installing new transmission vac modulator

[kuene]

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.

[SD Blue]

Here is an excellent write-up for the W123:
W123 Modulator Adjustment DIY - measure it the 'right' way

[kuene]

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.

[Carpenterman]

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.

[dieseldan44]

^^^ 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)

[SD Blue]

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.

[kuene]

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?

[chasinthesun]

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.

[kuene]

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?

[86-300sdl]

Originally Posted by kuene

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?

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.

[kuene]

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

[kuene]

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

[kuene]

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?

[Rogviler]

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

-Rog

[diesellover 92]

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