How can you tell when a U-joint is bad?

Dear Car Talk

Dear Car Talk | Sep 01, 1998

Dear Tom and Ray:

How do you tell when a particular U-joint is bad? I have the classic
squeaking noise of a bad U-joint, but my truck (a Ford F150) has three
different U-joints. I tried prying each of them with a screwdriver,
figuring there would be some "play" in the bad one, but I can't tell. --

TOM: You really can't tell with the driveshaft still installed. You have to
take it out and flex the joints, Roland. That's often the only way to tell
whether a U-joint is bad.

RAY: A universal joint (U-joint) is a connector that allows the driveshaft
(or anything else) to operate at a variety of different angles. And to do
that, it has to flex in two different directions.

TOM: And there are two ways U-joints usually fail. Over time, the little
needle bearings can wear out, in which case the joint will loosen up and
get too much "slop" in it. That usually causes a high-speed vibration, or a
clanking noise when you shift from Drive to Reverse.

RAY: U-Joints can also fail by seizing. That happens when water gets into
the joint and displaces the grease. And then the needle bearings rust, and
the joint stops moving in one or both directions.

TOM: If a joint has failed due to slop, you often CAN tell by prying at it
with a screwdriver. But if it's seized, the only way to tell is by removing
the driveshaft and flexing it to see if it bends smoothly in each direction.

RAY: Two other suggestions, Roland. Once you have the driveshaft out, you
might as well replace all three joints. If you're doing it yourself, they
only cost about 10 bucks apiece, and it'll save you the trouble of removing
the drive shaft again NEXT weekend.

TOM: And also, see if you can buy replacement joints with grease fittings.
Some of them allow you to grease the joint, and that grease pushes the
water out and makes the joint less likely to seize again.

* * *

Wait! Before you buy a car, make sure you read Tom and Ray's guide, "How to
Buy a Great Used Car: Things Detroit and Tokyo Don't Want You to Know."
Send $3 and a stamped (55 cents), self-addressed, No. 10 envelope to Used
Car, PO Box 5541, Riverton, NJ 08077-5541.


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