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Rebuilt diff, now major leaking


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Just buttoned up a full rear-end rebuild, including the diff. Quick drive around town at 30-40 mph everything fine and dry. 

 

Took her on a 60-mile highway speed drive and when I got back, found that most of the entire back end is covered in what smells like gear oil. Doesn’t seem like the back cover, but quite hard to tell for sure. I plan to remove the diff, check how much oil is left, re-fill and take it for a shorter high-speed drive to see if I can narrow down the source of the leak.

 

This is my first rodeo with a diff rebuild so not sure what to check besides the obvious front and rear seals. Anything else to check for clues? All the seals and gaskets were renewed. 

 

I’m also wondering/suspicious of the breather vent on the back cover. How is this supposed to work, ideally?

 

I guess the renewed cv joints also a possible leak source but it doesn’t look like the black grease from the rebuild kit. 

 

Have mercy on this noob wrench monkey. :)

Edited by MikeBernardo
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Before you remove the diff, spray and wipe everything down with brake cleaner to remove most of the grease/oil. Once it's all clean, then go for a short drive and inspect it again.  That should show you where it's leaking.  If it's the back cover, no biggy.  A new gasket and proper torque should eliminate that.  If it's the front seal that's a bigger problem as it takes experience and special tools, IMHO.  If the output seals are leaking that too can be remedied with proper seals and torque.  

 

Again, before you remove the diff, drain the oil into a container and measure the amount. The leak may not be as bad as you think. 

 

Worst scenario...take it to a driveline specialist to re-assemble. 

 

Good luck.

 

 

 

 

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73 Inka Tii #2762958

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Was it filled to the correct level? If it is over filled it will throw oil out the breather at higher speeds when it warms up.  With the car sitting level remove the fill plug on the side of the diff, if oil comes out it’s over full.  If it is just let it drain until it stops, replace the plug, clean it up and go have another drive.  Also if the breather is plugged you will pressurize the diff and it WILL shove oil past the gaskets and seals (if you did some kind of media blast to clean the rear cover you may have plugged the vent hole) 

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1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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11 minutes ago, Preyupy said:

Was it filled to the correct level? If it is over filled it will throw oil out the breather at higher speeds when it warms up.  With the car sitting level remove the fill plug on the side of the diff, if oil comes out it’s over full.  If it is just let it drain until it stops, replace the plug, clean it up and go have another drive.  Also if the breather is plugged you will pressurize the diff and it WILL shove oil past the gaskets and seals (if you did some kind of media blast to clean the rear cover you may have plugged the vent hole) 

 

Yep I believe I did fill it to the right level. Pump in oil until it starts coming out the fill hole.

 

Blocked breather sounds possible. That's the one thing I might not have checked correctly. I didn't media blast the back cover, but the entire diff was *really* dirty before I rebuilt, so quite possible the breather is not as clear as it should be.

 

What's the right way to check for clogged breather? I'm guessing just try to blow through it with the back cover off? What kind of resistance should I expect?

 

Before and after:

 

IMG_1294.jpg

IMG_2335.jpg

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14 hours ago, MikeBernardo said:

This is my first rodeo with a diff rebuild 

Please define when saying "diff rebuild" 

5 hours ago, MikeBernardo said:

What's the right way to check for clogged breather?

If diff still installed under car you can simply attach piece of clear hose (20" long or so) that fits over breather tube and maybe a clamp and blow through tube. you should be able blow through for 10-20 seconds if breather tube is not plugged and no more. Upon removing tube from mouth should feel and hear air exhausted. 

76 2002 Sienabraun

2015 BMW F10

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5 minutes ago, Buckeye said:

Please define when saying "diff rebuild"

 

Right. I mean replacing all bearings and seals. I know a lot of people say to bring it to a professional for this if you don't know what you're doing, but there was a lot of good info on here which made it fairly straightforward. I don't *think* I messed it up. ?

 

6 minutes ago, Buckeye said:

If diff still installed under car you can simply attach piece of clear hose (20" long or so) that fits over breather tube and maybe a clamp and blow through tube. you should be able blow through for 10-20 seconds if breather tube is not plugged and no more. Upon removing tube from mouth should feel and hear air exhausted. 

 

Good tip. I will give that a try, thanks.

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4 minutes ago, MikeBernardo said:

replacing all bearings and seals.

 

What was your technique on the front seal?

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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Oh, sorry.  I was referring to putting the proper torque on the nut that uses a crush sleeve.  I have read about people marking the position of the nut prior to loosening and then carefully putting it back there using the old sleeve, as opposed to crushing a new one.  Apparently it can be a finicky process.

 

edit- I guess that probably has nothing to do with whether it leaks... more to do with diff longevity.

Edited by '76mintgrün'02

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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1 minute ago, '76mintgrün'02 said:

Oh, sorry.  I was referring to putting the proper torque on the nut that uses a crush sleeve.  I have read about people marking the position of the nut prior to loosening and then carefully putting it back there using the old sleeve, as opposed to crushing a new one.  Apparently it can be a finicky process.

 

Right. I didn't trust that method. I got a couple extra crush sleeves and got it to correct turning torque on a new sleeve. Of course I messed up the first crush sleeve and had to re-do. No joke, it's like a couple of degrees between not enough and WAY TOO MUCH.

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Yeah, that one sounds tricky.  That's why Toby says buy two sleeves!  ( you must have read his posts :) )

 

I recently noticed that my differential is a bit oily.  This thread will prod me into checking and topping off the oil.  I'm putting off the seal installation until I refurbish the sub-frame... but have been saying that for years now.

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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10 minutes ago, '76mintgrün'02 said:

That's why Toby says buy two sleeves!  ( you must have read his posts :) )

 

YUP!

 

10 minutes ago, '76mintgrün'02 said:

I recently noticed that my differential is a bit oily.  This thread will prod me into checking and topping off the oil.  I'm putting off the seal installation until I refurbish the sub-frame... but have been saying that for years now.

 

I just redid mine. All new rubber. When I bought it, everything was dry rotted and cracked (maybe even original). Driving it now is a night and day difference. SO much better.

 

Now just to fix this leak. (I know, famous last words... ?)

 

Some useful links I collected during the diff project:

Rebuild kits:

 

Edited by MikeBernardo
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1 hour ago, MikeBernardo said:

got it to correct turning torque on a new sleeve

Do you mean pinion turning torque?  If so, you realize that a tapered bearing that has been running has also "been run in" and therefore should not be retorqued to a new bearing preload value or the second time it "runs in", it craps out.  Rather, a used bearing should be preloaded to only the resistance it had when disassembled.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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