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Old 09-13-2012, 02:48 PM
Mercedes Metro
Join Date: Sep 2012
Location: Central Oregon
Posts: 73
3/2 Vacuum Valve ... who do I trust?

Greetings Everyone,
I'm new to this whole world, but learning as fast as I can.
I am going to be transplanting a 213K-ish 617 from a 1981 300SD into my 1946 International Metro.
I'm currently in the process of doing some small tweaks to the 300SD ...that are easy to do without removing the engine.

I took apart my 3/2 valve cover today, and found the classic worn-out vacuum valve cams.
The actual valve bodies were also broken! (the thin section near the pin had snapped off).

Side note: the transmission does shift slightly 'harsh' between 1/2 when cold, but better as the vehicles warms up. i believe i have the pressure control rod tensioned correctly. I have not done a full vacuum system check yet.
Side note #2, the EGR is partially blocked off right now, but i plan on putting a delete-kit with plates over them and completely removing it from my system.

Okay, back to my post's title: who do i trust about the entire 3/2 valve system.

  • One source says "Some argue that you should just remove the 3/2 valves, plug off the EGR, and plug the two vacuum lines going the the VCSV. I strongly argue against that. I will agree it is possible to get some transmissions shifting better by doing this - especially if there were vacuum leaks at multiple locations in the 3/2 valve assembly as well leaks in the EGR itself. But this is a “bandaid” repair. If you want to get your engine burning clean (who likes to ride behind a smoking diesel) and get the maximum performance out of your transmission, then I say repair the 3/2 valve assemblies and associated connections. Come on, we are not talking about big bucks here!"
  • effectively that it is indeed important to shifting performance. They effectively say it has an effect on the VCV on the injector pump.
  • another says: "Older diesel Mercedes cars with an automatic transmission tend to shift harder than other cars you may be use to. Some times the transmission just does not shift quite right. While there are many items that can go arye, one thing is for sure, there is a 99.9% chance your vacuum valve levers are worn and not working properly"
  • BUT:
  • here Simple=Better says that the 3/2 system is pointless in a post to the form
  • and more of the same here as well if you search for 'proper 3 2 vacuum valve'

SOOOOOOO ... who do I trust?

If I trust the 'keep the 3/2' ... the i'm looking at about 100$ worth of repairs (two sets of valves) ... and if so ... how do i re-plumb within the valve cover to completely delete the EGR?

If I trust the 'delete' ...then can i effectively remove the entire cover and parts within the cover ... and then plug the three-way line from #3 in the 3/2 valve near #63 in this picture (attached)?

wow ... wait until i have the engine pulled and do the 'heavy lifting'?!?!!!

thanks for any and all replies


Sorry, competing web forums/sales sites cannot be linked or discussed on this forum!

ohhh ... soooooooo sorry about the competing sites ... didn't mean anything by it. i've also edited those bits out! --- geoff
Attached Thumbnails
3/2 Vacuum Valve ... who do I trust?-egr_plumbing.jpg  

Last edited by geoffraynak; 09-13-2012 at 06:49 PM. Reason: links to competing sites.
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Old 09-13-2012, 05:29 PM
vstech's Avatar
Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,287
Sorry for the post getting flagged, new members cannot post links in their threads.
also, competing websites are not allowed to be mentioned or linked to on this site! thanks.

Welcome to the forum!
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
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1987 190D 2.5-5SPEED!!!

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1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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Old 09-13-2012, 06:47 PM
Mercedes Metro
Join Date: Sep 2012
Location: Central Oregon
Posts: 73
thanks for the honest welcome...
should have read the whole EULA!

hope my thread makes it through now that i've edited.
i just added those links as point/counter-point.

thanks everyone

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Old 09-13-2012, 07:39 PM
Diesel911's Avatar
Registered User
Join Date: Sep 2007
Location: Long Beach,CA
Posts: 27,362
I have no issue with someone who wants to keep the EGR functioning. If so you need to fix the Valves.

I opted to simly disconnect the Vacuum Hose to the EGR and left everthing else the same. I had previously replaced the little worn Levers on the Valve before I knew what they did.
84 300D, 82 Volvo 244Gl Diesel
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Old 09-13-2012, 07:44 PM
Registered User
Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,141
Note from the diagram that the 3/2 valves are for control of the EGR. Most have blocked the EGR (for testing purposes ;>) which causes extreme carbon build up in the intake manifold.

This also eliminates some weak spots in the vacuum control to the transmission. Proper vacuum will cause shifting to be much smoother. And no, "expecting the transmission to shift harshly on an older MB" is not an informed response. Also, don't mess with the vacuum modulator until you have checked everything else. Even if it has a vacuum leak, the repair may be as simple as replacement of a little rubber cap.

Here are a few links to help you out: (Some are a little long but they certainly help in the understanding of the system.)
It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...
EGR elimination, 617 engine

84 300SD 350K+ miles ( Blue Belle )
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Old 09-14-2012, 03:26 AM
TnBob's Avatar
Registered User
Join Date: Dec 2009
Location: Shelbyville, Tn
Posts: 1,907
The arms are available
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."
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Old 09-14-2012, 03:41 AM
fashion victim immunizer
Join Date: Feb 2012
Location: oakland
Posts: 930
on your 1981 i dont believe the 3/2 valves control shifting. there ARE a few model years where the 3/2 valve did assist with shifting and wasnt just for operating the EGR. if you want to just button everything up the way it came from the factory, as a previous poster mentioned, you can buy the plastic arms for the 3/2 valves separately very cheaply. you just push the pin out of the valve, install the new arm, and push the pin back in.,
1981 NA 300D 310k miles
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Old 09-14-2012, 04:39 AM
cho's Avatar
cho cho is offline
diesel power
Join Date: Dec 2011
Location: Europe
Posts: 933
I would recommend it

hi mate,

I completely removed EGR and 3/2 valve,... never looked back.

no carbon buildup and one possible point of vacuum leakage less.


w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered
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Old 09-14-2012, 06:51 AM
oldsinner111's Avatar
love all animals
Join Date: Nov 2008
Location: bristol,tn
Posts: 5,349
I removed all that crap.Don't remove if your living in communist states like california
If I'm a butt,ignore,I have mood swings
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Old 09-14-2012, 12:07 PM
Mercedes Metro
Join Date: Sep 2012
Location: Central Oregon
Posts: 73
thanks for all the advice!

anyway, i took all the vac lines and re-plumbed to remover the 3-ways ...
took it for a drive last night
it was awesome and no clunking...
my guess is that there were vac-leaks causing the harsh shifts.
after transplant, i'll re-do the vac-lines and get it smooth as summer butter.

i've also ordered a EGR delete kit from BC.

in the mean time, i removed the upper EGR connector ... it was 50-60% clogged.
one solution = 3 more projects.

thanks everyone!
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