My friend has a mercury mariner with the new 4x4 system. He has taken it to the dealer several times and they say nothing is wrong but the rearend will not kick in. It never gets any power even with the front wheels spinning on ice can anyone give me some ideas on what might be wrong.

 

How do you know it isnt working?
Can you actually see that the rear wheels are not spinning?
The dealer should be able to see that if it is true.

 

I would also think the dealer service dept. should be able to determine this by putting the vehicle on a lift and manually engaging the 4 wheel drive system.

If your friend is driving on ice could it be all the drive wheels are spinning and not getting tracton and he just thinks the back wheels are not spinning?

I am not saying there is nothing wrong, but I would think this would be an easy diagnostic for dealer service dept.

 

if the rear end is a open diff then only 1 tire will spin if it is a l/s both will spin. i bet with 4x4 engaged he only has 2 tires moving , which would account for poor traction.
one tire up front and one in the rear.

 

You bring up an interesting point, what type of stock rear end do the Escape and Mariner have? I had always thought you needed to install Detroit Lockers to get all 4 wheels to turn...

 

It's an open diff front and back. Honda uses a similar system in the Pilot/MDX, but it locks the rear shafts together without using a differntial at all with a switch on the dash. It works using electronically controlled clutch packs, similar to a limited slip diff at the rear.

 

Both front and rear have open diffs.
And, nobody has a LS or locker available, bummer.

 

I don't want to sound dumb, but I guess I am.... could you explain this in laymans language, lol...in other words, which wheels are the drive wheels, front and rear when the vehicle is in Auto 4 WD, and if you manually put the Escape in 4 wheel drive do both rear wheels become drive wheels along with one or two front wheels turning?? I am confused .

Thanks for any info...

 

Differentials are very hard to imagine to anyone without some mechanical knowledge of torque and traction.

Here is a very undetailed explaination of the drive system in Escapes and Tribs and Mariners:

Open differentials at front and rear axles will NEVER allow both tires on an axle to push. We have (actually most 4 wheel drivers have) 2 wheel drive, one in the front and one in the back.

 

Okay, that is what I thought. So actually calling a SUV 4 wheel drive is a misnomer. In reality they are two wheel drive vehicles...One more thing, remember the old Posi-traction rears on GM cars, one wheel started to slip the opposite wheel engaged as a drive wheel? Do the rear wheels on the Escape or Mariner do this also? They call this a limited slip differential now a days...

 

Nope, hence the use of the term open differential and not locked (or limited slip) differential.

 

No the rear end never comes in at all he has had it in many different conditions. There is no manual over ride like in the explorer with auto 4x4. So they tell him that there is nothing wrong. any ideas at all.

 

Technically this is not true. The basic idea of one wheel-drive really only applies when wheel slippage occurs, due to differnt amounts of traction available. A differential ALWAYS sends equal amounts of torque to both wheels, but essentailly allows the torque to follow the path of least resistance, the outer wheel in a turn, or a wheel that has lost traction.

http://auto.howstuffworks.com/differntial.htm


The 4wd system on the Escape senses a difference in wheel speed between the front axles and rear axles, thus engaging the fluid rotor and clutches in the driveline, sending power to the rear diff, which then seperates the power equally to the rear wheels, to which the same open-diff mechanics apply.

In 4x4 on mode the rotor is partially engaged, causing a quicker reaction of the system when the fluid expands.

 

It should be fairly easy to tell, once all four wheels are off the ground, you will immediately have a difference in axle speeds, which should engage the rear end if it is working properly. I wouldn't recommend trying it yourself on jackstands in the garage, but it's a pretty simple procedure.

There is no positive way to tell in a situation offraod where you haven't become completely stuck and spinning one front-wheel to no avail.

 

You notice I said UNDETAILED explaination. Without knowledge of differentials, what I said works out to be sort-of correct.

By the way, the power goes to the inside wheel, due to less distance traveled.