Clickety-clackety mechanical sound while accelerating

[David Verzilli]

I know it's a dumb way to put it! Here are the details:

Occurs only while accelerating (any speed, slow...highway)
Up hill for sure
NEVER (and I mean never) in 4wd, ONLY in 2wd
Will do it for 10 seconds (?) then quiet.
Does it hot or cold, driving short or long
If I turn on the 4A while clacking (at about 30 mph), the sound goes away.
Sounds the loudest on the driver side, definitely under the vehicle

Have had three mechanics look at it, they say: not the engine, nothing loose, not the brakes or wheels. To me, it sounds like a bad UJoint, but what do I know? Drained and replaced the transfer case fluid (as per Ford instructions). Any ideas? Bad transfer case? thanks for any input.

 

[99WhiteC5Coupe]

I know it's a dumb way to put it! Here are the details:

Occurs only while accelerating (any speed, slow...highway)
Up hill for sure
NEVER (and I mean never) in 4wd, ONLY in 2wd
Will do it for 10 seconds (?) then quiet.
Does it hot or cold, driving short or long
If I turn on the 4A while clacking (at about 30 mph), the sound goes away.
Sounds the loudest on the driver side, definitely under the vehicle

Have had three mechanics look at it, they say: not the engine, nothing loose, not the brakes or wheels. To me, it sounds like a bad UJoint, but what do I know? Drained and replaced the transfer case fluid (as per Ford instructions). Any ideas? Bad transfer case? thanks for any input.

Year, make, model?

I’d bet you have a vacuum leak in the 4WD system - typically the IWE vacuum check valve.

On the 2015 - 2017 models, the valve is inline with the vacuum line, near the IWE vacuum solenoid (neat the brake booster).

It is an inexpensive part and can be replaced in less than five minutes.

Ford had issue a TSB (I don’t have a copy now) that instructed dealers to replace the valve if there was an issue with the IWE engagement on the front wheels.

My 2015 did the same thing when going uphill. I replaced the valve according to the TSB when my Ford dealer said they couldn’t find the problem (still under warranty then).

Although the check valve is sold separately, it also comes as part of a short vacuum harness.

If you need more information - just post. I can post a picture of the valve and/or the harness or check valve part number (based upon your model year).

Here is a later Ford TSB with a good illustration of the valve location: https://static.nhtsa.gov/odi/tsbs/2018/MC-10149748-9999.pdf

 

[David Verzilli]

Sorry. 2009 Ford Expedition, 5.4. Thanks for the input. Also, in the meantime, how long (time and distance) is it permissible to drive in 4A?

 

[99WhiteC5Coupe]

Sorry. 2009 Ford Expedition, 5.4. Thanks for the input. Also, in the meantime, how long (time and distance) is it permissible to drive in 4A?

My manual states 4A is appropriate for all driving conditions - with no limit on time or distance.

 

[David Verzilli]

99, thanks for the input. I think you hit the nail on the head. I looked at a bunch of YT vids and they all sounded exactly like my situation. I'm going to try replacing the solenoid first (myself) and see what happens. If that doesn't work, then I will have to talk with my local mechanic. I need to do the front brakes soon, so that would probably be the best time to do the actuators.

 

[99WhiteC5Coupe]

99, thanks for the input. I think you hit the nail on the head. I looked at a bunch of YT vids and they all sounded exactly like my situation. I'm going to try replacing the solenoid first (myself) and see what happens. If that doesn't work, then I will have to talk with my local mechanic. I need to do the front brakes soon, so that would probably be the best time to do the actuators.

In addition to replacing the IWE engagement solenoid - I would replace the vacuum check valve at the same time. It is very easy to replace and is only several dollars for a Ford OEM part.

If the check valve is leaking internally, it will not permit the IWE system to hold vacuum under high load, causing your problem. Good luck.