Before attempting to DIY this repair, please read this entire blog. CARspec gets phone calls about DIYers struggling with this repair often and this blog was written to address the most frequently asked questions.
2004-2009 Toyota Prius vehicles can be prone to a growling or grinding noise from the front wheels, a noise that gets louder with speed or worse when turning. The most likely cause outside of a brake concern (meaning brakes that are worn to the point of abnormal noise like metal on metal contact) is excessive wear of the front wheel bearings. As the second generation (2004-2009) Prius has aged, this issue has become more common.
Inspecting for the issue is straightforward: while both front wheels are unloaded (i.e. off the ground safely) the front wheel is rotated by a technician while another listens with a mechanic’s stethoscope. A failed bearing will have a noticeable growling or grinding noise from the knuckle or bearing housing when inspected this way. The bearing may also have free play in extreme circumstances – you may be able to wiggle the wheel top to bottom or side to side.
The root cause of the issue is wear to the bearing race inside the front hub and bearing assembly. Here’s a new hub and bearing for reference:
The bearing is sold preinstalled to its housing, with a hub pressed in as well. Also picture above is the axle tone wheel’s deflector. This protects the axle’s high and low ridges of the tone wheel (used for the ABS’s wheel speed sensor to detect rotation of the axle). This deflector is pressed into the hub and bearing assembly from the back and must be removed to install a new hub and bearing assembly. We strongly encourage anyone attempting this repair to get a new deflector, as the old one is typically bent beyond repair upon removal. The deflector must be reinstalled to protect the axle’s tone wheel from road debris.
While the hub and bearing assembly appears an easy repair, often the bearing housing is seized into the front knuckle. Here are some precautions to take and inspections to undergo before starting this repair:
- Inspect the wheel speed sensor and securing bolt before starting. The wheel speed sensor goes through the knuckle and into a relief in the deflector and as such the deflector must be removed to perform this repair. If you can’t get the bolt or sensor out, this is best known beforehand. A new sensor (sensor seized) or precision drilling of the broken speed sensor securing bolt (bolt seized) may be required.
- If the vehicle is operated in the rust belt, the hub and bearing assembly will be seized to the knuckle. CARspec technicians are often forced to use a combination of an acetylene torch, air hammers, sledge hammers, chisels and the 20-ton press to separate the bearing housing from the knuckle.
- Clean the knuckle of corrosion before installing the new hub and bearing assembly. Failure to do so will result in the new hub and bearing assembly being seized in place and potentially the securing bolt holes misaligned. You’ll be doing the job twice in this case.
- The knuckle may be damaged beyond repair removing the hub and bearing. This scenario is more likely the more rusty the car is overall. Don’t be surprised if the knuckle requires replacement. CARspec notes to each guest with this repair that there is an unlikely potential for a new knuckle being needed, either because the hub and bearing refuse to come out at all, or the knuckle was bent while the technician tried to use the press to free the hub and bearing. The knuckle can crack if the corrosion is severe enough.
- Get a new axle nut if the threads aren’t perfect. An imperfect axle nut can seized during reinstallation, requiring the entire axle be pulled to be repaired. Save yourself the trouble and get a new axle nut if there is any question about the old one. The axle threads can be repairs with a 22mm by 1.5 pitch die.
CARspec stocks all the Toyota Genuine parts to perform this repair. If you have a growling or grinding noise from your 2004-2009 Prius, don’t hesitate to set up an appointment to have it inspected by calling us at (952)426-4798 today!