Differential vent mystery

The weather's been so good in the last few days that
I'm breaking into the box of PartsShop stuff in the garage,
and dewinterizing the 380SL for a bit of coast driving.
A small benefit of global warming?

One item that I never solved last year was the service
of the differential vent. No problems with access to or
opening the fill and drain ports, but I've never cleaned the
top vent and I understand that's an important parallel job.

I've read the old threads on the subject, and by getting
up close I can -see- what I think is the vent. Short 2 or 3 cm
cylinder on the right upper side of the diff, pointing straight up,
with a metal cap on top of it.

Okay so far. But the cap looks odd. Crimped, actually. It
is close fitting on part of the circumference of its lip, and
flared out on the rest of the lip. It is definitely noncircular,
though I can't tell if it was originally circular and then bent
by the crimping.

It's kinda triangular in shape by feel. And it's visibly a bit
loose to the touch, either by hand or with a tool (no idea
how I'm going to get a box wrench onto this thing). It does
not release by light upward pressure. Haven't been able to
figure out how to turn it counterclockwise with a tool; it will
not turn CCW with finger torque.

Really weird. This doesn't sound like what the vent ought
to look like. Am wondering if this crimp job is someone's
old hack from poor maintenance -- if they lost the real
original vent cap and bodged this new thing on as a quick fix.

If anyone can put me right on this question, I'd be both
amazed and grateful. (Note: My mail's messed up. Replies
that aren't posted here probably won't get to me. Regrets.)

Ron H

[gdaley]

It sure sounds exactly like the crimped cap that the Saab 900 Borg-Warner auto trans uses on the differential cover plate. They can be readily lifted with a small pliers and snapped back on, recrimping with a few gentle ball peen taps if needed.

[jcyuhn]

That's definately the vent, and it looks exactly as you have described on all the Benzs I have owned.

Access is always a problem. It was easy on my 123 chassis, extremely difficult on my 210 chassis, and is impossible on my 124 chassis wagon.

The only option may be to drop the differential to get access. As this seems a bit much work simply to clean the thing, don't think I'd do it unless there was a specific problem to address.

Originally posted by jcyuhn
That's definately the vent, and it looks exactly as you have described on all the Benzs I have owned.

Access is always a problem. It was easy on my 123 chassis, extremely difficult on my 210 chassis, and is impossible on my 124 chassis wagon.

The only option may be to drop the differential to get access. As this seems a bit much work simply to clean the thing, don't think I'd do it unless there was a specific problem to address.

Am I ever glad to have had the feedback above from you two!

Dove in today and gently prised the closest crimped edge up
(actually the only edge I could get to -- you're right, there is
a severe access deficit). The vent cap popped up and off.

Out in the sunlight, it looks like a circular cap that's been
crimped down to a triangular shape. Just stamped metal.

The screen part of the vent is, I assume, still in place. I can
see a bright lip of metal at the top of the vent cylinder, and
by reaching (all the way around from the front of the diff, ugh)
I can palpate what feels like screen material on top.

Other posts about the vent have said things like "soak it in
diesel to clean it up," and such. Does this screen come out?
Or the entire vent cylinder?

I've reached around and up with a clean shop rag and wiped
the top of it. No nasty matter present, just light gear oil in
what looks like good condition.

Ron H

[jcyuhn]

Sounds like you don't need to worry. Then entire vent is just screwed into the differential housing. There are flats for a wrench at the base of the vent - though access may be so tight they are rendered useless. But in theory, the entire thing unscrews.

Originally posted by jcyuhn
Sounds like you don't need to worry. Then entire vent is just screwed into the differential housing. There are flats for a wrench at the base of the vent - though access may be so tight they are rendered useless. But in theory, the entire thing unscrews.

Actually, I just had the beast out! My first attempt was with
a 19mm box. Didn't fit. A 17 box seemed to fit but was too long
to allow any torque to be applied.

Used a small pipe wrench instead. It unscrewed right smartly.

The vent looks dirty on the outside but clean on the inside.
Turns out that it -is- a 17 after all.

There's a little felt disc inside the vent top. PartsShop guys,
is this a regular field service item? Is there a part number?

The one thing I would have done differently here was to
have used something tougher (nozzle of a pressure washer?)
to clean the top deck of the diff before removing the vent.

I'm concerned about gritty particulates falling in, and I did
clean first, but apparently not enough. A shop rag wipe on
the diff top with the vent removed showed lots of crud there.
Dr. Murphy says that some of it probably went down the
threaded tap for the vent.

What I think I'll do now is clean and replace the vent
(and felt disc?), then run two quick successive changes with
el cheapo generic gear oil to flush out any crud that fell in
during the vent service. Should suffice, yes?

Then I'll do one more change with Mobil 1 gear oil, and
put this to bed for now.

Ron H