rear diff oil leak

[tc80211]

ok. '83 r65
saw a small bit of oil ocming from rear diff and noticed rear brake was fairly ineffective...
so took off the wheel and replaced the o-rings on the brake cam... oil gone, all good...
ride 100 miles and the oil is back. Any thoughts? possibly main seal? How much of a pain is that to replace?

[Bob_Roller]

It's not a big job, about 2 hours of work .

I've done three so far .

The oil seal and a paper gasket are all you need .

[Tony Smith]

It's not a big job, about 2 hours of work .

I've done three so far .

The oil seal and a paper gasket are all you need .

Thank you Bob, saved me looking it up, I will need to do mine soon I suspect as it has dripped oil in a puddle where it sat for 20 years. I might get lucky and it takes up when it starts being used, but somehow I doubt it.

[tc80211]

Anything I need to be cautioned with when changing oil seal and paper gasket?

[arvo92]

My experience - i changed the seal and 200kms it was fine. Then it started to dribble a bit again. I took the wheel off and saw a fine thread of rubber hanging from the seal where the seal touches the differential.

So what I plan to do next is to check so I am fully sure the contact area between the seal and metal is smooth as a pie without any cracks, dents, sharp points. The same issue probably ruined my last seal and now the new one.

The seal change itself is very easy. You try whatever method works to get the old seal off. Some drill holes into it and put self tapping screws in and then pull from different angles. I just put a screwdriver behind the seal and poked it out. Not the most professional way but it came out easily enough. I just could not get it other way.

I did mine in a rush. Do not do that. Make sure everything is clean and smooth, possibly grease free when fitting a new seal. New seal does not require special tool. Just push it in from different sides. i used a block of softwood.

[montmil]

Anything I need to be cautioned with when changing oil seal and paper gasket?

Yes.

After the brake shoes, brake camshaft and Cardan cover nuts and wavy washers are removed, you note two (2) empty threaded holes. These accept a 5mm thread bolt which when tightened evenly, will lift the Cardan cover.

It will likely be necessary to heat the Cardan cover and tap the drive splines to remover the cover from the crown gear assembly. Use a plastic mallet, not a framing hammer! Note the location of a thick spacer and a large diameter shim. Don't lose 'em. Reinstall as you found them. I use a Harbor Freight cheap-o heat gun and it works great. Spit sizzle is the temp you're looking for.

After the large seal is removed, get busy cleaning off all the old gasket material from the Cardan cover and the final drive case. Every tiny bit must be removed or you risk creating a leak. No sharp scrapers! Both surfaces must be absolutely clean as the paper gasket is a part of the shim setting for the final drive crown and pinion gears.

Check the area where the seal rides just aft of the splines. Look for any nicks or damage.

Note the depth of the original oil seal. Most are installed at a "bottomed out" position as determined by the Cardan design. Some owners that have discovered excessive wear or slight damage in the seal contact area have had positive result in setting the seal less than full depth. I cannot encourage this idea but some folks do this.

Reheat the Cardan cover as an aid to placing it back on the crown gear. Remember the order of components. You must be very cautious of damaging the fragile lip of the oil seal. Those splines might just be hungry.

Trim a 12oz beverage can, smooth the cut edges. Repeat... SMOOTH the cut edges. Place the fancy install tool over the splines, lube it with some gear oil, ease the heated Cardan cover into position and remove the semi-official BMW install tool. You remembered the paper gasket, right?

No goop on the gasket! Install as is. A little dab of grease will aid holding it in position. New wavy washers and torque to spec.

Have I forgotten anything...?

[tc80211]

awesome! Thanks!

[Luca]

To add to Monte's excellent post;

The paper gasket only fits on the cover one way.  Best to get it lined up before heating up the cover so that you're not flipping the gasket around while your cover loses heat.  I didn't do that and found that the final drive didn't want to turn once I had the cover snugged down.

Not to worry:  a little extra heat and plastic hammer taps around the center will get everything back where it belongs.


The reason I went under the final drive cover is BMW's lousy brake cam o-ring design.  They failed once and ruined the extra-expensive LS shoes... then the new set failed within a year and oiled the brakes again.  I ended up driving out the brass brake cam bushings making a stainless one piece bushing (the BMW one I ordered was about .007" too skinny to press fit).  The bushing is sealed to the FD and cover with Loctite.  If you've got the time and make--or find somebody to make--a bushing, it's a very worthwhile upgrade IMO.

[montmil]

... The paper gasket only fits on the cover one way.  Best to get it lined up before heating up the cover so that you're not flipping the gasket around while your cover loses heat.  I didn't do that and found that the final drive didn't want to turn once I had the cover snugged down.

Best to give a little twist of the splines prior to snugging down the Cardan cover. Confirm that the pinion and crown gear are properly engaged. Had that little discovery while chasing oil weeps on the R100S.