EA82- disconnect rear axles for better MPG?

[Andy FitzGibbon]

This fall, my girlfriend and I are planning to drive my 85 GL wagon across the country. Obviously, 99% of the trip will be in front wheel drive (though probably will use 4WD a little). Do yall think it's worth it to disconnect the rear axles for increased MPG?

Thanks,

Andy

[Manarius]

You're still towing around differential anyways. I can't imagine that removing the rear axles would save you more than 20-25 lb.

[SuBrat84]

You're still towing around differential anyways. I can't imagine that removing the rear axles would save you more than 20-25 lb.

 

I think he is more concerned with "drag" than the weight (probably would keep the axles in the back?) I seriously doubt take the rear axles out would reduce your gas mileage. If it did it would be nominal. The differentials would still be spinning... the motor still has to turn just as much crap. Probably would be a waste of time.

[Skip]

Sorry Su but this is incorrect

" The differentials would still be spinning... the motor still has to turn just as much crap"

 

With the car in FWD and the axles removed the rear diff

 

and back half of the center tranfer would not be spinning.

 

Let's speculate .5 MPG increase

 

X-country = ~3000 miles

at 25 MPG = 120 gallons

at 25.5 MPG = 117.6 gallons

 

2.5 gallon = ~ 625 pennies.

Enough for a Big Rat and fries with a M snake for desert??

[RavenTBK]

Let's speculate .5 MPG increase

 

X-country = ~3000 miles

at 25 MPG = 120 gallons

at 25.5 MPG = 117.6 gallons

 

2.5 gallon = ~ 625 pennies.

Enough for a Big Rat and fries with a M snake for desert??

Hell, that makes it completely worth it right there. Free food is always a good thing.

[hooziewhatsit]

I actually did this for a while last summer. I didn't see any big (or small) increases in mileage I've gotten the best mileage gains... by just driving slower (55 instead of 65) :-\

 

ymmv,

-Dave

[daeron]

suggestion: get ahold of a $10 campbell hausfeld 12v air pump from wal mart.

 

Properly inflated tires ensure maximum fuel mileage, and the pump will go with you everywhere.

[idosubaru]

not worth it.

a search will yield all your answers and details on why it's not worth it.

[Andy FitzGibbon]

Thanks for all the replies.

We have to go across the country and back, so figure 6000 miles rather than 3000... so me AND my GF would get a meal:lol:

Still not worth it. Pretty much what I figured, but thought I'd check others experiences.

Uhh... grossgary, what sort of "answers and details" would I find by searching that are not already layed out in this thread? Seems pretty clear cut to me, just wanted to check with someone who had actually tried it.

Andy

[idosubaru]

there's a "search" button on the gray bar up top, being a newer user i didn't know if you knew about it. this question gets asked all the time, so you could have found your own answer in about 60 seconds without ever posting. including more details on why it doesn't "work".

[Frank B]

Proprely inflated tires, 32-38 psi.

Take out all the junk that you don't need, reduce weight.

And drive sensibly. No fast starts, drive the speed limit or less.

And wash and wax the car. Less drag.

Keep your engine in tune.

Don't expect much but that's about all you can do.

 

Realistically, you may get worse mileage than what your used to since you'll have two adult bodies, and luggage/gear with you to tote acrossed the country so all that will weigh your car down a bit.

[Nug]

And wash and wax the car. Less drag.

 

Hot Rod magazine was doing some wind tunnel testing, and found that the nastiest primer paint job had the exact CD as something that was all waxed up.

[Andy FitzGibbon]

there's a "search" button on the gray bar up top, being a newer user i didn't know if you knew about it. this question gets asked all the time, so you could have found your own answer in about 60 seconds without ever posting. including more details on why it doesn't "work".

 

Yes, I do know about the search function and have used it many times, to get a lot of good information. I searched around for maybe 15 minutes before starting this thread, and didn't come up with anything that specifically answered my question.

Just now, I spent 15 more minutes searching, using the following terms in various configurations, in and out of quotation marks:

 

EA82

ea82

axle

mpg

MPG

fuel economy

rear axle

mileage

 

and came up with one thread that was close, though it was talking about new gen FT4WD cars and the 2WD fuse. The search engine wouldn't even pick up anything when I searched for MPG (in upper and lower case). I tried to look at as many threads as possible, but I don't have unlimited time to read all the ones with titles like "Stupid Question" or "SuBaRRRRRRRRRu".

I found plenty of threads dealing with other ways to improve mileage, but that's not what I'm after- I already know about and do all of them. My question, specifically, was the effect on mileage caused by disconnecting the rear axles of an EA82 wagon.

In about half an hour of searching, I came up with zero posts that specifically answer this question.

I got several answers by starting this thread, one even from a guy who tried exactly what I was asking about. So much for 60 seconds...

[baccaruda]

the search engine doesn't acknowledge terms of 3 characters or less. Thanks for giving it a shot though.

 

To minimize the drag, make sure your wheel bearings are in good shape and that your tires are properly inflated and in good shape as well.

 

While you may see the driveshaft rotating while in 2WD (presumably by driving while hanging backwards out the driver's door looking under the car ) it is because the wheels and axles are rotating the diff and driveshaft "upstream" and it is freewheeling inside the output area of the trans.

Also, as the 4WD driveline stuff is sort of working backwards when not engaged, it has a lot of smaller gears pushing larger gears, which would be a less efficient way to apply force, but that means that it's relatively low-torque when compared to applying the power from the transmission to "downstream."

 

you could make the car 2WD by pulling the halfshafts, diff, and driveshaft, and putting a plugged CV boot over the tailshaft exit to contain gear oil, but you'd be shaving about 150lbs max.. the diff is 65lbs wet, the halfshafts are about 15lbs each max, and the driveshaft is about 15lbs too I think. I've only ever weighed the diff.

 

If you really want to save gas, install a vacuum gauge so that you can tell when the engine's running more efficiently.

[goobaroo]

i would say for that type of distance it would be worth it. you would lose a tremendous amount of rotational weight (the axles, the diff gears, the drive shaft). yes the engine doesnt have to drive them when in 2wd but it still has to get them spinning when the car starts rolling, and keep them spinning when ur driving. thats going to suck up HP and effect your gas milage. I say go for it, what have u got to lose? have fun driving cross country, its quite an experience, i did it with my family when i was younger...in an old VW camper Bus, for two weeks.....it was amazing!

[WoodsWagon]

I'd say you would save a fair bit. There are 2 u-joints, the ring and pinion, the carrier bearings (both of which run in 90 weight oil), and 4 cv joints. The weight isn't that much, but the frictional losses are. There is noticiable resistance when you're just hand spinning the wheels with the rear end lifted up. That resistance goes way up the faster the shafts are turning. I'd say that you would save noticeable amounts of fuel by dropping the two rear halfshafts.

 

If mine weren't rusted solid to the stub axels in the back, I'd do it when I travel out to wyoming. How close togther are you doing the two cross country trips? Taking the same route? You could run a test, keep track of your milage with them in one way, and out the other.

[nipper]

I'm actually going to lean on the side of gaining 2-3 mpg. Here is why. Removing the rear axles you disconnect the car from the drive train. You now have disconnected the rotational masses of the rear axles, the differential, the driveshaft, and the internals of the tranny. That is a lot of inertia to free the drive train up from. you also will notice some improvement in pickup.

 

http://www.cars101.com/oldsubaru.html#1985

 

Now you wont see as much improvement as listed on the link, since you still have the dead weight on the car, but you will see some.

 

 

At 2.50 a gallon and 25mpg it costs .100 a mile to operate. (1200 a year)

At 2.50 a gallon and 28 mpg it costs .089 a mile to operate (1068 a year)

 

Above numbers are at 12,000 miles a year

Damn those numbers are depressing.

 

nipper