300CD Change Tranny Fluid
 

The 85 300 CD that I am the caretaker for needs the tranny fluid changed. Last time I did this job I noticed that the torque converter drain screw went in with some dreaded aluminum thread about to strip feel, so I really don't want to remove it again. Any tried and true suggestions about a way to change the tranny fluid without touching that screw?

Yes, don’t drain the torque converter but it will only be draining some of the fluid.
The torque converter is all steel so idk about the threads stripping.

X2, drain the pan, remove it, clean it, replace the gasket, replace the filter and refill. I've had good results with Valvoline MaxLife ATF. If desired you could do a drain and refill of the pan without removing it at the next oil change.

Don't mess with the converter drain plug, it could be a can of worms.

I've also had good results with Lubegard additive.

My 2c, I’d look into the issue.

It’s probably thin metal, but I don’t think it’s aluminum. The torque value isn’t much. There should be a crush washer. And remember that the threads are likely oiled so reduce torque by up to 20%. If there is an issue, better to know about it and fix it than to have it leak on the road.

If that doesn’t work, just use the pan drain, so a drain and refill, drive it 25-50 miles, then do the fluid and filter service. The MB setup is about the cleanest ATF job I’ve ever encountered.

I've been using this for a while now in the 1998 E300 with good results.

If the tc drain plug has thread lock on it that could possibly make it "feel" like it is about to strip? Just wondering.

On my 85' 300TD there is a thing about 'underfilling' the trans when cold.
IIRC the dipstick should read 1cm below the full mark when cold,

then when it is fully heated up (after lots of driving)

the dipstick will read perfectly full.


In other words, if you fill it up to the full-mark on the dipstick (cold of course),
it will be over-filled
and can cause problems.


There are discussions about this, basically the ATF level does go up when warm.
Good to know so you don't waste ATF.

+1 on MaxLife
I wouldn't mess with the torque converter, ESPECIALLY if the car isn't yours.
That car is really old and no telling what kind of gunk could break loose in there,
at least thats what ive read.

You can use the Yumling method to flush the TC. It is documented on the w210s. I believe the write ups may be on Benzworld. Most newer trans do not have a plug on the TC, so to fully drain it, they use a method of taking off the trans cooler hose and using the pump of the trans to push new fluid in to the TC and thus pump the old out via the unnattached hose.

However, I would as suggest above, investigate and fix it. Last thing you want is it stripping on its own while you are miles away from home and to be left stranded.

Here is a link to the method I was refering to..
https://www.benzworld.org/threads/flushed-my-tranny.1371714/

Torque Converter Drain Plug
 

No way would I ever fail to drain this, as it holds much more fluid and crap that does the pan and filter .

You'll need a 5MM ATF Allen wrench, I prefer to use a 3/8Z" drive one, don't loose/forget the small sealing washer .

ATF expands about 10% when fully warmed up so fill to the lower dipstick mark then test drive it hard to fully warm up and add a little bit at a time until it's at the full mark .

Clean around the tranny BEFORE
you open it up ! .