installing new transmission vac modulator - Page 2 - PeachParts Mercedes-Benz Forum

my123ca · #16 02-28-2017, 09:07 PM

IIRC, you have to loosen a big nut somewhere in front of the DS. I remember using a 46mm and a 41 mm wrench.

kuene · #17 03-01-2017, 02:19 PM

my123cs - does loosening that big nut then allow for rotation so you have access to the 3 nut/bolts that hold the shaft to the trans?

Rogviler · #18 03-01-2017, 02:30 PM

The big nut only allows the driveshaft to slide into itself so you can shorten it to get it out (and separate it once it's out).

With both rear wheels on the ground the driveshaft won't turn.

-Rog

kuene · #19 03-04-2017, 01:54 PM

OK. Progress has been made. I've successfully removed the old modulator and am ready to install new one - green type, this is an 82 Turbo, 300d.

Now a question for those that have installed this new type of modulator, with the white cap that allows for some adjustments without removing the cap. It seems to me, that the only way the cap can go on (because of the notches) it is at it's fullest clock-wise position - and once on, the only direction you can turn it is count-er-clockwise, which I believe reduces the pressure. Does this mean that out of the box, the modulator is set at its most clockwise/highest pressure setting? Because once you put that cap on, the only adjustment is down, as far as I can deduce from playing with it.

kuene · #20 03-07-2017, 05:32 PM

I wanted to share my continued struggles with replacing this modulator. Hopefully, will help others considering the job, and perhaps others will chime in with any tips.

After a couple aborted attempts to access the old modulator for removal, I finally was able to get enough room to work and remove. Here is what I have done so far and where I am stuck.

1) loosened the fan shroud

2) disconnect throttle linkage (little clip near firewall, and rod comes out)

3) loosened the 46mm nut a couple turns on the short section of drive shaft

4) removed the 6 bolts/nuts on flex disc between transmission and driveshaft.
a) this requires getting 1 rear wheel off the ground so you can rotate the shaft for access
b) I'm not sure this "disconnected" the drive shaft, but it all seemed to give me more wiggle room than when I had attempted without doing this the first time.

5) removed the 4 bolts and the transmission mount bracket. then removed the bracket (2 bolts) from the rubber mount piece.

6) lowered the rear of transmission on a floor jack as far as it will sag pretty much

7) wedged the rear of transmission over to the passenger side as far as I could with a little 1x2 piece of wood strapping

8) cleaned the area around the modulator with degreaser

9) removed the two 5mm allen head screws - I used a 1/2 ratchet with a flat (not ball-end) hex socket - had just enough room to get them out.

10) very carefully rocked and pulled to remove the old modulator straight out - avoided breaking thrust pin as it came out.

Paused for the night.

11) leaving the white cap off (it’s much harder to get on and off than the old rubber black caps), I prepared new modulator o-ring and thrust pin for insertion by coating with trans fluid

12) gently put thrust pin in the hole, it feels like it may almost get lost in there but it doesn't.

13) set metal mounting plate into groove of new modulator and careful navigate it up and into position over port

14) pressed modulator, carefully, straight into hole and attempted to seat all the way until the mounting plate is about flush with transmission’s threaded holes.

This is where things ground to a halt. No matter what, I could not press the modulator in. There is extremely limited space (less than a few inches) to apply any direct pressure, so you are using your fingers only. When I pulled the modulator out between attempts, I noticed the o-ring would occasionally show some uneven deformation, as if it weren't seated correctly. Here is a picture of the o-ring down in the port, it is seated comfortable there - I could probe with my finger and this felt correct.

I will note that it was cold (30s) and an unheated garage. Thinking that might be my problem, I let a little space heater run up under the tranny for a while to warm it up, and I used a heat gun (on low) to soften up the o-ring each time I tried to insert the modulator. Didn’t help - though I would imagine all of this would be easier in warmer weather.

When you pull the new style modulator out (at least in my case) the o-ring usually stays in the port, so you have to fish it back out each time. The old modulator had a groove/channel where the o-ring sat, and it stays put. The new style modulator just has the o-ring resting up against one ledge, but not seated in a channel with walls on both sides. This means it can easily slide back off as you pull the modulator out. Here is a pic of my old modulator next to the new modulator - you can kinda see what i’m talking about if you look closely at the o-ring end of each.

The new modulator is definitely different than the old modulator, but in all the documentation (including from our pal Kent at m*******source) the new modulator is quite different in design of all the components. Then I started to google, and landed on this benz world post.

Is it possible that this particular new modulator is NOT the right part for my car? I have to admit, I just searched for the proper modulator by my vehicle model and year, and not by close inspection of transmission stamped model number.

While I was never able to get the new modulator seated properly, I did get it close (I thought) at one point and was able to get the mounting plate screwed down with the hex heads. I then started up the engine and the fluid started leaking out immediately. I then tried the old one again - and it went back in without much difficulty. I then removed the super old, hard and flattened o-ring, and put the new o-ring on the old modulator, thinking it may not go in - but it did. Started up, no leaks.

My understanding was that the new style green modulators (126-270-92-79-M22) were drop-ins for the old green ones. But they also still manufacture (not MBZ) ones that look like that old style (Trucktec 126-270-92-79-M90). Pelican sells them both. Are these really interchangeable?

Is anyone here personally experienced in swapping the old one that I have pictured above, with the new style?

Carpenterman · #21 03-07-2017, 07:49 PM

I was wondering if you would have the same experience I did.

I, as well, was unable to get the new-style modulator to not leak. When I removed it, the O ring was badly deformed. I tried a replacement O ring and the same thing happened. As you said, the O ring seats on the shoulder in the transmission and against the body of the modulator. The shoulder, however, has a gap or cutout in its circumference (for drainback, I assume) that I felt would not seat the O ring completely.

I figured that I had made some sort of an installation mistake or maybe it was the wrong part. Since replacement was a preventative measure, I just put the old one back in and went down the road.

I, too, would like to know what is going on. The one that didn't work was sold to me as a compatible replacement.

kuene · #22 03-14-2017, 04:53 PM

sorry to bump this - but the thread was sitting dormant at 666 views - which seems like a bad idea. And I also wanted to know if ANYBODY knows what the deal is with these new MB green vac modulators that don't seem to fit into 723 trannies that have the original green vac modulator.

diesellover 92 · #23 03-14-2017, 05:25 PM

I ordered my updated modulator from pelican parts as it was cheaper then mercedes xxxxx. Mine is not green but black with the updated internals i dont know if that makes a difference. I have not tried to install mine, waiting for warmer weather.

dennislarock · #24 03-14-2017, 08:49 PM

I did order a new o-ring for the original MB Modulator that I attempted to replace. I will see how the *new* improved MB modulator fits as I now have the tranny out... if, it still doesn't fit... I have a the new o-ring for the original MB modulator.

kuene · #25 03-15-2017, 09:34 AM

I also bought some new orings, and a new rubber cap for old one. Gonna do a vac test with new cap.

I also ordered a new "old" style green modulator made by trucktec - was pretty cheap.

But if you get the new style one in dennislarock, let us know. Inmight give it a try (and have to wait until the weather heats up anyway.)