380sl Strange Smoking

[Paoli380]

Hello- I've owned a 380sl (1984) for about 5 years now and just found this forum. It runs really well, but when I stop the car abruptly on a slight downhill grade, it will smoke terribly for about 15 seconds or so. It's a very white smoke and there are plumes of it. I drive it about 1400 miles a month, and it might smoke just once or twice. There is no pattern of weather or temp that affects it--just a slight downward grade. When it happens, it also almost stalls out as well.

Could this be the trans modulator? Any thoughts would be appreciated. My mechanic is stumped because he cannot replicate it to see the problem.

[JPMOSE]

Large volumes of white smoke is typically the vacuum modulator (transmission). This should be easy to verify under the hood by disconnecting the vacuum line to the transmission and checking for fluid deposits. Hopefully, that's all it is! Good luck.

[Tims450SL]

As in all bullet proof mercedes transmissions, if you do not have a filter change they will begin to deteriorate. The filter is not expensive; but you want the person doing the new trans filter to already know that they have to drain the tourqe converter also- If they do not know that - do not let them do the job. Your trans will stop smoking and act like new. A clogged filter backs up the pressure so it is adviseable to service it- $150 is much cheaper than $4000 +

[Mike D]

Possibly a leaky or previously leaky brake master cylinder. The "abrupt" stop is the clue. You'll probably find a bit of brake fluid sloshing about in the booster.

Whe you come to a hard stop, downhill, the fluid slops forward, up into the vacuum line and into the combustion chamber. Brake fluid burns but not all that well hence the "stalling" as the engine tries to digest it. Lots and lots of white "smoke screen" smoke.

[Roncallo]

Originally Posted by Paoli380

Hello- I've owned a 380sl (1984) for about 5 years now and just found this forum. It runs really well, but when I stop the car abruptly on a slight downhill grade, it will smoke terribly for about 15 seconds or so. It's a very white smoke and there are plumes of it. I drive it about 1400 miles a month, and it might smoke just once or twice. There is no pattern of weather or temp that affects it--just a slight downward grade. When it happens, it also almost stalls out as well.

Could this be the trans modulator? Any thoughts would be appreciated. My mechanic is stumped because he cannot replicate it to see the problem.

My 560SL did somewhat the same thing. It had 200K miles on it and burnt oil regularly although barely enough to have visible smoking and it ran very strong and smooth. One day I was stopped to talk to someone the car was on a fairy steep down hill grade. after about 30 seconds the car started smoking like a mosquito fogger. I thought I cracked a piston ring or something. I got the car off the hill and started driving it and it cleared up in about 1 mile. I never had the problem again although I'm sure I would have if I stopped down hill again.

Now I suppose you are going to want to know what it was that caused the problem. Unfortunately I never ran it to ground, because I pulled the engine out to put in a V-12. But I do believe this is an intake valve seal problem and I'm sure it would be reduced significantly with just valve seals. Also in doing the valve seals the guides could be easily checked at the same time.

John Roncallo

[Walrus]

I vote brake master cyl...

[Roncallo]

Originally Posted by Walrus

I vote brake master cyl...

It certainly was not in my case as I replaced the master and rubber hoses as a mater of age when I got the car and I always check and suction out vacume boosters when I do this.

However I would not rule that out in Paoli380's case as his occurs during hard braking. Mine had nothing to do with breaking.

John Roncallo

[Tims450SL]

i want to know more about the v-12 in the 560SL....

[JoJoDFG]

In my case, I too was in denial that it could be blow-by. But after several trips to the trusted indy and no resolution of the white smoke, or ability to re-create the smoke on test drives, I took him to the scene of the crime i.e. my long downhill which is approx 15-20 degrees and wallah---blow-by diagnosis. After pulling the head, he showed me what was happening. BTW, my indy has been servicing my '84 380 since it was 2 yrs old and has kept 'er going great...we're at 195K now and one of these days he say's we'll have to address the transmission, which is slow to engage in reverse...and has been for the last 60k. But hey, when it quits we'll replace it since reverse will probably go first and the car isn't too heavy to reverse/push out of either the garage or a parking spot. I am amazed it hasn't failed yet.
Also, I took the groups recommendation and replaced my lousy stock Becker Mexico with the Becker am/fm/single cd in dash from the BeckerUSA web site, and love it. It even says Mercedes Benz on the front. I also had the RCA i-pod jack installed which works well even though it doesn't charge the i-pod. Oh, and I crammed some new 4" speakers in the dash. Heed the advise to take an old speaker with you for sizing. You can cheat the width somewhat but NOT the depth without some Macgyver dremel action. It is so great to have some decent music after 24 years!
Thank you all...
Jo

[Paoli380]

Thanks to everyone for the advice! The shop I took it to knew nothing of the problem and couldn't replicate it, so I asked them to replace the trans modulator and check the vac lines on the master cyl. The brake vac lines were fine, and even the vac lines by the trans modulator didn't show obvious signs of fluid.

They replaced the trans modulator (48 dollar part, 85 in labor), and it doesn't smoke any more. I'm really amazed because I thought it would be a long shot, but I've taken it to the hill the caused the smoking and ran it 5 times. Not a puff. The car actually shifts much better now (it used to have a hard shift from 1st to 2nd and from park to reverse). Now it shifts very smoothly and adjusts well. I'm pretty happy since the car hasn't driven so well since I've owned it (I thought the rough shift was just how it naturally ran). Thanks again for the tips!

[Mike D]

Glad to hear it worked out so easily! Thanks for the follow-up.