Hello everyone:

I have read many posts relating to hard shifts and read in detail the page by Steve Brotherton regarding tuning vacuum for the trans modulator.
My transmission shifts are hard when everything warms up and are especially hard when cold. I have measured vacuum at the vacuum amplifier port to the transmission and get about 7" of vacuum constantly to near full throttle. When floored to full throttle I get a great downshift and vacuum goes to about 1". Overall though the vacuum level stays constant through normal acceleration , just increasing to about 8" or so at higher RPM's. I see no decrease in vacuum as should occur with normal speed increase or as I depress the pedal further down. I have also measured the vacuum feeding the amplifier from the variable vacuum control on the IP and get about 12".
What I am thinking is that I have no vacuum bleed off by the vacuum control on the IP.
My understanding is that the vacuum to the trans should decrease proportionately as the accelerator is depressed and that I should get less and less vacuum.

Any thoughts or comments would be greatly appreciated.
Thanks.

I found my problem . The ARV and EGR vacuum circuits had significant vacuum leaks to prevent the VCV and amplifier to reach high enough vacuum level to control the modulator vac level by bleeding off through the VCV.
I have since plugged off the the EGR and ALR lines and am getting very nice shifts.
Since I don't want to recirculate exhaust to intake or reduce boost by shunting intake air past the compressor , this was a much needed "repair" .

Yep, that's a common problem with the EGR system.

For reference, can you kindly take a vacuum reading at idle on the TRA line to the modulator and post it on the thread.

I'd like to get some additional data on this vacuum level.

TIA

I'll get the vacuum values posted as soon as I get a chance. I still need to adjust the VCV at idle to the MB spec of 385 mbar +/- 25 mbar.

Do you have any more info on your problem, I'm under the understanding that I'm having the same problem in my 87 300sdl too.

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The problem as described in my previous post was simply that the shifts were too hard in all gears.
The objective is to get the vacuum at the modulator - -from the vacuum amplifier to drop from the idle value to about 0" at full throttle. This produces smooth shifts - usually ..... with everything else working correctly.
To address the problem you should first check your vacuum circuits attached to the transmission vacuum amplifier as well as the pressure to the vacuum amplifier. If you do not have a stable vacuum of 10.6" to 12.1" at idle at the transmission port on the vacuum amplifier then you need to start isolating the vacuum lines to determine if you have a vacuum leak and where it is coming from. You should as well check the the line coming from the VCV (vacuum control valve) to the vacuum amplifier when you have fixed any vacuum leaks. This is the vacuum line that has the green damper in-line to the vacuum amplifier. Check the green dampers as well as they do sometimes leak at the seams. This vacuum line at idle should have a range as listed above per MB specs and should decrease as you increase engine speed. The manifold pressure port at the bottom of the vacuum amplifier can be checked by placing a tee in the ALDA line (ALDA is on top of the injection pump). This will also tell you if your switchover valve (over-boost safety control) is getting a supply from the intake.
The ARV is the Air Recirculation Valve on the turbo found on California cars - not Federal cars normally. The EGR is the Exhaust Gas Recirculation valve.
The ARV and EGR are by controlled 2 vacuum transducers that are located on the passenger side of the engine under the air cleaner and that are connected to the vacuum pump by a 5 way vacuum connector near the top of the vacuum pump.
By disconnecting the ARV AND EGR lines from the 5 way vacuum connector at the vacuum pump and plugging the ports in the connector that go to the ARV and EGR you can isolate that side of the vacuum system and fairly well check the VCV, Trans Vacuum , Switchover valve lines etc...
You need to verify that all is OK on the trans vacuum side of the system. You can as well for "Analysis" keep the ARV and EGR lines from the 5 way connector disconnected and/or plugged and keep the ports on the 5 way vacuum connector plugged that supply the ARV and EGR.
The VCV is adjustable to set at idle and full throttle ( 0" ) vacuum output to the vacuum amplifier. The VCV bolts (top and bottom) are loosened and the control can be rotated to adjust the vacuum level created by the VCV.
The actual vacuum you measure at the transmission port of the vacuum amplifier could be as high as 17" depending on the different vacuum levels you have supplied to the amplifier and the pressure level from the manifold.
The transmission modulator is the other adjustment that can be performed after you have fixed all of the supply systems to the vacuum amplifier. The modulator is adjustable by removing the cap on the modulator and slightly pulling out the "T" shaped adjuster to rotate the element in the modulator counter clockwise (usually) to soften the shifts. Do this in small increments - like 1/4 turn or so and recheck shifts. Be sure to re-seat the adjusting "T" in the modulator and replace cap. The old style modulators had slots cut into the shoulder that the "T" sets into. The newer modulators have the slots to hold the "T" in the cap.
You may not need to do this if you have corrected a vacuum leak where you have incorrect vacuum or vacuum that is not variable to the transmission modulator.
Another bit of info, some very precise individuals measure the modulator pressure to set the modulator correctly. This probably is not be necessary especially on an older transmission. I would try the vacuum checks first then if your shifts are still hard, adjust the modulator. Be sure that your transmission is correctly filled with fluid.
On my 300SDL at near full throttle I get get about 1" vacuum - gauge error.
Below are links to the vacuum diagram for the 603.961 CA version.
One is large enough to print and the other is for web viewing.
If you need more info let me know.
http://www.mesaswest.com/om603/vac/603961cavac_print.jpg
http://www.mesaswest.com/om603/vac/603961cavac_small.jpg
http://www.mesaswest.com/om603/vac/603961cavac_legend_small.jpg
http://www.mesaswest.com/om603/vac/603961cavac_legend_print.jpg

Attached Thumbnails

 

If your SDL is a Federal of course you will not have the Air recirculation valve on the turbo but you will have the EGR. The vac transducer for the ARV will be gone as well. The vac diagram is virtually the same for California and federal .
If you need the vac diagram for the federal version I can post a link for that as well.

Hello Brian:
Finally got a chance to get vac readings.
At idle on the amp. port to the trans 15" Hg.
On the VCV line to the amplifier 11.25" Hg.

Chuck

__________________
1986 300SDL 201K Daily Driver
1984 300D In Progress
1989 240GL 196K Swedish Brick
1984 300SD -- Sold 289K
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That's quite high.

Are the shifts soft and slow?

The shifts below 2K rpm are not really soft, I would say smooth and not slow.
As rpm levels increases above 2K, shifting becomes a bit firmer.
My understanding from the FSM is that the vacuum level from the VCV
should be about 11.3" Hg +/-. From reading the Brotherton essay regarding this I understand that the output to the trans could be as high as 17" Hg.
Perhaps I misread Brotherton.

__________________
1986 300SDL 201K Daily Driver
1984 300D In Progress
1989 240GL 196K Swedish Brick
1984 300SD -- Sold 289K
------------------------------

Below is what I was referring to in my previous response regarding 15" Hg at the modulator - quoted from Continental Imports by Steve Brotherton -
http://www.continentalimports.com/ser_ic20242.html

"The most important modification came with the 1985 model and is continued on all subsequent ones. It involved the addition of a vacuum amplifier to the system (see Fig. 7). The amplifier takes a large vacuum supply, the proportioning vacuum signal and a boost signal and creates the final signal to the transmission. This device did two things. First, it incorporated the input of boost to further tailor the load control of the modulator vacuum signal. The vacuum at the modulator now starts high - 12-17 in. - and is reduced to about five inches through straight throttle movement. As boost builds, the vacuum is further reduced to zero only at full boost. "

__________________
1986 300SDL 201K Daily Driver
1984 300D In Progress
1989 240GL 196K Swedish Brick
1984 300SD -- Sold 289K
------------------------------

I mention that it's high based upon all of the previous vehicles that I have encountered. Most run in the 12"-14" range. If there is no flaring and the shifts are comfortable for you............then there's no issue.

When Brotherton mentions 12"-17", he also is tapping his experience. However, I find it impossible that M/B would allow a 6" range on the vacuum to the modulator from the factory. Some variable is not quite to spec.

Hi Chuck,

My 87 300SDL also shifts hard. I'd like to make sure I do not have vacuum leak issues before I mess with the modulator. Can you kindly post the federal diagram?

Also, I checked the EGR valve with my Mityvac. I think it may have a leak. The vacuum reading holds initially but slowly goes down. Is this normal? I am thinking that it isn't.

Thanks.

Carlos

Find the vacuum pump.

Just above the vacuum pump will be a five way connector. One from the pump.........two to the left side of the vehicle.........and two more to the right side of the vehicle. Disconnect and plug the vacuum supply to the right side of the vehicle. Everything on that side can be eliminated. Once you do this, your hard shifts will likely be fixed.

If you'd prefer a cleaner look, you can get an "F" connector from the dealer..........one supply from the pump.........and two for the left side of the vehicle.

....and while you are looking at that 5 way connector. Inspect the line that runs down to the vacuum pump. It's isolated, gets a lot of engine heat, and is easily overlooked.

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