Transmission Vacuum Modulator Valve

[brettj]

Changed the transmission fluid and filter in the 450SE today. The transmission has been at times slow to change gears and sometimes shifts hard. I did notice that my vacuum modulator was covered in rust. Are the symptoms of my transmission indicative of a bad modulator? Are these valves easy to purchase or will it be a major expense like a manifold pressure sensor? Is replacing this valve a simple job?

[WGB]

If it is covered in rust it will be the old metal type.

It modulates the oil pressure on the automatic.

New replacement is plastic and cost me $67.95 from autohausaz.com 6 weeks ago.

See the thread I started here a few weeks ago on fitting it without a gauge to set it.

Bill

[oscar]

Metal ones are still available for 73-76 models and cost about $10 more than the plastic ones at autohaus.  I don't know whether plastic ones can be fitted to the older model transmissions or not.

If your modulator has gone, the classic sign is of white smoke at idle as auto trans fluid is sucked through a perforated diaphragm into the intake.  If you're not getting white smoke at all but still getting hard shifts, thoroughly check the vacuum hose running from the modulator back to the engine.  When my vac hose cracked wide open near the banjo fitting on the modulator my trans was very hard on the downshift between 2nd and 1st.   If you do decide to replace the modulator regardless, make sure you don't loose the pin that goes into the trans housing and may be loosely connected to the modulator. 

I found it hard to undo the modulator on mine because it was on so tight but it is only a matter of undoing the vacuum connection then unscrewing the modulator making sure the pin comes with it.  Place the pin in the new modulator and screw it back on.  I remember loctite or something similar being recommended to hold the pin to the modulator before you screw it in so you don't loose it but mine was a snug enough fit I didn't have to worry about it.

If there's still hard shifting after the vac hose and modulator check out fine and/or have been replaced, you could add some A/T conditioning fluid and if that doesn't work you might be looking at an overhaul.  Either to clean it out or more likely to replace the friction discs.  They don't cost much but the work involved is basically a rebuild which would involve a decent labour cost.

[brettj]

I saw the AutoHaus modulators and thought that they looked like the metal one that is in my transmission.

Oscar, I think you just solved another problem that the 450 has, tons of white smoke coming from the exhaust. Usually the smoke comes comes out pretty heavy at cold start and once the motor warms up it disappears. Occasionally I see it very lightly when the motor is warm.

Where can I find a transmission diagram of the modulator and vac hose? Looked in the service manual library and couldn't find anything. I found the modulator and what looks like the pin in my illustrated parts manual but that diagram is not very helpful.

[oscar]

Have to make sure this white smoke isn't vapour.  Is the white smoke you see a vapour like a fog or does it hang round and wont dissipate.  That's the big difference with white smoke and white vapour.  Not to mention the smell.  A/T fluid burning stinks.  Next time you start up cold, stand near the cloud and take a whiff.  Don't over do it of course but you should be able to tell the difference if it smells like ordinary exhaust fumes, probably a little rich, and exhaust that's burning A/T fluid.   Also check to see if you're loosing A/T fluid.

I'm not sure where a modlulator diagram is.  I know Haynes has nothing on them.  Here's a pic though of mine taken last year.  it's a prick of a place to get to so far as you have to jack the car up and put it on stands and then it's still hard to get a decent photo.  I'd previously replaced the modulator but obviously had extended the angle of the banjo connector to the vac hose too much.  The vac hose was cracked wide open leading to really sudden shifts. 

If I were you I'd undo just that banjo fitting and vac hose connected to it and inspect the inside of the vacuum hose and inside the modulator where the banjo connects to.  If there's a hint of A/T fluid in it, you'll know the modulator is bad.

[brettj]

It seems that the white smoke most likely is water vapor as I  notice a lot of water coming out of the tail pipe as well. The smell from the exhaust has not changed at all being your normal exhaust gas odor.  Perhaps my modulator is just starting to go? I have not noticed a loss of transmission fluid.

When you replace a modulator and vac line do you have to adjust it? I just changed the trans fluid . Will I have to drain the fluid again to change this valve?

[oscar]

No.  I can't see how anything can be adjusted although apparently there are differently sized pins available.  That's the only variable for these modulators.  You can safely unscrew the modulator and put another one on without doing anything to the fluid.  The fluid will be all in the pan and the torque converter.  Apart from a couple of drips I didn't have any fluid pour out.  The modulator is above the fluid level.  Changing the modulator as a precaution and to rule that piece of equipment out as being faulty isn't a bad idea.  It's what I did.

As for the water vapour thing.  If it's really cold in your neck of the woods at this time of year I wouldn't be too concerned however I would keep an eye on your coolant level.  Worst case scenario is if it is excess moisture that's causing the vapour then it's possible there's a head gasket leak.  Check you oil for a milky appearance too.  Personally I think it's just because it's winter over there.

[koan]

The transmission has been at times slow to change gears and sometimes shifts hard.

As oscar says the hard shifts can be a bad vacuum modulator or a leak plumbing in the plumbing between the vacuum modulator and the inlet manifold.

"Slow to change", that can be interpreted a couple of ways.

If it means it holds on to gears tool long when lightly accelerating your throttle position rod or cable needs adjusting.

if a manual  gear change is delayed, say moving the selector from D to 2 doesn't change instantly that's pretty normal, the book says up to 2 seconds.

The serious one is long drawn out change where a 1-2 or 2-3 shift takes time to complete with the engine revs increasing during the shift (known as "flaring"), that's an indication that the seals on the pistons and clutches are getting old and stiff. A fluid change might help for a while. Hard changes when cold that improve when warm indicate the same thing.

koan

[brettj]

Thanks for the replies.

Oscar, I agree that changing that old modulator is a good idea. The casing is very rusty which my not be an indication that it is gone but since everything that I am replacing is original equipment it may well be time.

As for the water vapor, it has been a brutal winter here in Massachusetts. Today we had our 15th snowstorm of the year  with another 10 inches of snow! My car has been taken out of the garage and really  driven only short distances of about 10 miles since December.  I imagine a lot of condensation has built up in the motor. The oil is never sludgy but I did notice sludge on the oil cap last week. I took the car in for service on Saturday We changed the oil but before doing so let the car run for about ten minutes with a treatment of engine sludge remover, drained the old oil and then put in new oil and oil filter. Hopefully that's the end of the sludge. I think the water vapor issue will end once it warms up and I start driving the car on a regular basis again.


Koan, The transmission seems to take too long to shift in a situation like this, when you pull out of a driveway and accelerate slowly to increase speed in the street. The motor does not seem to rev up or peak in this situation. Nor does it give you a hard shift.   I think I've adjusted the throttle rod in the past.  If you move the rod forward that will quicken the shift or was it backwards to quicken the shift ?

[koan]

The transmission seems to take too long to shift in a situation like this, when you pull out of a driveway and accelerate slowly to increase speed in the street. The motor does not seem to rev up or peak in this situation. Nor does it give you a hard shift.

Does it improve when the car is warmed up or does stay like that?
If it stays like that it's probably just the throttle rod

I think I've adjusted the throttle rod in the past.  If you move the rod forward that will quicken the shift or was it backwards to quicken the shift ?

It's easy to work out. if the rod is adjusted so it moves more in direction of opening throttle the changes will be held longer, you need to go the other way.

koan

[brettj]

The changes seem to stay about the same whether the motor is cold or warm.  I'll take a look at the rod adjustment.

[Big_Richard]

Also, with that rod, when its disconnected, if you rattle it, it should not make a metalic clanging noise to where it connects on the transmission. it should have quite a firm grip down there. Id say 99% of w116's have the bushing totally disintegrated on the end of that rod where it connects to the transmission.

Without it, correct adjustment of the rod will NEVER be acheived.