. From there, the power works through the transmission portion to the differential which is either integrated directly into the transaxle case or bolts immediately to the transmission housing.

When inspecting the exterior case of a transaxle, pay special attention to any impacts and look for cracks. Transaxles typically utilize an aluminum housing and aluminum tends to crack and break when impacted. One of the reasons engineers use aluminum is because it is quite ridged and will retain its form under normal use. Unfortunately, this rigidness becomes a detriment during a collision. While this is bad for the crashed car, it is good for those of us doing the inspecting as, generally, aluminum damage stands out quite well.

Broken bell housing/case 2004 Chevrolet Monte Carlo

This cooler from a 2004 Chrysler minivan has separated from its mount during a collision. Tricky to spot but if let go the long term vibrations will cause cooler or related component failures.

Typical axle shaft

Bell housing
The bell housing is the section of the transaxle that bolts to the engine. This is a common spot for fracture as the aluminum can be pretty thin in spots. Any signs of cracking or fractures should be a flag that the transmission will need to be removed and inspected more carefully. Either the entire transmission will need to be replaced or, for the more technically savvy, the damaged housing can be replaced. When inspecting the bell housing, do not forget to look at the engine too. Many cars utilize an aluminum block engine and if a transmission is damaged often the engine will suffer damage as well.

Transmission case
Cracks in the automatic transmission case often result in leaks because you have an internal pump pressurizing passages inside the case. So, if you have a crashed car spewing out transmission fluid that is an indicator the main housing of the transaxle may been fractured. Usually just cleaning off the fluids and having a helper start the car and cycle through the gears is sufficient to nail down the source. Manual transmission cases generally won’t spew fluid running so you may have to drive and re-inspect for leaks. Sometimes a chunk of case will break off and not create a leak. Inspect mount locations carefully because they often take the brunt of a collision.

Transmission coolers
Like case sections, damaged transmission coolers tend to leak badly when the engine is running. Keep in mind transmission coolers are exclusive to automatic type transmissions. Generally, if equipped, the cooler will be located in front of or integrated into the radiator.

Differential
The differential is used to convert the power coming from the transmission and split it to both drive tires in a way that allows for smooth driving. Like the transmission case, these housings are typically aluminum; however, they may not leak with just the engine running and in gear. Like with a manual transmission, this is something that may need to be driven and double checked post repair. On top of physical damage externally, differentials can be broken internally during a collision so when performing quality control check post repair pay attention to any odd noises or vibrations.

Axle shafts
All FWD cars have 2 axle shafts that deliver power from the differential to the wheels. These are a very common component broken during a collision. They are comprised of 3 major components: shaft, joint (2) and boot (also 2). Shafts and joints break and boots tear. Any damage to these components should be remedied by replacing the respective assemblies.

Wire harness, solenoid packs and ECM are often exposed and easy to damage in a collision, visual inspection can often identify damaged components.

ATF is no longer something that is ideally kept in bulk containers, using the correct fluid is part of being a professional. If you are not stocking, multiple transmission fluid options you are doing it wrong!

Electrical
You won’t find a modern car that doesn’t have some sort of wire or sensor going to it. Many automatic transmissions even have Electronic Control Modules (ECMs) and/or solenoid packs mounted externally to the case. Damage to ECMs, solenoid pack or sensors warrant replacement. Damaged wire harnesses should be assessed for either reconstructing or replacing depending on your shops skill level. Do not try and reuse cracked or smashed electrical connectors and remember that ECM and solenoid pack replacement may require special manufacturer specific scan tool procedures or programming to get them operational.

Fluids
Often overlooked, it is important as a service professional to make sure you are putting the correct Automatic Transmission Fluid (ATF) in when you are topping up after a repair. Red is not an indication of transmission fluid type and failure to use the OEM spec fluid could cause shifting concerns or, even worse, a premature failure. Universal transmission fluids often do not meet the OEM spec. Use your service information to ensure you are ordering the right ATF.

Taking the time to identify powertrain concerns while doing your post collision damage assessment adds a higher level of service for your customer and will bring a lot of money to your bottom line in broken components. Failing to take the time to verify the condition of power-train components is doing your clients a huge disservice!