That vacuum line that you are referring to is being shared by a number of vacuum consumers - ie doors, cutoff switch, egr and turbo. I would check for leaks first. Also test the check valve. Ive replaced those check valves a number of times since i had my car.

That black vent line under the vacuum control valve is a vent line. I dont think it does anything. Look at the vacuum diagram, find #85, That line will loop inside the car compartment and end up under the v. control valve. Dont ask me why. I dont see any need for it.

How do I test the check valve and which one are you referring to?

I have been having late shifting in my 617 (85 300Dt California) with 722.416 tranny (I think). Many of you have been real helpful, especially Brian (thanks). Here's the deal ...

I put a "T" in all the lines in and around the Vac amplifier (special to '85 617) to test vacuum (not at the same time obviously). Here's what I got:

Main Vac Supply from Booster line at amp input: 22" at idle.
Tranny Line at amp output: 17" idle, stays at 12" under acceleration all the way up tach to 4K RPM, will spike down to 5" if I stomp on the gas, and I mean stomp.
VCV line from switchover valve: 14" at idle dropping to 7" as soon as I press on accelerator and staying that way thru acceleration.
Boost line from IP area: Nuthin!! O" even underway full power.

Apparently my setup is more like a 722.3, which can be viewed here ...

www.ultrahot.com/vacuum/722_vacuum_func.jpg

This seems quacked to me. Any help you could provide would be appreciated.

** I deleted the other thread; sorry; I am with you.

All of the data that you have provided makes perfect sense.

The entire problem with the transmission must be put aside for the moment until we determine why you have NO BOOST.

The readings all are entirely correct, and, if the boost was present, the vacuum would drop down below 2" when under heavy load.

Additionally, the late shifting may be caused by the fact that you have NO BOOST.

You need that much more pedal to make the vehicle go and this will delay the shifts much more than normal.

So, please leave all transmission issues aside for now until the boost problem is corrected.

Please setup the gauge to test the boost directly off the manifold, BEFORE it reaches the overboost protection valve. See if you get any boost in this line (with the vehicle moving and under load).

If boost is still non-existant, then it's time to start looking at the turbo/wastegate. Did we not do this already???

Edited: I trust that you are using a proper boost gauge for measurement of manifold pressure. You can't use the vacuum gauge.

Oh oh. I did not use a boost gauge. I have a Mityvac. Now it all makes sense. I have to get back out there. Sorry.

What is a proper boost gauge and where can I get one? Obviously there is no boost when you are testing with a vac gauge.

I like this one:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7963108495&category=38660

There are many others on e-bay.

So there's no way around this huh? The vac specs to tranny require me confirming that there's boost I assume? I got gauges and crap coming out of my arse. Do they have em at auto parts stores or is this a specialty type gig. I mean, I got one in my TDI I am tempted to rip out!

You definitely need a gauge for confirming boost. They have them at auto parts stores. You might end up paying a bit more than e-bay, however.

The TDI's gauge should work fine as a temporary device. But, make sure that it is a mechanical gauge. If it's an electrical gauge, you would need to remove the transducer from the engine. Now you are into problems.

The boost is factored in with pedal position. If you have no boost, you have no power, so you'll drive around with it gunned to keep things moving. That is why one should fix performance problems before looking into tranny shifting behavior ones. On the W123s, which I believe share a very similiar bleeder valve, the spec is to set the little lever 10mm from it's stop with the motor running. Then adjust the nut until it is at 4-6"hg, theoretically this is the perfect spot but since we are talking about a worn valve it is only a starting point. You want the vacuum as close to 0"hg as possible at WOT but must be at least 13"hg at idle otherwise you'll get some clunking.

I almost forgot the most important part, the valve is not bad as bad ones will not go past 14"hg no matter how the nut is set or if the arm is all the way at the start. I have about 5 of them in my garage, I'm still looking for one that actually works rather than leaks it off.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

I haven't done anything to the tranny b/c I thought it was something in the Vac all along. My goal now is to carve out some time to properly check boost, then work from there. Just curious, the adjustments you refer to (e.g. 4-6") are at which valve?

Jeff is referring to he adjustments for earlier W123 vehicles that send the vacuum from the VCV directly to the transmission.

Yours is definitely different becuase it bleeds vacuum and sends it to the transducer. I would not use the values from the earlier W123 vehicles without confirmation that they are proper for the '85 CA.

Ok, thanks. I was thinking of grabbing this cheapy JC Whitney boost tester. I dont foresee needing anything more spendy; course, if you think or even suspect this boost gauge is trash let me know.

http://www.jcwhitney.com/autoparts/Product/showCustom-0/Pr-p_Product.CATENTRY_ID:2008841/c-10101/Nty-1/p-2008841/Ntx-mode+matchallpartial/N-10101/tf-Browse/sct-body/s-10101/th-StoreCatalogDisplay/Ntk-AllTextSearchGroup/ss-10101?Ntt=boost

I can't tell from the description whether the gauge is mechanical or not. I suspect that it is because it has both pressure and vacuum on the same gauge.

You might want to ask them before you purchase it.

My SDL was having an opposite problem. I was getting a ton of flare at the 2-3 ad 3-4 shifts. Teed the vacumm going to the transmission and found full 22 in vacumm! Pulled the line off and plugged it until I can verify if it is the amp or the VCV. Strongly suspect the VCV. Wonder how much those cost!