Measured 9" vac early on. Shortly after tweaking the vac modulator. That's when I knew I needed to do something under the hood. After I adjusted the gap to 0.5mm the vac dropped to 5-6". Assumed this was because of the gap adjustment. Then I adjusted the nut under the plastic dome to get 15". After that it stopped bleeding down at WOT. Will do some more checking tomorrow.

Where did the measure in the 9"? On the main vacuum line from the pump? after the VCV? before the VCV? at the door lock line? If the vacuum at the branch from the main line is only 9" the problem isn't in the transmission circuit but somewhere else.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

In the 300SD the door locks do not work off this vacuum. There is a separate pump in the trunk for door locks. Not like 300D.

What you need to know is the level of vacuum in the system as a whole. At sea level it should read around 21". If the whole system is low, it would account for why you aren't getting enough vacuum at the tranny at idle to smooth out the shifts.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry - my vac is now set to 15". Downshift is perfect. Upshifts are perfect except I am getting a little flare because I have too much vac. There is no bleed down between vav and vacuum modulator for some reason and that is obviously causing the slight flare. I am trying to track down the reason for that now.

Something has changed because yesterday there was almost instant bleed down when I hit the accelerator.

When you say that your vacuum is set for 15" now, what do you mean by that? The system as a whole simply produces vacuum to the maximum level of 21" or so at sea level. To my knowledge, there is no way of setting the vacuum in the system. It seems to me that you are measuring the amount of vacuum going to the tranny, whereas, you first need to measure the level of the vacuum in the system to see whether it is normal or not.
I say this because when I have a clunking downshift, it is caused by a problem in the whole system, and not by a problem specific to the vacuum transmission controls. So, when you adjusted your vacuum (which I assume you did by altering the VCV), you may have adapted the VCV to a system in which the overall vacuum is low and that is why you are still experiencing problems.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry - I am not sure you understand where I am now. I adjusted the vcv so the tranny gets 15" vac and the upshift and downshift is now OK. For some reason I am getting no bleed down when driving so even at WOT the tranny is receiving 15 " vac. With no bleed down I am getting some flare in 3-4 upshift and a little flare sometimes in 2-3 upshift.

I am not sure what question you are addressing since I have resolved the problemmatic downshift clunk. Are you saying that overall system vac level could be the reason I am getting no bleed down now? I have never seemed to suffer from low vac and have not had a problem with engine shutoff. I also got great bleed down before adjusting the screw under the plastic dome on the vcv.

Yes, that's what I'm saying. If the reason you were getting hard downshifts was because 15" was the maximum level of the vacuum system and it wasn't enough to avoid hard downshifts with the VCV in its original position and you adapted the VCV to get soft downshifts with a total of 15" of vacuum when it was originally set to function with 21" of vacuum, then that might explain the continuing problems with flaring on the upshifts.
15" may be adequate to shut off the engine but not adequate to control the transmission properly. I don't know the amount of vacuum necessary for proper transmission function but without a measurement of the vacuum produced in your system, I think your shooting in the dark as to the exact cause of the problem. If there's 21" of vacuum in the system (outside of the transmission system) then I think you can focus on the transmission portion as the source of the problem. Without knowing that I can't see a reason to keep focusing on the VCV.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Kerry - I did not get bad downshifts at 15"; they happened when the system was at 9". As soon as I adjusted it up to 15" the bad downshift clunks went away.

Per the MB instructions the specs of the transmission are between 10-15". At WOT the system is supposed to bleed down to zero so that it gets good upshifts. The vcv obviously takes system vac and adjusts it to a specific setting, in my case 15". The throttle linkage is connected to the vcv and at WOT the vcv lever moves to a stop and the bleed down occurs so that the tranny can shift with no vac.

No idea what is the MB design to accommodate downshift but in my car when pulling 15" vac it downshifts perfectly.

Now the only thing that is not working is the bleed off. I may have damaged the vcv (but I do not know how) and that is why there is no longer any bleed off - stopped happening yesterday.

I understand that but parts of the system are controlled by orfices which limit the amount of available vacuum. Without knowing the condition of the basic provider of vacuum--the pump--the rest of the system can't be reliably diagnosed. In other words, the transmission control system assumes there is 21" of vacuum available and operates to reduce that vacuum to the amount appropriate for transmission function, if there isn't 21" of vacuum available then the transmission control system is out of kilter. You can't know if the VCV is the cause of the current problem without knowing the amount of vacuum that the transmission control system is being fed and from which the reduction is being made.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Making sure the vacuum system is working properly is important, as well as the throttle linkages. (the rack should see full stop to complete rest)

It sounds like you have adjusted the vacuum to the highest setting. If you are getting a flare, turn the VCV back just a hair and try again.

This will be trial and error for a while, but now that you what to do... it should be straight forward.

If you find that you cannot remove the flare or the shifts are too 'long' then you will have to make adjustments at the modulator and repeat the VCV adjustments.

repeat as necessary.

__________________

JT - I think I have it under control now. Any idea why the vac stopped bleeding off at WOT?

Also any idea on a 300SD where you would plug in the mityvac to check overall system vac which I understand should be 21'\"?

The brown line going to the ignition switch should give you overall system level as would the main line to the climate control system. I think that line is green.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks; I will look.

OK, just looked and now I am stumped. There seems to be no green line anywhere. There is a brown with black stripe line that goes from its own outlet at the back of the vcv and from there through the firewall; maybe three feet of line. I hooked in the mityvac, started the engine, and get zero vacuum. Then I unhooked it all and hooked the mityvac to the outlet at the end of the vcv; still zero vac but the engine will not turn off - even using the shutoff lever - until I unplug the mityvac.

The other brown line is connected in common with several other lines near the brake booster; they all feed off the brake line and some seem to go to the brake booster. However several including the brown are brought back together in a rubber Y at the firewall with a single line continuing through the firewall. Seeing them using a common feed I put the mityvac between the 1/2 inch brake line and the line that feeds the brown and everything else near the brake booster.

Testing I find zero vacuum.

So I cannot seem to find the vac line for the total system although both brown lines go either directly or indirectly through the firewall.

Are you putting the Mity Vac in-line or directly into the end of a vacuum line? If you put it directly on to the line coming out of the main 1/2 brake line, you should get system vacuum coming from the pump.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13