Is my transmission modulator okay??? - Page 2 - PeachParts Mercedes-Benz Forum

engatwork · #16 08-31-2003, 12:06 PM

mikael - make sure they drain the torque converter too. The engine has to be rolled to get the torque converter drain plug at the bottom and then can be removed/installed. Disregard this if you are having it "flushed".

mikaelw2001 · #17 09-01-2003, 11:24 AM

Hi again all,

Yesterday I did an additional adjustment of the modulator and now I´m quite close of having it all right. There´s still a tiny bit of flare in the 3-4 during warm up and at about 40% throttle and the 2-3 is a bit hard after warm -up but I´ll get that sorted out now that I see that the adjustment of the modulator is working.

Right now I´m just happy that the transmission is so close to be correct that I probably wait until I had the filter changed and new fluid in before I do the final tweaking.

Jim - Your reply indicates that there´s a drain plug in the torque converter that I can acces through the bell housing (which I never noticed before).

Is it sitting underneath the bell housing?

Many thanks/ Mikael

mplafleur · #18 09-09-2003, 10:49 PM

The transmission shop that rebuilt my 300SDL tranny told me my problem with flaring while cold was a modulator issue. He said that at cold, the seals were leaking and when the trans is hot, it seals fine and the shifts are normal.

Now, do I need to replace the modulator, or just the seal?

Am I going to have to drop the tranny to replace this?

#19 09-10-2003, 11:15 AM

I can't speak to this vintage of modulator, but my experience with older MB versions may be of some help. Yes, if you are finding ATF under the cap, the modulator is bad. Adjustments will help lessen the flaring but not eliminate them entirely. After installing a new one on a 79' 280, which are supposed to be properly set out of the box, I was still getting slippage and cranked the key clockwise quite a bit. With no improvement, I took the car to a tranny shop which pressure tested the fluid and found I had 300# of pressure in the tranny when 150# is normal (they said). Diagnosis was that because the original modulator had failed completely causing very hard shifting, which I neglected for a few weeks, a piece had broken off one of the pistons, causing the flare/slippage, and no amount of adjustment to the new modulator would cure that problem. But the point is that continuing to crank the modulator adjustment without seeing shift improvement could raise internal transmission fluild pressure to the point of blowing seals.

Fixing/replacing the modulator should cure your remaining flare problem, and while there are benz trannys that will flare for tens of thousands of miles with no other apparant problems; you should fix it ASAP as sooner or later the flaring will cause band wear to the point that transmission surgery will be needed.

On my older vintage MBs, the modulator swap was very easy, but you need to drain the ATF from the tranny first as otherwise it will pour from the modulator hole when the old unit is pulled. Draining the Torque convertor isn't needed to just swap the modulator. And of the two I've changed, there is a pin in the center of the modulator assembly that must be re-installed as it does not come with the new unit, and which may be frozen into the old modulator with dried out ATF. A quick check for vacuum leaks can be done by pulling the vacuum hose off the modulator cap and simply feeling for suction with your finger over the hose with the engine running.

mplafleur · #20 09-10-2003, 10:22 PM

The symptoms are such:

Cold engine: Flares for first shift only (2-3). All other shifts are fine. Must ease up on throttle for smooth shift.

Warm engine (40 deg C): All shifts OK.

There is no in-between. Either it slips or it doesn't. I've tried it where the temp is just below 40 and it slips, pull over, wait a moment only, temp now at 40 and shift is OK. This is repeatable 100% of the time.

The tech said it was the seals in the modulator. The modulator is where the vacuum hose connects, right?

I can't tell the color, although the black piece where the vacuum hose connects has a green mark on it. I think my modulator is supposed to be brown, which is the expensive one of course.