What's the difference between adjusting the VCV and the blue vac amp? 85 300D - PeachParts Mercedes-Benz Forum

dieseldan44 · #1 02-23-2009, 10:19 PM

Backstory:

Sort of a strange happening. On my 85 the shifting was perfect. Decided to disable the EGR system. Plugged the two vacuum supply lines to the valves, and go for a drive. The shifts are now mushy. Discovered that the switchover valve at the end of one of the orifice's didn;t hold any vacuum. So the shifting was good, even with a straight leak through the orange .5mm orifice. Maybe it had been adjusted to this state by another mechanic in the past. Who knows.

The Point:

So I need to decrease vacuum. I have been around the block with this on the 82 and know the VCV well, but the 85 has the blue amp. Wondering what the difference is between adjusting the blue amp and VCV. Do they affect different portions of the control curve?

Also, how do you adjust the blue pod? I see the adjustment area, but i cant see what tool goes in there to make the adjustment...

Thanks,
dd

Brian Carlton · #2 02-23-2009, 10:49 PM

Firstly, let me qualify my comments to the '86 vehicle and upward. I believe the '85 is an anomaly and it has a different VCV that is coupled with the amplifier.

So.........for the '86 and '87 diesels:

The VCV needs to be adjusted per the manual...........no real capability of varying it to suit a specific transmission or operating condition. Try to adjust it and you find that it will permit wild 2-3 flaring on occasion, for no apparent reason.

I "think" the '85 is different and has the older VCV that gives you the capability of adjustment underneath the dome on the side............but, you'd need to verify this.

On the underside of the amplifier is a black plastic cover. Remove the cover and you'll find a 4mm plastic hex screw.........recessed. If you turn this screw clockwise, the vacuum will be reduced to the transmission and the shifts will firm up.

dieseldan44 · #3 02-23-2009, 11:24 PM

Thanks Brian. Hmmm, there's no black cover on the adjustment area of my blue pod, thats probably where Ill want to start. That pod, at least on the 85, is receiving a boost signal from the ALDA, so I didn't know if it only acted in certain boost conditions etc. Is there an explanation of what the pod's vacuum curve is somewhere hidden in a manual?

Quote:

Originally Posted by Brian Carlton

I "think" the '85 is different and has the older VCV that gives you the capability of adjustment underneath the dome on the side............but, you'd need to verify this.

The VCV is indeed the same as the earlier turbo W123 models.

As a sort of side note, the 85 300D federal is vacuum routing is identical to the 300D 85 'California' diagrams I have seen here and at other sites.

Ill hook up a vac gauge tomorrow and adjust to what it needs to be. Ill report back how it goes.

dd

Brian Carlton · #4 02-23-2009, 11:29 PM

Quote:

Originally Posted by dieseldan44

Thanks Brian. Hmmm, there's no black cover on the adjustment area of my blue pod, thats probably where Ill want to start. That pod, at least on the 85, is receiving a boost signal from the ALDA, so I didn't know if it only acted in certain boost conditions etc. Is there an explanation of what the pod's vacuum curve is somewhere hidden in a manual?

The VCV is indeed the same as the earlier turbo W123 models.

As a sort of side note, the 85 300D federal is vacuum routing is identical to the 300D 85 'California' diagrams I have seen here and at other sites.

Ill hook up a vac gauge tomorrow and adjust to what it needs to be. Ill report back how it goes.

dd

Sorry, my error. You'll need to remove the amplifier from the vehicle and find the black plastic cap on the underside. You'll never see it in the installed condition.

If you can adjust the VCV, I'd do that first. With that style VCV, you can adjust it right in the driveway with the engine shutdown. Just connect the Mityvac to the vacuum supply line and pump it up. It should stop at the idle value for vacuum and bleed the remainder away. If there is a significant leak downstream, you won't be able to pump it up.........it'll bleed off too fast for an accurate reading.

Jeremy5848 · #5 02-24-2009, 12:29 AM

Brian is right, the '85 has a different VCV. Unfortunately, I've never played with mine, only with the '87, so I can't give advice.

jt20 · #6 02-24-2009, 12:36 AM

I don't think the VCV should be your first adjustment, Dan. Ensure its properly functioning and reaching its stop point.

The first adjustments you make should be on the VacAmp. There is great control and accuracy there. Look for a maroon-ish cap on the underside of the disk. There is a male allen head in there and I beleive B.C. is correct about the size.

Why did you plug "lines" to the EGR... there is only one.

dieseldan44 · #7 02-24-2009, 08:55 AM

Quote:

Originally Posted by jt20

I don't think the VCV should be your first adjustment, Dan. Ensure its properly functioning and reaching its stop point.

The first adjustments you make should be on the VacAmp. There is great control and accuracy there. Look for a maroon-ish cap on the underside of the disk. There is a male allen head in there and I beleive B.C. is correct about the size.

Why did you plug "lines" to the EGR... there is only one.

Sorry for being imprecise. There are two switchover valves on the driver's side inner fender. One for the EGR, one for the ARV. I plugged the vacuum supply going to both of these. I know I don't want the EGR in, I dont think I want the ARV either, right? Besides, the ARV switchover valve is malfunctioning.

I am taking these out so I can make room for more important emission reduction valves in the area :-)

I'll experiment later today and report back how it goes.

dd

jt20 · #8 02-25-2009, 02:12 AM

Quote:

Originally Posted by dieseldan44

Sorry for being imprecise. There are two switchover valves on the driver's side inner fender. One for the EGR, one for the ARV. I plugged the vacuum supply going to both of these. I know I don't want the EGR in, I dont think I want the ARV either, right? Besides, the ARV switchover valve is malfunctioning.

I am taking these out so I can make room for more important emission reduction valves in the area :-)

I'll experiment later today and report back how it goes.

dd

Definite no on the EGR.

I have yet to read anything convincing on the ARV. The more experienced members on here have yet to come to a consensus on its actual function. GSXR has some good info on it and decided plugging it had no effect.
I am curious though, how do you know its acting up? I plugged mine as well out of curiosity.