This week I noticed a clunk noise in the back of my 2004 Toyota Highlander when I change between Drive and Reverse and when I ease up on the gas pedal after accelerating. After checking it out, my mechanic told me that I have failed bearings in the driveshaft U-joint.
On most cars, this would be a relatively inexpensive repair, but Toyota has staked in the bearings so they are not replaceable. Toyota's solution to my problem is for me to spend $1,900 on a new driveshaft. Is there a good mechanical engineering reason for this? -- Dave
When car makers say you have to replace the entire driveshaft instead of just the worn universal joint, are they giving you the shaft?
David Weatherhead, automotive instructor at Centennial College in Toronto, says "The research and development department felt it was a good idea" is his standard, if unclear, answer for students who ask why an auto maker would choose to do this.
Universal joints allow for minor changes in driveline angle without stressing the spinning driveshaft, Weatherhead says.
"All of the movement in a universal joint takes place between the trunion, needle bearings and end cap," Weatherhead says. "The cap must be secure in the driveshaft yoke. Methods of attachment are snap ring, injected nylon and staking."
Many car manufacturers now use staking, where the metal is peened over, to seal the U-joint into place. Why? "It reduces the amount of vibration and is said to prolong life," Weatherhead says.
And staking saves time and money when cars are built, says Naleen Jit, automotive instructor at the British Columbia Institute of Technology in Burnaby.
"I think in the end consumers what a reliable product, time and money saved on production can be put towards a better engineered product," Jit says.
We asked Toyota for their explanation.
"The drive shaft in this vehicle is phased and balanced per Toyota's specification as a unit at the factory level to maintain quality and consistent ride comfort among other things," Melanie Testani, Public Relations Manager for Toyota Canada, said in an email. "If the customer is seeking an explanation of the repair details for his vehicle in particular, we do recommend that he asks his Toyota Dealership service department for further assistance in understanding what is required."
You can buy aftermarket U-joints and get them replaced separately, while keeping the original driveshaft.
"There are parts available which allow the replacement of the individual universal joints on the Toyota Highlander but in order to do this there is a risk of damaging the shaft in the process," he says. "If the universal joints are not installed correctly they will cause vibrations and possible noise while driving."
And getting a mechanic to replace just the u joint won't save you money. Jit says.
"Having a technician replace a driveshaft is more cost effective for the customer since it will cost more time and money to replace universal joints," he says. "Customer need to be aware that in some cases trying save some money on these types of repairs will end up costing more in the end."
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