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Thread: Replacing Vacuum Modulator

  1. #1
    Senior Member jaymanek's Avatar
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    Replacing Vacuum Modulator

    Hi All,

    In an effort to try and sort my leaking transmission, I have been closely looking at all items bolted to the box with my borescope camera.

    I am now fairly convinced the leak is coming from the vac modulator.

    The initial source seems to be the forward most retaining bolt, but I cant see how fluid would escape from here, so most likely its the vac modulator itself leaking on that side.

    I could just try and replace the sealing rings, but the modulator is not too expensive as a kit. A1262709179.

    I cannot find any details on how best to set this item up.. Anyone have any tips on how to get it somewhere close to begin with? Or is it suck it and see?

    The trans is shifting great at the moment so dont really want to mess that up.

    Thanks

    Jay

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  3. #2
    .036 Hoonigan™
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    Re: Replacing Vacuum Modulator

    Jay, the modulator is a minor nuisance to R&R in the car, due to limited space to work. It may help to lower the rear of the tranny down a few inches to gain a bit more room, if needed.

    It's a fairly simple job, but be careful that the O-ring doesn't fold over as the modulator is pressed into place. If you have a spare transmission laying around the shop, practice on that first. Adjustment is trial & error but they are usually pretty close out of the box, assuming you get the correct modulator. There are multiple part numbers, each with different pressure ratings; 126-270-91-79 is correct for the 500E. Coarse adjustment is 1 turn, fine is 1/2 turn or less. You want zero flare at WOT upshifts, with acceptably smooth/quick part throttle shifts. You may not need to adjust it at all though.

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  5. #3
    Senior Member jaymanek's Avatar
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    Re: Replacing Vacuum Modulator

    Quote Originally Posted by gsxr View Post
    Jay, the modulator is a minor nuisance to R&R in the car, due to limited space to work. It may help to lower the rear of the tranny down a few inches to gain a bit more room, if needed.

    It's a fairly simple job, but be careful that the O-ring doesn't fold over as the modulator is pressed into place. If you have a spare transmission laying around the shop, practice on that first. Adjustment is trial & error but they are usually pretty close out of the box, assuming you get the correct modulator. There are multiple part numbers, each with different pressure ratings; 126-270-91-79 is correct for the 500E. Coarse adjustment is 1 turn, fine is 1/2 turn or less. You want zero flare at WOT upshifts, with acceptably smooth/quick part throttle shifts. You may not need to adjust it at all though.
    Thanks.. space is certainly a problem. I had to use various wobbly hex sockets to try and get to the bolt..

    I didn’t remove the actual modulator though. Will give it a go.

    I do have a w126 box on the floor to play with so will take a look.

    Thanks!

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  7. #4
    500E Terminus Illuminatus DerFuror's Avatar
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    Re: Replacing Vacuum Modulator

    The vacuum modulator oring was the source of a transmission leak on my tranny a few years ago. <-- link

    An incorrectly installed oring will eventually instigate a leak. For some reason, it appears some transmission repairers choose to install the vacuum modulator oring into its bore seat, rather than properly upon the modulator body.

    There are many potential sources for leaks in that general area of the transmission, and it can be difficult to pinpoint the failure source. I discovered my oring's condition upon physical inspection after removing the modulator from the transmission housing. I replaced this oring (and most all of the transmission orings/seals), and eliminated the leak.

    Your transmission may have a suffered a similar fate.
    " Destination ???, It's the ride that takes you there! "
    1993 500E W124.036 040/271
    1965 220b W111.010 Heckflosse

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  9. #5
    Senior Member jaymanek's Avatar
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    Re: Replacing Vacuum Modulator

    Replaced the part today... It was a little difficult due to lack of space and visibility.

    I did not have to make any adjustments, shifts are still nice and smooth as before.

    My leak is vastly improved. Afer a longish drive I am only getting a couple of drops on the floor. Before I was getting a small patch.

    That said, I still do have a leak.

    My next suspect is the shifter seal? The leak is certainly from the area of the modulator and NSS switch.

    I have ordered another seal for the modulator, just incase it didnt seat correctly and I will try to replace the shifter seal too.

    I am a little annoyed with my transmission builder.. All of this would have taken moments to replace when on the bench and all seals come as part of the rebuild kit which im sure he would have ordered.
    I didnt get charged a lot for the trans rebuild, so I guess he only did all the inside parts... But I asked him to go over the whole thing...

  10. #6
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    Re: Replacing Vacuum Modulator

    The shifter selector rod seal is a possible leak point... but that is a RPITA to replace. Need to lower the trans as far as possible (may need to disconnect exhaust, and flex disc) so the rod can slide out of the trans housing. Otherwise it bumps into the chassis and you can't remove it. Replacing the seal is even more fun. You can pack paper towels into this area to more positively identify the exact source, but you are correct, in that area it's pretty much either the modulator or the selector rod seal.

    If the trans was supposed to be rebuilt (which by definition includes ALL external seals!)... yeah... I'd be a little perturbed too. This stuff is a breeze on the bench, and miserable on the car. Photos below show the shaft sliding out so you can then mess with the seal R&R.

    Hopefully it's something else!

    Attached Images Attached Images

  11. #7
    Senior Member jaymanek's Avatar
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    Re: Replacing Vacuum Modulator

    Based on that, I am going to try another seal on the Modulator incase it didnt seat properly. Its easy to seat the modulator when transmission is out as you can put pressure on it. Its more difficult with it in position.

    If that doesnt cure it, ill revisit at a time when I can drop the transmission completely and replace every seal I can think of.

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  13. #8
    500E Terminus Illuminatus DerFuror's Avatar
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    Re: Replacing Vacuum Modulator

    Quote Originally Posted by gsxr View Post
    The shifter selector rod seal is a possible leak point... but that is a RPITA to replace.
    With my transmission leak, I replaced the selector shaft seal first (without removing transmission). Click here for the HOW TO. The factory seal driver is highly recommended for performing the task. My replacement was successful but, a bit later on, the modulator valve seal began leaking.

    At that point, I removed the transmission from the car & replaced most all oring/seals. For those unfamiliar with the replacement process, always lube the new orings with clean ATF prior to installation. Do not install dry.


    PS: On a trivial side note, (while reviewing the HOW TO) I see it was during this June 2014 timeframe that gsxr just beat me out of acquiring the last available fan shroud.

    It took me 4 years to finally acquire a pristine complete assembly. Timing is everything.
    " Destination ???, It's the ride that takes you there! "
    1993 500E W124.036 040/271
    1965 220b W111.010 Heckflosse

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  15. #9
    Senior Member jaymanek's Avatar
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    Re: Replacing Vacuum Modulator

    I think im going to be in a similar boat. If the second vac pod seal doesnt cure it, then over winter I will remove the whole box and just go through it myself. That way ill know its been done.

    For the moment, the leak isnt bad enough to worry about. I have other cars that drip more than this. Its just that I want to get it right given all the work this car has had.

  16. #10
    Senior Member jaymanek's Avatar
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    Re: Replacing Vacuum Modulator



    Guess what, I had pinched it. Yes I did use plenty of lube.

    Then I pinched another seal.

    On third attempt I had my colleague held an inspection camera whilst I lined up the seal. Very difficult to see the correct angle from underneath the car.. pushing at the wrong angle simply slices the seal.

    Anyway, after a test drive, totally dry!!

    Relieved!

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