BUMPERS AND BRUISES
Evolution of the car’s shock absorber
Duct tape isn’t meant to hold together a car. But I’ve often seen the strong, silver tape (although it now comes in many colours, and even patterns) used in an attempt to mend cracks or keep a bumper skin attached to a vehicle.
I saw a Mazda the other day where the rear bumper skin was artistically duct taped to the quarter panel. That got me thinking about bumpers.
From the earliest days, automobiles were outfitted with steel guards at each end of the vehicle to help protect the body panels in low-speed impacts and to act as crash protectors in high-speed collisions. Back then, bumpers were usually bolted directly to the frame rails.
As automobile design progressed, many bumpers became large and in charge: think American cars such as 1950s Cadillacs. But in the early 1970s, U.S. and Canadian government crash regulations and increased interest in pedestrian safety resulted in changes to bumper design. Bumpers had to protect sensitive vehicle components such as lights and gas tanks in eight-km/h impacts up front and four-km/h impacts at the rear and offer some give if a pedestrian was struck.
Some manufacturers responded with bumper shock absorbers, and they acted exactly as the name suggests. No longer was the bumper bolted directly to the frame; instead, it was mounted on small shock absorbers that were meant to compress and spring back upon low-speed impact.
“Sometimes, those shocks would have to be replaced,” said veteran autobody repairman Ken Friesen when questioned about bumpers.
“I think it was around 1973 when bumper design really started to change,” said Friesen, proprietor of Concours Collision Centres Ltd. in Calgary. “In 1972, a Corvette had chrome steel bumpers front and rear, but in 1973, the car had gone to a plastic front and chrome metal rear. In 1968, Pontiac gave the GTO a steel front guard wrapped in urethane, and that changed the look of that vehicle.”
Other manufacturers, such as MGB, introduced in mid-year 1974 the “rubber bumper B.” To continue selling cars in North America, MG replaced its distinctive chrome metal guards with a steel protector covered in thick black rubber, both front and rear, and raised the ride height by 25mm.
Friesen said it was in the early 1980s that bumper structure changed. That’s when the U.S. government enacted more new regulations, and unibody vehicle construction became the norm.
Guards became what Friesen called a reinforcement bar, usually made of a high-strength material such as steel, but sometimes plastic, bolted to the underlying body structure. Over the reinforcement bar there’s often a layer of high-density foam capped off with a urethane “bumper cover” or fascia.
It doesn’t take much of an impact to wreck this fascia, and in a low-speed impact, the cover often gets cracked or otherwise damaged. On older vehicles equipped with a broken fascia, the duct tape fix might work in a pinch. But that isn’t true for newer ones.
“It’s really important now, with all of the cameras and sensors (embedded in the bumper covers of many new vehicles), that the cover goes back together correctly after a collision,” Friesen explained.
“A sensor that’s off by just a millimetre can cause the computer to throw all kinds of codes, and affect how a safety system is supposed to work.”
In years past, Friesen said, a fascia was often repaired by reinforcing the crack with a glass-fibre material on the inside, followed by grooving and then filling the outside before painting.
“It can take three, four or five hours at roughly $100 an hour, including materials, to fix,” Friesen said. “On an average modern car like a Chrysler, Ford, GM, Honda or Kia, for example, you can buy an OEM (original equipment manufacturer) fascia for about as much as it would cost to fix.”
While there once was a brisk trade in remanufactured bumper skins, many OEMs have lowered their prices, effectively killing off the practice.
“And here’s the clincher,” Friesen said. “Locally, there’s nowhere to recycle a bumper skin. I have to cut it in half so it fits in the Dumpster and, unfortunately, it’s going straight into the landfill.”