This problem started a couple months after having new spark plugs done with Motorcraft plugs as a maintenance precaution. I drive on a winding mountain rd and in the exact same place on that road everyday as I am letting off the accelerator going down hill slightly its starts to knock and shake. when I accelerate it goes away Last weekend when I was on the Interstate 80 going to Reno I hit an area again where I let off the accelerator going downhill and as soon as I started to accelerate going uphill my truck started to lose power and shake like crazy finally I just let off the gas completely for about ten seconds and it went away. Its obviously getting worse and I am worried. Any suggestions? I had the differential fluid changed last summer. I am always doing preventative maintenance since I know Ford has a serious issue with this.

I bought this truck and I noticed a severe shutter and shake in the truck. I also noticed on right turns and take off while accelerating, I could hear and feel a clunk in the rear differential. Ford is fully aware of this problem and will not take responsibility or accountability for this common problem. Ford dealer stated this is a very common problem and it is huge engineering problem that Ford will not admit to. Apparently it is the rear differential issue and clutch pack issue. I had a Chevy truck before this POS Ford and I would have kept the Chevy but needed a 4 door truck. I will DEFINITELY never by a f-n Ford product in my life. I have 2 other COMMON problems with this truck and I will post them (separately). Ford if you actually read this post........READ this.........FIX the problem for the folks that are stuck with these problems......And for you folks THINKING of buying a Ford product.......READ this..............DON'T BUY A FORD!!!!!!!!!!!!!!!!!!!!!!!!!!!!! TRUST ME........Thank you!!!

Severe shaking at 40mph. I have to pull off the road--very dangerous. Took it to the auto mechanic on 11-25-10 and was told that it was the emergency brake. They saw that the e-brake pads had differential oil on them so he replaced the pads, emergency brake lines, and axle seals plus the rotor. Took it back on the road today, Interstate 83 @ 50 mph started shaking again so severely that I had to pull off the road. Extremely dangerous lots of truck traffic. I called the mechanic as soon as I got to work. He told me to drop it off again, and he will take a look at it again.. It will cost me again. Major pain since I use my truck for work.

Had been experiencing shudders when accelerating from a stop, particularly if I was turning. On a couple of occasions, I experienced significant shaking while driving down the road at 45-55 mph. I did some research on F-150 forums and found the recommended solution was to change the differential fluid to 75W-140 full synthetic with added friction modifier.

I drained and replaced the fluid myself for about $80. The oil is about $16/quart, the bottle of friction modifier is about $5 and a tube of RTV was less than $5. The truck needed a couple of days' driving to work in the friction modifier, but has been perfect ever since.

Severe shaking at 40mph. I have to pull off the road--very dangerous. Took it to the delaer yesterday and they thought it was the emergency brake. They took off the tiures and brakes and saw that the e-brake pads had differential oil on them--replaced pads, emergency brake lines, and axle seals. Paid $730 and then drove 5 miles and the damn thing started shaking again. Took it back to dealer and head mechanic went for a ride with me. As is standard, the fricken truck ran fine. Going back tomorrow.

After about a year the vibrating started very intermittently at about 50 mph. Feels like driving on a washboard road. Dealer notified twice, but can't diagnose since it could not be duplicated. The only way to clear this is to pull off the road, stop, and turn off vehicle. This usually works, or sometimes engaging 4 wheel drive and turning off when stopped will work. Has not failed in the past 15K miles. The truck now has 43K miles and I really like it, but I think I'm on a time bomb for a huge repair bill if I keep it. I'm done with Fords!

I bought it at 30K and had no problems other than a little shaking while accelerating. Mechanic said to keep rear diff oil changed every 30k and it would last for another 100K. Problem is oil change is 90 bucks a pop. Anyway, at 125k had the thing rebuilt by Ford for around 1300 bucks. 23K later, another 600 bucks from a local mechanic instead of dealership. I've driven it maybe 1500 miles since then and the damn thing is shaking and grinding again. Suggested that I get a rear end from a newer model...the mechanic at the dealership said all 2004 rear diffs were screwed due to tooling problems at factory. Otherwise, I love it

I love my truck. If only she wasn't built under the Ford name. It started as a small shutter going uphill with light acceleration. Now she shutters every time I accelerate from a stop. I took it in to be seen and they told me it sounds like the drivetrain. Of course, I had waited until the 36,000 mile warranty had expired. A man has to work and can't afford $391.61 per week for a rental car. I just put up with the stammering and will have to fix it myself. I'm not afraid to start pulling things apart. My baby is paid for and I sure don't want another truck payment. Those Toyota's sure look nice; but, I'm not telling my baby blue that I'm looking.

The vibration felt as if it was coming from the front end of the vehicle. Once it started (during acceleration and at approx. 50 mph) I had to pull over and come to a complete stop. Front end was checked, nothing was found. I was due for new tires so I replaced them with a different brand and slightly different size. The problem would still occur at random. A Ford service center diagnosed the problem as a rear differential clutch pack. They replaced it under my extended warranty. 6,000 miles have since been added to the truck and the problem has not returned.

I am finding more and more people with this shaking problem with the 2004 fi50 4x4. We need to all somehow get emails sent to attorney general. to get these recalled. The last time was very dangerous as I was on the highway and suddenly it started shaking (feels like ya came onto a washboard road.) then gets worse. I had to slow quickly and get to shoulder and shut truck off and wait a bit then it seems to be ok till only god knows when and where it will do it again. I am a disabled veteran and it looks like I will soon trade this in and be driving a Nissan or Toyota to the Veterans hospital in Ann Arbor Michigan, cause I don't like Dodge, and my buddies have lots a trouble with their Silverados and especially the Colorado trans. The Ford dealer thinks I am nuts doesn't want to admit these f150 do this.Its a shame too because I really really like my f150 but I am tired of worrying about what is about to break and how much it will cost to fix it..