[Gramps380]

At idle vacuum is right at a steady 17, once it's shifted into gear (drive or reverse) the vacuum drops to around 10. What vacuum lines should I be looking for?

I've downloaded a version of the engine service manual and looked at a bunch of the vacuum diagrams posted here but I'm at a loss. All the ones I can see are tested leak free.

I have the dash open, could it be one of the lines behind the glove box? Door lock, windows, A/C, antenna all work fine.

Could there be a line going to the transmission?

I've been browsing this forum since December and found some great advice so thank you very much!! My grandfather passed away last year and left me this beauty. We were both car guys. This is really her only issue, other than that she's perfect!

Thanks in advance for the help.
Marc

 

[Gramps380]

1985 380sl btw

 

[dugald]

You are using a vacuum gauge to measure?
There is a line going to the transmission.
Does the tranny shift properly?

 

[Gramps380]

Yes, I'm using a vacuum gauge. It's seems like it does shift ok. It's hard to take her for a ride at speed cause it's barely running in gear. Where should I look for the line? Drivers side? Passenger?

 

[dugald]

It's hard to take her for a ride at speed cause it's barely running in gear.

What's that mean?

 

[Gramps380]

What's that mean?

Getting the car out on main roads/busy streets and getting up to a decent cruising speed is tough because the car wants to stall anytime I come to a stop. Can't tell if it shifts properly from going around the neighborhood. I'd lean toward it shifts ok. Feels like it holds onto gears a little too long.

I'm going to take a long look for this vacuum line going to the trans. Anyone have a rough idea where it's located?

 

[nobby]

Getting the car out on main roads/busy streets and getting up to a decent cruising speed is tough because the car wants to stall anytime I come to a stop. Can't tell if it shifts properly from going around the neighborhood. I'd lean toward it shifts ok. Feels like it holds onto gears a little too long.

I'm going to take a long look for this vacuum line going to the trans. Anyone have a rough idea where it's located?

It will be connected to the modulator on the side of the trani which should look similar to this:

 

[rowdie]

The valve is on the left side of the trans. The vacuum line connects to the main line at the right rear of the intake plenum. If this line leaks it would be constant not just in gear.

Check the engine timing.

 

[dugald]

Your OP said all was perfect except for a mysterious drop in vacuum. Now you say the engine dies at stops. It seems the vacuum drop is a result of a faltering engine.
I think you need to provide a fuller explanation of what's happening ...
What are the rpms at idle, in neutral and in gear? Does the engine accelerate freely in neutral and in gear? Any smells or signs of running rich.
The more detail, the better chance of useful help.

 

[ejboyd5]

Adjust your idle speed to raise the RPM.

 

[Gramps380]

Quick update...I found the leak!! It wasn't the line going to the transmission but you guys pointed me in the right direction. Tucked behind the engine and under throttle linkage. Got it plugged and it made huge difference. Still have to trace the leak further down the line (vacuum hose that runs into cabin) but at least she runs smooth now.

Thanks again for the help!!