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  #1  
Old 03-20-2009, 02:27 PM
Richard Howard
 
Join Date: Nov 2008
Location: Western NC Mountains
Posts: 69
Advice Needed - 82 300SD - 722.303 Trans

I finally got the 82 W126 300SD on the road for testing after correcting many areas of neglected maintenance. I need advice on how to proceed with getting the 126 270 2801 722.303 02 250139 transmission to shift properly.

I don't know the car's complete history but there was an engine swap done, installing a 617.950 from a 78 W116 300SD. This engine does not have any vacuum regulating valve on the IP to adjust vacuum levels to the transmission's modulator (green cover).

After reading Brian Carlton's and Steve Brotherton's excellent information on making vacuum changes to affect transmission operation I started by checking vacuum levels. I found 20" at the brake booster and an excessive 18" at the three-way junction's ports for the line to the IP shutoff valve and to the transmission. What's really surprising is the presence of a white restrictor (0.8mm orifice) in this line just towards the vacuum source.

With 18" vacuum to the transmission, shifts are soft but clearly evident and with no flaring. With no vacuum applied to the transmission, shifts are much firmer, almost hard, but not so firm as to risk driveline damage.

Did the 1978 300SD ever have any means of adjusting vacuum to the transmission modulator?

Any suggestions about how to best reduce vacuum to about 10" for this transmission? Would several 0.8mm restrictors in series produce sufficient vacuum reduction, via an additive effect? Also, any way to provide some reduction from 10" as throttle pressure increases?

Since my first-time involvement with this transmission's modulator adjustment T-key resulted in my pulling it out completely, is there a basic setting of x-number of clockwise turns from some point of minimum spring resistance? (This modulator has a piston or plunger on its inner end that tapers to a small length of tube having about a 1.0mm orifice; no circular spring is visible.)

Thanks very much for any information and opinions...

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Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951

Last edited by Richard Howard; 03-20-2009 at 05:22 PM.
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  #2  
Old 03-20-2009, 05:18 PM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Quote:
Originally Posted by Richard Howard View Post

After reading Brian Carleton's and Steve Brotherton's excellent information on making vacuum changes to affect transmission operation I started by checking vacuum levels. I found 20" at the brake booster and an excessive 18" at the three-way junction's ports for the line to the IP shutoff valve and to the transmission. What's really surprising is the presence of a white restrictor (0.8mm orifice) in this line just towards the vacuum source.
Firstly, it's important to measure the vacuum in the proper place. If you're measuring the vacuum to the shutoff valve, you're not in the proper place.

Find the line from the T above the VCV to the modulator. Disconnect the line from the T and install your Mityvac in it's place.

Start the engine and read the gauge at idle. I doubt that it will read 18" if the orifice is in place upstream of the VCV.

Report back with result.
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  #3  
Old 03-20-2009, 06:00 PM
Richard Howard
 
Join Date: Nov 2008
Location: Western NC Mountains
Posts: 69
I'm certain that my 82 W126 300SD does not have a VCV on this replacement engine from the 78 W116 300SD. There also is no vacuum control assembly on top of the valve cover, where the black plastic cam would operate the two small reed-like fingers to control vacuum from several ports.

My suspicion is that when the engine swap was made for a prior owner, the VCV that was on the original W126's engine wasn't installed on the 617.950's IP. I don't see any location with unused tapped holes, so perhaps this IP never had a VCV. That's why I asked whether the 78 300SD ever had a means of varying vacuum to the modulator on whatever transmission was used in that model. Hmm... that may be the answer - maybe the 78 300SD transmission didn't require any vacuum?

I'm now sure that I do not have the component that would produce the necessary drop in vacuum level needed by the 722.303's modulator. I'll continue by trying several restrictors connected in series in an attempt to reduce vacuum close to 10" and route that to the transmission. I think I'll also need to just not provide any variability of vacuum and let the trans operate with 10" vacuum. It shouldn't be that significant since I'm not the type of driver that would use maximum throttle and have shifts occur under that condition.

Thanks, Brian, for a quick response.
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Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951
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  #4  
Old 03-20-2009, 06:27 PM
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Quote:
Originally Posted by Richard Howard View Post
I'm certain that my 82 W126 300SD does not have a VCV on this replacement engine from the 78 W116 300SD.
You can completely ignore my first reply. I wasn't aware that you had an earlier engine/transmission for this vehicle.

You'll need to get some guidance from those with a 116. That system is quite a bit different from the later W126 vehicles. I don't have specific knowledge of proper modulator vacuum levels for it.
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  #5  
Old 03-20-2009, 06:43 PM
Richard Howard
 
Join Date: Nov 2008
Location: Western NC Mountains
Posts: 69
Disregard my earlier reply as far as there not being a VCV on this IP. I looked again and realized that what I thought was part of the IP's shutoff valve is actually the VCV.

I believe that what made me think otherwise was the fact that the vacuum supply port of the VCV had nothing attached - only the surge damper was connected. (I had some doubts about the qualifications of the guy I talked with who did maintenance on this car when I first looked at it.)

I've now removed the VCV and after opening the cavity containing the spring, found it loaded with crud and some water. I'll try cleaning it in mineral spirits followed by a rinse-off with spray brake cleaner. I'll then reinstall, with vacuum supplied, and will see what vacuum level I get at the output port.

Sorry for the mistake - don't have any really detailed documentation on this engine and car so far. Thanks again for a great mercedesshop website and all those who generously contribute their knowledge and experience.

More results later...
__________________
Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951
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  #6  
Old 03-25-2009, 08:15 PM
Richard Howard
 
Join Date: Nov 2008
Location: Western NC Mountains
Posts: 69
I was able to effectively clean the old vacuum control valve's internal working parts area (from the IP of the 617.950 from a '78 W116.120 that's in my '82 300SD) using mineral spirits with a 1" wide brush followed by a rinse off with spray brake cleaner.

The valve now provides a smooth reduction of vacuum from the supply of 20" down to about 1" as shown on my vacuum gauge. The operation is linear and without any abrupt changes.

When checking availability of a new VCV for this engine at a MB dealer I found that MB #123.070.00.46 and MB #617.070.02.46 are no longer available and that no stock exists in Germany.

My problem now consists of being unable to adjust this VCV to lower the vacuum level to the transmission modulator down to 10" at idle and still be able to open the throttle beyond half-way. I'll next post a new thread describing this situation in more detail and ask for assistance.
__________________
Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951
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  #7  
Old 03-25-2009, 08:45 PM
Richard Howard
 
Join Date: Nov 2008
Location: Western NC Mountains
Posts: 69
Vacuum Control Valve - 617.950 - '78 300SD

I'm presently puzzled by the inability to adjust the VCV on a 617.950 from a '78 300SD W116.120. This VCV has no adjustment capability on the valve itself as the valve has only the operating lever on its shaft extending from the valve housing.

I have found the elongated slot on the lever on the backside of the IP where the ball stud is mounted that carries the adjustable threaded rod that links to the VCV's operating lever. Various adjustments of these two points do not seem to allow the desired vacuum control to be achieved.

When the threaded VCV control rod and the position of its ball stud in the slot are adjusted to allow suitable throttle movement and a 0.5mm clearance against the VCV's stop pin, there is no reduction of vacuum from 20" at the idle position.

Conversely, when the VCV control rod and the ball stud are adjusted to rotate the VCV operating lever to a higher position to reduce vacuum level to 10" at idle, then the movement of the throttle linkage is limited to about half-way, because the control rod causes the VCV lever to hit the stop pin on the VCV.

I've determined that the orifice restrictors (mine is 0.8mm, color is white) serve to control vacuum flow, not vacuum level, so this is not a means to reduce vacuum level to what the transmission modulator should see at idle.

Does anyone know how to correctly adjust this VCV to achieve its purpose?

Are there any suggestions as to what other method can be used to reduce vacuum level to a desired figure? A bleed to atmosphere doesn't seem reasonable in this area since it would also compromise what the brake booster and other vacuum users in the car require.

Thanks very much for any ideas or opinions...
__________________
Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951
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  #8  
Old 03-25-2009, 09:14 PM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
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Quote:
Originally Posted by Richard Howard View Post
The valve now provides a smooth reduction of vacuum from the supply of 20" down to about 1" as shown on my vacuum gauge. The operation is linear and without any abrupt changes.
This is a classic sign of a missing orifice upstream of the VCV. The VCV cannot dump much vacuum when the rack is closed...........thereby requiring that orifice to function properly.
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  #9  
Old 03-25-2009, 09:25 PM
Benzaholic
 
Join Date: Nov 2008
Location: Upstate NY
Posts: 25
If you have the white plastic VCV on the IP (not sure on 1978) there's a cap that pops off to reveal the adjustment. CCW reduces vacuum, CW increases.
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  #10  
Old 03-26-2009, 06:34 AM
Admiral-Third World Fleet
 
Join Date: Feb 2002
Location: Central FL
Posts: 3,069
Hit the junkyards until you come up with a VCV that is adjustable. They are out there......
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  #11  
Old 03-26-2009, 03:17 PM
Richard Howard
 
Join Date: Nov 2008
Location: Western NC Mountains
Posts: 69
Just took off the VCV from the IP for another look in good light at the workbench, looked for a removable cap as akimball442 mentioned above... None found... I then again removed the two screws holding the cover over the coiled flat spring and reconsidered the shaft carrying the 10mm nut with an 8mm jambnut against it.

I had thought that this served to only adjust tension on the spring, a preload of sorts. I then changed its setting with the engine running and a vacuum gauge attached. You're correct - the spring preload determines how much vacuum is dumped before additional valve movement is applied.

I've now set this VCV to begin additional dumping action at 10" vacuum; the transmission modulator now gets its correct baseline amount at idle speed. I reset the VCV's control rod for .5mm clearance at the stop pin.

It's too bad that understanding and knowledge appears usually only after a period of time wasted...

__________________
Respect, protect, and maintain complex systems - whether natural or of German design, to benefit from their full potential.

1982 300SD W126.120 with an OM617.950 from a W116.120
1984 300SD W126.120 with an OM617.951
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