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

Samuel M. Ross · #1 07-16-2008, 12:54 AM

Quote:

Originally Posted by herring

Ok, first I have to say I was a little overoptimistic on my "cure". While it certainly did help things, the 1-2 and 2-3 shifts are still not smooth. The best I can say is that if I accelerate "just so" I can get them to be smooth...which is an improvement. And they're always smoother than before.

To recap, I've got a line coming directly off a large-diameter trunk line, which goes through a "Y" connector. One branch goes to the VCV (through the flying saucer), the other goes to the transmission. Where the 2mm orifice was (and where the 0.8mm orifice is now) is past the "Y" going to the VCV. So this has the effect of "diverting" more vacuum to the transmission.

I played around a bit today, putting the orifice on the "input" side of the "Y" (reducing flow to both the VCV and the trans). It made things slightly worse. I then removed the orifice altogether and capped off the line to the VCV, so 100% of the vacuum went to the trans. Very smooth, but no power due to being always in too high a gear, and slow shifts. Stupid me left the Mityvac behind so I didn't measure vacuum but now I have a sense of what's going on. Ideally, the trans needs more vacuum than it gets now, but not all that the pump can put out. IOW, an even-smaller orifice (if such a thing existed) to the VCV would be ideal.

I will still probably work on restoring the flow to the switchover valves on top of the engine. I did the puff test today, as far as I could. Again referring to the above diagram, this is part # 71.

Air blown in hole 1 comes out hole 3.
Air blown in hole 5 comes out hole 4.

This is at idle.

Hole 2 on my vehicle is broken off at the connector and capped off with a bolt on the hose side. This could be the reason my system was so "hacked".

Question: If I don't want the EGR valve anyway, it seems like there wouldn't be any reason to restore the hole 1/3 flow (which just goes to the EGR valve). Am I right on this? So what else does the switchover valve do?

Herring - I'm sorry but as much as I would like to follow along with your situation, I'm really having trouble and the thing that really frustrates me is that I know that IF you could take the vacuum diagram and edit it graphically as I would do [IF in your situation]... I know this block I'm having would NOT be there!!? IF you have the skills to edit "JPG" graphics files... especially using colors to show more closely how your Tranny-Shifter Vacuum control system has been modified and presently exists... please do so!! IF NOT, in the future, please refer to components by their number designation on the diagram!!

But in the mean time let me try to get some clarity with these Q(s):
(a) I think by large-diameter trunk line you are referring to the large vacuum line between the vacuum pump and the brake booster reservoir?
(b) Im just not sure as to what you are calling the flying saucer) !??

I'll let you chew on these 2 Q(s) and I'll come back in a separate POST to try and address the last part of your last POST!
Regards,

Samuel M. Ross · #2 07-16-2008, 01:18 AM

Herring,
Switchover Valve ports #1 & #3:
So on the double mechanical "switchover valves" inside the black box that is controlled by linkage to the throttle [#64/#64a]... so I basically guessed correctly that at idle at least ports #1 & #3 interconnect and thus these provide a simple ON/OFF vacuum signal for the EGR system so it is OFF at idle. Just in case you decide to restore your EGR system to full operation, I'm thinking this vacuum signal might also be present at a higher throttle position!
Switchover Valve ports #4 & #5:
Once again it looks like I am at least partially correct. As to the #2 port, I admit that I must NOT claim to fully understand why there is such a feedback line from what I call the "bleeder" side of the VCV [#65]. My best speculation is that at certain throttle possitions, this line provides a moderate-to-strong vacuum via this line as a means to nullify the VCV's bleeding effect through the line that vents under the dash... and thus nullifies a tranny shift under certain load/throttle conditions.

The later models muddy my understanding of such " stuff " even further... and the 1985 CA cars also add another 5 components to the system that are in or related to and accomplish a much more precide tranny-shifter control and feel of luxury!

Your Question now:
Blocking OFF the EGR system - Yes, so long as the #1 & #3 ports are serving only the EGR system and as long as your STATE dose not arrest you and drag you off to jail for not having it hooked up, I would simplify things [at least for now] by putting golf tee(s) in the line that goes to #1 & #3 [just in case] and also the rubber "T-connector" that supplies vacuum to #1.

Closing Sidebar - On both our much simplier 1980 models, I have learned to use the throttle to help me control shifting... and have found with a little practice I can do quite well at this... basically by backing off on the throttle just enough to make for a smoother shift between:
(a) 1st & 2nd gear..................... by feel
(b) 2nd & 3rd............... @ just before 25 mph........... and
(c) 3rd & 4th............... @ ~30 mph and above !
I feel that doing this (1) minimizes wear on the tranny and (2) allows me to drive more for economy by keeping the RPMs down!
For economy, I'm even running 35 psi "all the way round" in the tires!
It's too soon to give a report on any favorable results!
Regards,