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  #1  
Old 07-22-2007, 02:32 PM
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1987 300SDL Vacuum Woes (really tight shifts)

Good Morning All,

First off let me say that I ran across this site by accident and have so far found it to be a tremendous help. I'm finding though that there's almost TOO much information out there and I'm having trouble deciphering it.

Let's start from the beginning. I bought this 1987 300SDL at the beginning of the week so I don't have a lot of experience with the names of components.

The MAIN problem: The transmission makes full throttle shifts even at partial throttle. They're super tight and cause lurching in every gear. It also holds in each gear for what seems to be an excessively long time. So... after researching a bit here, I've come to the conclusion that there's an issue with the vacuum modulator. And so began my vacuum woes!!! Mercedes and their darn vacuum actuators.

With Mighty Vac in hand I went searching and found so many leaks, I just don't know what to do.

Here's what I've got so far:
1) disconnected line to vacuum modulator (on trans) and pulled vacuum, it holds. Pulled vacuum on vacuum amplifier (? -- it's the blue thingy with all the 4 ports mounted to the driver's side fender (see pic)).

That's where the good ends.

The vacuum pod attached to the diesel injection system (see pic) will not hold vacuum, but from what I've read, I don't think it's supposed to... How do I test this thing??

There is a pressure line from the intake manifold to a 3-way switch that then goes into the bottom of the (blue) vacuum amplifier. How is this supposed to work?

Coming from the vacuum pump, there's a big line that goes to the brake booster, and tees off for the engine stop switch. I repaired the leak in that system, so this branch is golden!

Also coming from the vacuum pump is a smaller vacuum line that splits 4 ways: 1) EGR 2) Intake bypass something-er-other 3) Cabin vacuum accessories (climate control) 4) Transmission

1) and 2) leak at the valves under the air box, won't hold vacuum, how do I test these valves?? how are they supposed to operate??

3) Cabin vacuum: turned off very small leak, defrost very small leak, all other BIG leak. The dash has to come out to replace (cracked, so I figure I'll fuss with the climate control stuff later.

4) with 1, 2, 3 disabled I turn my attention to the transmission. First I need to test these actuators to figure out if they're working properly. If I need to replace it... what is it called??

Thank you very much to anyone who can help!!!

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1987 300SDL Vacuum Woes (really tight shifts)-img_6415.jpg   1987 300SDL Vacuum Woes (really tight shifts)-img_6416.jpg  
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  #2  
Old 07-22-2007, 02:34 PM
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Quote:
Originally Posted by Garrett90250 View Post

The MAIN problem: The transmission makes full throttle shifts even at partial throttle. They're super tight and cause lurching in every gear. It also holds in each gear for what seems to be an excessively long time. So... after researching a bit here, I've come to the conclusion that there's an issue with the vacuum modulator. And so began my vacuum woes!!! Mercedes and their darn vacuum actuators.
Welcome to the forum.

This is not a vacuum problem.........although you may also have additional vacuum problems............

Find the kickdown switch beneath the accelerator pedal and unplug it. Take the vehicle for a drive and report back.
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Old 07-22-2007, 03:18 PM
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**Correction**

I unplugged the kickdown switch and took it for a drive, then plugged it back in to compare... No change. However, I should correct my original statement as it does NOT hold it in a gear for an excessively long time. It will shift as low as about 1500 RPM and the 3-4 shift will happen even sooner. Full throttle and the shifts occur at about 4500 RPM.

The crispness of the shifts is still VERY harsh at every shift in every gear regardless of speed or throttle position.

It's also a serious dog right off the line, but as soon as the turbo spools up, it hauls! I've read a bunch about an adjustment to the ALDA, but don't want to touch that till I have the vacuum issues taken care of... Could poor vacuum cause this?

Given my revised explanation, does this look like a vacuum issue or is there something else I should be chasing?

Incidentally, thank you VERY much for the QUICK response!
-Garrett
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Old 07-22-2007, 03:27 PM
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Bad data wastes your time and mine.........with meaningless exercises that don't accomplish anything. Naturally, the kickdown switch is fine, because you don't have any symptoms of a bad kickdown switch, once you revised the post.

Go under the hood and find the vacuum pump. Follow the small line to a five way split. Two of these lines go over to the right side of the engine and two lines go over to the left side of the engine near the IP.

Disconnect the two lines that go to the right side of the engine and cap the two openings in the five way splitter.

Look for any old and cracked vacuum lines from the splitter all the way to the various devices on the left side of the engine, including lines to and from the vacuum amplifer (blue flying saucer). Any soft or cracked hoses must be replaced. If the hoses are original, replace them before returning for any more discussion.
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  #5  
Old 07-22-2007, 03:43 PM
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Thank you! My apologies for my original mis-information.

Openings on the right side (to EGR etc) capped. I've plugged every line on the left side of the engine, and specifically located and replaced each of the problematic vacuum lines and fittings.

I got to the point of isolating the components and found myself a bit stumped as I clearly don't understand how the vacuum amplifier or the vacuum component mounted near the injection pump (one with the red hoses going to it in the pic above) work.

The Mighty Vac will pull and hold a good vacuum from the vacuum amplifier to the transmission and the vacuum amplifier will hold vacuum when applied to the port in the center on the top.

So I'm pretty sure the point I'm sitting at now is that I have the transmission portion of the vacuum system isolated (hopefully), have tested all of the associated lines independently, and have tested the top side of the vacuum amplifier.

Any ideas on how to proceed?
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  #6  
Old 07-22-2007, 03:54 PM
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Quote:
Originally Posted by Garrett90250 View Post
I've plugged every line on the left side of the engine..........
I'm not following this statement. The left side of the engine contains all the controls that are necessary for proper transmission function. If you plug any lines that lead to the left side of the engine, the system won't function as designed.
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Old 07-22-2007, 04:50 PM
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More Description

rather than plugged I should have said, isolated the line without any components and vacuum tested that portion to ensure that there aren't any leaks in the line.

Problem solved-ish

Found a leaky y-coupling. All the vac lines and couplings on the left side of the engine have now been replaced and I've been able to verify vacuum level to the transmission both before and after the vacuum amplifier while driving.

Before the amplifier, I am reading a pretty steady 20-23 in-Hg.
After the amplifier, but before the green damper thingy, I read about 10-12 in-Hg that will then drop to zero during full throttle higher RPM acceleration.

Do these readings sound correct?
What about the stuff on the right side of the engine?

Thanks again!
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Old 07-22-2007, 05:21 PM
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Quote:
Originally Posted by Garrett90250 View Post
Before the amplifier, I am reading a pretty steady 20-23 in-Hg.
After the amplifier, but before the green damper thingy, I read about 10-12 in-Hg that will then drop to zero during full throttle higher RPM acceleration.

Do these readings sound correct?
What about the stuff on the right side of the engine?

Thanks again!
Those readings are fine. The harsh shifts should now be eliminated.

The right side only concerns EGR and ARV operation, neither of which you'll be concerned with.

Now, remove the ALDA completely from that vehicle and watch the transformation at low rpm's. Do a search under my name and "ALDA" to find the thread relating to this task.

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