Central Locking ' 85 300D - PeachParts Mercedes-Benz Forum

Alan S · #1 07-17-2002, 11:11 AM

My door locks don't work. Nothing happens when I lock or unlock the drivers door, or any other door for that matter. I took apart the drivers door, nothing loose. Can someone please shed some light and tell me where to begin? I've searched the forums and most have issues with a single door failure or intermittant failure. I have total failure, please help...Thanks

190D22 · #2 07-17-2002, 12:17 PM

Check fuses and central locking pump.

autozen · #3 07-17-2002, 12:26 PM

The 85 300DT doesn't have a central locking pump. Open the hood and check all the vacuum connections located between the engine and brake booster. If you don't find a problem there, you will need a hand held vacuum pump and copies of group 80 pages from the 123 chassos manual. When you are checking the vacuum lines in the engine compartment, the yellow one is the supply for the lock system.

Good luck,
Peter

Alan S · #4 07-17-2002, 12:58 PM

Well, as per a previous post, I removed the drivers floor mat, got into the vacuum wires, and applied vacuum to all doors, all doors opened and closed, so I believe I've narrowed it down to a leak in the engine bay. There seems to be a check valve in the engine bay near the firewall that connects to the yellow hose, do those ever fail? I'll continue the hunt. Thanks again for all the help.

surfblau · #5 07-17-2002, 02:24 PM

But they are easy to test also.

You should see if you can apply a vacuum to the engine side of the yellow 1into2 check valve (the single line side of the valve). Use your mity vac (you better get one if you don't already have one).

You will have to pump a lot by hand, because you will be evacuating the vacuum reservior. Maybe 50 hand pumps to get 15 psi. See if it holds. If not, start working your way back toward the the individual locks to find the leaking circuit. Make sure and test some of the lines, not just the elements. Often the lines crack and the elements are otherwise ok.

Best of luck.

#6 07-17-2002, 05:57 PM

I have an 82 SD so I am not sure this will help but I found out my actuator (mounted by the spare in the trunk) had to be replace because it wasn't there.
Got one ($100) and the doors work fine.
Still need to make the trunk work.

Alan S · #7 07-17-2002, 06:09 PM

Ok, I hope I'm not beating a dead horse, but here it goes. I went and bought a mighty vac. I first tested the lines in the engine bay. I hooked up the mighty vac to the line that leaves the check valve and then splits into two, one yellow and red(lock), and one yellow green(unlock). I then locked the drivers door with all other doors unlocked. Pumped about 30 times, all doors locked, including fuel door. Great! Then I unlocked drivers door, pumped away, nothing happened, infact the mighty max seemed to have overheated!. So then I went back into the car, hooked up mighty to hoses in drivers floorboard, once in the unlock(yellow green), all doors unlocked, then to lock(yellow red), all doors locked. So have I made any progress? I have a feeling the trouble lies in the drivers door. Thanks again guys.

surfblau · #8 07-17-2002, 07:04 PM

Oh yeah, you are the guy from IGH, already having fun I see.

You are on your way. You have probably established that the problem is not in the drivers door.

Check out the four way junction(s) under the passenger side footwell. There are two similar looking circuits there. You may as well check both, though the unlock circuit is probably the problem.

One each circuit (at the four way junction), there will be one line running forward toward the passenger door hinge. Connect mighty vac up and make sure that it holds vac. If either does not, check that line and element. In the mean time, you can plug that area of the locking system and the remainder of your locks will work as normal

Do this for both the unlock and the locking circuit going to the passenger door. If both accuate the lock and hold pressure, move on to one of the lines running aft.

The aftward line that goes to the reservior will take a lot of pumping to evacuate. Other lines will be much easier.

Let me know if you need any more help (I will be checking email later this evening).

MVK · #9 07-17-2002, 10:14 PM

check all the rubber connectors. esp those around the oil filter. I think its one of those simple things.

MVK

Alan S · #10 07-21-2002, 10:14 PM

Just got back from a trip and ready to tackle it again. Ok, I think we are almost there. Today, I bypassed the little check valve that sits almost on top of the fuel filter, guess what? door locks all worked!! Tell me I have a bad check valve. Do they go bad or am I on the wrong path. Thanks again for working with me fella's

MVK · #11 07-21-2002, 10:28 PM

Hi alan Now that you have removed the checkvalve, its very easy to see if its functioning well.
I think it has a little arrow or something on it indicating the flow direction. Check with a vacuum tester. The check valve should allow flow in only one direction. Its quite possible that it was blocked or malfunctioned so that it will now allow the vacuum to travel thru.

I have never had a failure so far so I have not done the troubleshooting first hand.
Seek the opinion of other members on this issue.

MVK

speedy300Dturbo · #12 07-21-2002, 11:58 PM

Check the vacuum supply tank, which is on the underside of the rear package shelf, accessible from the trunk. Make sure the yellow line is in there nice and tight, and that the rubber grommet is in good condition.

surfblau · #13 07-22-2002, 12:03 AM

The valve has two outputs on one side and one on the downstrea,/vacuum pump side. You should be able to plug one of the two upstream sides, connect mity vac to the other one (leave the downstream side open).

Will this configuration hold vac? If not, that is your problem.

The following attempt at a schematic may only display with non proportional fonts.

Vac pump side door lock side

............................... ____connect vac tester here
.....leave open____/
...............................\____ plug here

Does that make sense....

Alan S · #14 07-25-2002, 02:04 PM

As it turns out, I did in fact have a faulty check valve and a leaking passenger door actuator. I replaced both, and everything works beautifuly, I couldn't have done it without fellow posters. Thanks for your time, this board rocks!!

surfblau · #15 07-25-2002, 06:27 PM

This is the third out of three 300's that I have had experience with that the passenger door ended up being partially or wholly to blame.

later