Subaru Outback Forums banner

1 - 5 of 5 Posts

·
Registered
1999 & 2002 Legacy Outback auto
Joined
·
85 Posts
Discussion Starter #1
How can I tell if the awd is working or if it has any issues? How can I identify my drivetrain config? (how many lsds are in this thing, what type etc...)

Im new to this and really have no idea what goes on between the trans and wheels.

Thanks,
Bob
 

·
Registered
Joined
·
18,179 Posts
cars101.com is a good source for "what's on the car?", at least for a start.

You have the 4 cylinder engine, with the 4-speed automatic transmission (4EAT, Phase II).

The AWD system uses a computer-controlled, hydraulically-actuated, variable-engagement multi-plate clutch (MPT). In simple terms, the drive shaft to the front differential, which drives the front wheels, is always connected to the transmission through a pair of gears. One of the gears is connected to the input of the MPT. The output side of the MPT is connected to the drive shaft going to the rear differential, which drives the rear wheels.

Whenever the engine is running and the transmission is not in P or N, the MPT clutch is engaged to some degree; in other words, power is always transferred from the input to the rear differential. However, the clutch is not 100% engaged because if it were, this would cause instability, especially when turning, due to an effect commonly referred to as "torque bind" and the need for the front and rear drives to turn at different speeds. With torque bind, when the car is being turned, one or more wheels will hop or skip. The effect is well known to operators of 4WD vehicles when the transfer system and differentials are locked. Consequently, the MPT is engaged, but can still allow some slippage so that when cornering the front and rear drives can rotate at different speeds.

When the AWD control system detects that one or more wheels is slipping, or under heavy acceleration, the pressure on the MPT is increased. The reaction time, in a properly operating system is so fast that it isn't noticed.

When the AWD is working properly, there should never be a situation where one or more front wheels is slipping and neither rear wheel is turning. At least one rear should be spinning as well, but this is hard to tell from the driver's seat. You'd have to find a slippery slope, and have two observers on either side of the car. Position the car on the slope, stop, and then try to accelerate rapidly while the observers note which wheels spin. Again, as noted, if either front wheel spins, at least one should as well, but not necessarily on the same side. Note: With the basic AWD drive train, it's still possible to get stuck if one front wheel and one rear wheel are slipping. If the car has a limited slip rear differential, this might help if the other rear wheel has good traction. Later cars with VDC introduce a further level of control at each wheel.

Based on this description, if a front wheel spins and neither rear does, the AWD isn't working. Another possible problem with the AWD is that the MPT fails and becomes permanently engaged. In this case you will find the car sort of hesitating periodically while making tight turns at low speed.

The AWD can be disabled (that is, put the car into front wheel drive only mode) by inserting a fuse in a special FWD socket in the engine compartment. This is used when an odd size tire, such as the temporary spare, is being used. It can also be used to diagnose some symptoms. When the fuse is in, a FWD (or AWD) warning light should come on in the instrument panel.

Otherwise, make sure the AT Oil Temp warning light and the CEL do come on when the key is turned to ON but the engine is not started, and that they go out when the engine is started. If either flash at any time, there is a problem. (These, along with the other warning lights are described in the Owner's Manual.)

There's lots of discussion here about AWD, problems, fixes etc., but unless you're experiencing symptoms, don't fret. It's a good system.

That said, if you don't have a service record for the car, consider some maintenance items relating to the drive train, such as changing the front and rear differential gear oil, and the automatic transmission fluid. There's threads in the Do-it-yourself sub-forum here with details and lots of related discussion.
 

·
Registered
2005 Outback XT Limited 5MT
Joined
·
104 Posts
1999 outback auto with a 2.5L

4.44 final drive ratio
open diffs front and rear
phase 2 transmission with spin on filter
 

·
Registered
1999 & 2002 Legacy Outback auto
Joined
·
85 Posts
Discussion Starter #4
Freaking cool, guys. Open diffs, huh? are LSDs avail?
 

·
Registered
01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
Joined
·
1,401 Posts
outbacks 01 - 04 have a vlsd rear diff. and the ones from the auto trans cars match your 4.44 final drive ratio.

you can look for parts at: Car-Part.com--Used Auto Parts Market put in your zip and sort by distance, shipping can be expensive.
 
1 - 5 of 5 Posts
Top