Flushing transmission, new fluid leads to slippage: myth or reality?
 

Like a moron I did some damage to my SDL tranny by running it with too much fluid. One day it would not do anything except in first and reverse. I have kicked myself for it many times. For a while I thought I had ruined it. But then after a year of sitting it I miraculously found it was working pretty well.

By then I had corrected the fluid level, I took it out on the freeway to see if it would slip - it never did. So I've been driving it more. A few days ago at a stoplight it would not move in drive. I put it down to low and took off - when I shifted up it behaved normally.

I checked the fluid while warm, it was a tad bit high, I siphoned off maybe 6 fluid ounces. It then read right at the add mark so I put some back in. I noticed it was not bright red. It was brownish red, which only makes sense.

I'm thinking new fluid and filter would be a good idea, but then I started reading that I might be disappointed. It will be a while before I buy a rebuilt tranny.

Any opinions?

I do a flush every 25K miles, around three years for me. If it starts to slip after a flush it needed a rebuild.

As Jorn says but the interval I run out to is 40k to 50k miles.

I would drop the pan/filter and then position the torque converter with the drain on the bottom and drain it too. It takes a while to drain the TC. You should find a magnet in the pan that will need to be cleaned off. Don't be alarmed by the debris on the magnet.

I would not as much "flush" it as drain everything and refill.

I'd drop the pan, change the filter and drain the converter. I wouldn't do a flush with a machine. Exchanging the fluid through the cooling lines and changing the filter is ok but not with a machine and flush/cleaning chemicals.

When the fluid looks really bad and the transmission is presenting problems I'd leave it alone. If the fluid looks decent service it and continue to service it on schedule.

i read your signature. it says the sdl has 300k miles. NEVER had a trans rebuilt? NEVER changed the atf before? supposed to be every 30k miles. you're on fumes now.

try this. drain the pan and keep the fluid. refill with with 1 new atf. then refill with the used atf. this way you gradually introduce fresh fluid. gonna take a couple of years if you do this once a month. more work but cheaper that a trans.

me, i'd pull the trans and get it done. 300k is a lot.

He messed-up BAD....

I'd of never done what he's done....

Oh hell yes, I effed up pretty bad. And you're a dumbass, I can fix the transmission, let's see you fix yourself.

It's not the original transmission. I bought it in 2017 with 303303 on the odo. I remember the figure because it was a palindrome. Who knows, maybe a sign. :wacko:

It had a tranny fluid leak, seals no doubt. I had to check it every two or three days. In late 2019 I blew the radiator, luckily the idiot light caught my eye, I hadn't seen the needle going up to the red line. Popped the hood, it was all steam, at least it wasn't black smoke.

I put in one of those aluminum radiators, it ran fine until early 2021 when it started billowing white smoke, and finally gave up the ghost. I found out later it was a blown head gasket, it's what we all suspected.

I had gotten some prior work done on it that I couldn't do from a Vietnamese mechanic who cut his teeth on Mercedes diesels in the old country where they were pretty common. He's something of an OM603-ophile, owns two 350SDs. He somehow ran across an 87 SDL with 130 K, a really strong motor and a so-so transmission. I never did get the whole story. The body had been near totaled, but still drivable - he said the engine felt really good, and the compression checked excellent. He pulled it and the drivetrain, called me up, put it all in.

The fact that I blew it with the transmission haunts me, I don't know how I could be so stupid. I could try to make the excuse of the cancer treatment I was going through at the time, chemotherapy the whole works, but that doesn't really cover it. I've done pretty well with some other vehicles on maintenance. Took my 87 BMW 325I to 425K doing all my own work, changed the fluid, timing belts, etc. on schedule.

I'm healthy now, I just need to make the car healthy. A rebuilt tranny is in my future. But if I could get some service out of this one for as long as possible, that would help.

With installation I paid around $2500 for a rebuild transmission from Sun Valley Transmissions. My transmission blew up halfway to SF from LA, still made it to SF and back to LA without second and reverse.

In my opinion you probably didn't do damage by the slight overfill. It is possible but unlikely.

That would be an attractive price. I've seen accounts that have it $2500 just for the rebuilt transmission plus installation another $1200 perhaps by my guy.

In the old days, I would've changed the tranny myself. Various floor jacks, time, and stubbornness available. But I've heard the SDL tranny install is pretty tough. I did my last tranny quite a while ago, '02, my 325i E30. I thought that for only a 2.5 L engine it might be halfway lightweight.

OMG that was a tough one man job on the garage floor. And I was stronger then.

It's a dilemma. Not knowing is always tough. The business about the fluid being full of micro friction devices sometimes known as metal shavings is sort of a trip.

Here's a possibility. Drain all the fluid, save it and the old filter and put in new stuff.

If I suddenly get a wild increase in slippage, I'll drain it and put back the old filter and fluid. If indeed the micro friction from wear is real, don't need a nice clean filter extracting all of that from the broken-in fluid.

On a related note since the tranny started acting up two years ago I've seen two really clean SDL's at Pick n Pull, both with transmissions intact. There's something cruel about not being able to contact the seller, the last owner. I can only imagine they would be plenty happy to give some brief insight into the health of the transmission. I've tried it. The best answer I can get is I would need an DMV insider to get me that name and phone number just from the VIN. I might need to cultivate a Pick and pull insider, and offer them a not creepy bribe so that I could call some guy up and politely ask him if that tranny's still working.

Doing a flush and filter change would be a dress rehearsal for checking a boneyard tranny to see what the fluid, filter, and magnet looked like. I don't think they puncture the bottom of transmissions to drain the fluid the way they do on drain pans sometimes - very strange -I went looking for a drain pan. They all had big holes in them. But even if they did, I could use the cover off my existing tranny.

A tranny is $250 at Pick 'n Pull. I'm wondering if one that was clean inside is worth the gamble. Also, I would need to come up with some way to catch the fluid. Wouldn't want to be wallowing in it and wouldn't want to piss anyone off.

There are many different angles of approach...kinda have to pick one and hope for the best. My choice would be drop the pan, clean things up, replace the filter and fresh fluid. Lastly add a tube of Lubegard.

If the transmission is so worn that this makes it worse it was on its way out.

That does sound like a good approach. My only question and it might be a tough one to answer, if it makes it worse should I put back in the old fluid and filter? It's not running that badly now, I don't quite get it. There is a chance that new fluid might flush out valuable debris, metal filings, whatever and it will slip even with the old fluid put back in.

In a lousy dilemma, the cleanest boneyard SDL I've ever seen (3 weeks ago) is still on the Portland South Pick n' Pull yard. I was passing through, not much time, had to pick up riders going south. I got a couple of things, oh my God so much more would be worth a looksee. No idea if the tranny is still on it. They don't give you that info I don't think. I'm going to have to be ready to pop a tranny pan any time I find one.

https://www.picknpull.com/check-inventory/vehicle-details/WDBCB25D0GA252137

if you call them, they might be able to tell you the mileage. then you decide whether it's worth a look if there is a trans and price it out.

First you dont flush . you remove the pan , change the filter [ important ] / pan gasket , you drain the converter , you put 3 quarts in , start car , add another 3 , check level , you may need another 1/2 quart .

Thanks for that. I spent so many years with my 5 speed E30 cars I am not real experienced at maintaining auto trannies.

I'm sure some people might think it a bit foolish to try to keep this old thing going. Something about it, just feels like class, luxury, performance in one. The new used engine I had put in is incredibly good.

I read some years back that the 300SDL is considered by many to have been the golden age of Mercedes diesel.

There have subsequent engines with more hp, but you can't even get the latest diesel model in the US, I think I have that right, the S class with a really happening engine. But it's a complicated engine methinks. The OM603 might be almost as durable as the 617 but more powerful, in stock form anyway. I like the looks of my car, the front end feels really sweet, I really like the leg room in the backseat. I've done some big group trips and sitting in the backseat on the passenger side is ideal for watching the instrument panel. The legroom is just incredible, especially for a car that gets 25mpg.

Here I am at a hippie fair in North Central Washington. I woke up after my first night and someone had put this doll on my roof rack, sort of tied in place. I still have it.

https://i.postimg.cc/CLzk6ptn/IMG-6009.png

IMHO, it may be best to either one, do nothing other than add Lubegard or two replace only the filter in case the old one is restricting oil flow, catch and reuse the old fluid and still add Lubegard. The problem with new fluid is that if the clutches are on the razor edge of failing the new fluid will hasten that and putting the old fluid back won't reverse it.

Just curious is there any delay in the reverse gear engagement?

In the interim explore your best options for rebuilding the existing transmission (Sun Valley) or finding a good used one.

No, haven't noticed any delay going into reverse. It seems now and then there's a funny hiccup, but nothing that lasts long enough to look like an identifiable problem.

Put back old filter - no.

Put back old fluid? You could but it probably wouldn't help a lot. In addition to removing fluid with particles in suspension, the new fluid will clean the clutches some and you won't return material to the clutches no matter what is done.