Auto Repair Q&A



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CV Boot

Outer CV Boot on 4WD

All front wheel and four wheel drive vehicles will have a constant velocity boot (CV boot). In fact, they'll have four, two on each front axle for FWD vehicles and two more per axle on the rear of 4WD vehicles.

What is the CV Boot?

The CV boot protects the CV joint from outside debris and water while holding in the grease that keeps the joint lubricated. The CV joint itself supply even torque to the wheels as they turn (in the front) and as the suspension moves up and down (on all four). Each axle has two, an inner and outer.

Typical 4WD Outer CV Boot

When the CV Boot Fails

The outer are the ones which will fail the most often, with something (often overheating brakes or just age) causing a tear in the boot. This will leak out the grease in the boot and allow dirt and debris to get inside, grating on the CV joint. If the torn boot is not replaced quickly, the whole joint will fail, resulting in a much costlier replacement.

Most good mechanics will check the CV boots when the car is up on a lift (or they are under the vehicle) changing the oil or doing other routine maintenance. On nearly every vehicle, the outer CV boots are easily visible.

Replacing the CV Boot

The boots and grease are very inexpensive and on most vehicles will cost about $20 per side for outer joints. The costs to replace are mostly in the time required, since the axle must be removed (on 4WDs, these are often called "half-shafts").

A shop will charge about 1-1/2 hours of labor plus the parts for this job (per axle). So expect to pay $100-$150 for the job.

Safety Concerns

When a CV boot tears, it should be replaced immediately. The longer you drive on it, the more likely you are to ruin the CV joint underneath. When the CV joint fails, the wheel will nearly come off the vehicle, falling at an odd angle. This can cause a severe accident, especially at highway speeds.

So replace it very quickly. A $150 job now can save $700 or more later if the whole joint must be repalced.

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