Independent Rear-Suspension

My Escape’s IRS. (Photo by BobbaLew.)

Illustrated above is one of the main reasons I bought my Ford Escape: Independent Rear-Suspension.
I’d be bopping down the road, get passed by or fall behind an Escape, and I could see the elegant suspension swing-arms at the bottom of the suspension.
They’re angled slightly downward, and stretch out from the center differential, which is solidly mounted to the car-chassis, out toward the axle-ends at the wheels. —The shock-absorbers mount to the ends of those swing-arms.
This is the opposite of what has been seen for eons, a solid rear-axle connecting the two rear-tires. A center differential is in the middle of the axle.
A central tube (the drive-shaft) takes the engine’s power from the front of the car back to that differential and axle.
There are universal-joints to accommodate drive-shaft angling, often at both ends.
Independent Rear-Suspension is a great design. I think the Escape IRS was original to Mazda. Ford affiliated with Japan’s Mazda some time ago, and its original Escape, the first version, was essentially the Mazda Tribute SUV.
(Mazda’s pickup at the time was the Ford Ranger.)
The Mazda-Ford alliance developed some great cars, particularly the Ford Probe.
What I have is the second Escape, slightly rebodied, but essentially still the Mazda. I don’t know who did it, Ford or Mazda. Mazda’s Tribute was upgraded at the same time.
But I think the chassis is Mazda. Later Ford put Independent Rear-Suspension (IRS) on the larger Explorer SUV. It’s not on the Mustang yet; I doubt that differential could take Mustang’s potential power output.
Ford’s new Escape is European-based; no longer a Mazda. To me it also looks ridiculous. I wouldn’t touch it with a 10-foot pole!
Independent Rear-Suspension is a superior design. It does a good job of accommodating bumpy pavement.
Ragged-edge racecars, as opposed to NASCAR, all have Independent Rear-Suspension. NASCAR doesn’t. It still uses a solid rear-axle with the differential mounted therein. (They call ‘em taxi-cabs!)
NASCAR’s race-tracks are usually smooth enough to allow the older layout. —Although the cars might handle better with IRS.
They handle quite well as it is.
The main advantage to Independent Rear-Suspension is taking the differential’s heavy weight out of bump-compliance.
The differential is no longer suspended with the wheels.
With the older layout, a bump has to move the differential’s heavy mass along with the wheels.
The differential’s mass will also slow return of a tire to pavement.
Without that heavy mass the tire will more quickly return to pavement.
With Independent Rear-Suspension, the differential is mounted to the car-chassis. It’s no longer in the rear-axle.
That is, the differential is not suspended. The rear tires can more readily accommodate pavement irregularities.
Independent Rear-Suspension also separates the bumped tire from its opposite tire.
With the older layout, both tires are affected by a bump to one side. The tires are connected by a solid axle. With Independent Rear-Suspension they aren’t.
One tire can be bumped without affecting the opposite tire.
Despite that, the solid rear-axle with differential has been made to handle quite well.
Never-the-less, Independent Rear-Suspension is state-of-the-art.
I used to notice the affects of a suspended differential on my Chevrolet Vega (a ’72).
The chassis was so stiff (before it rusted), the Vega handled great.
But toss it into a bumpy curve, and the back-end would jump to the outside as the heavy rear-axle took its time getting back to pavement.
Give it a few years — i.e. let it rust — and all bets were off.
The front fenderwells contributed to chassis-stiffness. When they rusted away, the front-end of the car drooped.
I really liked that Vega at first. My previous car (a Triumph TR250), by comparison, was an aluminum ladder. —But my Vega rusted to smithereens!
Independent Rear-Suspension on an SUV is a stretch. My Honda CR-V (a 2003) also had Independent Rear-Suspension. Many of the SUVs I’ve seen are the older layout.
Both the Escape and the CR-V are All-Wheel-Drive. I need All-Wheel-Drive to -a) easily negotiate icy farm-tracks chasing trains, and -b) reduce the likelihood of having to snowblow my long driveway.
The fact an SUV is frequently All-Wheel-Drive requires getting the engine-output to the rear axle. If not All-Wheel-Drive, the Escape and CR-V are Front Wheel Drive.
The engines in the Escape and CR-V are transverse, between the front-wheels, 90 degrees from the length of the car.
The older layout usually has the engine parallel to the length of the car.
Both the Escape and the CR-V have to turn the engine output 90 degrees to rotate that driveshaft. (You can see it in my picture below.)
So you might as well design in Independent Rear-Suspension.
Mazda designed it into their Tribute SUV, the first version of the Escape; and it’s still there in my Escape, the second version. (The second version still has the Mazda chassis.)
It sure attracted me: an SUV with a state-of-the-art chassis. My CR-V was also Independent Rear-Suspension, but not as dog-friendly as the Escape, among other problems.
The CR-V was a great train-chaser, but it was 10 years old. —Plus there were detriments about it, and worst of all it wasn’t dog-friendly.
So every time I saw an Escape I noticed that Independent Rear-Suspension.

I’ve included the photo below to indicate I finally did what did in the past, which was “get out and get under.”


Get out and get under. (That big canister at right is a muffler.) (Photo by BobbaLew.)

That is, I drove my Escape over my pit.
My garage has a pit. We designed it into our new-house construction. That is, our builder had to build in a pit.
It’s not elaborate. It’s only cinder-block walls with a concrete floor.
I have to insert a ladder to get down into it.
Our builder took a major hit building that pit.
The town wanted ventilation. The builder had to install an eight-inch PVC vent-pipe that set him back $500.
Our builder was fair about that. He swallowed the expense.
I never used the pit much, just for oil-changes, and once transmission-fluid.
Not too long ago, an old friend, since deceased, a retired RTS bus-driver, brought out his hotrod ’49 Ford to use my pit.
We attempted to remove the steering-box. We got quite far, but failed. There was a trick to it: mainly removing floor-panels. But we never would have got that far without that pit. —Disconnecting the Pittman-arm, for example.
’49 Ford steering-boxes were notoriously sloppy. Centered the steering-wheel had almost a full turn of play.
A modified Volvo steering-box could be installed to replace the original Ford steering-box, and thereby reduce the play.
That was what happened, although our first intent was to see if the Ford steering-box needed to be rebuilt (overhauled). —It didn’t.
My friend never saw any benefit from that Volvo steering-box. He had Parkinson’s Disease, and was already quite weak. The Volvo steering-box was manageable for me, but too much for him.
’49 Fords aren’t power-steering.
So, take my Escape over my pit. —Took long enough!
Used to be I’d throughly check every car I purchased. Was it within my wherewithal? Was service easy? Could I work on it myself, change the oil, etc?
I’d pop the hood before I purchased it; if I didn’t check out the underneath before I purchased it, I did almost as soon as I brought it home.
30 years ago owners could still work on their cars. I worked on my cars from my Vega on, but as I got older things got more complex. Changing oil was all I ended up doing.
The last vehicle I changed oil on was my Toyota Sienna minivan. My pit made it easier.
I tried with my CR-V, but the oil-filter was a guaranteed skinned knuckle. My Honda dealer did “oil-changes for life,” so I farmed it out to them.
As I got older I gave up using my pit. I even farmed out oil-changes for the van.
My pit had a cover; 4-by-6 timbers above the pit.
My builder left a four-inch recess atop the cinder-block, so I could put in those timbers.
4-by-6s were supposed to support a car, but I’ve never missed. The town wanted me to install steel tire-barriers to keep a car out of the pit. I never did.
What I do is drive my car over the covered pit, and then remove the timbers.
I also store my heavy wooden extension-ladder atop the cover. To uncover my pit I have to remove that ladder first.
As I began doing all this, it seemed I might be attempting more than I should. I’m 69 years old. Strength seems to be withering, especially in my legs.
I dragged out the ladder, and then drove my Escape over the still-covered pit.
I then removed a couple timbers, inserted my step-ladder, went down in the pit, and began removing the rest of the cover-timbers.
It was the most I’ve ever removed, all but one. There are 31 timbers, so I removed 30.
Changing the oil on our van required removal of eight. Changing the transmission-fluid on our old Chevrolet Astrovan required 16 or more.
Once the cover was removed, I got my camera, and took the picture.
Now to reassemble everything.
I reinstalled the cover-timbers, and backed my Escape out from over my pit.
Next was relocating my heavy extension-ladder atop the pit-cover.
I attempted to lift the right ladder-side to straighten out the pull-rope.
I tripped and lost my balance, and fell heavily onto the concrete garage-floor.
I landed on the same left knee I pranged about a month ago when I fell on ice at the park.
“Should I even be doing this at my age?” I thought as I got back up.
My left-knee hurt, but not enough to call 9-1-1.
With IRS the heavy differential is not suspended. It’s not compromising bump-response in a corner.
I’ve had Independent Rear-Suspensions that both looked and acted terrible.
But on my Escape it looks and acts great.
In the ‘70s I remember a local off-road rallyist who rallied a Triumph TR6. It had Independent Rear-Suspension, a terrible design. He was tempted to take out the IRS and install the solid-axle with center-differential from a TR4.
The rules wouldn’t have allowed that!
The TR6 was a stylish upgrade after the TR250 (in England the TR5), one of which I had. It was a ’68, and had Independent Rear-Suspension.
It was a terrible design. One got the feeling Independent Rear-Suspension got engineered in just so Triumph could say they had IRS. (The TR4A was a TR4 with Independent Rear-Suspension.)
The bottom swing-arms were aluminum, and one of mine got bent out of alignment in an accident.
The bottom swing-arms were stubby, just so they could be hinged to a frame, which the TR series still had.
The bottom swing-arms of my Escape are long, as if the whole car was designed for IRS from the beginning.
The Escape is unit-construction. There’s no frame.

• “We” (“our”) is my wife-and-I. She died April 17th, 2012. Together we designed the house I’m still living in.
• “RTS” is Regional Transit Service in Rochester, NY, a public employer, the transit-bus operator in Rochester and environs. For 16&1/2 years (1977-1993) I drove transit bus for RTS. My stroke October 26, 1993 ended that. I retired on medical-disability.