blue vacuum transducer

[jrd]

On my 1987 300D, shifts are too hard at low RPMs and too soft when more power is being applied. What seems to be happening is that the vacuum is too low during gentle driving but too much when power is applied. I get 10" Hg vacuum at the TRA port on the blue vac transducer (disc shaped device near alarm horn on driver's side fender), but the vacuum does not change when I rev the engine. What is inside the riveted-shut vacuum transducer? Another @(*#*(*! rubber diaphragm?





Thank you!

[stevebfl]

Read my article on this subject and see if it answers your questions. http://www.continentalimports.com/ser_ic20242.html

[jrd]

Great article, thank you!



It looks like someone has messed with the injection pump adjustment before, which explains why the maximum vacuum is 10" Hg instead of the recommended 15". The lack of bleed-off suggests a problem with the blue vacuum amp or its adjustment screw setting.



What the article did not mention was how the vacuum amp works internally, i.e. whether it has a rubber diaphragm or operates on some other principle. If it has a 15 year old rubber diaphragm, I will be wasting my time trying to adjust it. Once a few months ago I put a rubber cap on the TRA terminal and drove the car with vac gauge connected elsewhere, and a loud howling sound came out of the vacuum amp.



How is the vacuum regulated in the injection pump? Is there a diaphragm there too?

I'm curious as to where this "source tee" is (supposed to be) located.

[per eriksson]

Interesting,
I have the same problem with the shifts since I got the adjustments on the cable and modulator pressure correct.

I'm going to measure the vacuum supplied to the modulator as soon as I recieve my gauge next week.

A quick check makes me suspect I have some sort of problem with the vacuumvalve on the IP because it seems to be totally insensitive of adjustments but I'm not sure yet.

I quoted a new one from the dealer and it was about 75USD so I think I might get one from the junkyard for comparing mine with.

My car does not have the transducer, only a green check valve directly inline with the modulator but the valve on the IP works the same way.

Let us know what you find and I'll do the same.

[stevebfl]

The system is fairly intricate and my article spends a great deal more on the questions you ask than can be writen here.

The amplifier is NOT adjustable. But, as I wrote there are an almost infinite combination of other possible adjustments. Read the article, understand how the system works and do the adjustment 10-30 times and school will begin. The article explains what the amplifier inputs are and their inter-relationships. It starts with the basic system which really never changes. You must understand that first.

[jrd]

Steve,

I disconnected everything and pulled the blue vacuum amp. There IS an adjustment on the underside, covered by a black cap. The adjustment DOES change the behavior of the device, because I tried it with the MityVac. Unfortunately I am having difficulty determining whether or not it is bad. If I pull on the VCV port, I get a humming sound from the device and the vacuum does not hold at all. The Mityvc holds vacuum very well if I draw on the pressure port (PRE with the retainer clip). If I plug the VAC and TRA ports with my fingers and pull a vacuum on the VCV port, the vacuum leaks down at 1" Hg per second. If I cover the VAC port and pull a vacuum on the TRA port, the vacuum rises to 5" Hg and will not go higher (makes a humming sound if I try). The pressure port seems to hold positive pressure with a gradual leakdown.

I tried making the adjustment on the injection pump device and, before I disconnected the blue amplifier, I noticed a change in top level vacuum as was described in your article. The vacuum levels still did not drop as expected when I pulled the accelerator linkage.

Similarly, with the line to the VCV left wide open, which should produce vacuum at the modulator port at the boost threshold, the modulator vacuum did not drop as expected. Turbo boost did result in some drop of the vacuum.

I am interested also in where the "source tee" is that you mention briefly. Which source are we talking about here, and where would the vacuum restriction be that is supposed to prevent a high biased vacuum?

Thank you,

[surfblau]

I was just wondering if you were able to determine if that was your bad component.

I have a bad vac component - either the modulator, the vcv or the amp and am looking for a way to narrow it down further.

alec

[jrd]

Three problems worked together in my case:

1- Import Motors in oakland charged me a good deal of money to twist the VCV to 10" and crank the modulator a few turns.with no apparent attention to spec, so the vacuumw as preset to 10" all the time. Worked okay with their lousy modulator adjustment, but not on the rebuilt trans.

2-There was a clog in the restrictor leading to the VCV. That's right, a piece of crud holding the vacuum high.

3-Several connections were worn out and leaky, so I purchased new tubing AND restrictors and replumbed it all.from the factory diagram.

Seems to be fine with the original blue saucer. It would be nice if anyone actually new what was inside--but no one does.

Justin