How to pull the diff fill plug 560SEL
 

Tried to pull the fill plug on the differential today to change the gear oil. What I found was the self leveling valve (or related equipment) was in the way. My 14mm allen socket is about 2 inches long, and while I can get the allen in the plug I cannot get a ratchet or breaker on the socket.

I tried putting a 14mm box on the allen before placing the allen in the plug, but couldn't get enough leverage to move the plug. How do those of you with self leveling get your fill plug out?

I've done it the same way, but I used an extra wrench for more leverage. You can also try with a crescent wrench on the allen. That plug shouldn't be too tight.
If everything else fails you can always drop the differential. It's only three bolts. Techs probably use a regular 14mm allen key (not common in a DIY tool box).

Vin

would a wobble extension help? i picked up a set of these for cheap at harbor freight, all different lengths. i had a similar problem spot and the wobble extension went in at an angle.
how about a makeshift cheater bar on the box wrench, i keep odd lengths of metal tubes for this purpose...

I don't have a wobbler (maybe I should get one) but I do have a universal extension, unfortunately it adds too much length. I'll give the box wrench to the allen another try, using a second box wrench to the open end, or a cheater pipe to gain leverage.

I'm also wondering (now that it is morning and I have a clearer head :) ), could the fact that I have the car "floating" change the relationship of the diff to the leveling valve/lever/etc? What I mean is the car is on stands and the rear suspension is at full extension. Would having the weight of the car on the suspension (on the ground) allow more room to access the fill plug? If so, I may just wait until she's off the stands.

Tried again today using the 14mm box to the allen, then a 17mm box to the 14mm open end. Gave me a good deal of length, but still could not budge it. Next time I try I'll try a length of pipe, see if a little more length gets it out. Last resort, I guess, will be heat.

When removing my diff plug, probably the first time since 1988, I got it off only after using a 3 foot pipe around the ratchet. I wasn't able to budge it (even with the pipe) until I got up from on my back under the car, and on my knees, behind the car, and then pulled on the pipe.

I feel a little uncomfortable about putting a torch on the differential fill plug, but I can't explain why. :)

Maybe you can have some success with cleaning around the fill plug and then using penetrating oil. To get mine out the first time (on a '82 300D with plenty of room to work) I had to use a pretty good sized 1/2-in drive ratchet and my feet while holding on to the rear bumper.

I think you just need a little more leverage on the wrench.

(They really don't need to be all THAT tight..... :) )

Ken300D

I have had to use pipe extensions on the allen wrench to remove these fittings from the differential on just about every Mercedes I have owned. At least the first time. I doubt you would need to use any heat, just get enough pipe to yield the torque required to break it loose. May need better leverage than lying on your back as Rich 126 said. Good luck!

Just curious, but has anyone had any type of rear differential failure related to the lack of changing the diff oil? Or are we all just wasting our time buying 14mm special hex heads (that only Auto Zone sells), and using pipe extensions?

Rich126,

Autozone is one of many sources. I bought my 14mm hex key from a local industrial hardware supply shop ($4 or so).

Changing the diff fluid is just good ol' preventative maintenance.

I can tell you from experience with my former daily driver (a Trans Am GTA with a limited slip diff) that the fluid does wear out. That car had a bad clunk in the rear when going around a tight left corner. A little research (a lot of worry) later, and I found out that this was a common indicator that the diff fluid is tired. So, while it may be a different make, the fluid experiences the same environment and does not maintain it's characteristics indefinitely.

It's a 20 minute job every few years (assuming you can get the plug out.) Well worth doing.

i want to sugest a universal joint but if you have no clearence then that wont work either as you have to put the allen key bit on the univ joint.. i suggest the allen key a 12 in cresent wrench, and a piece of pipe, lots of liquid wrench(that stuff is worth its weight in gold) dont forget to eat your wheaties!.

another solution
 

I had the same problem changing the gear oil on my 1985 bmw 535i. I finally got it out with a hex key from sears that a friend cut about 2" off with an electric grinder. We then used a 2 foot pipe on the end of it to get enough torque and also used a wood plank pressed against the tool to keep it from popping out of the plug. We still ruined the plug and had to replace it. The replacement plug from bmw was different (i guess lots of people had the same problem).

Update: still no joy
 

Well, I decided to gain some room to get at the plug and unbolted the leveling valve. Didn't crack open the lines, just unbolted the bracket from the chassis and let it hang. This gave me enough room to get the allen socket and a breaker on the plug. Then using a 4 foot piece of black pipe for a cheater, went to town.

Couldn't budge it. I am going to hold off until I can move the car. I think I just don't have enough clearance to get it to pop. Once I can move the car, I'll run the back end up on the ramps and gain a few inches clearance.

Mike:

Sears sells 1/4" - 3/8" - 1/2" pipe-type inserts that come in a small red plastic pouch. Usually locked up in the cases with their other hand tools. There's very little protrusion from these. You slip the appropriate extension into your 14mm, then use a long open-end wrench on the extension.
These gadgets are designed for working in tight places. Don't remember the Sears part number.

When I do my 126 differential fluid, I first back the car up on ramps in order to secure enough clearance to slide a piece of pipe over the end of the open-end wrench.

I used a hammer and a 14mm allan wrench. You could also use a old spark plug wrench/socket over the 14mm allan key as a cheater also.

The main problem I had before was getting diff. oil into the differential fill plug . I think I spilled more initially than I filled. You can use a old lotion pump bottle and vinyl tubing for that or buy a differential pump from any auto store.