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Forcedes 08-26-2007 01:41 PM

Rear main seal questions
I am in the process of replacing my rear main seal on my 80 300 SD. I have dropped the upper oil pan and checked the lower half of the seal and it doesn't look too bad. I was reading old threads on thei topic and I came across some discussion on the two ball berarings that are stuffed in the back of the engine block plugging oil galleries. How do you remove those if they are leaking? Is there any way to replace them? I really don't want to put everything back together only to have to take it all apart again when it still leaks. Any info you might have is greatly appreaciated.


ForcedInduction 08-26-2007 01:49 PM

3 Attachment(s)
The two balls have to be knocked out with a long rod through ports on the front of the engine.

Oil seals can look great and still leak.

Forcedes 08-26-2007 01:58 PM

What are the odds that the gallery plugs "balls" are leaking. I had a real good look back there I was expecting a lot more oil considering how much it was leaking, I was looking for wash spots where fresh oil washes away old oil mixed with dust. I couldn't find any of that, and evereything looked dry, even directly underneath the gallerey plugs. I am assuming that the ports for knocking out the plugs are under the timing chain cover.

ForcedInduction 08-26-2007 02:04 PM

There is no timing chain cover. One port is by the tachometer pickup sensor and the other is blocked behind the vibration damper.

Forcedes 08-26-2007 02:13 PM

HA shows how much I know. I wonder if it's worth it to knock them out and replace them with a pipe plug.The real killer here is the engine only has 185000 KM (115000 miles) on it I figure the problem is more from under use and seals etc drying out.

ForcedInduction 08-26-2007 02:20 PM

Since you already have the upper pan removed, I'd just replace the rear seal, put it all back together and spray a can or two of brake cleaner around the flywheel area to clean it out. Run it long enough to get the engine warm and then peek though torque converter viewing hole and look for any fresh oil streams.

Odds are it's the rear seal leaking but Mercedes would not have a plug kit available if the balls didn't have a chance of leaking.

Forcedes 08-26-2007 02:28 PM

Yeah I guess since it's this far apart a guy should just do it all. Thanks for the help.Once I get this done my next project is to rebuild my turbo. I have a seal kit on order now. Hopefully this will be the last of my problems for a while.Thanks again.

t walgamuth 08-26-2007 09:11 PM

are you sure the rear mains are leaking?

I have had some pretty tired benz motors and never had a rear seal leak yet.

Tom W

Forcedes 08-26-2007 11:02 PM

Well it is definetly somthing from between the engine and trans. I wahsed the engine down really well and ran it for a while checked for leaks in the simpler spots such as the oil filter adaptor.I have just replaced the valve cover gasket and no it's not pinched. I checke under the car while the engine was running and I could see oil moving form the seam between engine and trans and running forward along the oil pan. I am quite confident that something between the engine and trans is leaking. My next step is to replace the lower half of the rear main seal, Bolt up the oil pans, install the adaptor plate and flywheel, then crank the engine to create oil pressure and check for leaks. If I get brave I may even start her up with the trans removed. Hopefully it was just the lower half of the rear main otherwise I am looking a a lot more work.

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