Vacuum Problems, engine/transmission 1987 300D - PeachParts Mercedes-Benz Forum

Tpawlik · #1 10-07-2010, 08:42 AM

I have been reading lots of threads on repairing the vacuum system and I have a good picture of the system. But could still use some help. My shut off lever is hanging very low and the transmission is shifting horribly.
I have a solid 20 hg at the smaller hose coming from the pump. I have about 15 hg going into the top of the flying saucer. I have to check the rest of the lines tonight.
When the engine is idleing and I remove the line from the intake manifold, there is no vacuum or pressure. Which should I have? I removed the fitting and cleaned it, but it was not clogged.
I removed line b at the VCV that goes to the key switch and there is no vacuum there either. Is this right? I read that the vacuum is rerouted when you turn off the key. The key does kill the engine.
I have already disconnected everything on the right side of the engine and plugged the two lines on the five way at the pump.
Also, I read that a new VCV is no longer available, if I need one, is this correct?
Thanks.

sixto · #2 10-07-2010, 05:47 PM

Check the output of the flying saucer. It's the other topside port with the damper (big green cylinder). You should see at least 15" Hg while idling.

The boost signal line from the intake manifold to the ALDA will likely register neither vacuum nor pressure while idling. There is no air throttle so the free flow provides all the air the engine can ingest. Result is negligible vacuum at idle. The turbo isn't pressurizing intake air at idle so there's no pressure to measure.

Vacuum supply for the key switch doesn't come from the VCV. It comes from the check valve along the big vacuum line to the brake booster. If the shutoff level hangs low, see if it pops up if you disconnect the vacuum line from the shutoff actuator on the IP. If so, you might have a bad key switch or a restricted vent in the key switch. When the engine is running, there should be no vacuum provided to the shutoff actuator. Turning the key to run should vent that line and keep it vented. Should also block the key switch supply line.

I have not heard that the VCV is no longer available. The original part number has been superseded but I don't know the difference between old and new. Did you check with folks at FastLane?

Sixto
87 300D

Tpawlik · #3 10-08-2010, 08:11 AM

Sixto, I have issues. The output to the trans is only 6.5 hg and it takes about 15 seconds for it to reach that number. The VCV line under the VA was off and the trans line was crossed with one coming from Y29.
I switched those around and reconnected the VCV line. I also removed the damper to get more vacuum to the modulator. It is up shifting much better, but flaring occasionally. Downshifts are also better.
Pulling the line off the shut off actuator does nothing there is no vacuum in that line.
I did rev the engine and feel pressure from the manifold fitting to Y30.
It appears that I am going to have to remove the hard plastic lines one by one and replace them along with the rubber connectors.
Until I find all the leaks, will adjusting the VCV put more vacuum into the system?

sixto · #4 10-08-2010, 03:54 PM

What's the vacuum reading into and out of the VCV at idle? Is the vacuum gauge indicator steady or does it fluctuate?

You can try bypassing the flying saucer to isolate the problem. Hook up the line from the VCV output to the flying saucer directly to the transmission. Keep one damper in that line. Shifts will be stiff until the transmission fluid warms up if you're not running synthetic then it should feel reasonably normal.

If you feel upshifts as you creep to a stop, that's a sign of insufficient vacuum at idle.

While you're checking for vacuum leaks, have you checked that the coolant temp VSV is behaving as it should? IIRC it should allow extra vacuum under 50*F and boost from the ALDA line above 50*F. If the VSV is fine, maybe the temp sensor by the water pump isn't clicking off and on at 50*F as it should. I forget if it goes from open circuit to closed at 50*F or the other way. Easy to check.

Check also that the slightly bigger vacuum line that branches from the flying saucer vacuum supply line holds vacuum. There's a vacuum reservoir in the left fender seemingly only for the transmission modulator. It takes a good many pumps of the MityVac to build a vacuum in the reservoir but it should hold indefinitely.

Sixto
87 300D

Tpawlik · #5 10-08-2010, 06:02 PM

On the port for the line with the #72 damper I have 6.5 HG steady. It takes a couple of seconds to slowly get to 6.5. The other port connected to the Y has nothing on it and neither does the line from the Y.
As far as shifting, it's on the mushy side unless you are pushing it a little. Way better than before.
VSV? You have exceeded my Mercedes security level!
I pumped up the reservoir to 15 HG and it did not waiver.

sixto · #6 10-08-2010, 10:16 PM

VSV is vacuum switching valve. Y29 and Y30 in the diagram.

There are two dampers (72) in the system. Do you mean the one right atop the VCV or the one atop the flying saucer?

Low vacuum and mushy shifting don't compute.

Did you try bypassing the flying saucer?

Sixto
87 300D

sixto · #7 10-08-2010, 11:00 PM

XXXX shows the original VCV 1233001033 is still available for $72 list. The replacement VCV 1403000833 $165 list.

Sixto
87 300D

Tpawlik · #8 10-09-2010, 08:52 AM

I connected the mighty vac directly to the VCV ports. I have not bypassed the BFS. Are you saying I need to remove the vacuum line that goes into the top of the BFS and connect it directly to the trans line with the damper back in place near the BFS? I will try that and report back.

Tpawlik · #9 10-09-2010, 12:48 PM

Connected the vacuum line to the BFS directly to the trans line. Firmer shifts,
but the trans does not like it if I start to accelerate, have to liftoff and hit the brakes. It thuds badly. (upshifting?)
I still have no vacuum going in or out of the VCV

Tpawlik · #10 10-09-2010, 01:11 PM

Sorry for the rambling messages. I checked the line from the pump (21 HG)thru the five way. I had two small leaks. I now have 5HG on the line going to the center of the VCV, the line with the green damper near the VCV. Nothing coming out of the other port. I can pull all the lines off the VCV and the engine still runs.

sixto · #11 10-09-2010, 02:42 PM

This ain't no gasser that needs controlled vacuum to idle. These cars need vacuum to stop

What I meant is to connect the output of the VCV, the line with the green damper, directly to the line going to the transmission, the line with a hooked rubber connector atop the vacuum amplifier.

I'm not sure I follow all your test points but I'm pretty sure your VCV needs attention. If you have a second vacuum gauge, attach it to the damper just after the VCV. Apply vacuum with a MityVac to the VCV supply port. The VCV should steadily hold some amount of vacuum while you're pumping and bleed the vacuum when you stop pumping. If you can't pump fast enough for the VCV to hold vacuum, the VCV isn't doing its job.

Sixto
87 300D

Tpawlik · #12 10-09-2010, 04:50 PM

I was thinking about buying a vacuum guage instead of using the MityVac. I could probably use it on my 62 Strarfire, It runs on gas!!!
I will let you know what happens.
Do you know what makes the $165 VCV more better than the $72 one? Besides $93
Thanks for your help. Depending on my problem, the learning curve can be steep.

sixto · #13 10-09-2010, 09:08 PM

It has a 140 prefix part number. Everything for a W140 is more expensive

Sixto
87 300D