Adjusting vacuum on '87 300D

[Rob124]

After experiencing sluggish performance on my '87 300D, I adjusted the Alda by turning the screw, a bit at a time, until I reached 2 turns CCW. Low-RPM performance improved markedly. I subsequently rebuilt the Alda with a new shaft seal, but left the setting alone. Performance has remained unchanged, and probably acceptable. All through this process, though, I've experienced flaring at low throttle settings, most notably 2-3 shifts. Even the 1-2 shifts often seem premature. Repairing the Alda didn't affect the flaring.

Now I've measured the vacuum at the transmission line, with the following results:

Cold: idle--13.5" (but reaching as high as 16" by just letting it sit for a while in the driveway after starting), 1/4 throttle--12.5", 1/2 throttle--8" (didn't get values for higher throttle settings when cold) .

Hot: idle--13", 1/4 throttle--12", 1/2 throttle--5.5", 3/4 throttle and above--4".

Since I'm experiencing flaring mostly at 1/4 throttle and below, then should I conclude that 12 to 12.5" is just too high? Should I start by cranking down the vacuum amp?

Rob

[Jmana]

I got some improvement on mine by adjusting the modulator adjustment on the side of the tranny. I had to turn it clockwise about 3 full turns. It sometimes still flares, there doesn't seem to be any rhyme or reason as to when it does it though.

[sixto]

How do you crank down the vacuum amp? Do you mean adjusting the vacuum controller thingy on the side of the IP?

Sixto
93 300SD

[Rob124]

The 87s have a separate vacuum amplifier on the wheel well, an output of which feeds into the transmission. I thought it was possible to adjust it on the bottom, but haven't tried.

[sixto]

I don't see this document listed in the W124 manual but it would apply to the 87 300D if there is such a device hanging off the IP -

http://mb.braingears.com/126_DISC1/program/Engine/602_603/07.1-170.pdf

It provides specs at idle of 11.4 +/- 0.7 inHg so it seems that 12.5 inHg might be a tad high. Of course if there's no such device on the side of your IP...

Sixto
93 300SD

[Jmana]

The amp is adjustable, with a 4 mm socket, but I think it will only affect the vacuum when the engine is cold.

[Jmana]

Originally Posted by sixto

I don't see this document listed in the W124 manual but it would apply to the 87 300D if there is such a device hanging off the IP -

http://mb.braingears.com/126_DISC1/program/Engine/602_603/07.1-170.pdf

It provides specs at idle of 11.4 +/- 0.7 inHg so it seems that 12.5 inHg might be a tad high. Of course if there's no such device on the side of your IP...

Sixto
93 300SD

I have a question about adjusting this. It says to loosen the two bolts, then run it at full throttle, and turn the vcv until resistance is felt, then tighten the bolts. Does this mean to have it at full throttle the whole time?

[Samuel M. Ross]

Originally Posted by Rob124

After experiencing sluggish performance on my '87 300D, I adjusted the Alda by turning the screw, a bit at a time, until I reached 2 turns CCW. Low-RPM performance improved markedly. I subsequently rebuilt the Alda with a new shaft seal, but left the setting alone. Performance has remained unchanged, and probably acceptable. All through this process, though, I've experienced flaring at low throttle settings, most notably 2-3 shifts. Even the 1-2 shifts often seem premature. Repairing the Alda didn't affect the flaring.

Now I've measured the vacuum at the transmission line, with the following results:

Cold: idle--13.5" (but reaching as high as 16" by just letting it sit for a while in the driveway after starting), 1/4 throttle--12.5", 1/2 throttle--8" (didn't get values for higher throttle settings when cold) .

Hot: idle--13", 1/4 throttle--12", 1/2 throttle--5.5", 3/4 throttle and above--4".

Since I'm experiencing flaring mostly at 1/4 throttle and below, then should I conclude that 12 to 12.5" is just too high? Should I start by cranking down the vacuum amp?

Rob

... I say again "zero" experience with this late a model diesel MBZ. But having said this, I am of the belief that when any of these all-IMPORTANT engine vacuum systems [that also controls the transmission shifts]... when one of these systems is only slightly out-of-specs, I would suspect that it might be something as simple as dirt/crud clogging one or more restricted orifices. My favorite resource for vacuum diagrams [ www.PeterSchmid.Com ] does not have diagrams for any model later than 85 models so I was not able to verify whether your's has restricted orifices installed.

So let me just advise you to find any such plastic orifices on your car and clean them by using "Simple Green" or other solvent and then blowing out with air. Also be sure to include the "T"s that take off from the vacuum pump-to-brake booster vacuum line, especially the one that supplies vacuum to this same engine vacuum system. So do a little checking/cleaning BEFORE you get too deep into more complex possibilities.

Side-Bar Observaction/Speculation - The initial gradual increase in your vacuum reading while at idle might be a reflection of the fact that the vacuum reservoir is being emptied of air by a vacuum pump that has a volume or capacity deficiency... but please put this one in the "Pure Speculation" category!

Best regards,
Sam

[Brian Carlton]

Originally Posted by Rob124

After experiencing sluggish performance on my '87 300D, I adjusted the Alda by turning the screw, a bit at a time, until I reached 2 turns CCW. Low-RPM performance improved markedly. I subsequently rebuilt the Alda with a new shaft seal, but left the setting alone. Performance has remained unchanged, and probably acceptable. All through this process, though, I've experienced flaring at low throttle settings, most notably 2-3 shifts. Even the 1-2 shifts often seem premature. Repairing the Alda didn't affect the flaring.

Now I've measured the vacuum at the transmission line, with the following results:

Cold: idle--13.5" (but reaching as high as 16" by just letting it sit for a while in the driveway after starting), 1/4 throttle--12.5", 1/2 throttle--8" (didn't get values for higher throttle settings when cold) .

Hot: idle--13", 1/4 throttle--12", 1/2 throttle--5.5", 3/4 throttle and above--4".

Since I'm experiencing flaring mostly at 1/4 throttle and below, then should I conclude that 12 to 12.5" is just too high? Should I start by cranking down the vacuum amp?

Rob

I've observed that the 603's with this transmission package seem to be set quite "soft". If the vehicle is within specificaitons, you'll get that slight "flare" on the 2-3 shift on occasion and the 3-4 will also be a bit mushy.

So, on the '87, I did adjust the amplifier to the minumum setting. Turn the adjustment screw fully clockwise and the output from the amplifier should be about 10" or so at idle. I also ignored the manual and set the VCV so that it's output was also at a minimum (10").

The '87 now performs very well without any flare, and I did not need to adjust the modulator to achieve this.

[Rob124]

Thanks for all the inputs! I turned the screw on the vacuum amp full CW, and shifts are now much crisper, especially the 1-2 shift. No flaring detected yet. May not mess with the modulator at all--we'll see how it does with this change.

Sometimes I think the Alda could use additional tweaking--occasionally seems a bit sluggish off the line. And there's no black smoke, even when I punch it. Maybe that would help the shifting a bit, too.

Rob

[Brian Carlton]

Originally Posted by Rob124

Sometimes I think the Alda could use additional tweaking--occasionally seems a bit sluggish off the line. And there's no black smoke, even when I punch it. Maybe that would help the shifting a bit, too.

Rob

Use the same approach as you would for women:

"Take it off".........

[gsxr]

1) Set the VCV on the side of the IP per the factory procedure - this usually ends up with the VCV set right in the middle of the adjustment range. I tried to "firm up" shifts by tweaking this and instead of weird, intermittent flaring. The VCV apparently does not like to be outside the factory adjustment.

2) Usually, the modulator is set just firm enough so there is zero flare under WOT shifts.

3) Fresh fluid & filter, right? RIGHT? If you don't know when it was last done, forget monkeying with vacuum settings until you do the fluid/filter change. (Every 30kmi, btw, for normal service... 15kmi for severe service.)

4) The engine power output needs to be normal, meaning a proper ALDA adjustment, and also there can't be any leaks or plugged lines in either the vacuum OR pressure plumbing. (The amplifier senses boost pressure and only gives a 'max firm' shift when boost is present - this softens part-throttle shifts.)

5) I have never needed to touch the adjustments on the bottom of the BFS (Blue Flying Saucer, the amplifer on the fender). So far, every 603 I've messed with has had the tranny operation corrected by items 1-4 above. I did eliminate the "cold shift softening" circuit, which operates under 50°C, by unplugging the wire to the sensor in front of the t-stat housing. On my cars this just made the tranny flare for a few minutes until the engine warmed up. Without it, shifts are perfect cold AND hot... I run Mobil-1 ATF, which might have something to do with that, though.

Required reading, if you've never seen this article:
http://www.continentalimports.com/ser_ic20242.html

[Rob124]

Dave,

The ATF was last flushed and changed 7,000 miles ago, but not with Mobil 1. Doing that is on my list, but I need to find a place that sells it first. I cleaned and tested both switchover valves, which were pretty cruddy, before overhauling the ALDA. I've now turned the vacuum amp adjustment back one turn CCW (leaving it at one turn CW from stock), which still seems to help reduce flaring, but doesn't present the abrupt 1-2 shifts I saw after turning it full CW. Would you consider it unlikely that a properly-functioning ALDA would need to be adjusted 2 turns CCW before making a significant improvement to performance? I'm actually thinking of turning it another quarter turn to see how it helps low-rpm performance.
I'm a little apprehensive about messing with the VCV, based on your comments.

Originally Posted by Rob124

Dave,

The ATF was last flushed and changed 7,000 miles ago, but not with Mobil 1. Doing that is on my list, but I need to find a place that sells it first.

http://www.autobarn.net/oil25201.html