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Diagnosing Power-Train Damage

Ever suffer from “post traumatic tail light syndrome” — as the customer drives off in his newly repaired vehicle, you wonder if you found all the damage? To help, techs offer insight on finding elusive mechanical problems.

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After a vehicle is released to the customer, do you ever wonder — as he drives his newly repaired car off into the sunset — that you may not have found all the damage?

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"Post traumatic taillight syndrome," as some in the industry call it, seems to be quite common. As you watch the taillights of a customer’s vehicle get dimmer in the distance, you sometimes second guess your diagnosis and repair. Was I thorough enough? Did I check and then re-check all the right components?

Most estimators use an A-to-Z process during vehicle inspection to build an estimate that includes mechanical damage done to axles, spindles and other components in the direct path of force caused by a collision. But to get a handle on the not-so-evident damage that might show up in engine, transmission, and primary and secondary drive-line components, I spoke with fellow collision specialists, as well as transmission/drive-train techs.

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Big Troublemakers
C/V shafts and joint problems, which are often missed on the estimate of any particular job, were the first things everyone noted as troublesome. The biggest offender, they say, is the inside plunge joint on front-wheel-drive (FWD) vehicles. Chips in the hardened raze areas brought vehicles back because of vibration and noise upon acceleration and deceleration. Independent suspensions found on many new domestic, full-size trucks and four-wheel-drive (4WD) vehicles lead the way in such problems, say many shop owners.

The next obstacle, says Larry Warren of Warren Auto Works in Springfield, Mo., are bent axles on C/V-equipped vehicles, which are harder to spot than similar problems on rear-wheel-drive (RWD) vehicles. How do you go after a bent axle? Some techs simply pull both axle shafts and then remove the joints for inspection while the vehicle’s on the bench. Place the axle between centers or in a "v-block" setup to find any run-out.

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Four-wheel-drive hubs are often a big problem, say several techs. A new hub design found on ’97 and newer Ford trucks is vacuum controlled and is fragile and hard to work on. A direct hit to the wheel can wreck the vacuum seal, and though the hub may look OK, it won’t function. Other 4WD hubs incur damage to plastic engagement parts and suffer distorted casings after a solid hit. But that’s just the beginning. More 4WD problem areas may include transfer-case chain breakage (the shock from the impact can fracture an already worn chain that has a lot of lash), shearing of gear teeth on speed and reduction gears, cracked synchronizers, and twisted or bent-off-center axle tubes on housings. RWD and 4WD vehicles can also lose teeth on the final drive ring or pinion.

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Transmission Troubles
"The really big heartaches come from transmission problems that don’t show themselves for several hundred miles or so," says Barry Million of College Street Auto Body in Springfield, Mo. "At the very least, shops should run electronic diagnostics after a road test and include the results of this diagnostic forum as an FYI item on the service order."

Many collision shops already include analysis for other critical systems, such as supplemental restraint systems (air bags), anti-lock brake systems (ABS), traction-control systems (TCS) and active chassis and suspension systems (ACSS). Transmission diagnostics are just another way to verify that things work correctly.

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Automatic-transmission rebuilders at Counter Transmission in Reeds Spring, Mo., spoke of collision-damaged vehicles suffering from broken or bent parking pawls, as well as smashed linkage and broken mounts and brackets. Though rare, bent flex plates and damaged transmission input shafts or torque converters and pumps also have been found after a major hit. "A lot of this stuff goes to the bone yard," said John Mueller, service tech for Counter Transmission.

Also, transmissions with smashed pans, especially on the newer designs, are subject to kinked lube piping, say experts on automatic-transmission problem areas. A minor collision might result in a smashed pan, which is then replaced, but the kinked lube piping isn’t usually spotted until the vehicle is back with a transmission failure caused by the original collision.

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Engine Grief
If you’re really looking for troublesome components, says Pratt Ellison of Monroe Auto & Paint in greater Knoxville, Tenn., check out the engine of a roll-over vehicle that may have run for any length of time while it was upside down. Vehicles subject to this kind of damage, if they’re not totaled, must have the engine exchanged or torn down for an internal inspection. Problems you’d most likely find, says Ellison, are engine parts scored from a lack of continuous lubrication. The intrusion of fluids into alternate power-train cavities — for instance, transmission fluid that’s flowed past a worn or damaged seal into the transfer case — are common.

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"We once repaired a Toyota 4×4 that ran up-ended for less than three minutes. The engine seemed all right, but we wound up with real problems after [we released the vehicle and] the customer had it torn down by a dealer who was attempting to solve a valve-noise-related problem. The dealer found internal engine damage due to lack of lubrication," says Ellison. "That one came out of our own pocket."

As a side note on roll-overs, Dave Hebert — a mechanical-gearbox rebuilder at Go-Some-More Transmission in Pt. Pleasant, N.J. — says the really difficult-to-diagnose items can be as simple as deformed forks that prevent good shift feel. "A driver who grabs on to that stick shift for dear life during a roll-over can do some difficult-to-find damage to the shift quadrant."

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One Shop’s Suggestions
Top Craft Body Works in Springfield, Mo., looks at each vehicle as a separate case, says Steve Summey, spokesman for the company. This shop has seen lots of cracked cases on transmissions, damaged drive shafts, broken ears on transmission and engine castings, and displaced cradles. "If you have a bent C/V shaft, you can expect that the FWD cradle is moved over some. [Be sure to] measure it and restore it to spec," says Summey. Others agreed, and a few even go so far as to pull apart final drives on FWD vehicles.

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Side gear damage is rare, says one tech, but axle deflection can cause a seal to begin leaking in a couple hundred miles since it’ll be riding on an untried area if the axle has displaced it in the housing. Often, the water deflector can be bent, subjecting bearings to problems because of water spiraling down into the bearing cavity during wet-weather operation. Some later models can wreck steering-gear boxes, including fracturing worn drive gears.

The techs at Top Craft also change a lot of control-arm shafts, arm assemblies and tie-rod ends, as well as damaged racks. The trickiest items, says Summey, are internal problems in manual transmissions. "These things are the direct result of shocks that travel down through the drive train after mounts are grounded from deformation due to the initial effects of a collision."

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Diagnosing Power-Train Damage
Estimating the damage on any vehicle in your shop should involve a very comprehensive inspection of the entire vehicle, including all the mechanical components. The harder-hit vehicles should initially be evaluated for power-train damage, and insurance companies should be informed of any suspicions right away.

If you’re unsure of the degree of damage, an off-site inspection by an area expert may increase your chances of finding and repairing hard-to-find damage. An increased emphasis on dyno testing a vehicle for emissions might also be used as a fail-safe measure for mechanical-related comebacks.

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Talk with other shop owners who’ve seen and solved such power-train problems and learn from their mistakes. Above all, follow a set plan — like the A-to-Z process — while inspecting a damaged vehicle to be sure you’ve covered all mechanical components. You may not be fully cured of "post traumatic taillight syndrome," but you will at least be more confident in your estimator’s inspection and less likely to second guess your shop’s work as the customer drives off into the sunset.

Contributing editor Bob Leone, a retired shop owner, 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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