1999 Mercury Mountaineer - Chattering

Hello,
Thank you for taking the time to read this post.

I have a 1999 Mercury Mountaineer 5.0L - automatic transmission with about 174,000 miles on it.
A few months ago I had to replace the front "DAYNA" drive shaft.

Now I have noticed when I back up or move forward with the wheels turned I can feel this chattering vibration until I straighten out the wheels.
The chattering is almost like a bad clutch on a standard transmission.
If I drive slowly I can hear and feel a slight snap now and then in the rear. Once I get rolling along it is fine.
Could one of you "Pro's" let me know what the problem might be ?
Any information will be very much appreciated.
Thank You.
Rick

Welcome to the forum!

Since you have the 5.0L I suspect you have AWD. Can you confirm that? If not, and you have the part time 4WD, it would sound like you're driving with the 4WD engaged on dry pavement.

-Rod

Hi Rod,
Thank you for your reply.

I have the 5.0L AWD

When I have my wheels turned and back up or go forward I get the chattering vibration. It goes away when I pick up speed with the wheels straight.

I drove slowly and close past a line of side by side garages to see if I could hear any type of noise.
I heard this slight snap noise now and then. I could feel a little thump with each snap too.

The wheel bearings are fline.
Any information will be very much appreciated.
Thank you,
Rick

Does the clicking and chattering vary with vehicle speed? The click from the rear makes it sound a bit like there's a locking rear differential, but that shouldn't be the case wtih the AWD and it doesn't sound like it's been changed out. Someone recently posted in the Explorer forum about finding chipped ring and pinion gears that made a somewhat similar sound.

I'm at a loss here. I think if the issue were related to the front driveshaft or a u-joint that was recently replaced, it wouldn't matter if you had the wheels turned versus going straight. You might drain the center differential/transfer case and inspect the oil for a silvery color or abnormal debris. Heck, it's probably time to drain and replace the gear oil in both differentials as well, may as well do that. That's probably the next step after a thorough visual inspection of the drivetrain.

-Rod

Hi Rod,
Thanks again for your reply.
The chattering goes away at about 5 M.P.H.
It seems to be more pronounced when the wheels are turned.
The other day I stopped at the bottom of a small hill and the chattering and vibration was very noticable making it's way up.
Thank you for your advice, I appreciate it very much.
I will follow your recommendations.

Rick

From the description it seems like the problem would either be a differential issue or a problem with one of the CV joints in the front. I'd probably start by draining the differentials and the transfer case and inspecting the gear oils for signs of metal (either filings or a strong creamy gray appearance).

-Rod