Numbers... we need numbers !
 

[QUOTE=cscmc1;1476074]Thanks again, Sam.
So the modulator on the transmission controls shift quality AND timing? (i.e. it will allow elimination of "flare" and firm up the shifts AND the rpm at which the transmission shifts?) My shift quality is much better since I turned the modulator in one turn, but she now shifts later (i.e. runs too high in the rpm range before shifting to 3rd and 4th gears).
I did test the vacuum being supplied to the transmission, and it does indeed decrease with rpm. I will check again to see if that is still the case. I will also order a dashpot to add to the transmission vacuum line. /QUOTE]

Chris... We got to have some #(s)... for instance I'd like to know the readings when the system is reasonably "tight" and there are no known origin or unknown leaks... so close or clamp any of these off first... then read:
(a) the vacuum directly off of a "T" coming off the main Pmp-to-Brake booster line? and while you are reading this at idle, bring the engine speed up to ~2K and see how much it rises?,
(b) in the engine compartment off of a "T" installed in the line that goes down to the tranny modulator... read this at idle, and
(c) then read the vac again when you slightly advance the throttle enough to trip your 3/2 switchover valve... there can be a slight decrease... give me this reading and whether and what it dips to,
(d) then put enough vacuum line on this same "T" off your modulator line and place the hand pump under one of the windshield wiper blades where you can see it while driving... and observe while you drive around a bit. You are looking to see that under different speeds/loads... you are looking to see IF it "SMOOTHLY" transitions to a much lower [almost zero] reading... tell us how smoothly the vac drops and what reading it bottoms out at when you ptpttm [put the pedal to the metal] at say 30 mph. Don't burn rubber and get a ticket!
Regards

When it rains it pours! Just got back from a little jaunt to the parts place and the grocery store to pick up some flowers for the wifey, and observed the following:

First, the transmission started shifting at the proper (or at least much more reasonable) points on the way home. Interesting, and I haven't altered a thing in the last 24 hours.

Second, I have a nasty leak at the IP all of a sudden. About a drip per second. Need to sort that out pronto!

When I got home, I was curious, so I went to get my MightyVac and take a quck reading at the line to the transmission. I took at at the point where the line leaves the switchover valve. Initially it read about 16 pounds at idle, and decreased to about 5 as rpms headed toward redline. My switchover vale has a broken finger, so I suspect it's not working quite right yet. I am ordering one, among several other things, from Fastlane this week.

I stood up long enough to stretch my back, and by the time I ducked back under the hood, vacuum at idle was down to about 10 pounds. Go figure.

More leaks to track down -- both vacuum AND fuel now! Huzzah! :grin:

Here is one good way to reduce leaks under the hood!
 

Check out my photo at:
http://ericandkat.com/mercedes/W123VacDoorLockDiag.JPG
I would also purchase a yard of that small dia. MBZ vac. line and replace any 3-way, 4-way fittings that are too dry and hard to use the electric ties on for tightening as show in the Pic above!
Regards,

I was just getting caught up on this thread and read with interest this item about incorrect vacuum to the tranny causing differential wear over time. I purchased a mityvac and now that the weather is getting better and I have my benz out of the garage, I need to get my hard 1-2 shift problem solved. I replaced a few cracked vacuum hoses last fall and closed off the EGR system, which improved the 2-3 shift and softened the 1-2 shift.

But now to the point of my post: I have this rumbling that I feel when slowing down to an idle, and have assumed that I need to look at the univeral joint. But maybe it is the differential. If my problem is the differential, is it something that can "bust" suddenly and leave me standed, maybe doing further damage? I have never worked on a rear end. How involved is it to inspect the differential gear and replace it?

Drive line rumbling... hmmmmmmmmm !
 

RML - First off I confuse parts terms and confuse differential & universal all the time ! Take a look in your PM.

Yes, I think your "rumbling" probably is in the drive-line... and is in order of likelihood either:
(1) so many miles and wear-and-tear on your car that the differential[rear-end] is getting loose! A good way to diagnose this is to drain the oil and put in the heavier 140 weight gear oil. If this quiets things down some, you know you have found the problem... and you might want to keep the heay lubricant... realizing it will knock a little off your fuel mileage!,
(2) one or both of the two flex couplings in your drive line,
(3) one of your drive CV axles,
(4) the center support bearing and/or rubber mounting for this bearing, AND/OR
(5) also check the rubber support(s) that the differential hangs from or is supported by.
Regards,

Thanks for the transmission
 

Hello all. One month ago I bought a 1982 300D Turbo off a local used car lot, looking for a car I could (a) maintain myself and (b) eventually convert to run on waste vegetable oil. Body and interior immaculate, new Michelins. On test drive, noticed what I thought was "slipping" between 1-2 and 2-3 gears, but since the price was so good, thought I'd take a chance.

Began browsing the web, found DieselGiant, then Shopforum. Read extensively, bought about $100.00 worth of vacuum components, then began. And here's what happened.

With vacuum valve, checked Hg at brake booster, ~22" Hg, then checked components downstream. System would not hold vacuum. DieselGiant recommended checking master vacuum switch, found it to be good. Traced vacuum lines from master vacuum switch in driver door, found that at some point the yellow/red and yellow/green lines had been crossed, straightened that out. Found leaky actuators (driver's side rear door, trunk), replaced the former through Ebay ($25.00), latter removed and lines plugged. Pulled vacuum at master vacuum switch, all locks worked as advertised. Pulled vacuum at dual connector off principal vacuum line (one goes to master vacuum switch, other to vacuum reservoir), all locks worked. Cranked her up, door locks don't work. Test drove, transmission as before.

Came here. Found vacuum schematics (first BIG thank you), noticed valve in dash. Checked valve in dash after removing instrument panel, found valve installed backwards. Reversed valve. Checked vacuum at dual connector off principal vacuum line, door locks worked as advertised. Test drove, transmission as before.

Began serious work in engine compartment. Following DieselGiant, checked ALDA connections, found the lines to the ALDA switchover valve (on firewall next to brake booster) were disconnected from the valve and connected together. Reconnected to switchover valve. Removed and cleaned banjo bolt, reconnected. Test drove. Door locks worked as advertised (an indication of good system vacuum integrity), transmission as before.

Returned to engine compartment, read more on Shopforum, this thread, and discovered vacuum control valve (VCV). Tested vacuum, found it to be solid 14" Hg from the top connector. Test drove. Transmission as before. Went back to VCV, noticed for the first time that the rocker arm from the throttle linkage was disconnected from the metal lever on the back of the VCV. Which means my transmission was getting solid 14" Hg through all shifts (no wonder the "flaring," a more precise term, I have learned, than "slipping"). Reconnected rocker arm, which turned out to be frustrating because mine has a loose plastic clip to hold the rocker arm onto the metal lever on the VCV. Tested vacuum bleed from top connector, went smoothly (whew!) down from 14" to 0". Just for kicks, checked vacuum on line to transmission, found it to be solid. Test drove. No flares, though shifting was extremely soft (i.e., slight flare-like shifting between gears) and shifting occurred around 3200 RPM.

Following DieselGiant, replaced transmission vacuum valve levers (old ones were worn significantly), commonly referred to as 3/2 valves. Test drove. Still soft shifting and high RPM.

Came back, read more Shopforum. Learned about the control pressure cable (I believe it's referred to as a "Bowden" cable, obviously named so by a Florida State fan), adjusted it as per decription elsewhere here on Shopforum. Then read about vacuum adjustment on VCV. Removed plastic dome, adjusted nut (not screw) until vacuum ranged from 10" Hg down to 0". Test drove. NO NEED FOR A NEW TRANSMISSION. Shifting was extremely crisp (my tires tend to squawk a little between first and second, unless driving upgrade) and all gears shift dead-on 2300 RMP. And all of this with the EGR still connected.

Tonight, I adjusted VCV to 12" Hg initial vacuum to see if tomorrow the 1-2 shift is a little less harsh while not leading to minor flaring between 2-3. Again, big thanks to this forum, I do not need a new transmission.

Here's some learnings and questions I still have.

1. After all this, my cruise control began to work whereas it didn't before. Does the cruise control depend on a tight vacuum system?
2. Adjusting the control pressure cable: I tightened the cable to remove noticeable slack (right at the point of feeling resistance to the pull) at the point the metal connector was at rest, not against the metal stop between it and the cable bracket. The gap was around .15". Perhaps this is peculiar to my car, but by maintaining that at-rest gap I was able to fine tune shifts to current RPM.
3. One could, if one wanted an extreme exercise in frustration, adjust non-adjusting VCV by changing the height of the rocker arm connection to the throttle system. I imagine that would entail significant trial and error, since one would have to identify the exact point at which vacuum begins to bleed, then adjusting the rocker arm at-rest to connect the lever on the VCV at slightly before that point. Ugh. However, I'd bet that's what the designers intended, since different VCVs may begin to bleed off vacuum at different lever positions.
4. BTW, that flimsy plastic connector that ensures the rocker arm will stay on the lever on the VCV: I intend to replace it with a spring-lock, since the tip of the rocker arm has a groove around it. I was driving two days ago and the rocker arm slipped off - back to flaring between shifts.
5. Sam, regarding the orifice openings: I'm sure you're right, though I'm a newbie to MB's and am speaking as a rank amateur, that the orifices are fine tuning methods for delivering precise vacuum to the different components while ensuring that the brake booster always receives sufficient vacuum. That being said, I would not mess with them unless, for instance, I could not get sufficient vacuum at the VCV to reach my starting point of vacuum (formerly 14", then 10", now 12" Hg). I would love for a more physics-minded reader to give an description of how much a particular orifice size restricts vacuum, for instance, how much a .8 mm orifice restricts 22" Hg.

So, that's my story and I'm sticking to it. Again, huge thanks to this forum, particularly Brian and Sam. Though I still have some things to do (fuel low light always on, plastic door buffers in locking mechanism rotted), most are minor compared to my worries over the transmission.

"Rev"... that might just explain your "verbosity"!
 

"Reverend?" Jeff,
Wheeew! [sp?]… you were sure not at a loss for words!! Are you a Preacher or Priest? You included enough for three separate THREADS all in one POST! A bit of tongue-and-cheek advice – in the future think of these THREADS and the POSTS in each THREAD as being part of a huge technical database that will be archived and then in the future someone will be SEARCHING and seeking specific help on a technical problem [ just as you did ]… so it’s probably best for future readers IF we try to keep our POSTS in each THREAD consistent with the very first subject line of the THREAD… a subject line that it appears even the original author canNOT change. MOST of your POST falls into two different categories: (1) Engine/Transmission vacuum system, and (2) Door Lock vacuum system. This THREAD was intended to address the Engine/Transmission Vacuum.

Now that I have chided you, let me also compliment you for your dogged determination to solve your vacuum problems and your capacity to deal with so many different things that were wrong on your car in these vacuum systems.

I thank you for your compliments and recognition for myself and Brian in your POST. Such courtesy and civility is often overlooked by many of us who have become too familiar with one another here on the FORUM.

Regarding the subject of Door Lock Vacuum Control systems on W123 chassis cars, just in case you missed it, take a look at this THREAD:
http://www.peachparts.com/shopforum/diesel-discussion/160169-w123-vacuum-interlock-diagram.html
and more specifically at POST #5 :
http://www.peachparts.com/shopforum/1247118-post5.html
where you will find 3 links to space on a WebSite donated by someone I met on this FORUM… links to two different file formats of a color diagram for the W123 Vacuum System for the Door Lock System [ a good future reference to print and share with others ]:
http://ericandkat.com/mercedes/W123VacDoorLockDiag.doc
http://ericandkat.com/mercedes/W123VacDoorLockDiag.WMF
and another link to a photo showing how to use small electric wire ties to salvage many of the loose/leaking rubber vacuum connectors:
http://ericandkat.com/mercedes/W123VacDoorLockDiag.JPG

Welcome to the FORUM "Rev" and please try NOT to write your POSTs on Sunday!!
Regards,

I broke this plastic tee today trying to get the hose off to take a vacuum reading. I started the engine but it won't shut off. I pushed the broken tee to seal and the engine shut off. Not knowing what other problems this will cause I got creative. I tapped the broken tee with a 1/4 -20 tap (after drilling out with tap drill). I machined a nylon adapter on a lathe with 1/4-20 die and threaded it in the newly tapped tee and connected the hose and all's back to normal.:)

I want to see if I can make the transmission shift better. It flares sometimes starting from a standstill and jerks forward. It also makes a pronounced clunk coming to a stop. Are these signs of vacuum problems to the transmission vac modulator?

If you turn that clip on the linkage rod, it functions quite nicely.


As for the orifices, have you ever tried to set up a fish tank? If you have too much hose on one side of a splitter, you will get just about all your pressure through one (the shorter) hose. If you would put an orifice on the shorter line, you can force air flow from both. Same idea, but reversed.

"Funola"... that's fancy plastic machining work...
 

(1) Extra Ordinary Fixes - IF you are inclined to perform such intricate work on these brittle plastic T(s) in the Pump-to-Brake booster chamber... I would recommend you fashion a metal "T" in this, the main vacuum supply line.
(2) Tweaking the Engine/Tranny Vacuum Control System - Yep, this is why this THREAD was started by me more than 250 posts ago. For those of us on this THREAD to help ya, we need for you to go through a series of vacuum tests and report to us the results. I trust you have a vacuum hand pump/gauge... the tests include:
(a) tell us what year and model diesel you have,
(b) go to the website : http://www.peterschmid.com
(c) and then their webpage: http://www.peterschmid.com/vacuum.htm
(d) follow thru the menu structure and find the appropriate vacuum diagram for your year/model/engine car.
(e) report back to us with all of the above.
Regards,

I wouldn't call that intricate work. It was done in less than 1/2 hour and done out of necessity because it was broken. That's a great idea to make it out of metal so it will not break again. Is that just a plain tee or an orifice that I broke?

I will go through the procedure you outlined and report back. I do have a Mighty Vac. Thanks for the guidance. :)

Let's start with Year/Model and the correct vacuum diagram!
 

Funole,
A1 - I think most of the "T"(s) are also restricted orifices... that's why we need to try and find the proper vacuum diagram which will tell you [most of the time]. But even if it's not, you can put an in-line restricted orifice in the line just as MBZ did when they "tweaked" these cars as they came off the assembly line [IMHO]... or at least that's my explanation of their use of so many restricted orifices... orifices here and orifices there. I say that these were originally to do two things: (a) balance the vacuum to each specific vacuum using/powered component [as needed], and (b) to conserve vacuum for where it is absolutely needed... the vacuum assisted power brakes. I also think the later model cars went to a separate electric powered vacuum generated just for the door-lock, fuel door, and trunk-lock systems... they did this [IMHO] just to get away from possible lawsuits from the brakes being starved for vacuum when a door-lock diaphragm ruptured or a vacuum line pulled loose!
Regards,

The T's in my 1982 booster line were open (large holes).
The T's in my 1983 booster line were restricted.
When I ordered replacements, both lines sent had T's with the larger holes.

The only reason for having orifices of smaller size in the T's would be to increase vacuum to the brake booster, but as long as your system is tight enough to maintain ~25" to the booster, all is well.

One way or the other, the restrictions are needed...
 

1983/300CD,
One way or the other, the restrictions are needed... unless your vacuum pump is wearing out!

I have gauged the I.D. of some of several of these "T"(s) on the main vacuum line and found most to be ~0.8mm. IMHO I would equate "open" to be ~ 2mm or larger which is the opening in the largest of the MBZ in-line orifices... thus also IMHO, IF new replacement main vacuum lines come with "T"(s) that 2mm or larger openings, I believe it would be necessary to use in-line orifices that are 0.9mm or smaller to reduced the "strength" of the vacuum such that you would be able to properly adjust the vacuum on cars with a vacuum control valves [VCV] mounted on top of the Injection Pump (IP). Otherwise you would NOT be able to properly adjust the VCV so that the tranny's modulator valve would see the proper varying vacuum signal simulating changing throttle.

I agree that restricted orifices [whether in the main line "T"(s) or in-line orifices]... these are there to help "conserve" vacuum for the brake system, but IMHO these restrictions are also there to provide a final degree of "tweak" or control of the vacuum being supplied to the various vacuum using components... for example EGR, VDC, modulating valve etc.

So IMHO you either have to restrict the vacuum at the main line or bother there and later with in-line restriction(s). One of the diagrams on the www.PeterSchmid.Com WebSite actually gives you the sizes of the 6 or so color coded in-line orifices!
Check out: http://www.peterschmid.com/vacuum/1977_1985/617_95/1981_1984.jpg
Regards,

The 1982 was all original when I bought it (including booster line), and it had larger openings. My black after-VCV line reads 10" at idle and reduces to 0. Remember, it still has the orifice in-line before the Y connection leading to the top of the VCV.

That's tongue in cheek.

If the output from the vacuum pump dropped to sufficiently low levels (pump failing), the vacuum system wouldn't need the restrictions to keep airflow levels within specifications.

Naturally, you'd have no brakes at that point...............:eek:

There has been talk on this FORUM...
 

1983/300CD,
There has been talk on this FORUM about how one can drill out the "T"(s) in line between the main vacuum pump-to-booster chamber. I suspect this is most often done because the OEM restricted orifice "T"(s) do become clogged with dirt over time and instead of just cleaning them out with solvent and/or a piece of wire, many DIYers have just drilled them out with any bit they could get fit into the "T" !. As a retired Certified Safety Professional [CSP...not Prof. "PE" ], this is where I have taken issue by issuing CAUTION, CAUTION, after CAUTION by appealing to logic and reason. IMHO logic impells me to try and understand WHY these systems were designed the way they were. I also advocate installation of clear in-line air or fuel filters at the appropriate locations under the hood and under the dash to try and keep dirt out of the vacuum systems plumbing and in the case of the IP shut-off device line where it is in plain view under the hood, such a filter acts as a visual "tell-tale" to warn that the shut-off device is failing. The really BLACK engine oil of these diesels really stands out when sucked into filter on its way the ignition switch, eventually to drip on the pantsleg of driver's best slacks!
But I digress a bit didn't I.
Regards,

Holy crap Batman the transmission is shifting smoothly now! OK, I have an 83 300D turbo. I believe the vacuum diagram posted by Brain Carlton on page 2 of this thread represents my car. I pulled the hardline to the transmission modulator and noticed it was a little loose. Put a Mighty Vac on that line and it holds vacuum! Good start, the transmission modulator is good!. I pulled off the rubber T's and noted they were loose and oily. I washed the grease off and trimmed a little of the ends of the T's that are loose. I also noted the hard line to the VCV brass fitting was slightly bent and may be leaking. I didn't want to pull it off for fear of breaking it so I put a piece of duct tape around it temporarily. Put the T's back and went for a test drive and it felt like a different car. It now shifts up or down with no more banging of the gears. It is also shifting at different RPM's than before. So this thing I've read on the web that the 80's Mercedes transmissions are suppose to shift hard with an authoritative bang is apparently a lot of horse *****?

Brian,

I studied the vacuum lines to the black box on top of the valve cover and it does appear that it only control the EGR valve. I am puzzled why this DIY procedure at Dieselgiant http://dieselgiant.com/trannyleverreplace.htm specifically states that replacing the worn vacuum levers will fix transmission shifting problems?

The vacuum levers leak. Russell advocates replacing those levers so they don't leak. He sells the levers. He really cannot advocate removing the EGR levers completely.

Why not? :confused: There are people who advocate removing the EGR and plugging it up completely with a plate. :)

He wouldn't sell any levers.........;)

Tough! I think selling more plates is better than selling more levers. He really should update that procedure to tell people to first test if the 3/2 valve and levers are leaking before replacing them. It is possible and more likely that there are leaks elsewhere and replacing the levers alone will not fix transmission shifting problems. I think just bypasing that damm black box or getting rid of it altogether is the best course of action.:)

Well, for those of us in states that don't require diesels to have EGR equipment or are exempt after a certain age, it makes sense. But, I believe there are a few states which still require emissions tests for old diesels, so doing so may render your car unpassable to the emissions testers, unless you are cool with the guy or something.;)

It is unfortunate. The levers are fairly pricey and they simply achieve a properly running EGR system. He knows that such a system is undesirable for the long term.

I don't believe that there is any state that can detect a missing EGR valve with the exception of those that have very knowledgeable personnel who would realize that the valve is missing underhood. With the design of the plate, I'd bet against that as well.

Softening Hard 1-2 Shift?
 

Hello all. I wanted your input before I do what I'm thinking. After tweaking my trans, I still have a too-hard 1-2 shift. After thinking of ways to soften it without causing flare in the other shifts, I've wondered about the length of the rocker arm from the throttle linkage to my VCV. On mine, I have about 15-20 degrees of play before my VCV bleeds vacuum. My rocker arm is set to eliminate those degrees of play, so that immediately on throttle my VCV begins to bleed. What if I readjusted the length of the rocker arm so that my VCV retained those 15-20 degrees of play before bleeding vacuum. Would this soften the 1-2 shift without flaring the others? What do you think? I'm asking because I imagine - given how tight it is behind my VCV - that it's going to be a bear to get that rocker arm off. To my mind, that would keep the most vacuum to my trans during acceleration from stop, hopefully making the 1-2 shift (right now occurring at 2400 rpm) softer.

The rocker arm is set properly. Don't try to misadjust it.

If the VCV on that vehicle is adjustable, then attempt to raise the vacuum level slightly........by 2" or so.........and see if the 1-2 will soften a bit without causing flare on the 2-3. It's a bit of a balancing act. But, older 617's will all have a harsh 1-2. This was subsequently corrected in '84 with different valve body springs.

You can also adjust the Bowden cable for earlier shifts. If the 1-2 occurs at 1900 rpm, it will be much more tolerable than if it occurs at 2500 rpm.

imagination or for real?
 

After correcting the few loose vacuum connections, my transmission is shifting 100x better. The car also seems peppier and more responsive. Is the extra power for real or just my imagination.

I came across an old vacuum schematic which shows a switchover valve (w/lever) that functions to control the transmission. (It shows a mess of lines leading to the top of the VCV.) Neither of my cars operate this way, and it was probably a really early model (not specified on the sheet), but it did seem to exist at one point in the production of these cars.

I will see if I can dig it up again...

Some vehicles, prior to 1981 I believe, definitely used one of those vacuum levers for transmission control.

The only vehicles that I'm positive for which you can remove the entire affair are the 1982-1984 vehicles with the 617.

Here's some info on the orifices from the dealer. The yellow one was quoted at $1.70, red was $11.00!:eek: Blue is $1.20, white is no longer available, and brown is $3.70. I don't know about green at the moment.

With a lathe and metric drill bits, I can easily make any size orifice out of Nylon or Delrin. Getting the colors to match is a problem tho.

My transmission shifts way way too late

I don't have a tach but by ear it sounds like 3000-4000 for the 1-2. You just wait and wait for the thing to shift, sometimes doesn't even want to.

There is a green dashpot connected to a beige "thing" next to the IP. I tested the supply to this and at idle, its 0. When you rev it up, it goes to 5. This doesn't seem normal. What should be happening here?

This is on an old Buick?

Ya, Buick's diesel German model the 240D dated 1983

Not sure if the 240 has a kickdown switch or not. Maybe fellow owners will chime in.

If it does, the symptoms point to a stuck kickdown switch...........directly underneath the accelerator pedal. If it's there, unplug it and see if the symptoms change.

If the kickdown switch was stuck, wouldn't it never upshift?

I will be checking the kickdown switch none-the-less

dwoloz,
Brian is just funnin you in his POST above... but he does have a point. You should create a signature line similar to his above, or mine below. This way readers of your POSTs will know what MBZ Yr/Model you have.

Assuming your car is a MBZ, while you are taking vacuum readings with your gage, your readings thus far indicate that you are way low... thus you should go back to the vacuum SOURCE, the pump... and the best way to measure this is to put your gage on a the first "T" fitting that is directly on the large main vacuum line that runs from the vacuum pump [front left side of the engine]... runs back to the brake booster chamber on the firewall.
This should be 15 to 20 inches of vacuum. IF not, most likely you have a vacuum pump that needs rebuilding or replacing!
Regards,

Thanks for the replies

My vacuum pump seems to be functioning. I get a 21" at the brake booster.

However, here are the found problems so far:
Yellow vacuum lines for doors do not hold vacuum. Master vacuum switch probably bad, going to replace.
Green vacuum line to HVAC doesn't hold vacuum. Plugged for now.
Black vacuum line to reservoir doesn't hold vacuum. Don't know what to do about this.
3/2 vacuum valve doesn't hold vacuum.

My problem area is definitely on top of the valve cover in that black box. Replacing the first of the 3/2 valves may fix the issue.



I checked the kickdown switch and it is not stuck. Actually, the pedal never even reaches it. Thats a separate issue I have to deal with later.

Checking in
 

An update on my transmission shifting progress...

I have my vacuum system tight and functioning well. I have replaced a lot of stuff, all of it was bad. Now I have even shifts, but the transmission doesn't seem to respond much to increasing the vacuum. It just shifts firmly no matter what.

For anyone reading this, short of replacing the transmission, I think Ive lived the worst case scenario:

Replaced:
-Master Brake line (nipple broken - this fixed my uneven shifts)
-VCV (PO over adjusted it, got one from a yard car)
-adjusted linkages (way way off)
-modulator rubber cap, o ring
-modulator itself (also tested it and adjusted it)
-pin behind modulator (PO broke it trying to fix modulator)
-Brake Booster (leaking)
-all rubber lines and connectors
-lots of door lock items, door lock system plugged still
-shut off valve (leaking)
-also had to clean ignition housing (leaking shut off valve spit engine oil into it)
-oh, and the EGR crap is long gone

As I said, my shifts are still hard no matter what I do. My vacuum readings look good - no leaking, correct curve. My next step is to try a filter change and after that I am out of ideas.

dd

After all your hard work...
 

Dan,
I admire your hanging in there with your new/old Benz that obviously needed a lot of TLC. Ironically I just discovered something that might just help with the hard shifts [albeit probably a long shot] and it will co$t very little to try it.
I believe your Benz is a 1982 which means it should have an OEM "dashpot" or dampener vacuum chamber/orifice attached between the VCV and the vacuum line running to the modulating valve located on the tranny.
(1) Make certain there is a "dashpot" and that it holds vacuum, and
(2) IF the dashpot checks out OK, try this - Install an inexpensive inline disposable gas filter in the vacuum line that runs down to the tranny's modulator. This should be connected between the dashpot connection to this line... in the line between this connection and the line as it continues down to the modulator.
Some explanation is needed - As I understand it dashpots were first used on the 1981 models... and some 80(s) Benz(es) have multiple dashpots [aka dampeners] and as "dampener" implies, this dampens or delays the vacuum signal's effect or in the case of the daspot mounted on top of the VCV, its dampen delays the vacuum bleeding effect of the VCV. So in a similar way the addition of the inline fuel filter also serves to dramatically increase the vacuum-holding capacity between the VCV connection and the modulator so this further delays the VCV's action of bleeding off the vacuum signal to the modulator.
Like I said this is a bit of a long shot but there is at least a little engineering in my method and madness. The fuel filter considerably softened my 1980 240D's 1-2 shift and made the 3-4 shift not occur so early. I'm even thinking of replacing the dashpot I put on my Son's 1980 300D... replacing this dashpot with a filter. And IF you place such see-through inline fuel filter where it is readily visible, it also serves as a "tell-tale" to visibly show that there is tranny fluid being sucked up from a broken modulator. Similarly you can install a see-through filter in the IP shut-off's vacuum line as another "tell-tale"!
Let me know IF this helps with your hard shifts!
Regards,

Sam,

Thank you for the suggestion, Ill give it a shot. The only piece on my vacuum control system that I have not changed is the dashpot. I have another one, Ill test it and give it a try. I have nothing to lose.

Im concerned that my trans responds sluggishly to vacuum adjustment. People are talking about small vacuum changes making a big difference and such - this is not my case. The only way I can get my trans to flare is if I disconnect the throttle linkage to the VCV, so I'm running on 15 mmhg vacuum all of the time no matter what the throttle setting.

Ill give it a try as soon as I ge tthe car back up and running again. Unfortunately it needed and still needs a lot of TLC in many other areas. For exmaple, I think the PO put the wrong rear suspension components in the car.

What an adventure it's been.

I feel like I have a very good grasp on these vacuum control systems now (thanks to this thread), and Im looking forward to writing up a guide that summarizes a lot of the stuff in this thread. Ive almost all of the jobs except replace the valve body or trans itself...

dd

Long before I started this THREAD...
 

Dan,
As my last POST regarding my use of a fuel filter reveals, I'm still learning the subtleties of these vacuum systems and particularly those relating to how these tranny(s) shift... but long before I started this THREAD, I invested in a rebuilt tranny for my Son's 300D [below] with a 2-year warranty and my 1st MBZ has a bebuilt tranny with less than 30K miles on it... so I often wonder IF I could have revived my Son's car's tranny and squeezed out a few more miles... but it already had ~300K on it... do you even know how many yours has? If you run a check on your VIN you can usually get the I.D. #(s) for the original tranny in the report!
Regards,

awesome reading
 

Just did the central plug fix and my sd is shifting like the cats ### !!! Brian thanks for the help.:D

Jim

Jim... where did you come from...
 

... and what is the "central plug fix" ??
Regards,

Where did I come from?
 

Central plug on top the valve cover that contains the 3/2 switches, remove the vacum lines back to the T and cap off. Also removed the line to the themo valve. Result was awesome shifting. What a pleasure to drive now! 1983 sd by the way. (lovey) Where did I come from?

Jim

Hard shift on 76 300D, Vacuum issue?
 

Can anyone tell me if this all applies to a 1976 300D? I don't think so but I would like some expert advice. It shifts hard from 2nd at 20 mph (where it is designed to start out in) to third.
Regards,
Rich

Anytime. Glad it worked out for you. Those 3/2 valves are a constant source of leakage and they always cause hard shifts.

1978 300D auto trans problems
 

I've done multiple searches and I'm just not getting anywhere. Can anyone tell me if the auto trans on the 1978 vintage 300D's had a bowden cable or any kind of vacuum modulation? Looking at my vac lines at the initial t off the main line, I'm not seeing anything that looks like those things described in the various threads. It looks like they are only for HVAC(green), locks(yellow), shutoff (brown), red(?to rear vacuum reservoir), and black to climate control? I don't see anything else. I've got a wicked first shift (2-3) that occurs too late. Later shifts are better, but I think it sometimes downshifts too easily. I've lost my Haynes, but I'll buy another copy if anyone thinks it could be helpful. I have the FSM for the engine and body chassis but it's no help obviously. I just need a little bit of guidance here or maybe some pics to get started. About the only thing I've done so far is check the vac of the T at idle (I think it was 20mmHg). My wife loves this car in spite of many, many issues. Her attitude previously has been to readily dispose of cars if they had even the most simple problems and buy a new car. This is a huge shift in attitude that I can only attribute to the intangible w123 qualities that we all know and love.


Thanks for the help

Kevin
1979 240D manual
1978 300D auto