I have noticed really hard shifts recently so I checked for vacuum leaks and it seems like I'm getting a pretty good leak at the line that goes to the transmission itself. I'm guessing that's the vacuum modulator.

Is there any way to fix this?
thanks,
Nick

__________________
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Yes, you replace the modulator......

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I need to address this same problem in my 84 300D. I have read that there is an O ring in the modulater that accepts the vacuum line coming in. Can the O ring be replaced or is the modulator sealed and not servicable?

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It may not be the modulator, it may just be the little rubber cap that covers the shift-firmness adjustment. If it falls off/dries out/cracks it will leak out vacuum. A new one is like $1.25.....check the condition of that little rubber cap first! A modulator is messy and annoying to replace and costs almost $50. I actually did have my modulator fail and the symptoms of that are usually really soft/sliding shifts rather than real hard.

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What the what? Vacuum can leak out of that little cap!? If that's true then I just ordered a modulator that I don't need! My cap is ripped down the middle, but still attached... bummer! Also, I forgot to order a new cap. Sure the part is 1.25 but the shipping is like $10!

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Assuming you pulled vacuum from the engine bay.

Don't rule out the line itself either.

Interesting about the cap. I did not know that?

__________________
AJ

1985 300D (SOLD)

If your current modulator is original, you can bet that you need a new one.

A new modultor should come with a cap. But you will likely need a new modulator pin. It's tough to avoid breaking the installed one. If you can't afford to have the car out of service, I would recommend having a new pin on hand before you remove the modulator.

http://catalog.peachparts.com/searchitem.epc

The o-ring on the modulator seals fluid, not vacuum.

Didn't see the pin at that link... where does the pin go in the install?

__________________
'90 300SE --- 173k miles --- (Odometer just stopped working!)

'85 Cali 300D --- 193500 miles --- (Second one) Sold Nov '10

'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09

Look for part #126 277 93 75.

Ah, found it. Where does it belong in the install? Attached under the modulator?

__________________
'90 300SE --- 173k miles --- (Odometer just stopped working!)

'85 Cali 300D --- 193500 miles --- (Second one) Sold Nov '10

'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09

Yes. Think of it as a "push rod." Unless you can pull the modulator straight out of the transmission, you are likely to snap the original pin in the process of removing the modulator.

Dang! My modulator will be here tomorrow, and I didn't order a pin for it....

Does anyone know where I can get a pictorial of the modulator removal?

__________________
'90 300SE --- 173k miles --- (Odometer just stopped working!)

'85 Cali 300D --- 193500 miles --- (Second one) Sold Nov '10

'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09

Two bolts secure a retainer plate. Remove bolts, plate and vacuum line. Pull the modulator as straight out as possible. "Rocking" the modulator back and forth is all but guaranteed to break the pin.

Lowering the transmission crossmember will afford improved access.

My 1983 300D had the same shifting problem, tracing vacuum with
Mighty Vac I thought modulator was bad too.

Just the cap. I made a new cap.

Black RTV silicone, a dime, a model car tire.

I would imagine a cap could be made from all different possible materials.

So now I have a new spare modulator in the box.

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