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Resealing 2002 short neck and 320is LSD differentials

Go to solution Solved by Preyupy,

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I have two diffs., a standard 3.64 short neck and an LSD off a 320is.


I understand that the LSD came in both 3.64 and 3.91, and I'm not sure which this is. Is there any visual differentiation or should I just get on my back, count revolutions of input and output do the math?


Both likely have never been resealed, and I'd lke to do that if it is within my competence while I'm replacing rear suspension parts.


A few questions for you:


(1) Is this a straightforward pulling of three flanges and the back, and a reassembly with proper torqueing, or is there more to it that is best left to professionals?


(2) I'm having trouble locating info on the LSD. Does it take the same input/output seals as the 2002 4 speed?


Thnak you.

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You can remove the output shafts and replace the seals easily with the differential on the workbench.  If it is a e21 LSD unit the output flanges are held in place with spring clips and you can pull them out with a slide hammer or pry them out. The usual 02 diffs have the output flanges held in place with a bolt (this is obvious looking at the flange) or a C clip inside the differential  (you will need to take the rear cover off and remove the clips next to the spider gears.  


To replace the pinion seal you need to be much more careful.  The bearing preload is set with a crush sleeve. You need to mark the position of the flange to the pinion shaft as well as the position of the retaining nut.  You need to remove the lock plate around the nut and then with a thin walled 30mm socket remove the nut.  The flange will slide off the shaft (you might need a bit of force but DO NOT BEAT ON THE END OF THE PINION).  You can now replace the seal.  Make sure the flange is put back on lined up exactly like it was when you took it apart and with some red loctite torque the nut so that it is back to the same position as it was.  If you over or under tighten it you will mess up the pinion bearing preload.  


You can always look on the housing (see above) to see what ratio you MIGHT be working with but the most accurate way is to take the back cover off and count the gear teeth.  A lot of differentials have been apart in the last 50 years and they are not all still as advertised on the outside.  

Edited by Preyupy
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1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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In addition, the LS unit is loaded with a set of friction discs that provide the lock up.

They wear out over time, its recommended to check the percent of lock up and replace friction discs as required when its opened up.

The ratio is usually etched into the case rear passenger side or on a little tag under one of the bolts.

This is a good place to begin gathering knowledge

Doable for a well informed, properly equipped  DIYer but not exactly "straight forward"


Edited by tech71
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76 2002 Survivor

71 2002 Franzi

85 318i  Doris

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Thank you. I see we're both in Oregon; I'm in Eugene.


I think the replacement of the discs is way beyond my competence, but not a bad idea, as the unit has run for 100K in my possession, w/o service. Would you have a recommendation as to who I could take this to, if anyone "locally" could handle it?


Again, many thanks.

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10 minutes ago, schuetz1619 said:

I think the replacement of the discs is way beyond my competence

Maybe so, you would know better than me however, checking the breakaway friction should be with in your comfort zone. You would need a place to securely strap or bolt (better) down  the diff, a means to keep one flange from turning and a FT LB torque wrench to check. Its in the attachment.

I have no idea about someone locally to handle it, I was gone for a very long time and when I returned the only person I trusted (Dave Lumbra) had sadly, passed way

Edited by tech71

76 2002 Survivor

71 2002 Franzi

85 318i  Doris

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One more question:


are they leaking?


If they're not, I'd strongly suggest just changing the fluid and calling it a day.

The rubber from bygone days was variable in quality, just like it is today,

but if it's not leaking, then there's a bit of proof it's probably pretty good.

Your replacement seal may- or may not- be.


This is ESPECIALLY true of the pinion seal, as changing this one necessarily removes

some preload and static tension

on the pinion nut- and in turn, increases the possibility of it working loose.


The rear case seal's no big deal, tho- that's what RTV was invented for.




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"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Neither is leaking but one is in the closet and the LSD will be coming off the car soon for suspension and cleanup work, so I thought "two birds . . . ."


The LSD has been on my tii for 30 years and 103,000 miles; I don't even know if it works as an LSD any more or how to figure that out.


I very much appreciate the counsel not to touch what ain't broke. Thank you.


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