I have an intermittent problem with my 2002 Outback wagon. Occasionally, while driving at highway speed (with cruise control on), the rear wheels "judder" vigorously (violently?)-- I feel like I am driving on the rumble strip on the side of the interstate. There is no pulling , the vehicle tracks perfectly straight. Upon pulling over to the side of the highway and shutting off the car, and starting out again, the symptom remained. So, pulled over again and shut car off, then restarted engine, the problem went away.

 

The previous owner (my father in law) had the same problem 4 years ago, and the dealership replaced the differential.

 

I realize that intermitent problems are by their nature hard to diagnose, but any advice would be greatly appreciated.

 

Thanks-

John

Hello John and to the board!

 

Is this a manual trans or auto trans vehicle? How many miles?

 

Are all your tires the same brand, nominal size, treadwear, and proper air pressure? (they must all match within 1/4" circumference when measured with a tape measure otherwise AWD issues can occur).

 

It's a 5 speed manual, with approx 72,000 miles. I will check on the tires as soon as my 1yr old goes down for his nap!

Thanks-

John

 

---------

Is this a manual trans or auto trans vehicle? How many miles?

 

Are all your tires the same brand, nominal size, treadwear, and proper air pressure? (they must all match within 1/4" circumference when measured with a tape measure otherwise AWD issues can occur).

Especially look at your rear tires. I'm pretty sure your soob has the VLSD viscous limited slip rear diff. If the rear tire circumferences are different by much, it may be heating up the silicone oil quite a bit at high speed driving, thus sort of locking the rear axles together, and causing rumbling/wheel hoping/etc from the different tire circumferences?

Thank you for the advice, as soon as I defrost a bit I will check the circumference (it's getting a bit chilly here in Milwaukee, it's in the 20's and I don't have a space heater in the garage!) The tires all look to be in decent shape , as far as the treads go. They are all the same type. I checked the inflation of all 4 tires:

Fronts: LF= 28 and RF 28.5 psi ;

Rears: LR= 29.5 and RR= 29.

 

So a bit off, actually, a variation of 1.5 psi.

 

Again, thanks for the advice on checking the tires and the info about the differential oil. I am a shadetree mechanic at best and this is helpful information to have.

-John

I have an intermittent problem with my 2002 Outback wagon. Occasionally, while driving at highway speed (with cruise control on), the rear wheels "judder" vigorously (violently?)-- I feel like I am driving on the rumble strip on the side of the interstate. There is no pulling , the vehicle tracks perfectly straight. Upon pulling over to the side of the highway and shutting off the car, and starting out again, the symptom remained. So, pulled over again and shut car off, then restarted engine, the problem went away.

 

The previous owner (my father in law) had the same problem 4 years ago, and the dealership replaced the differential.

 

I realize that intermitent problems are by their nature hard to diagnose, but any advice would be greatly appreciated.

 

Thanks-

John

 

The Stock tire pressures for mine are 33 front / 30 rear.

Aren't your front tires supposed to be more than the rears?

 

Subaru tends to favor wheel travel over wheel damping.

Last car when it had 200k on it. I put nitrogen dampers on the rear.

Wow even the exhaust bounced less!

Is this some kind of computer generated awd wheel hop induced feedback or somthing:headbang: ?

 

Wheels. Shocks, Bearings, Sensors and Computer read out.

Cover the basics.

True, maybe set your tire pressures per the door plaquard. Then when you get the chance measure the circumferences. The AWD and LSD rear diff are completely mechanical on this vehicle.

 

Do you know which differential was replaced for the previous owner? (rear or center)? The center isn't really a 'differential' on this vehicle but sometimes people do call it the 'center differential'. Front diff is in with the manual trans.

Check the driveshaft ( propeller shaft ) universal joints. Especially the ones near the transmission rear and the other end at the differential.

 

When I have seen these go bad, they cause a shutter, usually starting in the 30mph range that then goes away when you go faster. Then as the joint gets worse, the speed range widens.

 

If you crawl under your car, look closely at each one. A bad one may still look good. Use a bright light and look for ANY rust or dust near the caps or journels. This is a sign of a worn universal. Also grab it and try to see if there is any play. Even a bad one still attached to the tranny may not have much play you can feel.

 

If you find any problem here, the universals are not a replaceable part. You have to get the entire driveshaft. And that can be upwards of $400.

AHA got ya porc

 

its a manual, so its a center differnetial with a viscous coupling.

 

Lets rule something out quickly. Go to a parking lot and drive in a tight circle at idle speed or a little bit more. The car should do this nice and smooth, with no lurching and almost no throttle.

 

 

Let us know.

 

PS your tires are low becuase its cold outside. Top them off as you get 1psi change for every 10 degree temp change.

 

nipper

38913AA101 & 33179AA030 & 806735210 VISCOUS COUPLING CENTER DIFFERENTIAL ASSEMBLY FOR 1999-2004 LEGACY OUTBACK MANUAL TRANS (with gasket, bearing and shaft seal) for cars produced up to 2 of 2004

I normally run 36 PSI all around. I think it helps with the fuel economy.

38913AA101 & 33179AA030 & 806735210 VISCOUS COUPLING CENTER DIFFERENTIAL ASSEMBLY FOR 1999-2004 LEGACY OUTBACK MANUAL TRANS (with gasket, bearing and shaft seal) for cars produced up to 2 of 2004

HA where are your fancy pictures now

 

heheheheeheh

 

 

nipper

The center isn't really a 'differential' on this vehicle but sometimes people do call it the 'center differential'. Front diff is in with the manual trans.

 

Manual trans Subaru DO HAVE a center differential. It is a true, real differential, not any different than the rear VLSD in fuction. It has a carrier, 2 bevels, 2 spiders, and a pinion shaft. It has the Viscous unit attached to one of the bevels. Mounted inside rear of the trans.

 

Automatics do not have a differential, they have a hydraulic pack.

 

 

 

To the OP, Have you considered that you might need new shocks?? Or the tire is out of balance?

 

If this where any other car, wheel hop=shock/wheel issues. Just because the Subaru has AWD, doesn't mean that it has to be a problem with he AWD.

 

Hear hoofbeats?...think horses.......not zebras

Hear hoofbeats?...think horses.......not zebras

 

He's in wisconsin, maybe moose or cows