mysterious dissappearing ATF???? - PeachParts Mercedes-Benz Forum

smittyinnola · #1 09-21-2008, 12:45 PM

Hello Forum Friends,

I have a new to me 82 300 CDT and am having a confounding problem. When I 1rst got the car the trasmission was shifting fine...no prblems. I had a worn trassmission mount replaced in Chattanooga TN where I bought it and then drove it home to Kentucky, no problems.

After having it home the transmission started shifting rougher and rougher on periodic errands out. I checked the ATF fluid and found that the level was scary low.

I added a quart of fluid and took her out for a spin. Shifted perfect. I waited a few hours and checked the level again (it was hard to get a reading right after filling the fluid went in the tube since it was coating the sides) the fluid was still low. I put in another quart.

The next day or 2 car started shifting rough again, I checked the fluid and it was super LOW again....Long story short I have now added 4 quarts of fluid and after the shortest drive the fluid level is close to empty again. There is NO ATF fluid leaking out the bottom. None! Where is the fluid going? Is it possible that their is some vacuum hose hooked up wrong somewhere that is sucking out the fluid???

I am mystified. Any ideas out there?

tangofox007 · #2 09-21-2008, 02:13 PM

Have you inspected the transmission cooling lines and hoses for leaks?

smittyinnola · #3 09-21-2008, 04:19 PM

Quote:

Originally Posted by tangofox007

Have you inspected the transmission cooling lines and hoses for leaks?

I haven't noticed any leaks anywhrere. I think after adding 4 qts of ATF and the fluid close to empty again it should have been hard to miss, shouldn't it? Thanks

jt20 · #4 09-21-2008, 02:14 PM

trans needs to be FULL OPERATING TEMP. Slight inclines in any direction mess with the readings. Find a level spot where you can repeatedly check your levels.

check levels in 'P' and 'N' and shift through all the gears beforehand

Alastair · #5 09-21-2008, 03:28 PM

The fluid May be going through the modulator valve, into the vacuum system and ending up in the engine....

According to the type of vac. pump, it may end up in the engine-sump or it may end up being burned in the engine via the vac-pump vent pipe to the air-filter....

smittyinnola · #6 09-21-2008, 04:22 PM

Quote:

Originally Posted by Alastair

The fluid May be going through the modulator valve, into the vacuum system and ending up in the engine....

According to the type of vac. pump, it may end up in the engine-sump or it may end up being burned in the engine via the vac-pump vent pipe to the air-filter....

Wowee, this could be it! Where is the modulator valve? How do I check? Could it be sucking out this much fluid?

Alastair · #7 09-22-2008, 02:11 PM

Quote:

Originally Posted by smittyinnola

Wowee, this could be it! Where is the modulator valve? How do I check? Could it be sucking out this much fluid?

The vacuum modulator valve is located on the Driver's side of the transmission case (assuming LHD American car) and connected to a valve on the Injection-pump, by a thin plastic semi-rigid pipe. From here, it goes to the cam-box where it connects to a vacuum 'micro-switch' then into a the main vac lines....

You can check for ATF fluid at any point along these pipes.. There should be no oil at all in those pipes....

Worth checking the radiator isnt full of ATF though as others have said, If it is then the trans cooler pipe in the bottom of the rad will have rotted. This could also allow water back into the transmission and this could seriously damage it!

JBG · #8 09-21-2008, 07:16 PM

Just a thought, it might be leaking out only when the car is running, not when shut off. I had a similar, though much less severe, issue with this back some time ago. The leak never got bad enough to pursue/track down (this was 8/9 months ago) and I check my fluid often now. I still get unpredictable readings even at full temp and on level ground. The dipstick just doesn't seem to give readable readings--one side of the thing is full halfway up, the other side dry, etc. etc. As long as there's fluid on it within the marks at some point on the dipstick I just go with it....

But yeah, look into the "leak only while driving" issue. Should drive you fairly close to insane trying to determine the source.

JBG

charmalu · #9 09-21-2008, 10:41 PM

there could be a possibility that the atf is leaking into the radiator?

Is the coolant reservoir overflowing and or have oil in it?

Charlie

bbboomer · #10 09-21-2008, 10:53 PM

Pull the vac modulator hose off the modulator. If it is leaking past the modulator the hose should be wet inside with ATF, mabe even full judging from the amount you are losing.
Look at the coolant to see if there is oil in it. You may have to disconnect a hose to check it if your car has a coolant recovery tank. If it has oil in it the coolant should be milky looking, maybe with beads of red mixed in not clear green like antifreeze.

turbobenz · #11 09-22-2008, 03:52 PM

i just fixed a mudulator that was leaking trans fluid in.

nickofoxford · #12 09-22-2008, 04:13 PM

I'd check your coolant level.. Charlie has a good point because the trans fluid is usually cooled in the bottom of the radiator and I've head of some cases where the trans fluid will leak into the coolant or even coolant into your tranny

Also, if this is a vacuum problem you should be able to take apart your air cleaner and see that it is soaked in fluid. Do you notice excessive smoke in your exhaust? That's a sign of burning ATF.

kerry · #13 09-22-2008, 04:21 PM

Check your engine oil level also.
It seems hard to believe that that much ATF can be drawn up thru the small vacuum lines and getting burned but in theory it seems the best explanation for the ATF to escape without leaving a trace. If it's going into your coolant, unless your coolant was really low, you'd be overflowing with 4 extra quarts.

smittyinnola · #14 09-22-2008, 08:20 PM

Hi Everyone thanks for your ideas,

Here's what I found. There is no ATF in the coolant, but the engine oil level is probably about 4 quarts high

. I found ATF in one of the vacuum lines...I am posting a photos of this below...same line in both pics. There was a lot of fluid in the bottom of the air filter housing, but I couldn't tell if it was ATF or not.

So help the newbie...what does this mean? Does this confirm the faulty trasmission modulator or not? What kind of fix am I looking at?

Thanks again.

tangofox007 · #15 09-22-2008, 08:32 PM

Quote:

Originally Posted by smittyinnola

Does this confirm the faulty trasmission modulator or not?

You must have a ruptured diaphragm in the modulator. Vacuum should be confined to the modulator itself. There is no other vacuum connection at the transmission.

Quote:

Originally Posted by smittyinnola

What kind of fix am I looking at?

A new modulator vavle should solve the problem. Buy a new pin while you are at it. Chances are good that the old one will break, if you have the plastic version. Then change the engine "fluid" and filter.

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