Diagnose a drivetrain noise, faint hammering sound at low speed while decelerating, slows with speed of vehicle...

[Slacker]

Diagnose a drivetrain noise, faint hammering sound at low speed while decelerating, slows with speed of vehicle...only at low speed while decelerating, in gear(auto/RWD) not heard if accelerating, even if just a touch on the gas.

Not an engine noise, it is in the drivetrain, I think it might be a rear wheel bearing or u-joint.


2000 Ford Crown Victoria v8/auto/RWD

if it is a rear wheel bearing, how hard is that to replace? never done one on the rear axle.

 

[Arkaign]

I'd guess U-joint, I had one go out on an '87 Ranger and it exhibited in pretty much that exact way.

 

[jagec]

I have a similar problem with mine.
I think it's a CV joint. (CV joints do the same thing as universal joints, they are just more expensive and work over a much broader range of angles without the binding problem that U-joints experience)

I don't think a bearing would stop making the noise under acceleration.

 

[Slacker]

I read on another site that a wheel bearing noise would not change with the speed of the vehicle, I dont quite understand this, I am guessing it is because the point of failure is in constant contact with the load surface and that a bearing failure would make a completely different noise than the one I am hearing.

The u joint is making sense to me, it is like the drive shaft is falling that short distance each revolution, torque holding it til the apex and gravity taking over from there.

If youhave ever driven at high speed on an old concrete highway with the gaps the noise is like that only at a higher rate and happening at the low speed circumstances I mentioned.

I know that u joints are just needle bearings in a cap on a 4 pointed body that joins the driveshaft to the output shaft in front and the diff yoke at the rear, what is it in this setup tha fails? has acap come off one point? or will the be needle bearings worn flat or worn away?


Anyway, I am sure glad it is likely a u joint, I know I can fix that easy enough, thanks for the help!

 

[imported_Truenofan]

probably not a u-joint. when u-joints go bad they usually cause vibrations, when mine went bad(drive shaft u-joint on the output side of the tranny, non-rebuildable) and shook the car like it had a giant rumble feature on a controller, it made your bum go numb(hah, it rhymes) on a ride longer than 20min.

 

[Arkaign]

If it's a U-joint, it's incredibly easy to diagnose in most vehicles. If you can get under your vehicle and physically see it and manipulate your driveshaft, you can see if there is any extra play. That's what my mechanic did with my Ranger, he just reached under there, wiggled it, and told me 'yep, it's going bad on ya'. Replaced it, and all was perfect.

EDIT : Your two biggest clues is that (1)- only happens in gear, and (2)- only happens when decelerating. This points to the drivetrain, and eliminates the motor/suspension from the possibilities. The transmission also seems extremely unlikely, or the problem would exhibit under more situations.

Some visuals here, and assorted tips :

http://www.vibratesoftware.com...r%20failing%20U-Joints.