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saeble

a tale of two diffs

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I have an 82 D/R 4WD wagon.

 

It had a shot rear diff. I pulled said diff and it has no final drive ratio sticker, long since fallen off.

 

I turned the prop input 20 times and got 6.5 turns of axle output shaft.

 

I then counted the turns on my replacement diff which I bought at a wreckers which is a 3.7 and got 5.75 turns of the axle output shaft.

 

Here's the issue.

 

The wrecker insists that vitually every soobie of the vintage mine is are all 3.7's. Only some direct import Brat/Brumby utes from Japan, (2nd hand, not thruough a soobie dealer), had 3.9's.

 

How do I tell what I should have in the car ? How can I tell what the front diff ratio is ? My suspisicion is that the previous owner has fitted the wrong rear diff to the car. What's likely to be damaged if this is the case ?

 

It looks as though the diff has been in there for quite some time. It looks original. Suffice to say I'm at a loss as to what I should be doing here..:)

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you need a three point niner back there.

 

assuming that's what you had, since it's different from the known 3.7, then the differential was probably correct for the car and didn't hurt anything on the way out. maybe it ran out of fluid or something.. if your trans feels OK after putting in a new 3.9 diff, then you'll know it's OK.

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****e.... looks like I may have to rebuild the old one, seeing as the wreckers cant seem to source a sound 3.9

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Yes, there were most definately 3.7 diffs in '82. For one, the automatics were 3.7, and the 2WD's were 3.7.

 

In AUS, all the Brumby's were 3.7 as well - weird, since all the Brat's here in the US were 3.9

 

It could be that the PO put the 3.9 in mistakenly, or thought he would get some strange benifit from it. If you ever ran the vehicle on dry pavement with a 3.7 in the front and a 3.9 in the rear.... that could account for the premature failure of the diff. I've seen a lot of diffs abused, but never seen one actually fail - except broken stub axles. Anything is possible of course.

 

Without knowing the gear ratios of the tranny (who knows - maybe he put a 3.9 tranny in as well!), it will be difficult to figure out the diff ratio.

 

I say put the 3.7 in, and see what happens on dry pavement - put it in 4WD and see if you can travel in a straight line without binding. If it does, then you'll need to source a 3.9 diff..... we have tons of them here in the states, and I'm sure someone would be willing to ship you the ring and pinion gears so you can have that 3.7 converted.

 

GD

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you definitely need a 3.90 ratio if it's a 4 speed D/R...

 

do you know what is wrong with your rear diff? if the ring gear and pinion are okay, then you could dis-assemble both diffs, and put the center of the 3.70 diff inot the 3.90 case using the 3.90 ring and pinion.

 

similar to this conversion.... http://www.ultimatesubaru.org/forum/article.php?a=36

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Ah...just weld Er up Solid, Thats what any good Tractor Mechanic would Do right GD....?????

 

As McBrat stated, pop the Rear Diff cover and inspect the innards for damage, Depending on What went you could get away with swapping out Spider gears..?

 

Good Luck, John

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Ah...just weld Er up Solid, Thats what any good Tractor Mechanic would Do right GD....?????

Probably - but not if the gears are shot. Likely a Tractor Mech would just pull the driveline and diff and replace the driveline with a spray paint can lid, a plastic garbage bag, and some bailing wire to keep the fluid in. Oh - and of course a gallon of cheap wal-mart 90 weight to keep the tranny full.... other options include parking it in the back 40 and driving the chevy, or even dropping the chevy drivetrain into the Brat..... with liberal use of bailing wire, duct tape, and a dirty sock for an air cleaner.

 

Replacing the gears is a bit of an operation, as proper shimming will be required with a different ring and pinion. Unless you have the right tools, and the knowledge, a transmission shop would be the place to look for help....

 

GD

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ok... NOW I'm confused....:)

 

The diff that was in the car is as much as I can tell a 3.9, and yet everyone says that AUs production wagons in 82 with D/R are supposed to be 3.7

 

I've since driven the 100k round trip to the wreckers to get a 3.9, which seems to be a very rare beast, everything else in stock was 3.7

 

Ok, so if it some idjut has put a 3.9 in a car set up for 3.7 (with a 3.7 front diff), deliberately and consciously, what's the advantage ? More launch from the lights ??

 

I think I'm going to bung the 3.9 replacement in and see what happens, if it starts doing strange shirt I'll put a 3.7 in...

 

...sigh... all I want to do is drive the danged thing. :)

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No advantage.... big disadvantage actually, since the wheels will bind up on hard surfaces. If that is the case, then I would find the PO, and beat him profusely about the head and shoulders.

 

Unless he wanted to run larger tires in the back to compensate!

 

GD

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Why hasn't anyone suggested that you take the rear cover off and look for the stamp on the ring gear??

 

That will tell you exactly what your ratio is and will end the debate with all. Swapping third members will not be cause for redoing the side bearing shims if he keeps the parts from each diff together.

 

Pull the cover and find the answer and then you'll know what to do. Besides that, you'll find out what the reason for failure is.

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I installed the 3.9 today... drove it a fair distance and it seems to be happy. Go figure. Who knows, perhaps its had some donor organs in the past.

 

Incidentally I also replaced the big phat rollpin in the gearshift linkage and man... I can get first, second and reverse without tearing a hole in the gearstick boot each side of the stick..:D

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