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2004 325i automagic
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Discussion Starter · #1 ·
About how thick/wide of a bead should I put down when resealing the rear diff cover?

I am using Loctite SI 5970 but the instructions don't specify bead size and neither does newtis. Meanwhile, the Bentley doesn't even address the rear diff cover removal/installation at all (chapter 331). I imagine the answer would be the same with any RTV gasket maker.

This is on a 2004 325i fwiw.
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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Its one of those things where the more you put on, the more will squeeze out of the joint and you'll have to wipe it off.

I use a 3 to 5 mm bead.
 

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2004 325i automagic
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Discussion Starter · #3 ·
Thanks for the feedback.

I know it needs not too much and not too little ... lol. Haven't had to make rtv gaskets very often so not quite sure where that line is...

Squeeze out is not a problem, stuff that squeezes in (the diff case) is more worrisome.
 

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Just seal it up, give it 12 to 24 hours for the RTV to go off then fill it with oil. The inside bead does not fall off or cause problems.
 

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2004 325i automagic
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Discussion Starter · #5 ·
Quick question, how clean is clean enough for the aluminum cover plate mating surface?

Its mostly clean (and very very smooth) but in a few areas there are some crusties remaining that I can barely feel with my finger. Definitely some paper gasket remnant or perhaps corrosion in some spots:

Auto part Engine Metal

Do I need to clean this off? The surface is otherwise so very smoothly machined that I hesitate to put sandpaper on it (even very fine grit like 1000). Should I get one of those 3m roloc bristle discs (white, 120 grit) for this?

Any good safe ways to clean this?


The rear diff housing mating surface feels absolutely smooth to the touch, despite the discoloration, so I am thinking the diff housing mating surface is good to go for the sealant. Here is a closeup of the left side surface.

Auto part Gear Differential Transmission part Hardware accessory


Fwiw, the diff cover came apart easily. Not sure it was actually leaking although on the car it was covered in grime almost completely around the perimeter before I cleaned it off. The left output shaft seal definitely was leaking, and possibly the right side as well.

In the picture below, the beige/lighter colored areas on the paper gasket correspond to the shiniest part of the diff housing around the bolt holes, where likely the best seal was made. Further away from the bolt holes, both the paper gasket and diff housing mating surface have a darker color but not sure if that means anything in terms of leaking.
Auto part Vehicle

Paper gasket lifted off the aluminum cover intact in one piece (with a plastic scraper blade):
Auto part Engine

Degreased both mating surfaces well using mineral spirits for now, will finish with acetone or brake part cleaner before applying sealant.
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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I use one of those plastic woven dish pads to clean up aluminium surfaces. It does not abrade the aluminium surface yet removes the old gasket and corrosion. We live in different parts of the world, so no use me giving you a brand name.

Remove the old paper gasket, corrosion etc. Degrease with your favorite degreaser and apply the RTV.
 

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2004 325i automagic
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Discussion Starter · #8 · (Edited)
We live in different parts of the world, so no use me giving you a brand name.
No worries, I found something non maring but it seems to be smoothing only, not removing the blemishes which I think are corrosion more than gasket remnants.


Scotch Brite and lacquer thinner, mineral spirits leaves a film prevents a good bond for RTV,
Any thoughts on what color Scotch Brite? I tested the maroon so called 'very fine' metal finishing pad in a top corner but it definitely affected the aluminum finish so I stopped using it. Perhaps a less agressive light grey pad?

I was able to smooth the mating surface with fine bronze wool and a blue no scratch scotch brite dish sponge without marring the finish. I can still feel a little bit but it is improved, so I might just keep working with these two for now.

About residue, I am going to clean degrease the cover when I'm done, and then clean the mating surfaces with acetone and brake part cleaner before sealing.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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We normally clean both contact areas. Apply a very thin film of sealant onto the cover, no spooging. Attach the gasket perfectly lined up and place contact surface down and place some weight on it. Doing so first is a good time saver.
After it sets up, we then apply the same thin film onto the differential. Bolt it up.

The gasket does 95% of the sealing. The VERY thin film of sealant provides adhesion and filling in of the irregular surface.
There's almost zero spooging of sealant on the outside, and more importantly on the inside.
 

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2004 325i automagic
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Discussion Starter · #10 ·
Good point ... I should clean the diff housing mating surface as well even though it feels smooth.

One clarification though ... no paper gasket is available anymore for the rear diff cover, as far as I can tell. Only using the loctite si 5970 gasket maker here.
 

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2004 325i automagic
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Discussion Starter · #11 ·
Ok, I have the diff cover feeling smooth using bronze wool & no scuff scotch brite pad,but there are still some visual blemishes. I don't think it can get any cleaner unless I step up to something more abrasive.

Is this good enough? I think I'll just put it back together and see how it holds up.

Auto part Engine

Fwiw, in the top right corner (non sealing surface) where the hole on the diff housing is) I experimented with a small brass wire wheel (non magnetic) on a dremel on a low setting, but it seemed to polish the surface without really cleaning it. It might have even left some brass behind on the aluminum. A nylon bristle brush on the dremel did nothing.

It really seems that to remove these blemishes I would need something actually abrasive like a 3m bristle brush disc (a white 120grit one) ...
 

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E30M3 Race F10 535 R1150Rt M Coupe
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You get the award for OCD. You're good to go.
The only way to get the blemishes out, is to have them milled or blanch ground.

One needs to be careful when chasing such. You can easily over work a section and have an uneven surface. It's aluminum so no worry's.
 

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RTV will cure a myriad of diseases- even OCD! The diff's not under pressure, so it'll seal just fine.

I don't ever use a gasket. And yes, 'almost no' sealer is necessary, as the fit between the case and the cover is so good.
The only important thing is to make sure there's 'just a little' in a perimeter INSIDE the bolts.

Otherwise fluid may leak through the bolts.

Don't stress it- if extra sealer gets into the diff, it's not going to hurt anything,
as there's no place it COULD do harm.

Unlike the engine...

t
 

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2004 325i automagic
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Discussion Starter · #14 ·
OCD award, lol ... yup, little bit ... the surface feels like its good to go but I dont have much experience in this area so a little confirmation is always helpful ... thanks!
 
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