Ever since I've owned my '82 300SD, the vacuum locks haven't worked. It sat in my garage for the longest time, so this was a nonissue. However, now that I'm actually parking this vehicle out in public, the fact that I cannot lock the doors is now an issue. It baffles me that the lock cannot simply be pushed down (or maybe there is something horribly wrong with my vacuum system.)

When I push down the driver's door lock, I hear the vacuum pump in the trunk come on. However, I cannot push down all of the locks. I think 3 out of 4 is the best I can do. Should I be able to lock all the doors manually?

You can't lock the driver door with the door open (I think Hondas are the same way). You have to lock it with the key after you get out. You should be able to lock the other doors by pushing down the lock button with that door open.

You'll have to lock the trunk manually as well and the fuel filler flap will remain unlocked.

Sixto
87 300D

I went and removed the vacuum pods and related linkage from all the doors. The plungers move very freely now and I have perfect working manual locks. It's not hard, about an hour's work, just save all the parts for when you decide to diagnose and repair the system. Otherwise it would be very expensive to replace it with dealer parts/linkages and you'd probably never do it.

My vacuum system was filled with air; when the car got hot in the sun it would pressurize and unlock the doors

I pulled my doors apart and disconnected all the vacuum mechanisms. Now my doors lock very easily, instead of the 15lb pushdown!


If you pull the door apart you can remove some linkage so that the drivers door can be locked while open, but I wouldn't recommend it(getting locked out is tons of fun!)

*EDIT*
Haha Caduceus you beat me to it!

That is exactly how I would describe it. It's almost as if the lines are filled with air, so when 3 out of 4 locks are down, it feels like I'm pushing against a cushion of air with the last lock.

I'll try disconnecting the linkage so that I can just lock manually.

Thanks, guys.

you may also be able to disconnect a line isolating the lock system and leave it open to prevent pushing down one button causing another one to pop up. You will have to plug the line to the rest of the vacuum system to allow for the rest of the vacuum system to still work.

That's what I did on my W123. I am sure you could do something similar on your 300SD.

__________________
Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY

On a 126 you can just vent the line in the trunk, because the locks are powered by a vac pump in the trunk, not the motor.

__________________
1988 Toyota Camry Wagon......CRUSHED
1988 Porsche 944.......SOLD
1984 300SD.....SOLD
1995 Honda Civic DX... Totaled 11/13/08
1991 Madza Miata 193K and counting.....Mercedes t3 Turbocharger in the works 10 pounds per RWHP FTW