2009 Ford Flex Limited: Suspension Walkaround
June 10, 2009
The 2009 Ford Flex sits crossways in my driveway and the right side wheels are off. Time to peek into the wheel wells to see what's going on in there.
Will we find any surprises?
The front end is made up of standard fare: There's a coil-over strut (yellow) and a welded steel lower control arm (green). Both attach to a cast aluminum hub carrier (white) that cuts down on unsprung mass a bit.
Here you can see the L-shaped lower control arm (yellow). It's made of two stamped steel halves that are welded together, a very common method of construction.
Like most front-wheel drive-based vehicles, the Flex has a transverse-mounted engine and transmission, and that means the steering rack (green) has to be located behind the axle centerline.
The rear control arm bushing is a large aluminum affair, and the way it's mounted makes it seem to hang in space. Here's why:
Say you hit a pothole. The upward force goes straight up into the spring and strut, but the wheel is also knocked back, and this force enters the arm at the lower ball joint (blue). The forward control arm bush fits tightly in a reinforced pocket with rubber shims on each side, so it absorbs most of the hit in the fore-aft direction. But in so doing it becomes a pivot, and that creates an in-n-out force (as opposed to a delicious hamburger) at the rear bushing, whose mounting is therefore optimized to handle forces in that direction.
Here's a close-up of the bush. The yellow arrow is pointing to a witness mark that shows where the bigger hits have been transmitting those inward forces. The bushing has a lot of rubber volume and there is a specifically engineered gap because you need a bit of give to absorb the hits to prevent harshness. The trick is not making it so gooey that it adversely affects the steering. The Flex has struck a good balance in this regard.
A high performance sports car can tolerate more harshness and needs surgically-precise steering, so you won't see the same solution on cars like that. Suspension tuning is all about managing conflicting requirements and matching the result to the intended use and customer expectations for a particular type of car.
The Flex's front stabilizer bar runs behind the steering rack, so it must loop up and over to meet up with the link. Looks weird, but it's no problem at all.
This, however, looks a little unusual. That gap between the stabilizer bar and it's bushing does not look right. Such a gap would reduce the efficiency of the stab bar, and might lead to noise. It's either worn or the bush for a larger bar was installed by mistake. I'll look into this and post a follow-up.
We're not hearing anything though, and the Flex seems to be performing well. If they need to be replaced, this looks like an easy DIY fix, too.
The stabilizer bar link mounts directly to the strut housing, however, so the motion ratio, at least, is 1:1 for high efficiency. Note also that the strut tube is flattened somewhat in the area of the sticker for extra clearance from the wheel and tire.
Ford can do this because these are twin-tube struts. A second tube within this tube is the precision-ground chamber where the piston runs up and down, and the space between is an oil reservoir. This makes it easy to weld-on various brackets and such, but it also makes it a thermos bottle that retains heat generated inside, by the valve. That's OK for a passenger car, but it's bad for track cars and off-road trucks because excessive heat leads to foaming and fade.
The Flex's front brakes consist of twin-piston (yellow) sliding calipers. The pins they slide on are hidden beneath the bellows (white); they need a dab of high-temperature grease inside to keep them sliding properly.
The rear of the Flex is a multilink set-up, with an upper arm (green) and three links. The black and white ones approximate a lower arm, and the final link (yellow) handles toe control.
This view shows that the toe link (green) is adjustable. All of the links bolt to a lightweight aluminum hub carrier/knuckle (black). A stabilizer bar (yellow) runs beneath it all.
As we've seen before, the long lower ling is spread wide (black) to serve as a lower spring mount. The upper end of the spring seats against the subframe (yellow) which in turn bolts to the body through good-sized bushings for extra isolation.
The stabilizer bar end link (yellow) and the rear shock absorber (white) both mount directly to the aluminum knuckle for maximum efficiency and precision.
The rear pivot of the rear supension's upper arm is precisely located by a pillow block that is securely bolted to the subframe.
There's a lot of space in the middle of this tangle of links for one good reason: You can get all-wheel drive in a Flex and a rear drive axle has to fit through it all.
The rear hubs are splined and ready for those axles. After all, why bother making two versions?
Minus points for the special Torx head bolts that locate the rear brake rotors. DIYers need to have a set of these handy.
Plus points, though, for the lug studs that have the last few threads removed to guide the nuts on without cross-threading.
Single piston sliding calipers do the work in back, and the rotors are mere solid discs. It's hard to tell from here, but that seems a bit light-duty for such a heavy people mover. Could this be why we just replaced the pads at just 25k miles? Probably not, but we're looking into it.
The big spring and cable indicate a mechanism that squeezes directly on the piston to create the parking brake function.
Our 2009 Ford Flex Limited wears P235/55R19 Hankook tires. Mounted on rims, the wheel and tire assembly weighs 55 pounds.
As you can see, these Hankooks have a 600 treadwear rating. Those numbers are so unreliable as to be about useless; we're going to come up short of 35,000 miles with these tires.
Dan Edmunds, Director of Vehicle Testing @ 25,719 miles