installing new transmission vac modulator
 

I'm going to attempt this on my 82 300D Turbo. My modulator is green, and on the driver side of the trans. I've searched for tips/photos/procedures around removing/installing the green-style modulator on transmissions still in the vehicle. My understanding is: it's a pain in the ass but there are some things you can do to make it easier - specifically making the work area more accessible.

Here are two tips I found on peachparts:

1. You can shove the trans a little to the side with a block of wood wedged against the tunnel. Be sure to loosen the fan shroud.


2. The modulator is very hard to get to, I have to disconnect the front of the driveshaft at the trans, and take the trans mounts off to let the trans sag enough to get up in there.

On the first tip: I'm not sure what the fan shroud is - this is something local, down in the tunnel, or is this the main fan shroud in the front of the engine/radiator area?

On the second tip: if i take the trans mount off, do I need to support the trans with a jack?

Would I go with one of these suggestions, or both? Are there any other tips or suggestions from those who have changed modulators while the trans in in the vehicle? I know this has been covered in various threads, but nothing definitive seems to be recorded and agreed upon.

If there is a good wiki or pdf to download that covers this - I'd gladly refer to that, but I didn't find anything yet.

Here is an excellent write-up for the W123:
http://www.peachparts.com/shopforum/diesel-discussion/190197-w123-modulator-adjustment-diy-measure-right-way.html

thanks sam. I actually used that writeup a few weeks ago to test the pressure port - which is ultimately how I've come to determine i need to swap in a new modulator. (will say that I picked up a cheap HF oil pressure test kit and the right size fitting is included)

that article however doesn't offer any tips on removing and installing new modulator. Just adjusting the modulator, getting to the pressure port, and reconnecting the vac hose was near impossible in the space. I have no idea how I'm going to get that module in or out.

I'll tell you my experience, if it helps.

Drop the trans mount support using a jack at the bottom of the pan. Lower the transmission and have someone watch the rear of the engine until it gets close to the firewall--be sure to loosen the fan shroud). Wedge something against the tunnel and move the trans over as far as you can toward the passenger side.

There are two hex head bolts (5mm IIRC) that hold a plate to the transmission body. The plate is what keeps the modulator secure. Remove the bolts, the plate, and pull the modulator straight out. Try not to move it too much sideways, as the older style modulator has a plastic rod that can break off inside.

Notice that the plate is indexed into a slot in the modulator body. That is the orientation to use when installing the new one. Put a thin coat of clean trans fluid on the new modulator to make it easier to install. Just push it firmly in until it bottoms.

Place the plate in the modulator slot and against the trans body and check to be sure the bolt holes line up. I use a plumber's mirror and a flashlight. Now the fun starts. It's time-consuming getting the bolts located and positioned correctly to get them started. I think I used one of those "L" shaped hex wrenches to get them started and finished with a hex socket and a 3/8" ratchet. Not much room to swing in such a tight location.

Hook the vacuum line back up and re-attach the trans support. Start the car and check for leaks.

^^^ this is how i did mine all those years ago. that transmission is still in service today on that car.

so happy people are still using that DIY :O)

I want to re-emphasize one thing that Carpenterman mentioned. The modulator needs to come straight out or you run the risk of snapping the plastic rod internally. Been there, done that.

ok. thanks. So I'm going to somehow "loosen" the fan shroud (not sure exactly what that entails in terms of what i unbolt or disconnect yet)

http://cdn4.pelicanparts.com/techarticles/Mercedes-W123/14-ENGINE-Fan_and_Shroud_Removal/images_small/pic01.jpg

and then, with a jack supporting the trans pan, unbolt this trans mount cross member thing?

http://cdn4.pelicanparts.com/techarticles/Mercedes-W123/111-TRANS-Transmission_Mount_Replacement/images_small/pic01.jpg

and then gently lower the trans a bit, while also pushing it towards the passenger side and wedging a block to hold it aside?

do i need to disconnect the driveshaft too? if so, which side of that disc should i attacK?

I would loosen the center link to the driveshafts ,its a joint between the 2driveshaft sections ,that should free up some movement but not sure its absolutly needed .I tried to pull one trans modulator at the yard and was unable to use it due to it being bad.They make allen tools with a balled end for tough to get to areas like these ,gives you alkot more wiggle room.

going to replace modulator this weekend. getting my checklist sorted. So I will be loosening fan shroud (and removing the rear trans mount) before gently lowering my trans a bit for better access. do I need to remove the fan from engine - or do I just unclip these metal clips from the shroud pictured here?

http://cdn4.pelicanparts.com/techart...mall/pic06.jpg

Re: Shroud
 

Yes remove those clips, And lift the shroud an inch or two upward to release the lower keepers (shroud tabs dropped into slots).

You want the shroud to just kind of hang around loose so it will move with the fan as you change the motor/trans pitch.

OK. So I had a bit of a frustrating saturday. I got to work with the car up on ramps, fan shroud disconnected, and I degreased and cleaned the area around the modulator. I removed the transmission bracket and carefully lowered the trans down on a jack about as far as it could go, being very careful and checking the engine position up against the firewall, etc.

Then I went to move the trans over as far as I could in the tunnel, using some wood to wedge and hold it - but I really couldn't get it to budge much more than an inch tops. I could see the modulator better now, but I could barely get my hand and an allen wrench in there, let alone be able to carefully withdraw the modulator straight out - so I abandoned for the time being - ran out of daylight.

Is my problem that I need to first disconnect the driveshaft at the transmission? Seems like that will be the only thing that would give me anything close to the side-to-side movement I'd need to get my hands in the space.

as always, thanks for any tips
-andrew

sorry to bump this - but have any folks her successfully replaced their trans vac modulator with the transmission in the car - and did they do it by disconnecting the driveshaft?

i want to re-attempt this weekend, want to do everything I can to make access more feasible in that area

Better weather is back so I'm back outside. Need some advice.

In order to reach my modulator for a replacement (and in addition to removing trans mount and letting it sag) I tried to disconnect my driveshaft for more wiggle room. But it seems nearly impossible to disconnect the shaft at the most forward flex-plate thing while the car is up on stands/ramps and the rear wheels are on the ground. I can't get access to all off the bolts/nuts because the shaft isn't going to rotate. Is there a good trick to do this? I've looked in the FSM and it's not really helping me. Am I missing something obvious?

Only way to rotate the driveshaft is to get one rear wheel up in the air, just enough so it'll spin.

-Rog

Following, is this similar on the 722.4 trans? I just ordered a shift kit and vac modulator

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

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?

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

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.

Update, lots more info, seeking wisdom/experience
 

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?

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.

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.

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.

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.

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.)