Question about 2004 Subaru Forester

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Need viscous couplings

Turning causes tire grinding and hopping like locked 4wd. What is the probability of needing viscous couplers?

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If i was u i would drain oil from diffs and top up again ,,, then find a area to drive on full lock either way for at least 10 mins either way ,,,, re drain oil and refilll and see if its ok ,,,,, if problem is still there remove driveshaft to rear and drive again to see if there is a problem in the rear ,,, ie if problem is still there its the front ,,, if gone its the rear

Posted on Nov 24, 2013


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When I select 4 wheel drive, why does it feel as though it is binding or dragging and whining while driving?

Depending on the specific vehicle many 4WD have a transfer case that will lock the front and rear drives shafts together. This configuration is only for slippery conditions like ice and snow or very wet or off road. When turning the radius is different between the front and rear so there is a lot of feedback to the steering wheel. This is created by the fact the front set of wheels and the rear set of wheels must make the same number of turns because of the locked transfer case.

If you attempt to drive on high friction surfaces the stress to the drive train is excessive and will cause damage. The whine and the bunny hop is the drive train attempting to release this tension. If you were on a slippery surface the tires would have much less resistance turning at slightly different rates.

Also critical is the tire size need to be the same. However even with perfectly matched tires the problem on dry surfaces remain the same.

The AWD vehicles are equipped with a third differential that allows for the difference between the rotation of the drive shafts so it can drive on dry pavement no problem. Some configurations allow the AWD to have the transfer case locked which falls into the first category where dry pavement is prohibited.

Some Jeeps have a viscous coupling in the transfer case that permits limited slip between front to rear but the resistance to slip increases as the deference increases as in the event one tire is slipping
These Jeeps still have the lock up option in the transfer case requiring dry pavement when engaged.

Hope this helps?


Jan 17, 2016 | Cars & Trucks

2 Answers

I own a 95 JGC V8. Every time I turn(in either direction) the entire vehicle skips and makes a horrible lurching sound. I got the CV joints replaced a couple of years ago, and the problem persisted. I...

This could be a bearing problem, but it sounds to me like the lowwer ball joints. Ball joints are difficult to check, but if they are rusty then they are probably bad. Bearings on the other hand are not that hard to check. raise the tire/s off the ground , grab the tire top and bottom and push in and out. if there is movement in and out then the bearing is bad.

May 22, 2011 | 2004 Jeep Grand Cherokee

1 Answer

99 Grand Cherokee. Started with locking or binding with loud clunks. After long drive, rear diff was smoking and was replaced. Just drove it and after shifting into all time 4wd and then back to 2wd did it...

Sounds like a bad transfer case. Generally what you experienced is caused by a tire mis-match but can also happen by itself sometimes. GC's use a fluid coupler that is supposed to engage 4wd when tires begin to slip. (coupler is pretty much the same as the mechanical clutch unit on your fan, only larger) If the coupler fails, symptoms like yours happen.

Mar 27, 2011 | 1999 Jeep Grand Cherokee

1 Answer

How do I know if my 4WD is working overtime in my vehicle? Everyone keeps telling me to drive in 2WD while riding in the city but I don't see an option for 2WD, My gear shift only reads: 4WD hi, Neutral,...

The transfer case in your Jeep has what's called a viscous coupler inside of it. Though you physically put it in 4 high, it does not operate the front wheels unless the rear wheels begin to slip. Therefore, driving on dry roads, you actually are only using the two rear wheels.
On direct engagement transfer cases, you would need to physically select 4wd. Those shouldn't be driven on dry roads extensively.
So, your friends are correct, pertaining to most 4x4"s but not yours (I don't know for sure if any other 4x4's use that system except for Land Rover).
One thing you need to know about yours is that you MUST always have the same exact tires on all four corners.... Size, brand and age. (rolling circumference) If you don't it will fool the transfer case into thinking a wheel is slipping and that will cause the coupler to fail, because it will stay engaged when it's not needed and overheat.
4 low is only used when in very deep snow or pulling a heavy load. Max speed in 4 low is about 15mph.

Feb 15, 2011 | 1995 Jeep Grand Cherokee

3 Answers

98 Grand Cherokee Loredo 4X4: When turning the wheel all the way right the back right tire seem to freeze up then lunge grabbing traction. The same happens when the wheel is turned all the way left. ...

Is this a manual 4 wheel drive system that can be shifted into 2 wheel drive? These type of systems should be in 2 wheel drive for tight turns. The drive train locks the differentials to make it 4 wheel drive and with the 4x4 engaged it creates this lunge grabbing effect.

Jan 23, 2011 | 1998 Jeep Grand Cherokee

1 Answer

Does the all wheel drive lock in and out on my astro van mine is staying locked in

This van uses a viscous coupling system much the same in function as the fan on your engine.There is a thick silicone fluid in a housing which is bolted to the water pump. While not mechanically locked,the thick fluid makes the fan turn with the engine.Your van has a transfer case which looks similar to a normal truck unit,but it has a viscous coupler inside ,not gears,so there is a slip factor between front and rear differentials.It is the internal friction of the fluid that drives the front differential,not a locked set of gears. Watch tire sizes, the difference in having 2 new and 2 used tires can cause a noticeable "drag".Always buy 4 tires of the same brand and size for your van.

Apr 09, 2010 | 2000 Chevrolet Astro

1 Answer

Does anyone know anything about a viscous disk in a drive shaft to a 1999 Jeep grand cherokee?

viscous coupler is inside the transfer case. Failure is not "chronic" but they do fail. Easiest way to make one fail is to use different sized tires front and back (one size at front, different on back. tires do not need to be marked differently as tire actual height varies with manufacturer)...,a one inch difference in height results in a 3inch difference in tire rolling distance. Since all your wheels are connected to a single point, the transfer case, eventually if everything was not permitted to slip, something would snap. With different rolling distances, the coupler needs to slip all the time, which causes it to overheat and fail. Being a mechanical component, they do fail all by themselves sometimes though.

Sep 13, 2009 | 1999 Jeep Cherokee

2 Answers

1995 Jeep, grinding,jolting wheel movement when turning

the jeeps with awd or full time 4wd have a viscous coupling in the transfer case that transmitts power to the front axle when the rear looses traction. if the tires on the jeep are mismatched or the tires are not properly inflated it can engage the awd thus forcing the front and rear axles to turn at the same speed. when turning, the front wheels must turn faster than the rear because they are following a wider arc than the rear, this causes binding in the drivetrain which is releived by the tires slipping on the pavement sporradicly. the viscous coupling is filled with fluid that, when heated by the friction of the input spinning faster than the output, locks the coupling. a mismatch in tire sizes or tire inflation can produce just enough heat to lock the coupling in summer, but not in winter. to make a long story short, these vehicles are very sensitive to diffeneces in tire diameters.

May 23, 2009 | 1995 Jeep Grand Cherokee

1 Answer

Quadra Trac II 4 wheel drive problem

Oil is added to transfer case through a plug usually located about half way up the back of the case.
When making a diagnosis, a good tech relies upon previous experience matching that to known symptoms, then upon teardown to verify his ideas. A good working knowledge is essential so the tech can picture in his mind what is happening inside the unit.(i once knew an old tech who could sit in the shop office and make a correct diagnosis as another tech drove a vehicle into the shop) That's rare, but there are good people out there! Your coupler may have to be removed, but that largely depends upon what the shop sees and feels.
Good luck

Apr 20, 2009 | 2000 Jeep Grand Cherokee

2 Answers


You probably have an issue with the A.D.D. (Auto Disconnect Device) on the front axle. That is what lights up the light. I'd need to know the year to get you better info. If it is newer, check the 4WD fuse under the dash. But, in any case, if it IS in 4WD, the vehicle will make tire noises on a real tight turn, and it will lurch on the same tight turn, like it is trying to drill itself into the street. 4Runners do not have a viscous coupling, in 4wd, all 4 wheels run the same RPM.

Sep 10, 2008 | 1990 Toyota 4Runner

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