Powertrain Considerations - BodyShop Business

Powertrain Considerations

It’s easy to spot a dented fender, a cracked headlight or a crumpled rear decklid. But since there’s more to a collision-damaged vehicle than meets the eye, powertrain damage should be a top consideration –– if you want to ensure your customers’ vehicles get thoroughly repaired

During the early days of the automobile, minor fender-benders between "tin lizzies" often produced damage that wasn’t apparent at first glance. Today’s collisions aren’t much different. Though the technology of vehicles and the equipment used to diagnose their damage have advanced, estimators must be vigilant when preparing estimates for vehicles involved in hard hits.

One area sometimes unchecked but often damaged in hard hits is the powertrain, which consists of the transmission, the drive shaft, various mounts and other related components. To help ensure that your customers’ vehicles are getting thoroughly repaired, I spoke with repair experts about diagnosing and repairing powertrain damage.

Collision Consequences
When I spoke with collision service director Jim Borroughs and ASE-certified collision tech Sharkey Gammel — both of Tri Lakes Ford/Chrysler in Branson, Mo. — they said displacement of the cradle, which affects drivetrain alignment, is the most common type of damage that may affect a vehicle’s powertrain.

"After some Chrysler minivans leave the shop, drive-shafts will pop out of the transaxle if the shop has failed to identify and repair [drivetrain] damage by restoring the geometry of the front mounting cradle," says Burroughs.

When a vehicle is hit straight on, problems can also include damaged mounting brackets and punctured liquid-filled mounts, which can slowly seep fluid and cause powertrain vibration after the vehicle has been released to the customer.

Depending on the vehicle’s frame design, a head-on collision can cause even greater powertrain damage. On unibody structures with a "torque box" design and energy diffusion (or crush zone) technology, the energy cell serves to protect occupants by spreading the energy away from support areas.

"In a direct frontal hit, the torque box may shift and damage another section of the unistructure," says Gammel. "Identifying and restoring this damage is the key to a perfect job. If full restoration doesn’t occur, the power train, suspension and steering unit almost always suffer disablement of some sort."

Gammel, who heads the collision repair team at Tri Lakes, says that to be sure no powertrain damage is missed, the shop utilizes the mechanical-service department to check problem areas in both automatic- and manual-transmission-equipped vehicles.

When examining a collision-damaged vehicle, be sure to look for cracked transmission housing and broken mounts. Also, be sure they perform pressure and function checks using compressed air on automatic transmissions.

When a vehicle is hit from the side, the result often includes bent axles and damaged C/V joints on the opposite side of the hit. Finding such C/V damage isn’t easy and may require that techs remove and disassemble the shafts for detailed inspection.

"Since most vehicle trailing axles are independently supported, we always look for a twist in the suspension points that might also create a drive-line pre-load problem," says Gammel.

Damage to critical powertrain components — including mounts, brackets, and spring and suspension anchors — is considered primary damage. But in side-on collisions, the force can damage tires and wheel alignment in addition to drive-train components. To be safe, Gammel suggests techs always check for possible secondary damage. If secondary damage has occurred and is to be repaired, techs must be careful not to over-pull primary areas and create even more problems in the powertrain.

Paul Burgant, an independent repair instructor from Odessa, Texas, says damage to the drivetrain should always be examined when a vehicle has been involved in a rollover. Vehicles that have run upside down without lubricant are likely to have internal damage. "Some transmissions are subject to lubricant-starvation problems in critical areas that supply planetaries and support bushings," Burgant says.

Such components will be scored almost as soon as the flow of lubricant stops. And if the powertrain runs while inverted for any length of time, the transmission will displace bushings and deposit material throughout the fluid-return and lubricating circuits.

Gammel agrees with Burgant’s damage assessment, adding that there’s almost always secondary damage to powertrain components when a vehicle has rolled over. Clutch hydraulic systems can pick up air, and getting the clutch system bled so the vehicle can be test driven is a challenge. According to Burgant, newer injector-type bleed-out equipment, which has all but replaced older pressure "bomb" type bleeders, can prove helpful in the repair process.

Rear-end collisions often cause some displacement in differential mounting or support fixtures. On rear-wheel-drive vehicles with independent rear suspensions with half shafts, damage can be similar to that found on front-wheel-drive systems. In a collision, rubber support mounts and torque arms are sometimes relocated and under tension thanks to twisted or out-of-position mounts at either end. These mounts should be free moving and allow for pivoting at the mounting point. Any tension will create unequal torque, which will impart a thrust or sideload into the drive line, causing a lead or pull. Rapid wear of parts and noise can also accompany this type of problem. To fix this, it’s necessary to reposition or replace the damaged mounts.

Other common problems mentioned by techs included crushed driveshafts on rear-wheel-drive vehicles and broken or twisted leaf spring mounts, shackles or hangers. Problems with side set or axle skew will sometimes require replacement of the vehicle’s differential housing. Burgant suggests that shops always look carefully at the drive-line angle, both at the differential and at the transmission or transfer case.

Drive away or "launch" vibration is also very common following a rear-end collision, says Burgant. This may occur when the rear differential moves too far out of position when the vehicle torque is first applied and may be due to improper drive-line angle or defective springs or torque arm mounts.

Solving Manual-Transmission Problems
When I spoke with a few techs about internal damage to manual gear boxes, most agreed that clutch pressure plates can frequently be damaged on stationary vehicles hit from the front or rear. Finding and repairing such damage is important. One tech said a recently repaired vehicle was returned to his shop suffering from clutch failure. The diaphragm-type clutch pressure plate showed unequal finger position and definite signs of uneven contact with the throwout bearing due to misalignment.

Cracked or broken gears and damaged synchronizers are often the direct result of a collision. Many techs I spoke with said such problems often won’t manifest for months or thousands of miles after the repair, so it’s important to check for damage while the vehicle is in the shop.

"When repairing one of these hard hits, a good mechanical inspection is necessary," says Burroughs. "Insurance companies should be made aware of high-risk items that might be problem areas down the road if they’re not replaced at the time the structure and refinish work is completed."

Damage Control
As vehicles have become more complex, so have repairs. There’s more to consider on a collision-damaged vehicle than a dented fender, a cracked headlight and a crumpled rear decklid. To ensure a complete repair and total payment, estimators need to document every inch of the vehicle, including the not-so-obvious damage that often occurs to a vehicle’s powertrain.

But diagnosing damage is only half the job. It’s up to your techs to ensure that a vehicle’s powertrain is restored to factory specs — and that your customers get the thorough repairs they deserve.

Writer Bob Leone, a retired shop owner and contributing editor to BodyShop Business, is ASE Three-Way Master Certified and is completing qualifications as a post-secondary automotive instructor in the vocational-school system in Missouri.

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