2006 Ford F-150

Suspension problem
2006 Ford F150 V8 Two Wheel Drive Automatic 50000 miles

I’ve got a 2 WD 2006 FORD F150 XLT (8200 GVW model) with a “Supercab” (extended cab) and long (8’) box (hence, long wheelbase) with a trailer-towing package. Bought second hand. Only 40,000 miles on the odometer. Wheels are 17” steel with four General M & S tires (6 ply tread - 2 ply Polyester + 2 ply nylon + 2 ply steel and 2 ply Polyester sidewall). Obviously a “work” truck, so I don’t expect it to ride like a Cadillac (or a Lincoln, if that is your preference).

Problem: With the box empty, when going over a bump/pot hole/speed bump, can feel a “shudder” (rapid up and down motion with a slight lateral component) through the driver’s seat (no excessive bounce upon impact and/or roll and no front end “diving” upon braking).

In a more or less controlled setting, when driving over a single speed bump in a paved shopping plaza parking lot at about 25 mph, can sense that the “shudder” does not occur when the front wheels make contact with the speed bump. Rear wheels pass over the speed bump and cab/driver’s seat “shudders”. Persists for 3-5 seconds.
Have replace the rear shocks with Monroe “Flex” as specified for the F150, 8200 GVW vehicle and there is only marginal, if any, improvement. Tried lowering tire pressure to 32 psi (rated at 65 psi when loaded to capacity) – no change. Leaf springs and shackles appear to be OK – no evidence of overloading on “overload bumpers”. No evidence of twist/crack(s)/repairs to frame. Cab is free to float - no solid attachments between frame and cab. Checked all eight body mounts – one nut missing - have since replaced. No effect. “Rubber donuts” in cab body mounts appear to be in good shape with no damage or deterioration. Was told that it was in a “minor” accident (sheet metal damage only - $4,700 (Cdn)).

Has the cab ever been removed for maintenance or repair? Could have given evidence of one nut missing but don’t know.

Obviously don’t want to spend more money needlessly and I would appreciate any help/suggestions that you can give me.
June 10, 2010.

First off let me say that there is no reason to remove the body to do any maitenance. If some one put in a body lift that would explain it. I would also check the shackel bushings and front end bushings.

Jun 12, 2010.
Racefan966: Thanks for your reply.
My mechanic, who is a fully certified Automotive Technician, test drove the truck and he then put it up on his hoist and checked all of the suspension and steering components, including the shackle bushings (hence my comment that the (rear) " springs and shackles appear to be OK" ) as well as the front end. He did not report any undue wear or play in the front end bushings.
My comment with regard to the possibility that the cab may have been removed was more in the context of possible damage from the accident (that I mentioned in my initial question) requiring that the cab be removed for repairs or to access some other component, as opposed to removing the cab for routine maintenance. Perhaps I should have clarified that.

As I inferred in my initial submission, after having my mechanic thoroughly check all of the steering and suspension components, my suspicion is that with the box empty the " shuddering" is the result of the bouncing of the rear wheels upon impact with a pot hole or speed bump (the replacement shocks obviously didn't solve the problem entirely) and the energy from this bouncing is coming through the frame, through the cab body mounts to the cab and hence to the driver's seat. In other words, the body mounts are not effectively isolating the cab of the truck from the frame, which is what they are supposed to do.
Assuming that my anaysis of the problem is correct and even though there is no visible deterioration in the rubber component in the body mounts that are currently on my truck, I would be interested in knowing whether or not: (1) you or any of your associates have run into this problem before? (2) if so, is this problem unique to the F150 - 8200 GVW model? (3) are the body mounts in the F-150 - 8200 GVW model the same body mounts that FORD uses in other F150 models? And, (4) have there been any recalls/TSBs regarding FORD body mounts for 2006 F-150s (I could not find any recalls/TSBs associated with this " shuddering" problem nor could I find any recalls/TSBs on this particular component using an online search)?
As you can appreciate, this problem is very frustrating and I do not want to spend additional monies trying to solve it if it is simply a characteristic of a " work truck" that I will either have to get used to or sell and replace it with a vehicle that has more of a " passenger car ride".
Thanks for your time.

Jun 14, 2010.
Let me say that first I found only one TSB on vibrations at higher speeds caused by the driveline. I understand that this only happens when you hit a bump? This is not common as I have a 95 F-150 that has been lifted and has eurothane mounts and I don't have this problem. I must ask what kind of accident was this truck in? Was it bad enough to do any frame damage? This can happen if the body is not tight enough or the frame is weak (from accident) and allows excesive movement. The front purch for the rear springs are rivited to the frame I take it that they didn't look like they are loose and moving?

Jun 15, 2010.
Racefan966: The " shudder" only happens when I hit a bump.
I found your comment re the urethane body mounts included in your lift kit for your '95 F-150 interesting. Do you know whether or not the OE body mounts that you removed from your truck were also made of urethane? If the body mounts on your truck (as well as my truck) were made from something other than urethane, based upon your experience, it might be worth my while to buy and install a lift kit with urethane body mounts even though it is not my intention to raise my truck. If it would give me a better ride without creating any other problems, it would be money well spent.
I was told that the accident only involved sheet metal and that there was no structural damage to the frame etc. Based upon my mechanics assessment of the frame etc. And the fact that the truck tracks true with no alignment or steering problems and no abnormal tire wear, I feel that it is safe to assume that the frame etc. Was not damaged as a result of this reported accident. The implication in my earlier comment with regard to the possible removal of the cab was with reference to the possibility that the OE body mounts were removed/replaced and not installed properly and/or are a cheap after-market body mount of inferior quality. As I said in my original submission, the existing body mounts appear to be installed correctly and there is no evidence of damage. Unfortunately, there is no way for me to tell whether the body mounts that are currently on this truck are of inferior quality.
Thanks for your time.

Jun 15, 2010.
Ok the factory ones are made of rubber and do give some where the urethane ones do not. You can get urethane mounts without lifting it as Energy Suspension does do body mount kits that are of stock height. Don't forget to check shock mounts to make sure that they aren't worn and that they are tight too as that can do this to some extent.

Jun 16, 2010.