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Full time FWD?

14 messages,  Last post on Aug 15, 2010 at 3:33 PM

You are in the Subaru Forester Maintenance & Repair Forum.

What is this discussion about? Subaru Forester, Transmission, SUV

Messages Page 1 of 2

#1 of 14 Full time FWD? by medic481

Aug 10, 2010 (12:01 pm)

I just bought a 2010 Forester. While thumbing thru the owner's manual, I saw the section addressing using the spare tire on vehicles with automatic transmissions. The instructions are to disable the AWD, by placing a jumper (fuse) in the fusebox. This got me wondering- could you leave the AWD disabled, and just use FWD? I live in the city, and don't need AWD, I just liked the car and features and the fact Consumer's Report loved it.

#2 of 14 Re: Full time FWD? [medic481] by xwesx

Aug 10, 2010 (12:04 pm)

Replying to: medic481 (Aug 10, 2010 12:01 pm)
It will not be good for the center differential over the long term plus you will most likely not see any fuel savings as a result of doing that. I suspect the rationale for inserting the fuse would be for increasing fuel economy?

#3 of 14 Re: Full time FWD? [xwesx] by medic481

Aug 10, 2010 (12:20 pm)

Replying to: xwesx (Aug 10, 2010 12:04 pm)
Not as much fuel savings, but I always understood that using four wheel drive on regular roads, was not good for the differential. All other 4x4's, like Jeep, tell you you that four wheel driving is best when used on snow, mud, etc, where the extra traction is required, and that once on asphalt, the vehicle should be returned to 2WD mode, as driving on asphalt while in 4 wheel mode will damage the front differential. Most of my "off roading" is going to consist of pulling into a store parking lot. Thought this might save on the wear and tear.

#4 of 14 Re: Full time FWD? [medic481] by xwesx

Aug 10, 2010 (1:01 pm)

Replying to: medic481 (Aug 10, 2010 12:20 pm)
No, not for this type of AWD system. Over the practical life of the car in normal use, you will never have a problem with the differentials.
 
If you wanted to run FWD only in this car, it would be a far better option to remove the rear driveshaft so as not to have the electronic override of the center differential engaged.

#5 of 14 Re: Full time FWD? [medic481] by rsholland

Aug 10, 2010 (1:21 pm)

Replying to: medic481 (Aug 10, 2010 12:20 pm)
That only applies to vehicles with old-fashioned "part-time 4WD," like most (not all, but most) trucks.
 
For vehicles with "full-time 4WD," like Subarus (AWD = 4WD), this is a non-issue. They're designed to operate all the time in 4WD/AWD.
 
Bob

#6 of 14 Re: Full time FWD? [medic481] by aatherton

Aug 10, 2010 (1:54 pm)

Replying to: medic481 (Aug 10, 2010 12:20 pm)
Subaru has a permanent AWD system, as opposed to a 2WD system that can be switched into 4WD like a Jeep.
 
As I understand it, a spare fuse is provided to energize a circuit to a solenoid that is part of the automatic transmission's clutch pack that apportions a varying percent of power to the rear wheels. The fuse gives the solenoid continuous power which disengages the rear drive train from power, turning AWD into FWD.
 
This feature is only for an automatic transmission when a compact spare is used on the rear (the compact spare should never be used on the front). The purpose of using FWD is to save the AWD drive train from damage from using the smaller size compact spare on the rear.
 
The solenoid is not designed for continuous duty, but will keep the car in FWD long enough to get the spare replaced. Something like 50 miles under 50 mph. I don't know what happens when the solenoid burns out from being continuously energized to keep the car in FWD, but it must not be good or many people with automatic transmissions would be using the FWD.
 
I have heard there is no improvement in mileage while in FWD as the unpowered rear wheels are still dragging the rear axles, differential, drive shaft and transmission.

#7 of 14 Re: Full time FWD? [xwesx] by medic481

Aug 10, 2010 (9:40 pm)

Replying to: xwesx (Aug 10, 2010 1:01 pm)
Thanks- I was curious after I started reading the manual. Not going to mess with it.

#8 of 14 Re: Full time FWD? [medic481] by aatherton

Aug 12, 2010 (3:50 am)

Replying to: medic481 (Aug 10, 2010 9:40 pm)
Here is a post by someone who rewired the transfer clutch solenoid to provide 50/50 lockup, like 4WD:
http://www.subaruforester.org/vbulletin/f89/4wd-demand-4eat-3091/#post66302

#9 of 14 Re: Full time FWD? [rsholland] by aatherton

Aug 12, 2010 (8:28 am)

Replying to: rsholland (Aug 10, 2010 1:21 pm)
"... vehicles with "full-time 4WD," like Subarus (AWD = 4WD)... They're designed to operate all the time in 4WD/AWD."
 
In 4WD vehicles there is a solid geared connection between the transmission and the wheels.
  
Subaru's AWD is different from 4WD in that there is no direct geared connection from the transmission to the wheels. Depending on the transmission, power goes through things like clutch packs and viscous couplings and multi-plate transfer clutch limited-slip centre differentials.
 
There is a good explanation of Subaru's AWD here:
http://www.subaruspecialists.com/mainframe/AllWheelDrive.html

#10 of 14 Re: Full time FWD? [aatherton] by rsholland

Aug 12, 2010 (8:58 am)

Replying to: aatherton (Aug 12, 2010 8:28 am)
4WD? AWD? It's just marketing. In other markets Subaru has in the past called their AWD, 4WD. They don't do it any more mainly because they want to present one consistent message worldwide.
 
Also, Honda's "Real-Time 4WD" is nothing but AWD, same with the so-called "4WD" on the Toyota RAV4 and Highlander.
 
In all those cases all 4 wheels are driven, hence 4WD. Like I said: It's just marketing, nothing more. I do agree with you that there are many different types of 4WD/AWD out there (part-time, full-time, plus low-range, on-demand, selectable, permanent, etc.), but in the end, if all the wheels are powered, it's still 4WD.
 
Bob

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