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Thunk when coasting at speed and then depressing gas pedal

First off, I would like to express my sincere thanks to all who have responded in the past to my posts seeking advice. I very much appreciate your efforts to help. I tried searching the internet for this condition but could not quite get the search wording right. In this case I am driving a 2005 Ford Escape V6, and when I am cruising at, say, 40mph, and I lift my foot from the gas pedal due to traffic conditions, when I depress the gas pedal again I get a thunk. If I depress it VERY slowly, no thunk, Also, no thunk when accelerating from a stop. Sometimes, but not always, I get a thunk when the transmission upshifts.

As I am writing this, CarTalk suggests this post, which is very close to what I am experiencing: Feeling a “bump” in the gas pedal after coasting…?

I changed the right front hydraulic motor mount right after I got this car about two months ago. Have only been driving it regular for about three weeks. Besides motor and transmission mounts, might there be anything else that could be causing this condition? Again, no thunk when taking off from a stop. This happens at faster and slower speeds than 40mph.

Thanks,
Jack

I would say u joints are a possibility, but then again probably not, as I assume a 2005 escape is front wheel drive?

Yes, it is a front wheel drive.

OK… You replaced your front motor mount… which basically keeps the engine from rising up and out of your hood or “doing a wheelie” lets say… Which direction do you think it tries to twist when you do the opposite? How bout the side and rear engine mounts?

I’d look into them in a serious manner. It wouldn’t be the CV joints because they usually dont manifest that symptom.

You can also do this test for bad mounts. Open your hood… Begin in park… Put in Drive and hold the brake and cycle the accelerator. On and off the gas. Watch engine. After that go from Reverse to Drive and give it a little gas in each gear. You may just recreate the actual sound…if so… you found another bad mount.

Let us know.

I certainly will let you know. After posting this I recall reading that you should not see daylight through the rubber bushing of the mm. When I was under the car a few days ago doing something else, I gave the mounts a look at and noticed daylight through one of them. I thought at the time that it was by design. Then read that it is not a good sign. I will have another look at them as soon as all the other things that are demanding my attention are satisfied.

Kind of odd, because most things that would cause a clunk during acceleration (bad mounts) should cause a clunk when taking off from a stop as well. If it happens at a certain speed, maybe it’s making the noise when it’s in a certain gear, or downshifting to a certain gear.

Dont forget and transmission mounts as well. I can speak from experience that you dont always get a thunk when accelerating but you can just feel it. If you have a whole set of bad mounts you should see a good deal of movement just from changing from park into gear. I dont know about the escape but look and see if it had a bobble strut, a small shock that dampens the engine movement, they go bad too.

This is an update on the problem described in the first post of this thread. I finally got around to inspecting the motor mounts and none look obviously bad. I enlisted the help of a neighbor and had him put the trans in reverse and drive from neutral and rev the engine with all the brakes on while I observed the movement of the engine. it seemed to move a lot when revved and held so I decided to measure the movement. From the extreme of reverse to extreme of drive I measured 1 inch of up and down movement measuring from the valve cover on the front of the engine to the radiator bracket, which is very close. Not sure if this is too much movement or just right. But seeing as how the mounts have 165K on them, I’m thinking maybe I should just replace them all. This thunk is actually something that is more felt than heard.

Jack

One inch doesn’t sound like it should be a problem but lay your hand on top of the engine and re-enlist you neighbor’s help.

What does laying my hand on top of the engine supposed to tell me?

Didn’t I read your post correctly?. I understood that you FELT the thud more than you heard it.

Oh, I see, yes, felt more than heard. That thunk only happens when I am going above 35 mph or so and take my foot off the gas and then reapply the gas. Since I last posted I asked my neighbor to go through the same procedure. This time I watched the front and rear mounts. They both have rubber bushings inside a round steel casing with a single bolt passing through a steel bushing in the middle of the rubber and connecting to the engine/trans. I could see the rubber flex up and down on both front and back mounts as the engine was revved up in both drive and reverse, but more interesting is that I could see the portion of the frame that the front mount is bolted to move. I will get under the vehicle tommorow to take a closer look.

Other possibilities to consider

  • something in the trunk or under the seat is rolling around, check especially spare tire area, jack
  • suspension components are stressed during acceleration, so could be a strut, strut mount, ball joint, etc
  • exhaust components move during acceleration also, so check cat, muffler, pipe supports

My Corolla makes a similar noise at times, more often after removing my foot from the gas pedal to begin coasting to reduce speed, and I think it is coming from the rear strut area.

I have devised a theory as to what is happening. The rubber in the motor mounts is fatigued, allowing more movement than when new. When traveling at freeway speeds, and the accelerator pedal is allowed to return to its resting state, the braking action of the engine, even with an automatic transmission, causes it to be torqued in the opposite direction from when the engine is supplying power to the wheels. When the accelerator pedal is once again depressed, the torque on the engine is reversed, slamming it from one extreme to the other. This makes sense, and based on that I ordered the front and rear mounts and will install them this weekend. I already changed the right mount. I will change the left mount or not based on what results I get from changing the front and back ones.

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Your thought is pretty much right on point.

The only other thing is that since this car is new to you, there may well be something somewhere that is loose and banging around. I’d check to see if the spare tire is secured well, and stick your head on the floor and look under the front seats with a flashlight. I once bought a car that had a thunk and it turned out to be a golf ball that had ended up in the space between the rear fender in front of the rear wheel and the side of the floor of the trunk.

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I am convinced that this thunk is definitely coming from somewhere along the drivetrain. The fact that it occurs under very specific conditions, for me, rules out loose stuff knocking around. It only occurs when going fast, accelerator is released and then reapplied. The reapplication of the accelerator pedal does not need to be severe for the thunk to occur. In fact, there is no descernible acceleration when reapplying accelerator pedal, so no sudden jerking movement of vehicle surging forward. Since the transmission is in overdrive at this point I would have to jam the accelerator to get it to downshift and get a surge of acceleration. But this doesn’t happen at all. The reapplication of the accelerator produces only a very gentle re-engagenent of power to the wheels, but the thunk occurs, nonetheless… unless I am excurciatingly gentle when depressing the pedal. Then it does not occur. But the main thing is that there is no descernible acceleration when depressing the pedal normally. This, in my mind, is what makes the motor mounts suspect.

Having said that I am not ruling out some other explanation, but I am certain that it is somewhere along the drivetrain.

The only other thought I have is some sort of looseness at the top of one of the front struts. The forces of acceleration vs. coasting would have effects on all the front suspension, both twisting forces and shifting of load from rear to front.

Thanks for the suggestion, wentwest. I will check out the front struts. Motor mounts due Friday and I hope to get them installed ASAP. What I fear most is that this problem is caused by some condition in the transaxle.

Welp, I changed the front and rear motor mounts, but still have the thunk. The rubber on the rear mount was completely separated from the metal casing on one side. The front one was cracked in several places but still one piece, so not a total waste of time and money. Still have the transmission mount to change, but doubt that is the problem. The top of the strut towers are both tight. Since it is not a severe problem I will put it on the back burner for a few days.

Jack

Sooner or later you’re going to find this clunk, because it will either dawn on you at some random moment or it will get worse. At least that’s how it works for me.