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1999 e300 td 324000 miles
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Discussion Starter #1
I have a 1983 300d turbo, with a bad modulator on the tranny, what is the best way to replace it? it looks like it is very hard to get to the screws holding the modulator in place
 

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1982 300CD
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5,140 Posts
You can get a gear wrech set with an adapter for a screwdriver tip if that's what it calls for.

BTW, here's a little info I saved from somewhere...
12.) You must have a modulator pressure gauge to do this properly. YOU CANNOT "BALLPARK" MODULATOR ADJUSTMENTS!!!! A gauge can be made with a simple banjo fitting, a hollow bolt scrounged from a fuel injection system and a 100 psi gauge. I won't go into it here, but I can get the specifics for anyone interested in fabricating one for themselves. You also need to know the exact model of your transmission. This can be found on the casting edge just above the pan on the RH side of the transmission. You'll probably have to clean the area to find the numbers. It's in a XXX.XXX format, such as 722.305, for example.

Once you have this information you have to consult a TDM (Technical Data Manual) for the correct modulator pressure.

13.) Directly below the vacuum modulator on the transmission is a 12mm bolt. This is a test port for the transmission hydraulic system. Clean the area around the bolt and modulator well. Remove the bolt and install the hollow bolt and banjo fitting on the end of the modulator test gauge. Remove and cap off the vacuum line from the modulating valve on the injection pump. You don't want a vacuum source on the transmission modulator during tests unless the TDM dictates it. In most cases it won't.

14.) With the proper modulator pressure determined from the TDM and speed that it is to measured at, road test the car while checking the pressure. If it's incorrect modulator pressure will have to be adjusted.

15.) To adjust modulator pressure, remove the black rubber cap on the top of the modulator. Inside there will be a small metal "T"-shaped "key". Pull it out slightly to disengage the top of the "T" from the modulator body. This is what keeps the adjusting pin from turning when the cap is in place and the "T" is fully inserted. With the "T" pulled out to disengage the top portion turn the "T" to increase or decrease pressure as desired. You can do this with the engine running and someone watching the gauge while you turn, or with the gauge in your field of vision. The setting at idle will be pretty close to the setting you get during the road test, amazingly enough.

Put the "T" back in place, replace the rubber cap and road test the car. Don't reconnect the vacuum line!!

16.) Repeat above procedure to achieve the proper modulator pressure. If you can't or shifts are still flaring or harsh, the modulator should probably be replaced (more about that in a minute.)

REPLACING THE MODULATOR:

If the modulator is the original one on the car it could probably stand to be updated. One way to tell is that the updated modulators have a green plastic body and a black cap on the adjusting "T". Order a new modulator from your parts supplier (part #126 270 9279 for an 83 300SD - Ed). It should come with the new modulator and a long black pin. The adjusting "T" and rubber cap will be included loose in a bag with the modulator.

1.) With the area around the modulator cleaned, remove the two 10mm bolts that hold the plate that holds the modulator in place. This is a flat metal plate that indexes in the slot on the neck of the modulator. Getting to the two bolts takes a little bit of gyration, but a 1/4" drive socket can do it. Move the plate out of the way and carefully pull the modulator out of it's hole. You may have to twist it a bit to get it to move. Pull it straight out of the hole, DO NOT ROCK IT!! Using a pair of needle nosed pliers or hemostats remove the pin from the hole where the modulator was located if it doesn't come out with the modulator. Note the way the pin was installed, as there is a little disk that's off center on the length of it. You need to know this when installing the new pin. BE CAREFUL!!! Don't break the pin off in the transmission or you'll be spending a lot of time trying to extract the pieces.

2.) Lubricate the "O"-ring on the new modulator with a few drops of ATF before installing. Place the new black plastic pin in the bore in the same direction and orientation the old one had (I think there's a small disk on it that's off-center on the length of it. I suspect it's to keep the pin centered in the bore. That's what I'm referring to.) NEVER reuse the old pin, as the new pin is a part of the update!! Carefully insert the modulator, twisting slightly if necessary, but ALWAYS keeping it perpendicular to the hole. If you don't you'll risk shearing the "O"-ring off.

3.) Once the modulator is installed put the metal plate back in place, install the bolts and torque to the correct values. Check modulator pressure as directed in step 14. Adjust as necessary.
__________________

I'll see if I can find the pressures for the modulator for you. I think I have those too somewhere.
 

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1982 300CD
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5,140 Posts
Modulator adjustment

Here's another post I've saved. I think this was from Mercedesshop.

Modulator Adjustment DIY - measure it the 'right' way

Why do you need to do this?: You need to do this to properly check the internal hydraulic pressure of the transmission, either during a debug OR you must do this after installing a new modulator (my case).

This only applies to automatics. You manual tranny people have it too easy anyways...

Overview: You are going to connect a psi gauge to a test port on your transmission's underside near your vacuum modulator. Then, turn the car on and make some adjustments, and then remove the gauge and you're done.

Theres a lot of talk about this on the forum - you NEED to set the pressure correctly. There's a right answer - it's not a rule of thumb or by feel measurement.

Time once you're ready to go: 60-90 minutes

Materials required:

- 12mm socket and socket wrench (I used 1/4" drive)
- 1 banjo bolt scrounged off of an ALDA on a yard car. I grabbed mine off of a later turbo model. The ALDA is the square unit on top of the injection pump on a turbo model. There is a banjo fitting leading into the ALDA from some clear tubing. Thats the one you want. Take the hollow bolt, two washers and banjo fitting
- a few feet of 3/16" ID vinyl tubing rated for 60 psi or more. I got mine at my local hardware store.
- a 0-100 psi gauge. I also got mine at a hardware store for $10. It had a 1/4" NPT fitting.
- 1/4 NPT to hose fitting adapter.
-some brake cleaner and paper towels for locating your transmission ID #
-teflon tape for NPT fitting
-ramps for front wheels. Jackstands can work too.
-chocks for rear wheels
-TDM printouts that are attached to the next post.

Gauge assembly:

-take your scrounged ALDA banjo bolt and hollow screw and clean it really thoroughly with brake cleaner. Clean it some more. Transmission fluid is going to go into this fitting, and then get sucked back into the transmission. You want this thing clean! Let it dry for a little while.
-attach your gauge to the hose fitting using some teflon tape.
- push the the ends of the vinyl hose onto the hose fittings on the gauge and the banjo bolt.
-make sure everything looks nice and tight. This stuff will be under 50-80 psi.
-wrap a plastic bag around the banjo bolt (keep it clean!) end of your gauge assembly and bring it to the car

The Main Event:
- make sure you have the right fluid level in your transmission.
- put front wheels on ramps. Jackstands can also work, but get them up high! Im a thin guy and I really appreciate the extra height the ramps give me.
-put e-brake on and chock the rear wheels. Safety first...
-turn car off and put in P.
-first you need to identify what exact model transmission you have. You can find the transmission ID on the passenger side of the tranny. It is located on a flat right above the front of the pan. You probably will ned a paper towel with a little brake cleaner to clean the area off. It may be obstructed a little bit by your exhaust pipe, but its there I promise. You are looking for a number that begins with 722.xxx
-before you get too dirty consult the TDM printout for your proper reading. I have a 722.315 and my number was 2.9 bar. Write down this number and concert it to psi. 1 bar = 14.5 psi.
- get under the car on the drivers side. You are looking for your vacuum modulator. Mine is green. Yours may be red or black. It's above the pan - you have to get right up under the transmission to see it.
- a little below and to the rear of the modulator is a 12mm bolt. This is your test port. Unscrew the bolt and put it to the side somewhere...you guessed it..Clean!.
-screw in your banjo bolt. Point the hose up and to the rear of the car. BE VERY CAREFUL to seat the bolt correctly. Check again. If you dont, fluid will spew everywhere when you do the test. Dont ask me how I know!!!!
-snug it down, but do not overtighten.
-look at figure 2 - this is how it looks, but you wont have red fluid in the line yet.
-check everything again, and crawl out from underneath the car.
-plug the vacuum line that dives down to the transmission from the engine compartment.
-start the car. Quickly look down and check for leaks. I bet all is well.
-look at figure 3. This is what you will see. Fluid will be running down the tube, but wont make it to the gauge. A pressure reading will be registering on the gauge - figure 1. This is normal - I thought it wasn't at first and got concerned.
-what you need to do next is make the adjustment. This is done on the modulator itself. There is a little black plastic cap that hides a t handle. To make the adjustment youll need to pull the cap off, pop the T handle out a little bit and screw IN to RAISE pressure, and screw OUT to LOWER pressure. Adjustment is a little bit at a time. I turned my t handle half a turn to lower is 2 bar. I did this with the car on above me - it was easy this way.
-NOTE: the TDM says to do this test at 50kmh while driving. BUT, every reptuable Benz mechanic I have talked to says the same reading can be obtained in park. Thats how they all do it. It sure is easier. I dont wat to think about trying to rig up a drivable version of this.
-the adjustment doesn't take long if you do it with the car running.
-once the correct reading is achieved, let the car idle for a bit and make sure the reading is nice and stable after the transmission is at operating temperature.
-turn the car off.
- take off the banjo bolt, reinstall the 12mm plug bolt. re install the modulator rubber cap. reconnect the vacuum line.
- remove chocks, take car off ramps. test drive the beast.

Enjoy!! You can now continue your transmission debug. Make adjustments by other means (VCV, orifices etc.), NOT by the modulator any more - your work here is done.



722.112 - 3.8 bar
722.117 - 3.0
722.118 - 3.0
722.120 - 2.8
722.122 - 3.8

1981 -
722.300 - 2.4
722.301 - 3.5
722.303 - 2.9
722.304 - 3.5

1982 -
722.300 - 2.8
722.303 - 2.9
722.309 - 2.8
722.310 - 3.7
722.312 - 3.7
722.315 - 2.9
 

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Premium Member
1999 e300 td 324000 miles
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3 Posts
Discussion Starter #5
thanks for the information, it is very helpful and I will let you know how it goes when I get the nerve to start it
 

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banjo bolt

Hi Greg,

Great post! Do you know what size banjo bolt it is? Ive been to a few junk yards around here and there are very few mercedes, even fewer with a diesel engine and I still havent found one with turbo (ALDA).

I found a few options on ebay, can you tell me the thread type/size on the banjo you have? I appreciate your help.

Banjo Bolt Kit M10x1.25mm T517Z T518Z Turbo Oil Feed

Banjo Bolt Kit M10x1.25mm T517Z T518Z Turbo Oil Feed: eBay Motors (item 380243646845 end time Jul-17-10 07:21:57 PDT)

Banjo Bolt Kit M12 x 1.5 GARRETT GT12 VOLVO SAAB Turbo

Banjo Bolt Kit M12 x 1.5 GARRETT GT12 VOLVO SAAB Turbo - eBay (item 270435215111 end time Jul-24-10 07:54:18 PDT)
 

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1984 300D
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5,070 Posts
I have read on the various forums that it is common for the Plastic Modulator Ping to break when you are removing the Trans Modulator.
They advised have a new one on hand before yous start the job.
 

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1981 300TD 360k--1966 230 165k--1970 280se 172k
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You'll make it easier on yourself if you drop the transmission mount bracket and the carrier bearing bracket and let the trans sag down to the limits of the engine mounts. It would be a good idea to disassemble the throttle linkage to prevent damage. Be sure to use a jack under the trans pan to do the lowering.

I just completed this job and I second the cautions about pulling the old one out as straight as possible.

My new green modulator came with a different pin design than the old one and a different cap. The new cap appears to have a ring of slots that holds the T handle into position once adjusted.
 

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You'll make it easier on yourself if you drop the transmission mount bracket and the carrier bearing bracket and let the trans sag down to the limits of the engine mounts. It would be a good idea to disassemble the throttle linkage to prevent damage. Be sure to use a jack under the trans pan to do the lowering.

I just completed this job and I second the cautions about pulling the old one out as straight as possible.

My new green modulator came with a different pin design than the old one and a different cap. The new cap appears to have a ring of slots that holds the T handle into position once adjusted.
Hi! Do I still need a banjo bolt to check the pressure if I let the tranny down a little as you specified for changing the modulator or will there be enough clearance for that?

Thanks!
 

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1981 300TD 360k--1966 230 165k--1970 280se 172k
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Yea, you'll need a banjo bolt to check the pressure. I took it off the alda of a parts car I own. I checked the pressure with the trans sagging, but I think it would be possible to reach the bolt with the trans fully mounted.

I was lucky. The new modulator came out of the box with the correct pressure. It looks like I wasted my money and time assembling a pressure gauge setup. You could just install the modulator and drive the car to see how it shifts. Adjust the modulator for crisp shifts without the vacuum hooked up, then hook up the vacuum and see if you like it.
 
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