Rear diff leak

[Uberwagon]

Hi all,

I had my rear diff rebuilt after a full underbody restoration was done.

Now when I go at speed I get a leak from the pinion seal. The spider was perfect, all seal faces are perfect, I replaced the seal with a new genuine one from Merc and still the problem is there.

I’ve tried to find the diff breather number but it shows me an abs bleed nipple instead.

a126 350 00 90

Is this the correct number ? It should be a 17mm hex part.

Dave!

 

[JC220]

Hi all,

I had my rear diff rebuilt after a full underbody restoration was done.

Now when I go at speed I get a leak from the pinion seal. The spider was perfect, all seal faces are perfect, I replaced the seal with a new genuine one from Merc and still the problem is there.

I’ve tried to find the diff breather number but it shows me an abs bleed nipple instead.

a126 350 00 90

Is this the correct number ? It should be a 17mm hex part.

Dave!

If you want to check the breather you can remove it and pry off the cap. Then there is a fairly dense piece of padding in there which can be removed and inspected to see if its clogged with grime or rust etc.

Ideally fit a new one of course but in any case do open up the old one to see if there are indeed any signs it was clogged.

What about the oil grade in the diff is it factory spec?

 

[gsxr]

Ditto all JC220's questions sbobr.

It's unlikely to be the breather, but as a test you can blow through a tube into the gear fill port (sealing the space with your hand). You should be able to blow through pretty freely. I've never seen a 210mm breather plugged enough to cause leaks. Also, IIRC, the breather is NLA new.

Are you working on a 500E diff here? Is the new genuine seal seated evenly? Was the OUTER edge of the seal seating area cleaned properly? A rear-end shop had professionally rebuilt the diff on a car I bought a few years ago, and it leaked from the pinion seal. Turns out they didn't clean the outer seal area (see photo below) which caused the leak. I had to remove the seal, clean up that area, and replace... afterwards it has been completely dry. Sloppy work from a "pro" shop.

 

[JC220]

Ditto all JC220's questions sbobr.

It's unlikely to be the breather, but as a test you can blow through a tube into the gear fill port (sealing the space with your hand). You should be able to blow through pretty freely. I've never seen a 210mm breather plugged enough to cause leaks. Also, IIRC, the breather is NLA new.

Are you working on a 500E diff here? Is the new genuine seal seated evenly? Was the OUTER edge of the seal seating area cleaned properly? A rear-end shop had professionally rebuilt the diff on a car I bought a few years ago, and it leaked from the pinion seal. Turns out they didn't clean the outer seal area (see photo below) which caused the leak. I had to remove the seal, clean up that area, and replace... afterwards it has been completely dry. Sloppy work from a "pro" shop.

Good point Dave I havent came across that before but since I do my own stunts I do clean it up.

I also (rightly or wrongly) apply a light smear of Loctite Gasket Dressing to the outer edge of any radial seal I install.

This does 2 things in my mind:

Lubricates the seal on installation preventing tearing of the rubber edges.

Gives a little extra protection against possible leaks.

Never had a leak yet doing this - fingers crossed. Also never found a vent to be blocked as you say Dave.

 

[gsxr]

I also (rightly or wrongly) apply a light smear of Loctite Gasket Dressing to the outer edge of any radial seal I install.

This does 2 things in my mind:
Lubricates the seal on installation preventing tearing of the rubber edges.
Gives a little extra protection against possible leaks.

Joe, I did the same thing when I installed the new seal, for the same reasons. I used a thin coat of Right Stuff or Loctite 5900 (forget which).

Forgot to note that in my case, I pinpointed the leak to the outer edge of the seal, to the housing... it wasn't the inside edge at the pinion shaft.

 

[Uberwagon]

Just to update on this…..

All the diff seals have now been replaced, I think the parts quality was suspect and the shop who did the rebuild are not forthcoming with the seals used.

Also, the diff breather was very hard to blow through, virtually no air coming out where a new genuine one is easy to blow through. So the poor seals and slightly higher pressure in the diff ganged up a bit I think.

I should have it back in a week or so and can do some more testing to confirm if the problem has gone.

Dave!