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Old 08-03-2003, 09:31 PM   #1
stimpy
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Default LSD/Open Diff Axle Compatability

When swapping rear differentials, the question is often posed: "What axles should I use?" A lot of controversy and confusion is brought about by this question and I think I may have a definitive answer on the subject.

First of all, you can reference my thread here to find those cars that had a rear LSD.

If you are equipping your car with an LSD, then chances are, you are going to need a new set of rear axles. Your current axles WILL bolt into the new differential, but they are not the same. You can see the spline count in this thread here to verify that they will appear to fit.

To select the axles needed, my first suggestion would be to source them when you purchase an LSD from any chassis except the GD chassis (unless, of course, you are converting your GD chassis to a rear LSD). If you already have the LSD and are in need of the axles, then refer to the first thread indicating which cars came with an LSD. You must note which type of axles are used (female or male) and match accordingly. The Legacy, Forester, pre-2002 RS and the 2002+ WRX Wagon should all share the same rear LSD axle dimensions and be interchangable so just find a car on the list and go for it. Some junkyards are VERY ingorant as to what works and what doesn't so to be safe, demand the exact car and don't settle for substitutions. It took an unnamed yard two different tries before I finally cancelled and went with somebody else.

Now for the next question: "Why do I need new axles if the ones I already own will fit?" The answer is their lengths. The rear LSD axles are 1cm (10mm) shorter than the corresponding open diff axles. While your open diff axles may bolt in and appear to fit, it could induce binding or other unforseen problems. People have reported using open diff axles with LSDs and vice-versa but it should not be taken as rule.

Lastly, "Are there any axles that are better than another?" The truth is, the CV strength should be equal between all of the Subaru axles. While there are visible differences, who has heard of a Subaru mulching a CV joint? Diameters will also vary with the WRX axles being the thickest, then the RS/Legacy/Forester LSD axles, then the remaining open diff axles. Again, who has heard of a Subaru twisting an axle? Probably not a significant concern.

To quiet the argument of the open diff axles fitting, here is a picture of some 2001 2.5RS rear LSD axles compared to rear open diff axles from two different cars. Note the length differences between left and right and between LSD and open diff.



One final note: notice that while the left-hand RS axle is shorter than the right-hand RS axle, the actual axle shaft is longer than the right-hand axle. The axle shaft lengths are given in the newer FSMs (2002+) but have no correlation to the actual axle length.

-Jon
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Last edited by stimpy; 08-03-2003 at 09:37 PM.
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Old 05-31-2005, 04:33 PM   #2
keirnna
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Can we please make this a sticky. Stimpy, do you still have the pictures?
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Old 06-02-2005, 10:21 PM   #3
keirnna
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Sticky, please!
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Old 10-07-2008, 10:36 PM   #4
toddvero
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Default VA-type diff

Can anybody confirm that a VA1 type diff can be found with LSD and can fit an Impreza 22 spline rear axle?

According to my research, all 2003 Baja had LSD as standard equipment, and the diff I pulled off a 2003 Baja was VA1 diff with a 152mm crown wheel (ring gear) and 22 spline (inner) axle. I thought all late model, viscous LSD were the 160mm ring gear, T type (bolt on carrier) diffs with 25 splines at the axle. Do I really have an LSD here?

I'm build a custom rear end out of Subaru parts for a project car. Any info appreciated.

Last edited by toddvero; 10-07-2008 at 11:00 PM. Reason: Clarity
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Old 10-08-2008, 05:23 PM   #5
Storm
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I can confirm that it WILL NOT. The bearings on the VA type (thread in carrier bearings) are smaller than the T-type and do not intermix. I find it surprising that your Baja came with the VA type rear diff.....that sounds fishy to me.

Jay Storm
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Old 10-19-2008, 03:38 PM   #6
toddvero
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Default Tiny LSDs

The local Subaru dealer helped me determine that the 2003 Baja diff I have is an LSD, though it has VA type threaded bearing carriers and a 152mm (6") ring gear. I had no idea Subaru made such tiny LSD's!
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Old 10-19-2008, 11:15 PM   #7
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That's very interesting.....
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Old 12-26-2008, 03:32 AM   #8
AWDalbert
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how about putting GD axles into a MY00 GM6 (GC) vlsd diff

so

05wrx axles into a 2000 subaru 2.5rs rear diff?

thanks
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Old 12-26-2008, 09:37 AM   #9
Jaxx
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i would think so both are 25 spline
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Old 03-16-2009, 11:53 PM   #10
B-Kerr
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Just FYI, I own a salvage yard, and most every yard uses a standard part interchange from ADP Hollander (or a derivative thereof). This interchange uses information provided by the manufacturers. It is true, many times parts will interchange, but if the manufacturer gives them different number, many times salvage facilities will not know they interchange unless they have experienced it first-hand.
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Old 03-17-2009, 10:21 AM   #11
Jaxx
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the big problem i found was that the interchange was wrong due to LSDs being an option

best method is to count the splines
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Old 03-17-2009, 01:20 PM   #12
B-Kerr
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I agree.
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Old 07-03-2011, 12:31 AM   #13
Smoke
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Zombie bump, but I've been searching around.

I have a Version 4 STi swap. Can the axles bolt into my current hubs? Is it only contingent on your bolt pattern?

I'm hoping I don't have to drastically upgrade my brakes/hubs to fit the axles.
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Old 07-03-2011, 10:49 PM   #14
Matt Monson
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I answered your PM, but will reply to the thread too for public benefit. Look in the tranny forum for SuberDave's hybrid axle conversion. Lets you run an R180 rear diff on your car with the stock outer stubs from your R160.
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Old 07-04-2011, 01:07 AM   #15
Smoke
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Thanks Matt. I plan on keeping my brakes the same right now until after the swap.

It's not like I'm going to see complete use of the LSD right away, so I'll wait.
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