It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ... - PeachParts Mercedes-Benz Forum

floydla1 · #1 02-13-2009, 11:52 PM

Hi folks,
The MB I have: '83 300SD 142K Mi Chassis W126 Engine: 617.95 Tranny: 722.3.
I have performed a full system leak test -- it holds vacuum well, about 0.2" Hg loss in ten minutes. The flaring at 2-3, which is not too bad, is occurring at ~5" Hg when acceleration is gradual. If I push the acceleration such that vacuum is less than 2" Hg, no flaring. It appears I am missing the first orifice (#62 on the vacuum line schematic) -- does anybody know what orifice size this is suppose to be?
Now, if I have plugged off the EGR valve, do the 3-2 valves now have a purpose? Looking at the vacuum diagram, I should by-pass them as well and avoid a potential source of leaks. No?
FYI, according to my MB dealership, the following orifices are no longer available in North America:
Red, 1.1 mm, PN 1162761029
Brown, 0.9mm PN 1162761429
White, 0.8mm PN 1162761229
This is my first exposure to the diesel engine -- loving it!

Samuel M. Ross · #2 02-14-2009, 01:22 AM

Quote:

Originally Posted by floydla1

Hi folks,
The MB I have: '83 300SD 142K Mi Chassis W126 Engine: 617.95 Tranny: 722.3.
I have performed a full system leak test -- it holds vacuum well, about 0.2" Hg loss in ten minutes. The flaring at 2-3, which is not too bad, is occurring at ~5" Hg when acceleration is gradual. If I push the acceleration such that vacuum is less than 2" Hg, no flaring.

It appears I am missing the first orifice (#62 on the vacuum line schematic) --does anybody know what orifice size this is suppose to be? - I think you will find that this orifice is part of the " T " that branches off the main vac. line between the Vac.Pmp.-to-Brake booster chamber. Many times we find that PO(s) have drilled out this orifice so you might have to add an "in-line" orifice just after the "T" [ for you probably one of the smaller ID orifices since it looks like you are looking to lower the vacuum your Engine/Tranny-Shifter Vacuum Control system is receiving from the vacuum pump. I notice that the vacuum diagrams at PeterSchmidTransmissions.Com ONLY show the orifice sizes for the CA 1984-1985 and the Fed 1985 diesels... and these are black [0.6mm] and an unknown color that is 0.5mm

Now, if I have plugged off the EGR valve, do the 3-2 valves now have a purpose?
I think most likely there remains a function for this mechanical "switchover valve" on your 1983 diesel... that of shutting off the VCV's bleeding effect when at idle... however IF this design was merely to properly interact with the EGR's functioning, then MAYBE this is no longer needed... but my 1980 240D model has this switchover valve and I know it was NOT designed withOUT an EGR... so I think this valve probably has a function that you should retain. Check its function with your vacuum gauge and see IF I'm guessing correct on this point

Looking at the vacuum diagram, I should by-pass them as well and avoid a potential source of leaks. No?
See my response immediately above!

FYI, according to my MB dealership, the following orifices are no longer available in North America:
Red, 1.1 mm, PN 1162761029
Brown, 0.9mm PN 1162761429
White, 0.8mm PN 1162761229
I still want to try and use an adjustable orifice ( aka an 1/8-inch needle valve ) as my orifice that throttles the vacuum where it first comes off the main/large vacuum line... in other words I would purposely drill-out the " T " and add the needle valve that would allow me to easily fine-tune the vacuum level in the Engine/Tranny-Shifter Vacuum Control System!
This is my first exposure to the diesel engine -- loving it!

Regards,

Brian Carlton · #3 02-14-2009, 10:04 AM

Quote:

Originally Posted by floydla1

Hi folks,
The MB I have: '83 300SD 142K Mi Chassis W126 Engine: 617.95 Tranny: 722.3.
I have performed a full system leak test -- it holds vacuum well, about 0.2" Hg loss in ten minutes. The flaring at 2-3, which is not too bad, is occurring at ~5" Hg when acceleration is gradual. If I push the acceleration such that vacuum is less than 2" Hg, no flaring. It appears I am missing the first orifice (#62 on the vacuum line schematic) -- does anybody know what orifice size this is suppose to be?
Now, if I have plugged off the EGR valve, do the 3-2 valves now have a purpose? Looking at the vacuum diagram, I should by-pass them as well and avoid a potential source of leaks. No?
FYI, according to my MB dealership, the following orifices are no longer available in North America:
Red, 1.1 mm, PN 1162761029
Brown, 0.9mm PN 1162761429
White, 0.8mm PN 1162761229
This is my first exposure to the diesel engine -- loving it!

Your orifice is in place and functioning properly. You can't find it because it's just a small round sliver of plastic between two rubber vacuum lines. If any dirt has accumulated, it's effectively invisible.

The first thing to do is to remove the 3-2 valves from that system. They only serve to run the EGR. Here is how to eliminate them:

http://www.peachparts.com/shopforum/showpost.php?p=1375506&postcount=5

After you remove the 3-2 valves, get a reading on the vacuum levels at idle and as you drive it. It's possible the flaring will increase. If so, report back and I'll show you what to do with it.

funola · #4 02-21-2009, 09:42 AM

I thought the 3/2 valve had something to do with transmission shift also? Not true? As I recall, Dieselgiant's site has a procedure to replace the 3/2 valve to restore proper shifting? Curious why it is called the 3/2 valve. I still have mine. Going to get rid of it now.

Quote:

Originally Posted by Brian Carlton

Your orifice is in place and functioning properly. You can't find it because it's just a small round sliver of plastic between two rubber vacuum lines. If any dirt has accumulated, it's effectively invisible.

The first thing to do is to remove the 3-2 valves from that system. They only serve to run the EGR. Here is how to eliminate them:

http://www.peachparts.com/shopforum/showpost.php?p=1375506&postcount=5

After you remove the 3-2 valves, get a reading on the vacuum levels at idle and as you drive it. It's possible the flaring will increase. If so, report back and I'll show you what to do with it.

Brian Carlton · #5 02-21-2009, 10:21 AM

Quote:

Originally Posted by funola

I thought the 3/2 valve had something to do with transmission shift also? Not true? As I recall, Dieselgiant's site has a procedure to replace the 3/2 valve to restore proper shifting? Curious why it is called the 3/2 valve. I still have mine. Going to get rid of it now.

It depends on the vehicle. My comments are vehicle specific. You can remove the valves on the 300D turbo.........not on the 240.

funola · #6 02-22-2009, 01:26 PM

Thanks Brian. Can you explain why?

Quote:

Originally Posted by Brian Carlton

It depends on the vehicle. My comments are vehicle specific. You can remove the valves on the 300D turbo.........not on the 240.

Brian Carlton · #7 02-22-2009, 01:33 PM

Quote:

Originally Posted by funola

Thanks Brian. Can you explain why?

The 300 turbos use the vacuum strictly to control the speed of the shift........not the timing of the shift. They have a Bowden cable for that purpose.

The older systems used vacuum to control the speed of the shift and to also delay the shift depending on the vacuum level. They didn't have a Bowden cable.

So, certain older vehicles........240's for sure.......cannot have those valves removed without affecting the transmission performance. I'm really not certain of the years and models that are related to this situation, but I'd presume that for any vehicle without a Bowden cable, it will certainly be applicable.