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Clunk when letting off the accelerator

stkelly

Well-Known Member
Joined
October 28, 2007
Messages
114
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City, State
Laytonsville, MD
Year, Model & Trim Level
'08 Mountaineer
Our 2008 Mountaineer was rear ended pretty hard last night. Hard enough the truck was pushed into the vehicle in front of us.

As soon as we drove away from the scene I felt and heard a fairly loud clunk when letting off of the accelerator. I can feel it in the steering wheel and floor boards. I checked the sway bar end links and they're nice and tight with no play. I don't see any noticeable lose mounts. It now clunks almost all the time when letting off the accelerator quickly. If I let off slowly it'll sometimes clunk but not always.

Any ideas what this could be? It never did this before being hit. I know it'll be a fight with the insurance since most of the damage is in the rear of the truck and it feels like this clunk is in the front drivetrain.

It may be a lost cause since the truck may be totalled due to the cost to fix vs the value. However, I'd really like to keep it running if I can.

Thanks in advance for any input!

2008 Mercury Mountaineer
V8 AWD
~143,000 miles
 



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Sounds like a driveshaft / differential bushings ?
I would jack up the rear, support the vehicle, and crawl under to see if you can move/shake the driveshafts, or use a pry bar to check all the mounting points of the differentials, transfer case, and transmission (all the bushings).
 






Sounds like a driveshaft / differential bushings ?
I would jack up the rear, support the vehicle, and crawl under to see if you can move/shake the driveshafts, or use a pry bar to check all the mounting points of the differentials, transfer case, and transmission (all the bushings).
That was my first thought also. But then I thought - unless it was really excessive how would the drivetrain be affected? He was in drive - was pushed the way the truck was heading - with the brakes on. Unless something was really bent where the diff mounts or the frame was bent enough to compress the driveshaft it would be hard to explain.
I would take a good look at the brakes. They were the component under tension when the hit occurred.
 






It could be that since the rear brakes take less load than the front brakes that the rear wheels turned where the fronts slid. If that was the case then maybe a Ujoint. Chunks on acceleration usually mean either a Ujoint or a motor mount. Now that I've typed that - check your motor mounts.
 






I didn't get a chance to jack up the truck, but shimmied under the back to investigate the damage more. It looks like the spare tire has been jammed into the rear suspension. I'm not sure if it's bent but everything is definitely shifted forward. The other driver had a Honda Accord and it went under the rear of the truck and caused most of the damage underneath.

I'll get it jacked up tomorrow and check all the mounts and UJoint.

Thanks for the suggestions!
 






I didn't get a chance to jack up the truck, but shimmied under the back to investigate the damage more. It looks like the spare tire has been jammed into the rear suspension. I'm not sure if it's bent but everything is definitely shifted forward. The other driver had a Honda Accord and it went under the rear of the truck and caused most of the damage underneath.

I'll get it jacked up tomorrow and check all the mounts and UJoint.

Thanks for the suggestions!
Ouch - you got hit harder than I thought. If I remember correctly the rear diff is mounted forward of the spare. If that got knocked out of whack then that would affect your whole rear geometry including your half shafts and your rear driveshaft. Please make sure the rear diff isn't leaking before you drive it any more.
 






samething happened with my 98..... although live axle vs irs.... my spare was totally jammed into the rear diff and probably saved me so much more damage but until I removed the spare everything felt and sounded jacked up....your tire is probably keeping the rear from moving in a normal fashion and making everything bind...... take off the spare and take another look, put it in first do 15-20mph and goose it a few times and listen before and after you remove the spare
 






I jacked up the truck and all bushings, mounts and universal joints look ok. At this point I'm guessing it's due to the spare tire being jammed into the rear suspension. I'd move it, but want to make sure insurance sees it incase that isn't the problem. I want them to see that everything underneath was pushed forward.

Thanks for the input!
 






Good call. Extra credit to MCF13 - good real world experience to add to the discussion.
 






Just to close out this thread, the insurance ended up totalling the truck. The spare was so jammed in they had to pry the tire out from the under body. However, even after removing the spare something in the drive train was still clunking. If it didn't clunk I was going to buy the truck from the insurance and repair it on the side. But with that noise who knows what other damage was going on.

It was a major bummer, never fun looking for a new vehicle during the holiday season. We ended up with a 2016 Expedition. So still in the Ford family.

Thanks again for all the help!
 






2016 Expedition, those came only with 3.5 EB ?

I wish they would offer the new 2018 Expedition with the 5.0 Coyote as well, that would be a perfect SUV for me, save for the $ 65,000 number on the window :)

How does it drive compare to Explorer ?
 






2016 Expedition, those came only with 3.5 EB ?

I wish they would offer the new 2018 Expedition with the 5.0 Coyote as well, that would be a perfect SUV for me, save for the $ 65,000 number on the window :)

How does it drive compare to Explorer ?

Yes, the 3.5 EB is the only choice. I also wish they had a NA engine available.

It drives really well, feels a lot smaller than it is. That is until you go to park it. We got a Limited with the 22" wheels and the CCD suspension. It's surprisingly smooth given the size of the wheels.

So far we're loving the ride and space. Three boys with friends and in sports the Explorer was getting tight!
 






I wouldn't be able to deal with the sub 5mpg...... yeah my foot would be into it all the time..... my parents bought a 2017 plat explorer and I'm just not impressed with its power even though torque says its 3.5L is getting 20psi of boost
 






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