where is my ATF going? - PeachParts Mercedes-Benz Forum

C32AMG · #1 01-31-2008, 09:38 PM

Quote:

Originally Posted by imagineaudio

hi, 1990 300e about 180,000 miles.

bought the car a few weeks ago w/ transmission problem. It would rev up and slip and sometimes not engage next gear. Checked the ATF, it was low. Added 2 qts and all was good. Transmission shifted a little harsh, but no slipping and no sticking in one gear. Also engaged in reverse muuuuch quicker.

So after about 60 miles or so the slipping and sticking came back. Added another 2 qts and life was good.

I've had to add ATF every 60-75 miles. I've probably added 8-10 qts, which I assume is more than it holds, so all the fluid in the system should be new fluid.

My problem is that I can't figure where it's leaking. It's not leaving any wet spots under the car and everything else under there is bone dry. Seems like a lot of fluid to loose so quickly w/ no traces....

Where is my ATF going?

If the modulator were defective, sucking fluid into the engine, you would see white smoke coming from the exhaust. I would check the radiator overflow tank for a strawberry color, which is transmission fluid mixed with coolant = faulty radiator.

imagineaudio · #2 01-31-2008, 11:01 PM

^^^ Hmmm.... I'll check for that. I do get some white smoke occasionally, but I haven't noticed if it corresponds to when I fill the ATF. It seems to only loose so much, around 2 qts.

Coolant level hasn't lost a drop since I got the car, and I would imagine 10 qts of ATF in the coolant would be painfully obvious.

The place I'm moving from was in foreclosure when I moved in and the unscrupulous landlords took me for a ride. I did some *****ing and moaning today to the bank that repo'd it and there gonna cut me a little check for my troubles, so I'll get the car to the shop next week and report back when I know more.

Arthur Dalton · #3 01-31-2008, 11:21 PM

Radiator/trans cooler is a remote possibility, but it would be my second thought.
Your observation of your vac line showing sponginess/swelling, along with hard shifting and rough running engine [possible oil soaked plugs causing misfires], along with vac leak , would indicate a bad modulator diagnosis...but that is just my first thought..the proof is when you take the line off and see..pretty simple to check.
With your info, Looks to me most probable cause would be modulator diaphragm is split..very common.
If they are not too bad, there would not be enough smoke to brings one attention to it, but it would be something to check for..

imagineaudio · #4 02-01-2008, 01:14 AM

I feel like such an @$$ for not checking this yet, but I just can't get under the car. I used the jack that came with the car to get a little look, but no way am I crawling under there with just that rinky thing between a car that weighs like a tank and my little peanut skull.

arthur, what your saying makes a lot of sense to me.

Interesting side note (to me), I pulled a few of the plug wires off, one at a time, i think 1, 5, 6 respectively and it made an imperceivable difference in the way the engine idled. Not even a hint of difference, really.

david spain · #5 02-01-2008, 03:43 AM

Have just replaced the vacuum modulator device (it was indeed broken!)with help from mechanic friend and a posting in this forum from dieseldan44 of 6/3/07 - thank you! I just need to know the correct pressure setting required for the 722.358 transmission unit and then my car will be back on the road.

I would suggest that unless you have proper ramps - or - jack stands that you have this work done professionally as you do need decent clear space under the transmission to work and a pressure gauge and fittings. It should not be too expensive (an hours work) most especially as you know the problem - the vacuum diaphram is broken allowing transmission fluid to get round it and to be sucked into cylinder 6 via the tube connected to the intake manifold. Makes sense once it's explained to you (as it was to me after months of looking for leaks!) - but a somewhat uniquely Mercedes way of managing things. By the way, the local Mercedes dealer was no help - only interested in selling me a new model!

Your comment about no effect felt by disconnecting one plug at a time is normal - one of the beauties of this straight 6 engine - I reckon I drove for thousands of miles with cylinder 6 not working due to the transmission oil pumping through it. By the way, since this fluid does not burn, I only occasonally noticed smoke - just had to keeep adding more fluid.

Good luck with all this.