'87 300D Questions - PeachParts Mercedes-Benz Forum

sublettm · #1 02-25-2007, 09:23 AM

Has anyone posted a good troubleshooting tree for the vacuum system on the above mentioned car? There was a great one posted for the 123 but I have never come across one for the 124. I am in great need of one so I can finally fix my locks.

Next questions pertains to the rear differential bushings. Mine are shot. Has anyone posted a good how to on the removal of these? I am tired of listening to the loud clunk coming from the rear end.

If someone can simply post the link to the above questions I'd appreciate it. I have looked through the archinves but have not been able to find exactly what I am looking for.

Thanks,

Bio300TDTdriver · #2 02-25-2007, 10:10 AM

The locks are run by a seperate vacuum pump that is under the rear seat. At least that's where it is located on my 124 wagon.

Chris

babymog · #3 02-25-2007, 10:21 AM

The '87 300D locks are push-pull, the pump is under the rear seat, also operates the rear headrests.
The early and late '87 are different pumps, not compatible, one has a black lid other a bright lid I believe.

TheDon · #4 02-25-2007, 10:21 AM

The pump could be in the trunk.

A trouble shooting tree?

Car doesn't shut off-------- vacuum issue.... thats all I know

but thats on my 617

sublettm · #5 02-25-2007, 07:00 PM

Guys, I am well aware that the pump is under the rear seat. I have already replaced this, and the locks still don't work. There is a thread for the 123 vacuum system detailing which color vacuum lines do what. I was hoping someone had done the same for the 124. I was also hoping someone knew what voltages should be on the different color wires going to the vacuum pump. I need this so I can be sure voltage is going where it is supposed to be.

I have troubleshot many vacuum leaks on the 123 but have not had to dig into the 124 for these problems yet.

I still need to know the best way to pull the differential mounts on this car. I am going to be taking a rather long road trip in the next few weeks and would like all of the problems fixed before I head out.

I replaced the motor mounts yesterday. Boy, that made a huge difference. You never really realize how bad they are until you replace them. The passenger side was a bear to get out.

Any help you all can give will be appreciated.

greasybenz · #6 02-25-2007, 07:27 PM

might be that the door lock acuators have a leak and need to be replaced as well.

speedy300Dturbo · #7 02-25-2007, 07:41 PM

"locks still don't work" is pretty vague. What happens when you turn the key @ the passenger's door or trunk? Can you hear the pump running, and if so, does it time out after a while? Do you have power at the red wire which plugs into the pump?

Replacement of the diff bushings involves removing the two 12mm hex bolts at the rear, the forward mounting bolts, and lowering the diff so you can fit the pulling tool in. You don't need special tools for the "stacked" front bushings but the two rearward facing ones requires a special pulling tool similar to this:

The factory tool is very expensive, but there are aftermarket versions that will get the job done.

sublettm · #8 02-25-2007, 08:55 PM

If i turn the key in the passenger door or the trunk locks, the door or trunk will lock but it will not lock the rest of the doors. If I try to lock, or unlock, the passenger door, then try to open that door, all I end up doing is setting off the alarm...quite annoying. I never seem to hear the pump running. I pulled the rear seat bottom out yesterday, then tried to lock and unlock the doors, hoping to hear the pump running but didn't. I will have to see if there is power at the red wire. I had no idea which wires did what. As I recall, there is a green wire, a blue wire, and a yellow wire. I don't recall seeing a red wire but will look again. Is the vacuum setup the same as the 123 as far as the plumbing goes? If so, troubleshooting for a vacuum leak will be simple. I understand that the vacuum source will start under the rear seat instead of under the hood.

As far as that tool goes...holy cow what is that???!!! Will a garden variety puller tool work to pull the bushings out? If not, I might have to engineer something.

Thanks for the help so far.

babymog · #9 02-25-2007, 09:31 PM

One difference is the valve for the rear-headrest drop, under the rear seat. If the alarm doesn't disarm with the key and the pump doesn't run, it sounds electrical.

speedy300Dturbo · #10 02-25-2007, 09:48 PM

There are two wiring plugs at the locking pump. One is a translucent round thing with a green, blue, and yellow wire. These wires are the trigger wires that carry 12V pulses from the front doors or trunk lock cylinders. The other plug is a rectangular one about 1 inch across which has two wires, a red and brown one which are 12V (always hot) and ground, respectively.

If the pump isn't running when the locks are actuated at either front door or the trunk, then you don't have power to the pump.

Leaks in the vacuum 124 locking system are pretty rare. It's a more robust design than the 123 with half as many lines.

sublettm · #11 02-25-2007, 10:12 PM

Does it make sense that I have two translucent plugs with 2 each yellow, green and blue wires? I forgot about the other rectangular plug. I will see if i have voltage on the red wire on that plug and report back. By the way, I have already checked the fuse. The fuse controls several other things and they all work properly...to include the headrest release.

babymog · #12 02-26-2007, 08:01 PM

Do you have Orthopedic Seats? If so, they use the pump air, and it is a different pump with different wiring. Damn expensive also, I had to buy one for around $500!!

sublettm · #13 02-27-2007, 12:54 AM

No, but my wife would sure like riding in it if it did. She says the seats are uncomfortable...I think she is crazy. Actually I'm glad it doesn't have this option as that would be just one more thing to fix. This car has needed constant maintenance since day one and I don't see any end in sight. Right now, I am just trying to get the necessities up to par...locks, front suspension, rear diff. mounts, etc. I keep telling myself that one day I won't have anything to fix. That will probably be the day the car dies a violent death.

sublettm · #14 03-04-2007, 05:20 PM

Ok, after replacing the balljoints and tie rods yesterday, I got back into troubleshooting the locks on the '87. I have approximately 1.9VDC on the red and brown wires at the vacuum pump under the rear seat. When i push down on the driver's lock, the voltage drops to about a half a volt. I understand that there is supposed to be 15VDC at this wire but have no idea why I don't. On another note, if I hook up my vacuum pump to the line coming off of the vacuum pump under the seat and pull a vacuum, all of the locks lock. This would indicate that there isn't a leak anywhere.

My questions is why do I have such a voltage drop? There is about 13 volts at the fuse in the box that controls the locks and other things. How can it drop down to 1.9 volts at the pump. I would venture a guess that if I can solve this mystery I will have working locks again. Please help.

Thanks,

aersloat · #15 03-05-2007, 04:40 AM

I went through the central locking troubleshooting process last year. Here is a link to a thread I posted. Long and the short of it is that there are several "terminal" connections in the raceway under the carpet and they often get corroded and don't maintain a good connection. If you have power issues at the pump this is probably where to look first. Resolder, seal, and heatshrink. I was getting 12v on a multimeter, but the connections were flakey enough that the pump would not run.