Stripped diff plug - PeachParts Mercedes-Benz Forum

Rooster300SD · #1 04-19-2011, 11:42 AM

Have an intermittent whining coming from the rear end
and from reading here think I need to change the differential oil.

It's a high pitched whining and it went away when I backed up. ??

Whether that's the problem or not, I've never changed the oil in it.
Got under and immediately saw that the upper allen bolt was rounded out.

What's the best way to get that huge bolt out?
Also, I didn't see just the plug for sale in Fastlane.

Thanks,
Jeff

vstech · #2 04-19-2011, 11:55 AM

oxy acetylene torch...

DO NOT CUT INTO THE DIFF!!! just heat the plug, and jam a larger wrench into the plug.
if you have a mig, you can kill two birds with one stone, and weld a large allen wrench into the hole, and use a standard socket to remove it.

leathermang · #3 04-19-2011, 11:56 AM

First , whether I can help on the stripped out part or not.... let me congratulate you on CHECKING THE FILL PLUG CONDITION BEFORE DRAINING THE OIL ....
In the past we have had some people who did not deal with the messed up FILL plug first...
and sure looked short sighted coming on and asking for quick help because they needed their car and could not put any oil back IN... LOL

Ok, I see Vstech has suggested oxy acet torch... which many people do not have... or would think twice about getting close to the third member ( with good reason )....

so.... a lower and safer tech ( pun ) way.... a rotary tool like a Dremel may can clean out and squared up the hole... and then install a bolt head in that hole with jbWeld or other epoxy.... let cure 24 hours... then put a nut onto the threads sticking out and use a ratchet or breaker bar to remove... use grade 8 bolt and nut .. that will have 6 lines radiating out from the center...

http://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

The differential ( no pun ) expansion rates of the steel plug and the differential can cause problems if not careful on the heat and cooling deal... thus I believe that the bolt method is safer for most people...

rs899 · #4 04-19-2011, 12:04 PM

Since the plug is on the back plate you can always get one (plate ) off a parts car.

leathermang · #5 04-19-2011, 12:04 PM

LOL,
I believe if you feel that you need to say " do not cut into the differential " that the entire suggestion as related to the intended listener is suspect...

charmalu · #6 04-19-2011, 12:07 PM

Rounded out = not good. That is a 14mm hex pit that fits it.

the easiest way (for me) would to run over to PNP and remove a rear cover from a 300D or 300SD and maybe some of the gasser W126 will work also. then if you don`t have one, you could upgrade to a finned cover.

4 13mm bolts hold the Diff mount to the body, & 2 22mm bolts hold the Diff mount to the cover. then 8 15mm? bolts hold the cover on.

Be sure to loosen the fill plug first

.

To drain your Diff, place a jack under it, remove the Diff mount, LOOSEN don`t remove the Diff cover bolts, and pop the cover and let it drain into a pan.

probably swap the covers in about 30min.

I replace the Diff in our 240 because it was rumbling, didn`t get a whine from it. drained the oil, and it had all this pretty sparkley metal flakes in it.

turned out to be the spider gears were loose and wobely in their shafts.

A few days ago I was at PNP, and came across this 80 300D Euro. looked under the rear to check the axles, and noted a bolt welded to the fill plug.

Charlie

leathermang · #7 04-19-2011, 12:22 PM

Quote:

Originally Posted by charmalu

.....A few days ago I was at PNP, and came across this 80 300D Euro. looked under the rear to check the axles, and noted a bolt welded to the fill plug.....Charlie

That would be a great PREventative maintenance suggestion.... like take the fill plug out, clean, weld in the bolt...
THEN replace....
Very tricky to do IN the car.... perhaps verging on NOT SAFE ... for you or the expansion rate of the plug... or the possibility of missing the plug and messing up the threads.... and having welded on things under cars laying on concrete ... watch out for sparks which fall and roll TOWARDS your chest... ouch....

winmutt · #8 04-19-2011, 02:07 PM

I vote for a new diff.

Rooster300SD · #9 04-19-2011, 02:21 PM

Checking in here on my lunch hour. Thanks all for the suggestions.

I think I'm going to clean out the bolt really well, shoot some Kroil
around it and try some kind of trick with the JB Weld.

Questions:
Is it OK to drive the car with the whine or should I let it sit?
Does the whine mean the diff is going bad anyway and, if so, and
I swap a new/used diff in should I get the same one or can I change it
to a differnet ratio?

Thanks,
Jeff

leathermang · #10 04-19-2011, 02:26 PM

If you have a way to let it sit..
that is much safer .. the more you drive it the potential for damage beyond repair increases..

Be sure you know the downsides to the other ratio you are thinking about going to....

charmalu · #11 04-19-2011, 02:30 PM

I would just drive it with the whine, nothing to hurt any worse than it is. maybe no long trips just to be safe.

If you decide to change out the differential, and go to a different ratio, then be sure to remove the speedometer from the donor car also. the spedo is geared to the differential. yours ratio is probably 3:07. If you can locate an 85, it has the 2:88. the 300D will also fit, but the spedo will not fit your dash.

I have seen more 85 300D`s than 85 300SD in the yards.

You have that PNP over on Sunrise there in Sacto. you can go on their website and see what cars/years etc... they have. won`t tell you what parts are on the car though, or condition.

Charlie

leathermang · #12 04-19-2011, 02:38 PM

Quote:

Originally Posted by charmalu

I would just drive it with the whine, nothing to hurt any worse than it is. maybe no long trips just to be safe....Charlie

Charlie .... DO YOU HAVE ESP OR WHAT ?
How can you be SURE on HIS car that he is not near a point where EXCESSIVE damage will occur if he continues to drive it ????
Saying that you would drive your car is fine.. you would pay for whatever bad might happen if your bet is wrong...
But why encourage him to take that side of the bet IF HE DOES NOT HAVE TO ?

vstech · #13 04-19-2011, 05:27 PM

yeah, speaking as one who has had a pinion bearing fail on the highway... fixing before it fails is much better option...

Rooster300SD · #14 04-19-2011, 08:28 PM

Been looking around for synthetic diff oil.
MB says to use 85-90 or 90 oil.
I can't find that in a synthetic oil here in town.

What oil does anyone use for the differential?

Thanks,
Jeff

vstech · #15 04-19-2011, 08:38 PM

75w90 Mobil1 is what I use.