Your shop may not see drivetrain assembly damage too often, but a clear understanding of drivetrain diagnosis and repair will keep you primed for the next time you do.
The tires screech, there is a loud bang, the driver and passenger are thrown forward, the airbags deploy and the front rails collapse along with the front sheet metal. These are all typical problems for the collision repair shop to handle…except for the fact that a 300 to 500-lb. engine and drivetrain assembly have continued their momentum forward after the crash.
The energy in a forward moving drivetrain assembly is pretty significant. All of this energy is held in place by the motor mounts. This requires a special inspection as engine/drivetrain mount damage is often difficult to detect. It is hidden by the mechanical components themselves, and even when you can do a visual inspection, you may not be able to detect that damage. A dynamic test may be in order. Using a pry bar or other tools to pry the engine up or sideways to detect mount damage is often necessary. Caution must be taken to avoid damaging the sheet metal or paint. Remember, that 500-lb. drivetrain assembly was stopped by the frame or structural rails.
What actually happens when the force of the drivetrain assembly continues forward is something that needs to be inspected each time a crash of this caliber happens. Some of the adjoining parts that need to be inspected for damage include the following: engine mounts and cradles, pulleys and belts, exhaust systems, fuel electrical components, air conditioning systems and secondary damage to the frame or structural rails. All hose lines and linkages should be checked for secondary damage as well.
Damage may exist to the engine or transmission itself. Mounting tabs or slots can be broken or bent. If this is the case, a further inspection may be needed. This type of damage can sometimes total a vehicle because of the cost of replacing an engine or transmission housing. Drive axles must be inspected as they are often involved in the collision. A close inspection with droplight or flashlight can reveal fluid leaks, which are usually an indication of mechanical problems.
If it is determined that frame or structural rails need to be replaced, we must consider the fact that the drivetrain assembly may need to be removed to do a proper job of fitting, measuring, welding, cosmetic repairs, corrosion protection and refinishing. All too often, these procedures are written up on the estimate with economics as the priority because the insurance company didn’t want to spend the money necessary to remove, inspect and replace the drivetrain. Sometimes the estimator just doesn’t understand the level of access needed by the repair technician to do the job properly, so it didn’t get written up for remove and install (R&I) operations.
Let’s assume the engine/drivetrain does have to come out of the car we just crashed. There are several things that dictate this decision. The structural rails are damaged past the point of repair, and we must section them just forward of the engine mounts. It has been determined that we can’t do a proper job without the removal of the engine/drivetrain assembly.
Once the decision has been made to remove the drivetrain, a good way to avoid mistakes is to take several photographs of the engine compartment. A video camera is also a good idea. Besides being a good reference source, it can also provide documentation of damages. Images of the damaged areas can often be used to clear up misunderstandings before, during and after repairs.
So what comes off first? Where do we start? The best source of information is the service manual specific to the vehicle. Included in these manuals are step-by-step instructions on how to remove and install drivetrains as an assembly or in parts. The service department at the dealership that sells these particular vehicles will have these service manuals available. They may be purchased from the manufacturer or borrowed from the dealer. Another great source of information is a set of instructions in a generic manual printed by non-OEM or aftermarket data and information sources such as MOTORS, Chilton, etc. These information sources provide detailed procedure explanations and drawings. These may be available in book form or on a CD. Another source of information is the I-CAR Technical Centre. If they don’t have the information you need, they can usually tell you where to obtain it. Their number is (800) 832-4990. Another source of information is TECH-COR. This is a collision testing and procedure documentation organization. They are a great source of information to the collision industry and the technicians working within the industry. They can be reached at their Web site, www.tech-cor.net.
Careful consideration must be given to all electronic and computer controlled systems. Everything must be disconnected according to the manual to avoid having to reprogram computers at the end of the repairs. John Fournerat is a collision/mechanical instructor in the Collision Repair and Refinishing program at the Universal Technical Institute in Houston. Fournerat says that improper disassembly is a critical but common mistake made by many technicians. “Always follow the instructions to the letter. If some things are done out of sequence, you may have to reprogram computers, etc. Pre-planning the repair is very important as well. The longer the vehicle is disassembled, the more time the computer capacitors have to drain down. A capacitor is an energy storage device designed to keep computers ‘alive’ when the vehicle is turned off or the battery is disconnected. The capacity of these devices and the time it takes to drain them can be found in the vehicle repair manuals in the disabling procedures. Reprogramming computers is expensive and sometimes can be avoided if proper planning is done.”
Proper tools must be used to disassemble and re-assemble the vehicle to avoid damaging parts and connectors. AC freon and engine coolant should be recovered and recycled or replaced depending on the recommendations of the manufacturers. Motor oil, power steering fluid, transmission and brake fluid, and all other fluids must be considered in the process. If fluids have spilled or leaked, hazardous materials charges are needed, as this material must be properly disposed of. If they are disposed of, they obviously need to be replaced.
The drivetrain is then unbolted following the instructions in a step-by-step fashion and set aside while other repairs are being performed. Fournerat also points out something that many technicians and estimators do not consider. “The drivetrain R & I operation takes up two working stalls, and in many cases, if one technician is assigned to do the job, they must get assistance from time to time to do the job,” he says.
Fournerat adds, “Keeping track of all small parts and fasteners is critical. Zip-lock plastic see-through bags are used to keep fasteners separated. Exhaust fasteners go in one bag and are marked as such. Care must be taken to prevent dirt, moisture and other contaminants from entering the engine components. We use golf tees to plug lines, balloons to cover tubes and hose ends, plastic bags and tape to cover others.” Each system of the drivetrain is separated in this fashion. “It makes the re-assembly process much easier. You should also be aware that many of the manufacturers use one-time-fasteners. These fasteners should be discarded and new ones ordered right away. This information is also found in the service manuals. If one-time-fasteners are reused, it could result in the failure of these fasteners,” he says.
Safety is also a consideration. Proper eyewear, ear protection, steel-toed boots and gloves are considered safety-conscious essentials.
Once the engine/drivetrain assembly is removed and collision and refinish procedures are complete, it is time to re-install the drivetrain assembly. The same manual must be used to re-assemble and re-install all parts and assemblies in the correct sequence. Routing of hoses and electrical wires is very important. If wires are routed incorrectly, it may affect the performance of the engine and other vital systems. Airbag wiring and sensor positions should be double-checked. Once again, the proper tools must be used to avoid damage to fasteners, connectors and components.
Testing the systems involved in the operation is next. Leak detection tests must be performed on the AC, fuel, cooling and brake systems. There are testing tools for most systems. All fluid levels—motor oil, transmission fluid, coolant, brake fluid, etc.—must be inspected and documented. We would hate to spoil all of this work by blowing the engine because of low or no oil, water, etc. Murphy’s Law is in effect here: “If any thing can go wrong, it will.” A checklist may be available in the repair manuals for a post repair inspection. It is always a good idea to review such a list and make sure everything is working as it was designed.
The last thing we need to do after all repairs are made is test drive the vehicle. Some of the computer systems may have to re-learn their functions. This may be true even if the timing of the job was good and none of the computer capacitors drained down completely. The fact that they were disconnected in the first place may have signaled them to partially shut down, and now it is necessary to drive the vehicle so that it can re-learn all functions. These procedures are often covered in the repair manuals as well.
Test-driving the vehicle is done to make sure all systems and parts are functioning at their pre-loss status. The repair manuals may describe this procedure as well. In some cases the vehicle will not be expected to run and perform as it should until it has had a chance to be driven for a specific amount of time or distance. This is needed for the re-learning processes of the computers.
This is all a matter of quality control. Do we want to conduct these tests ourselves—to find any errors that may be the result of human error or mechanical failure—or do we want the customer to be the first one to notice these things? We should be focusing on who our customer really is—the vehicle owner.
Drivetrain removal and re-installation is not rocket science, but it is not necessarily common for the collision technician, either. It may be worth the time to learn these procedures, as mechanical operations pay at a much higher rate than collision repair work. Why is that anyway? Maybe that’s a subject for another day....
