FX4 Ecoboost Rear End Clunk During Deceleration

[JME42]

I've noticed for the last few thousand miles that randomly during deceleration around 10-16 MPH I get a clunk coming from the rear of the truck during deceleration. It doesn't occur during a downshift. It's between downshifts and feels like a bowling ball is rolling around in the bed. Wondering if it's the RDU clutch engaging at low speed. Read of similar issues on other ford vehicles with the same AWD system and RDU with the viscous coupler/wet clutch. Going to hookup forscan and watch rear clutch engagement to see if that corresponds with the clunk. Happened before changing the rear RDU fluid and doesn't seem to have changed after changing the fluid. Anyone else having this issue?

Sponsored

 

[Montana]

Check that your spare is secured? Well, just get under and check that nothing is loose to begin with. Play in the driveshaft and the RDU.... that kind of stuff. I'd even check the suspension while I'm at it.

Doesn't sound good though. Have someone drive it while you watch or if you have a GoPro, strap it underneath for a couple short strolls.

The fact that it's random sounds like something is slipping and knocking where it shouldn't.

 

[JME42]

Check that your spare is secured? Well, just get under and check that nothing is loose to begin with. Play in the driveshaft and the RDU.... that kind of stuff. I'd even check the suspension while I'm at it.

Doesn't sound good though. Have someone drive it while you watch or if you have a GoPro, strap it underneath for a couple short strolls.

The fact that it's random sounds like something is slipping and knocking where it shouldn't.

Good point on having everything secure. Will double check everything before forscan diagnostics. However, I would think if it was something loose it would make the noise during other driving conditions especially over bumps.

 

[JME42]

Check that your spare is secured? Well, just get under and check that nothing is loose to begin with. Play in the driveshaft and the RDU.... that kind of stuff. I'd even check the suspension while I'm at it.

Doesn't sound good though. Have someone drive it while you watch or if you have a GoPro, strap it underneath for a couple short strolls.

The fact that it's random sounds like something is slipping and knocking where it shouldn't.

I checked under the truck and everything is secure, no suspension movement anywhere, driveshaft and half shafts felt solid at the RDU. So I went and hooked up forscan and got it to clunk immediately. It happens right at 16mph only while decelerating. See attached forscan images of PTU and RDU PIDs. The first picture is an event capture during a clunk. The second picture is the list of PIDs and the order they are plotted, see summary below as well.
-PTU_CLTCH_CMD
-RDU_CLTCH_OPEN
-RDU_MTRPOS_KISS
-RDU_MTR_POS
-RDU_TRQCAP_INF
-RDU_TRQ_REQ
-ROM_CHECK_AWD
The third, fourth, and fifth pictures are event captures without a clunk after performing an AWD module adaptive learning reset. I figured I would try an adaptation reset on that module to see if it would clear up the clunk or at least change it to further confirm my theory of the RDU being the issue or related to the issue. Had good results with cleaning up clunky shifting on an F150 with the notorious 10 speed. Sure enough it drives completely normal again. I exported those recordings to a csv file and will do some more detailed analysis tomorrow. Will report back with additional information and if the clunk seems to be gone still.

 

[JME42]

I should mention as well that I had about 5 recordings of clunk events that all looked identical to the first picture so I didnt post multiple pictures. However, I did post multiple pictures of the no clunk events because they all looked slightly different.

 

[Montana]

Awesome. Hopefully that solves it. Keep us updated.

 

[Beekeo]

I have never used forscan but I’m interested in learning more about what you’re showing

in the first image, the spike in the yellow line for -RDU_TRQCAP_INF is what I assume to be the “clunk” event?

was it engaging and then disengaging the driveshafts or doing something else?

 

[WildGrok]

I should mention as well that I had about 5 recordings of clunk events that all looked identical to the first picture so I didnt post multiple pictures. However, I did post multiple pictures of the no clunk events because they all looked slightly different.

Thanks for your detailed post, glad issue was fixed

 

[bgn]

I have the same issue. TCU relearn "fixed" it but I have no doubt it'll be back.

 

[THEMAV2022]

I took my Maverick 2.0 AWD FX4 27K miles into the Ford Dealership due to a clunking sound coming from underneath the truck. Only while taking off from a stop.
I had to get a tech to ride with me to let them hear the sound. I had my RDU and PTU drained and filled at 20K to be safe.
They thought it was the RDU so they drained and refilled. It did not fix the issue. I dont know why they thought to do that since I had it done at 20K.
Its been seven days and no solution. I was told they need to bring in (Ford) To help troubleshoot the issue. Any words of advice?

 

[Ford Motor Company]

I've noticed for the last few thousand miles that randomly during deceleration around 10-16 MPH I get a clunk coming from the rear of the truck during deceleration. It doesn't occur during a downshift. It's between downshifts and feels like a bowling ball is rolling around in the bed. Wondering if it's the RDU clutch engaging at low speed. Read of similar issues on other ford vehicles with the same AWD system and RDU with the viscous coupler/wet clutch. Going to hookup forscan and watch rear clutch engagement to see if that corresponds with the clunk. Happened before changing the rear RDU fluid and doesn't seem to have changed after changing the fluid. Anyone else having this issue?

Hi there! Will you send us a message with your VIN and your local Ford dealer? I can look into things on my end.

 

[jewc75]

I had the clunk as well, just did the reset and took it out to beat on it, no more clunk. thanks for posting a solution.

 

[WJOHNM]

I've noticed for the last few thousand miles that randomly during deceleration around 10-16 MPH I get a clunk coming from the rear of the truck during deceleration. It doesn't occur during a downshift. It's between downshifts and feels like a bowling ball is rolling around in the bed. Wondering if it's the RDU clutch engaging at low speed. Read of similar issues on other ford vehicles with the same AWD system and RDU with the viscous coupler/wet clutch. Going to hookup forscan and watch rear clutch engagement to see if that corresponds with the clunk. Happened before changing the rear RDU fluid and doesn't seem to have changed after changing the fluid. Anyone else having this issue?

I had a similar problem slowly pulling away from a light or stop sign at about 4k, I removed everything from the vehicle, remembering a customer I had many years ago had a thump on acceleration, we spent hours looking for the problem, turned out to be a beer mug under the passenger seat. didn't we look like fools. Have 8k now and I only hear it once and a while still scares me. Check under the seats.

 

[801Maverick801]

i feel like this could be the PTU.

 

[JME42]

Awesome. Hopefully that solves it. Keep us updated.

Truck drove perfectly today to and from work in lots of stop and go traffic where it would consistently clunk slowing down.

Sponsored