Some e21 differential questions

[mvliotta]

In my enthusiasm to get the 3.64 lsd ready for install I skipped a step or two. Back cover is sealed with RTV and torqued, and filled with gear oil, BUT I forgot to change the side flange seals…argh. 
 

 

These have four bolts securing the output flange and threaded holes to receive half shaft bolts.  A few questions:

 

1) Do these flanges just pop out by removing four bolts and pulling? So can I just drain oil and leave back cover on?

 

2) Is there a gasket (or RTV) needed between the  plate with 4 bolts and diff body?

 

3) Some have recommended using nuts to secure half shaft bolts as extra precaution. Does not look like there is any room behind the flange for locking nuts. Will only blue loctite do the job between half shaft bolts and flange threads?

Could not find all this info easily after some searching so apologies if I missed it. 
 

[TobyB]

Run it.

 

The side seals are pretty durable.

 

If it leaks, THEN go back in and pull it apart.

 

Am I misremembering, or can the side seals come out with the bearing caps still on?

 

t

 

[ray_]

20 minutes ago, TobyB said:

Run it.

 

The side seals are pretty durable.

 

If it leaks, THEN go back in and pull it apart.

 

Am I misremembering, or can the side seals come out with the bearing caps still on?

 

t

 

Yes.

[mvliotta]

Thanks Toby. 

Was thinking to do that, but it was already leaking a bit from the side cover because I didn’t realize the 4 side bolts were loose from the PO who checked out the lsd. 
 

So started experimenting…

 

 

Flanges popped right out as they have retaining rings. This is a ‘77. 
 

 

Will clean things up and  use blue loctite for the thru bolts … and get new side seals. 
 

 

Edited April 29, 2022 by mvliotta

[AceAndrew]

Use a thin smear of dirko on the OD of the seals. 

[0257]

1 minute ago, AceAndrew said:

Use a thin smear of dirko on the OD of the seals. 

I wish I had done this!

[TobyB]

Oh- and if the side caps have been loosened, it's wise to also clean and smear

the root of the flange.  Older diffs had an o- ring in there.

Very thin smear.

 

t

 

[Ian]

What flavor of Dirko sealant do you use for this application?

Speaking as a Dorko who wants to know!

[uai]

9 hours ago, TobyB said:

Older diffs had an o- ring in there.

81x2mm

[Conserv]

Rare early e21 LSD, Vince. The four-bolt side side covers were only used up to the 1979 model year. This example has a housing cast November 23, 1977 (“23L77”) and was assembled in January 1978 (“1” over “8”). Many of these early e21 LSD’s were 3.64’s, because the cars were 4-speeds — unlike the later 320is sub-model, which paired a 5-speed with a 3.91.

 

Enjoy!

 

Best regards,

 

Steve

 

 

[tzei]

And if you get new o rings then side caps can be very reluctant to go all the way back to the case. Take your time to not to nick them in assebly. Old ones are ”seated” so they don’t put up a fight. If they have not leaked i use them again.

[0257]

Resurrecting this good thread with a couple of question.  The factory output shaft o-rings for my early 320i diff (33 12 120 5302): what material and hardness are they?  I have procured from the O-Ring Store some correct-sized (81mm x 2mm) Buna-N 70 Duro o-rings.  Are these the right material and hardness?

 

Also, when I have used the factory 87x2 o-rings in the past, they have seemed awfully thin for the job.  Does anyone have experience using 2.5 or even 3 mm thick 0-rings?

[tzei]

Can't comment about that material but if it's good when submerged in oil, copes 120 C temp then i suppose it'll work. I remember oe o-rings to be soft(ish) - they only provide an oil seal so compressing like 0.1 - 0.2 mm should be enough. I think.

[TobyB]

They shouldn't be too thick- the original grooves aren't really very big.

 

Sometimes less is more.

 

t

 

[0257]

14 hours ago, TobyB said:

They shouldn't be too thick- the original grooves aren't really very big.

 

Sometimes less is more.

 

t

 

Each of y’all’s comments interesting.  When I installed the stock rings they felt so inadequately skinny I couldn’t imagine them doing the job..  But output flange/shafts is the only place the thing’s not leaking.  I’m about to go after the pinion seal again shortly, and if the o-rings I installed last year still look good I may just re-use them.