Door lock vacuum question 77 300d - PeachParts Mercedes-Benz Forum

kerry · #1 04-18-2008, 12:19 PM

I've sold my 77 300d but before the guy picks it up I told him I'd trace out the vacuum problem in the door lock system which I have simply had plugged for a while. I can't see a clear diagram of my system on the vacuum sticky.
Got a four way splitter under the hood with a a yellow and a yellow blue line. Neither of those will hold vacuum. The other outlet goes to the cruise control and it holds vacuum fine.
Under the driver's floor board there are two yellow/red and two yellow/green each set of which join at a three way with two heading forward and one backward on each set. The backward lines hold fine. Neither forward yellow/greens will hold vacuum and only one of the yellow/red holds vacuum. Anyone have any idea what these lines control?

Chad300tdt · #2 04-18-2008, 12:31 PM

In my car red and green stripes are lock and unlock. It sounds like you have bad lock actuators, or does that year not use a similar system to the 1985 300td? I'd guess that you just have the early style actuators.

Sbean · #3 04-18-2008, 12:39 PM

Leaky rubber actuators can sometimes be repaired using wet-suit glue and small pieces of rubber glove. It's working for me. Steve

kerry · #4 04-18-2008, 12:39 PM

OK. So I have one each of yellow/red and yellow/green heading back from the driver's seat area. These are ok. Can I assume that all lock/unlock behind the front doors are ok?
So I have both incoming unlock lines not holding vacuum at the driver's seat. What does this mean? Unlock circuit from driver's door is leaking? Does it say anything about the passenger door? Where do the lines for the passenger doors route?
One lock line incoming at the driver's footwell not holding. What does this tell me?

Chad300tdt · #5 04-18-2008, 12:41 PM

Quote:

Originally Posted by Sbean

Leaky rubber actuators can sometimes be repaired using wet-suit glue and small pieces of rubber glove. It's working for me. Steve

I repaired one with silicone adhesive and a finger from a latex glove. It held up until recently, and I just replaced it with a new one ($30). I got almost a year out of the repair though.

Chad300tdt · #6 04-18-2008, 12:48 PM

Quote:

Originally Posted by kerry

OK. So I have one each of yellow/red and yellow/green heading back from the driver's seat area. These are ok. Can I assume that all lock/unlock behind the front doors are ok?
So I have both incoming unlock lines not holding vacuum at the driver's seat. What does this mean? Unlock circuit from driver's door is leaking? Does it say anything about the passenger door? Where do the lines for the passenger doors route?
One lock line incoming at the driver's footwell not holding. What does this tell me?

At the driver side floor, there should be 2 lines going to the rear and 2 lines going to the passenger side. The one going to the rear is the driver rear door only. The ones going to the right are the passenger side doors, fuel door and trunk/hatch. You can further test those at the passenger side floor.

EDIT: This just tells you which area to look, Once you isolate, you should take off that door panel, the actuator may be OK, it could also be rotted vacuum connectors or both.

kerry · #7 04-18-2008, 12:56 PM

Mine does not seem to be configured that way. I have two yellow/greens coming from the front and two yellow/reds coming from the front both sets enter three way connectors with one yellow/red and one yellow/green heading to the back of the car. I don't see any lines heading towards the passenger door.

I'm now thinking it has to be a failure somewhere in the driver's door since I'm thinking all those lines have to be connected in the driver's door in order to control the other systems.

Chad300tdt · #8 04-18-2008, 12:59 PM

Maybe your next cluster is under the rear floor carpet then? You have to have lines going to the actuators in the passenger doors somewhere. Maybe they enter through the firewall on the passenger side.

kerry · #9 04-18-2008, 01:02 PM

Quote:

Originally Posted by Chad300tdt

Maybe your next cluster is under the rear floor carpet then? You have to have lines going to the actuators in the passenger doors somewhere. Maybe they enter through the firewall on the passenger side.

If that's true then I think I can exclude any problems in the passenger doors since both lines heading backwards hold vacuum fine.

Chad300tdt · #10 04-18-2008, 01:07 PM

Quote:

Originally Posted by kerry

If that's true then I think I can exclude any problems in the passenger doors since both lines heading backwards hold vacuum fine.

That sounds logical ... I would guess your fuel door and trunk are OK too then.

Did you make sure the yellow check valve at the firewall is working? You should be able to blow through it only one way. If you can blow through it both ways, it isn't "checking" the vacuum anymore. Mine was bad in addition to vacuum connectors and 1 lock actuator.

kerry · #11 04-18-2008, 01:23 PM

I haven't inspected the check valve. It's in front of the 4 way connector under the hood. I have two lines that wont hold vacuum coming off that 4 way. One is yellow and the other yellow/blue. Does anyone know what each of these lines does? I assume one is the door locks (yellow presumably) but I don't know the purpose of the yellow/blue line.

Chad300tdt · #12 04-18-2008, 01:32 PM

Quote:

Originally Posted by kerry

I haven't inspected the check valve. It's in front of the 4 way connector under the hood. I have two lines that wont hold vacuum coming off that 4 way. One is yellow and the other yellow/blue. Does anyone know what each of these lines does? I assume one is the door locks (yellow presumably) but I don't know the purpose of the yellow/blue line.

Out of the check valve should be two lines: the solid yellow is the supply to the driver door and the yellow with black stripe is the vac reservoir. Maybe yours is blue instead of black?

kerry · #13 04-18-2008, 01:35 PM

Quote:

Originally Posted by Chad300tdt

Out of the check valve should be two lines: the solid yellow is the supply to the driver door and the yellow with black stripe is the vac reservoir. Maybe yours is blue instead of black?

ahha. That would explain why it wouldn't pump up. I was trying to fill up the whole vacuum reservoir through that line.

Chad300tdt · #14 04-18-2008, 01:38 PM

Quote:

Originally Posted by kerry

ahha. That would explain why it wouldn't pump up. I was trying to fill up the whole vacuum reservoir through that line.

Yeah ... I tested mine and it took about 100 pumps.

kerry · #15 04-18-2008, 05:18 PM

More data;
Yellow main line between hood and driver's door holds vacuum--supply good
Both lock and unlock lines from driver's door leaking-problem in both sides somewhere.
Lines to back driver's door holding on both sides--excluded
Trunk lock holding both sides when tested at the diaphragm.--excluded
Remaining suspects: Both passenger doors and fuel door

There is a junction of both systems in passenger floor. Both reds going back from there hold. I think this must mean that all locking sides on back passenger door, trunk and fuel door are working. I yellow/green going back leaks, one holds. This must mean an unlock component on either trunk, fuel door or back passenger door is leaking. I've excluded trunk so it's the unlock side on either back passenger door or fuel door.
I yellow/red going forward from the junction under the passenger floor leaks. Am I right in assuming this must mean that the passenger lock diaphragm is leaking or the hose leaking between junction and pod?

So here's where I think I am. Bad passenger door pod. Bad passenger rear door pod or fuel door pod. I need to figure out how to determine which one this is.