Vacuum Pump issues, W116, 79 300sd

[reinventthewheel]

The automatic door locks dont work, the brake booster doesnt work, but no other problems (turns off fine, brakes still work but have to hit the pedal hard)

Do I need to replace the whole vacuum pump?
What can I do to check?

Also, any suggestions as to how to get the window down if the regulator is broken so I can replace the regulator?

[unkl300d]

if you have oil in the vac lines, the pump is out.

you might be able to replace the diaphram etc. or you have to replace the whole pump.
use the archives to search for more infos. check all your vac lines, maybe its just a leak or unfastened line.

pull off the door panel and unbolt the window from the regulator. you have to remove the rubber molding also. pull out the glass

if the regulator is jammed, cut it out.

use the archives and search function

[300SDog]

Auto door locks rarely work on car that old. You can pull the yellow and green airlines from the octopus looking rubber junction at the firewall, then plug the junction openings with golf tees and operate the doorlocks manually. This will also help you get a handle on rest of the vacuum system.

Who diagnosed the brake booster? It could be something really simple like the O-ring between the booster and brake master cylinder. Another culprit that takes out boosters is brake fluid leaking from the MC.

Regarding the vac pump, look for engine oil in the large vac line that leads to the intake manifold. Its a diaphragm inside the pump that cracks and wears out and then engine oil gets sucked into the manifold vac line. Rebuild kits include the diaphragm, gaskets etc. But having the engine shut down vacuum solenoid working is very good sign, that indicates the vac pump diaphragm may not be dead.

With the electric window you must just pull the door panel and then start unbolting accessible nuts'n bolts including the window tracks until the glass come crashing down. A piece of wood works well to keep it propped up as you tear into dismantling the electr window system and end up with a pile of nut'n bolts on the garage floor. Reassembly will be the tricky part, it helps to pull the other side door panel to have a protype example of how it oughta look when fully assembled.

And Welcome to the Vintage Forum. Things move slowly enough around here that you can return to this thread with new developments as the work progresses. We've got a couple of immortal threads going where entire cars have been rebuilt in one thread. Advanced search engine features are excellent here too.

[reinventthewheel]

Thanks for the replies and welcome

The brake booster wasn't diagnosed. The brake pedal is just hard to push and I read that the brake booster and locks were both operated by the vacuum pump, so I assumed they were both caused by probs in the vac pump.

Where's that junction at the firewall?

So, if I replace the vacuum pump that means my locks still might not work

someone else said the locks are operated by a separate pump in the trunk
is that true, or are they thinking of the later 300sd?

[ctaylor738]

I am surprised that the engine will shut off. That is usually the first to go if the pump is bad. That makes me wonder if the booster and one of the cabin elements are failing.

Easy to check - buy yourself a Mityvac kit and test the booster. Pull the line for the cabin vacuum, pump it up with the Mityvac, and see if the locks work.

[Wodnek]

In the 126 there is an electric vac pump, but not the 116.

Have you replaced the master cylinder lately? I ask, because if you forget the gasket between the master cylinder and the booster you will lose all your vacuum.
Go ahead and ask how I know this one!

[diametricalbenz]

Originally Posted by Wodnek

In the 126 there is an electric vac pump, but not the 116.

Have you replaced the master cylinder lately? I ask, because if you forget the gasket between the master cylinder and the booster you will lose all your vacuum.
Go ahead and ask how I know this one!

Enlighten us! I take it you were able to stop the car before going too far?

[byrdandcompany]

I just had the exact same problems with my 240d. Turns out that the booster was okay and it was siezed calipers in the rear. It could stop, but it took standing on it to do it. Have you taken a mitivac to the vacuum lines and seen how pressure you are getting? I would do that before you start replacing things.

[reinventthewheel]

So, I looked at the vacuum pump more and found out that the previous owner had sealed off one of the lines. Check the pressure of the pump and it's fine.
I guess there was a problem with the line so they cut it off from the pump to keep from losing pressure of the whole system.

[unkl300d]

Wadd I tellYa???

[jackw3306]

Just FYI M-B changed the vacuum pump design in the mid-1980 model year. M-B part no 000-230-1365 vacuum pump will NOT fit early 1980 and previous models 300SD. It tkes M-B part no 617-230-0165
DAMHIKT

Jackson