Stuck modulator sucked ATF into intake? - PeachParts Mercedes-Benz Forum

#1 10-17-2003, 09:41 PM

I changed the ATF and filter on the 300e, putting in 6 quarts of Mobil1 ATF. Cold but running, the fluid level on the dipstick only covered the bottom curl on the stick. I was leaving for a trip and decided to drive about 15 miles then check the level hot.
When I checked, there was none on the front or back of the dipstick, but a little on the side. Since I was within 1/2 quart of stated capacity I continued the 200 miles to Knoxville, the car ran fine. I left the car parked for two days there and left for work on Monday.

About 50 miles out at 85mph down a long steep hill with my foot off the throttle I noticed a fairly serious amount of smoke coming out the back of the car. The temp stayed steady, oil pressure did not move, no lights came on. The smoke stopped when starting up the next hill, and did not recur the remaining 100 miles. Everything else seemed normal.

Leaving work that night, the transmission slipped badly trying to get into drive, and during the 1/4 mile limp to the gas station. I put about 1/2 quart of off-brand transmission fluid in (ruining my Mobil1?) the transmission went into drive ok and I headed home. There was some flaring going thru the town about 50 miles away; at the stop sign 8 miles from my house, the trans slipped on takeoff.

I have seen posts indicating a sticking modulator can allow ATF to be sucked into the intake, and this would seem consistent with the symptoms I experienced.

Question is what to do now?
Can a sticking modulator be corrected, or is it simply replaced?
How do I confirm this is the problem?
How much fluid could I have lost on that hill?
I see fluid on the faces of the dipstick with the car cold and off, why can I see none with the engine running?
With the closest MB tech 70 miles away, is this something I should deal with rather than risk driving the car?

psfred · #2 10-18-2003, 03:10 PM

VAcuum tap for the modulator on the M103 is on the rear runner of the intake manifold. Presence of tranny fluid in the hose means a bad modulator.

Get the tranny filled to spec pronto, you don't want to fry it running it low of fluid.

Your description is the classic one for a bad modulator allowing fluid into the intake.

Peter

#3 10-19-2003, 06:13 AM

Thanks guys,

I replaced that vacuum hose this summer with the white translucent stuff from the MB Dealership. It does not show signs of pink; also I did not see obvious signs of oil in the rubber 'U' that connects the vacuum hose to the intake when I shined a flashlight into it. However, on checking the trans fluid level, it is quite low. Maybe enough to have cleaned out the vacuum line.

While trying to find fitings to adapt one of my vacuum pumps to the modulator hose, AZ rented me a hand operated vacuum pump with the proper adapters.
Will test the modulator during daylight hours Sunday.

#4 10-19-2003, 08:10 PM

So much for the comparatively painless solution.

The modulator held 14" vacuum for at least 10 minutes.

More worrisome is the ATF blown all over the exhaust system. I cannot seem to locate the source, although there seems to be more on the passenger side.

Even running, I can see no leaks. I will leave it on jack stands overnight and see if I get any puddles.

It is also slipping so badly I could not get it up ramps, which explains the jack stands.

Can any of the seals be replaced without removing the trans, or should I start shopping tow trucks?

psfred · #5 10-21-2003, 02:51 PM

Here we go!

Overfilling the tranny will result in the gear train foaming the oil. This will blow most of the oil out the top vent AND cause slipping. When it cools off, it's very low on trany fluid.

If you didn't drive it too much and the clutch packs aren't fried, filling to the correct level will fix this. If you fried the clutches from slippage, it's tranny swap time.

A leaking pan will also remove considerable oil from the tranny, and it may only leak hot. Make sure the "ears" on the corners aren't bent, this will make it leak big time.

Another source of leakage is the servo seals on the passenger side of the tranny. when they go bad, fluid dribbles any time that servo is applied. Sometimes the cover seal can be replaced with the tranny in the car, sometimes not depending on model and which servo is leaking.

Both will run the tranny fluid on the exhaust, making white smoke if you have enough leaking.

Front seal can leak, too, but that leaves fluid dripping of the bell housing only.

Peter

#6 10-22-2003, 06:42 AM

Peter,

The reluctance to go into gear occurred before the possible overfill of the trans. (should have been a 1/2 quart low before leakage according to spec) And bringing it to level (or possibly overfilling it) made it go into gear normally and perform quite well (freeway, a couple of complete stops, then highway) for 50 miles.

Since there is a heavier concentration of ATF on the passenger side and I could not identify a leak during idle, it seems logical to explore the servo possibility. Where would I look for directions to determine which servo is leaking? (I do not find much trans diag info on the CD, Haynes, or Bentley.) I have the ATSG manual on this trans, but have not had time to thoroughly dig thru it...the first copy I received had 8 pages missing.
This an an 88 300E with the 722.3xx box. Have not found where I wrote down the exact model.

psfred · #7 10-22-2003, 08:13 PM

Wipe it all clean and spray with white foot powder. Makes a big mess, but you can then see the leak as a red track in the white rather than attempting to see the remains of the trail of tranny juice.

Low fluid will allow air into the valves and clutch packs, and will cause troubles since it compresses and expands, unlike tranny fluid.

Dollar to a donut it's something associated with top or third gear, servo cover or accumulator cover.

Take a look at the power flow diagrams for the tranny and locate the associated accumulator and servo covers OR fluid passages -- I've seen a post where someone had a problem with a factory "blind" seal plug coming loose and leaking.

Doesn't take much fluid to move the car -- Big Blue (the 280 SE 4.5) made it down the drive, around the corner, and to the garage on about two cups of tranny fluid in the pan -- nothing came out when I took the filler tube off to drain it! This was after a cooler line cracked and coated the engine compartment with fluid a couple miles from home. Didn't even slip much!

Peter

#8 10-23-2003, 07:00 AM

Peter,

Sounds like a great troubleshooting strategy. One question; will I need to engage the trans and achieve shift to reproduce the leak (road test), or can I make this work at idle on jackstands? (if the servos only leak when engaged)

I have one more day left in the work-a-thon so I will try this Friday.

TROVERMAN · #9 10-23-2003, 08:32 AM

I have read your post and don't know if this will help: Just after purchasing my 1995 E320 Wagon w/40k on it, I look out the rear mirrors while going up a long hill at 70-75mph. White smoke just pouring out the back, really embarassing. Pulled it over at a Ford dealer, of all places, and you can see that tranny fluid has leaked all over the exhaust, and the cat. Got it home, wiped it all down, and drove it again. After driving a while, the smoke show happened again. Took it home and wiped it all down again, only this time I tightened all the bolts on the tranny pan, including the drain plug. Ever since, it has never smoked again (knock on wood) for about 2500 miles, and the transmission doesn't appear wet. However, on steep hills, it was slipping quite badly. Couldn't see any fluid on the stick, then some at the bottom, etc, cold / hot scenario, very hard to tell. So I add a 1/4 qt of Dextron 3 and then drive it, now it's overfilled, according to the stick. But it doesn't slip. I drain some out, and it appear good on the stick, if any, down a little, but now doesn't slip at all. However, it does shift a little clunky, never in the lower gears, but sometimes in the upper ones. Definitely check the tightness of your pan bolts, it appears to have solved the problem for me. All of my leakage coincidentally also appeared on the passenger side too...

psfred · #10 10-23-2003, 07:37 PM

Going to have to get it to upshift to get the servo to leak, and i recommend driving it. You can do this on jackstands, but if one wheel drags some, the other will be running a twice the speed indicated on the speedo -- can cause a tire to explode if overdone!

Pan can leak hot only, too, this won't show much unless it is blowing back onto the exhaust.

Overfilling will cause tranny fluid to blow out the top vent, too. Usually causes severe slip from foaming and clutch damage, too.

Peter

#11 10-24-2003, 05:46 AM

Peter,

In trying to prepare for the worst, I have called all the indies in Nashville and found out none of the major players rebuild trannies; all replace them. I am working on the theory that a shop capable, qualified and willing to rebuild a box might identify a problem that does not require a rebuild. It would intuitively seem less likely a 'we replace transmissions' shop would identify such a fault.

Expanding the search and by accident, I called a wholesale trans parts place who told me they thought one of their customers solely worked on Mercedes transmissions. They gave me his number.

I talked to Henry, who told me he only worked on Mercedes transmissions. I described the symptoms, and his first speculation was that it could be a servo leak.

My battle plan is as follows;
Tomorrow I will remove the excess fluid, clean the case, and hose it down with foot powder. If I can get it to shift in the first couple of 100 yards, I will take it onto the highway to get it into 4th gear.

If it will not shift in the first couple of hundred yards, I think I will have it towed to Henry and let him deal with it.

I don't know whether to be worried or elated... I asked him in a worst case scenario what he got for a rebuild.
The answer was $1000 including the kit.

However, when Nashville Transmission Parts tells me he buys more Mercedes parts than anyone else it sure seems to lend credibility...

psfred · #12 10-24-2003, 07:29 PM

Sounds like a good plan. MB trannies can be rebuilt, but you DO need to know excactly what you are doing to get them right. Considerable "extra" dissasembly is requried to get at all the seal, and there is enough wear on gears, carriers, bearings, and clutch drums that they all need to be checked and refinished or replaced (thrust washers on pinion gears are usually shot by 200,000 miles, for instance) if decent service is expected.

Good luck! Hopefully it is just a servo causing the leak and a stuck or broken spring causing the failure to shift (both are known problems).

Peter

zhandax · #13 04-23-2010, 07:51 AM

wh, just saw the bump so here is what happened;

I had heard about how great this MB mechanic was in Nashville, and I went there to talk to him about whatever issue I was trying to resolve. Since I was there, I had his guys change my transmission fluid and filter which was probably overdue. I noticed his guy removed my transmission pan with a cordless impact wrench and then I was called back into his office (I think I was looking for an entire lock set off a junk car of which he had a few).

The trans guy where I finally had the car towed reported that the trans pan was warped. I can only imagine that it was from re-installing it with the same cordless impact wrench (I do recall it was a Snap-On) which removed it. Apparently inconsistent torque among a number of bolts warped the pan after it stayed hot a sufficient period of time and sprayed the trans fluid out on the exhaust (which explains the cloud of smoke I saw out the rearview). The trans guy replaced the trans pan and there were no further problems.

I have not driven this car more than locally (~50 miles at a stretch or so (long story) but that should change in the next month or so) so don't leave for California with this advice without testing it.

I have since learned that there is only one crew in this town I trust to work on a German car and since that painful revelation, they are the only ones who touch any of my fleet and they do that infrequently (not because of any lack of confidence).