AWD to 2WD harmfull for the transmission?

[cgilb]

I own an automatic AWD Outback Wagon 1997. I had a problem of " vibrating
transmission ", I went to a specialist and he disengaged the AWD fonction by
inserting à 15amp. fuse in a small box under the hood where it is written
AWD.
As soon as he did it, we drove the car and the problem was solved and the
vibration disappeared but not repaired.

My question is: Anyone knows if it is harmful for the transmission to do
this?

My second question: I intend to put a switch (insead of a fuse) wired to
this box and use the AWD whenever I need it?

Since I have been driving on 2WD I have saved gas: 10 Liters / 100km instead
of 12 liters / 100km prior to doing this modification. In canadian imperial
gallons: 28.2 miles/ 1 imp.Gal. instead of 23.5 miles / 1 imp.gal.

Any comments on this is welcomed?

Claude

 

[Terry Hollis]

cgilb wrote:
--- snip ---

Since I have been driving on 2WD I have saved gas: 10 Liters / 100km
instead of 12 liters / 100km prior to doing this modification. In
canadian imperial gallons: 28.2 miles/ 1 imp.Gal. instead of 23.5
miles / 1 imp.gal.

Any comments on this is welcomed?

If you run an AWD vehicle as a 2WD vehicle, the fuel consumption should not
be affected.

This is because the friction losses resulting from the two additional diffs
and the transfer case churning oil remains the same; unless you actually
remove these units.

I suggest you reveiw your method of obtaining mpg figures.

 

[Catherine Hampton]

I suggest you reveiw your method of obtaining mpg figures.

Uh, Terry, I'd suggest he take his car to a mechanic that knows more about
Subarus. Maybe his figures are right.... And, since you're right that this
*shouldn't* make a difference in gas mileage, perhaps whatever was causing the
transmission shake also caused poor gas mileage?



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[Bruce Hoult]

Since I have been driving on 2WD I have saved gas: 10 Liters / 100km instead
of 12 liters / 100km prior to doing this modification. In canadian imperial
gallons: 28.2 miles/ 1 imp.Gal. instead of 23.5 miles / 1 imp.gal.

There's got to be something wrong. My 1995 2.5L automatic Legacy wagon
gets 10l/100km in the city and as little as 8.7 on the open road.

Even towing a 10m long glider trailer it's only about 11.

 

[mulder]

The FWD mode via that fuse is intended for temporary, emergency use only
such as when the car has to be towed with the wheels on the ground. It
is not meant to be left that way for normal driving.
From your description it sounds like there is a problem with one of the
differentials. You need to get this repaired ASAP rather than ignore it
by driving around with the fuse inserted. You also need to find a
different shop that knows more about Subarus as your present mechanic
apparently doesn't.

 

[cgilb]

Uh, Terry, I'd suggest he take his car to a mechanic that knows more about
Subarus. Maybe his figures are right.... And, since you're right that this
*shouldn't* make a difference in gas mileage, perhaps whatever was causing the
transmission shake also caused poor gas mileage?

In fact, it was a mechanic specialized in automatic transmission who did the
change in the fuse box. The Subaru dealer had nothing to say about that and
the only suggestion the mechanic had was to open the transmission and
replace some plates. A second opinion from a specialized transmission was
that there was nothing wrong with my transmission. The third one I saw
suggested the change to see if it would solve my transmission binding on
turns and it did. The increased gas milage is more a finding after the fuse
was inserted.

For the first 2 years I own this Subaru Outback wagon I have registered the
milage for every tank of gas. In the summer, I averaged 11.5 liters to 1
gallon imp. In the winter, this figure rose to 12.5-13 liters to 1gallon
imp. So it was a surprise to me to realize that inserting this fuse to
remove the AWD has reduced my gas consumption. To reduce the gas milage was
not what I was looking for!!

Everytime I fill the gas tank I always set the odometer to zero so that I
can check. I have been doing this because the needle gage is at empty when I
reach 375 km.
When I reach 500km more or less, I stop for refueling.

Thank you for giving me your opinion.

Claude

 

[cgilb]

I understand very well. My concern with the Subaru mechanic is that on a
previous Subaru Wagon 1985, the mechanic changed my radiator, the thermostat
the sensor on the motor for a problem of overheating that was not solved, to
finally teel me that it was the gage that was faulty. Later,I had to pay for
a cracked head that was causing the overheating. You may now understand why
I am sceptic as to what they advise me to do and it is the reason why I
seach for a second and third opinion. What would you do if you had to deal
with my problem? Go to a Subaru Dealer....again????? Thanks for your advice.

Claude

 

[mulder]

I hear you. Note that I didn't say to go to a dealer, I am well aware of
the fact that they are sometimes the least competent to work on even
their own cars. It really does vary widely from one to another.
It just seemed from what you had posted that your present mechanic was
not that familiar with the car and how to deal with the problem, but if
you are confident in his abilities then by all means stick with him. I
wanted to make the point that you shouldn't consider the fuse a real
"fix" and it wasn't a good idea to drive it for a long time that way.

 

[Bruce Hoult]

Everytime I fill the gas tank I always set the odometer to zero so that I
can check. I have been doing this because the needle gage is at empty when I
reach 375 km.
When I reach 500km more or less, I stop for refueling.

I do the same.

Around town I get pretty much exactly 100 km from each quarter tank,
then another 60 or 70 before the light comes on, then another 60 or 70
before it's empty.

On the open road each quarter tank lasts 110 - 120 km. I've gotten
close to 600 km a couple of times, cruising at 110 km/h (70 mph).

 

[hippo]

< < I own an automatic AWD Outback Wagon 1997. I had a problem of
"vibrating transmission ", I went to a specialist and he disengaged the
AWD fonction by inserting à 15amp. fuse in a small box under the hood
where it is
written AWD. As soon as he did it, we drove the car and the problem was
solved and the vibration disappeared but not repaired. > >

Sounds like the centre diff would be a good place to look first. At least
by removing the fuse he's given you temporary respite and probably
eliminated the trans and the front end as a cause all in one hit. Cool.
Also sounds like he's prepared to throw brain cells at a problem in the
first instance rather than large customer invoices - always a good sign
IME. Agree 2WD shouldn't use less fuel than 4WD in this scenario but
no-one seems to have told AWD Subarus the basic physics underlying this
principle - so they ignore it! Cheers

 

[Rob Munach]

In fact, it was a mechanic specialized in automatic transmission who did the
change in the fuse box. The Subaru dealer had nothing to say about that and
the only suggestion the mechanic had was to open the transmission and
replace some plates. A second opinion from a specialized transmission was
that there was nothing wrong with my transmission. The third one I saw
suggested the change to see if it would solve my transmission binding on
turns and it did. The increased gas milage is more a finding after the fuse
was inserted.

For the first 2 years I own this Subaru Outback wagon I have registered the
milage for every tank of gas. In the summer, I averaged 11.5 liters to 1
gallon imp. In the winter, this figure rose to 12.5-13 liters to 1gallon
imp. So it was a surprise to me to realize that inserting this fuse to
remove the AWD has reduced my gas consumption. To reduce the gas milage was
not what I was looking for!!

Everytime I fill the gas tank I always set the odometer to zero so that I
can check. I have been doing this because the needle gage is at empty when I
reach 375 km.
When I reach 500km more or less, I stop for refueling.

Thank you for giving me your opinion.

Claude

It sounds like your electronically controlled clutch pack (no center
diffs on this vehicle) needs to be replaced. This seems to be a common
problem.

 

[Danny Russell]

I understand very well. My concern with the Subaru mechanic is that on a
previous Subaru Wagon 1985, the mechanic changed my radiator, the thermostat
the sensor on the motor for a problem of overheating that was not solved, to
finally teel me that it was the gage that was faulty. Later,I had to pay for
a cracked head that was causing the overheating. You may now understand why
I am sceptic as to what they advise me to do and it is the reason why I
seach for a second and third opinion. What would you do if you had to deal
with my problem? Go to a Subaru Dealer....again????? Thanks for your advice.

Claude, tires with slightly different diameters due to wear, etc. could be causing your
chattering/binding
problem. -Danny

 

[cgilb]

Thanks Danny,

I'll check and let you know. I was also told that the circumference of the
tire had to be check, which I didn't do...???
Claude

 

[Danny Russell]

Thanks Danny,

I'll check and let you know. I was also told that the circumference of the
tire had to be check, which I didn't do...???
Claude

Well sure, a different diameter would translate to a different circumference.

There is a fairly narrow allowable tolerance, but I don't know what the spec figure is.

 

[mulder]

Rolling circumference of all four wheels/tires must be within 1/4".

 

[cgilb]

Yes, it's ¼ inch. Thank you for your advice.

Claude

 

[Brian K. M.]

The FWD mode via that fuse is intended for temporary, emergency use only

such as when the car has to be towed with the wheels on the ground. It
is not meant to be left that way for normal driving.

I would debate that due to the fact that the engine is running and
activating the pumps for the transmittion fluid. On most cars the
fluid is run through the radiator for cooling/warming so there is a
pump inline with the system.

Brian

 

[hippo]

Basically - just about any difference in wear between pairs of tyres may
put you over the 1/4". IME it doesn't have drastic short term effects,
(I've had to run completely different tyres front to back on more than one
occasion), whereas centre diff &/or centre clutch pack problems can stuff
things up quite quickly (like no apparent problem to 'failure to proceed'
in less than 1000km with ours!) Cheers