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Replacing Your Mercedes-Benz Distributor
 
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Pelican Technical Article:

Replacing Your Mercedes-Benz Distributor

Steve Vernon

Time:

2 hours2 hrs

Tab:

$2 to $475

Talent:

**

Tools:

6mm Allen, 6mm, 8mm wrenches, flathead screwdriver

Applicable Models:

Mercedes-Benz W126 (1981-91)

Parts Required:

Distributor cap, rotor, dust shield, vacuum advance, condenser wire

Hot Tip:

Mark the distributor before moving

Performance Gain:

Better running engine

Complementary Modification:

Check your timing

The distributor on the W126, like any distributor on any car, plays an important role in the smooth and efficient running of the engine, and while the distributor itself should last the life of the car, there are several components on or in it that wear out, need servicing or replacement over time. The first of these is the distributor cap. The W126 distributor cap has a cover built into it and is removed as one piece. To remove the cap, remove the two bolts holding the distributor cap to the distributor. Use a large flat head screwdriver, push the screw down and give it a half turn, it will pop up when released. You can now remove the cap and wires as one piece. Check the cap for dark and charred scorching on the inside as this can mean "arcing," meaning there may be a problem with the distributor.

With the cap off you can remove the rotor. There is a guide key that the rotor fits into that lines it up, do not try and force the rotor on any other way than sliding it into the guide key. Check the rotor of the same signs of wear as the cap and replace as needed. It is always a good idea to replace the cap and rotor together.

Replace the dust seal on the distributor while you are there, it simply lifts off the distributor. If you are going to be removing the distributor from the engine you will want to remove the vacuum line from the vacuum advance.

If you are going to remove or even move the distributor from its place in its mount you must mark precisely where it is located before doing so. The distributor is used to set the timing of the spark to the engine, and while we are not going to cover how to set your timing in this article if your engine is running fine and you are just removing the distributor to service its accessories, the car will not run properly if you do not return the distributor to its original spot. Mark its spot and use a 6m Allen to remove the distributor locator and fastener.

With the Allen removed you can lift the distributor straight out of the engine. The distributor shaft has very tight tolerances on it so lift it straight out.

You can now replace the seal on the shaft of the distributor.

With the distributor out of the engine you can use a 6mm wrench and remove and replace the condenser wire that sends a signal to the CDI unit.

Remove the wire from the distributor and follow it ignition control box on the inner left fender right beside the coil. It just unplugs from the box.

You can now also replace the vacuum advance unit by removing the two flathead screws holding it in place. When replacing this pay special attention to the small springs it is attached to as they control the advance on the distributor.

Installation is the reverse of removal.

The W126 distributor cap has a cover built into it and is removed as one piece.
Figure 1

The W126 distributor cap has a cover built into it and is removed as one piece. To remove the cap, remove the two bolts (red arrows) holding the distributor cap to the distributor. Use a large flat head screwdriver, push the screw down and give it a half turn, it will pop up when released.

You can now remove the cap and wires as one piece.
Figure 2

You can now remove the cap and wires as one piece. Check the cap for dark and charred scorching on the inside (red arrow), this can be signs of arcing meaning they may be a problem with the vacuum advance on the distributor. This cap looks used but fine.

With the cap off you can remove the rotor.
Figure 3

With the cap off you can remove the rotor. There is a guide key that the rotor fits into that lines it up (red arrow), do not try and force the rotor on any other way than sliding it into the guide key. Check the rotor of the same signs of wear as the cap and replace as needed. It is always a good idea to replace the cap and rotor together.

Replace the dust seal on the distributor (red arrow) while you are there, it simply lifts off the distributor.
Figure 4

Replace the dust seal on the distributor (red arrow) while you are there, it simply lifts off the distributor. If you are going to be removing the distributor from the engine you will want to remove the vacuum line (green arrow) from the vacuum advance.

If you are going to remove or even move the distributor from its place in its mount you must mark precisely where it is located before doing so.
Figure 5

If you are going to remove or even move the distributor from its place in its mount you must mark precisely where it is located before doing so. The distributor is used to set the timing of the spark to the engine, and while we are not going to cover how to set your timing in this article if your engine is running fine and you are just removing the distributor to service its accessories, the car will not run fine if you do not return the distributor to its original spot. Mark its spot and use a 6mm (red arrow) Allen to remove the distributor locator and fastener.

This photo illustrates the piece that fits between the distributor and its mount (red arrow) and is used to mark the position as well as hold it in that position.
Figure 6

This photo illustrates the piece that fits between the distributor and its mount (red arrow) and is used to mark the position as well as hold it in that position.

Pull the distributor straight out of the engine (red arrows).
Figure 7

Pull the distributor straight out of the engine (red arrows).

The red arrow shows the seal on the shaft of the distributor.
Figure 8

The red arrow shows the seal on the shaft of the distributor. It is a good idea to replace this every time you remove the distributor.

With the distributor out of the engine you can use a 6mm wrench and remove and replace the condenser wire (red arrow) that sends a signal to the ignition control unit.
Figure 9

With the distributor out of the engine you can use a 6mm wrench and remove and replace the condenser wire (red arrow) that sends a signal to the ignition control unit.

Remove the wire from the distributor and follow it ignition control box on the inner left fender right beside the coil.
Figure 10

Remove the wire from the distributor and follow it ignition control box on the inner left fender right beside the coil. It just unplugs from the box (red arrow).

This photo illustrates the condenser wire (red arrow) removed from the distributor.
Figure 11

This photo illustrates the condenser wire (red arrow) removed from the distributor.

Use a flathead screwdriver and remove the vacuum advance from the distributor (yellow arrow).
Figure 12

Use a flathead screwdriver and remove the vacuum advance from the distributor (yellow arrow). Use caution when replacing this as the small springs in the distributor control the advance on the timing and you should not over stretch these. Installation is the reverse of removal Insert Keywords and Phrases: Distributor Distributor cap Rotor dust shield Vacuum advance Condenser wire CDI unit

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Comments and Suggestions:
angelo Comments: How to follow the ignition on distribuitor for mercedes benz 380 to conect the wire?, i have in my left valve heat show 1-5-4-8-6-3-7-2 that i have to rotate to conect de wire to the right side?? star from the mark or a litle nerve that is on the distribuitor..??
March 17, 2016
  Followup from the Pelican Staff: The distributor cap is labeled with the cylinder number. Connect each wire to the corresponding cylinder.


front < 1 2 3 4 > rear passenger side

< 5 6 7 8 > driver side


Firing order 1 5 4 8 6 3 7 2

http://www.pelicanparts.com/techarticles/Mercedes-W126/05-BASICS-Replacing_Your_Ignition_Wires_Rotor_Distributor_Cap/05-BASICS-Replacing_Your_Ignition_Wires_Rotor_Distributor_Cap.htm - Nick at Pelican Parts
 
Eric Comments: Very Helpful. On my grey market Germany VIN 1973 450SL the distributor hold-down screw was 5mm, as opposed to 6mm, but all else the same.
Cheers!
September 18, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Gab Chartier Comments: Hi Nick,
It is Gab with the 380SL, I changed the condenser... no luck?
So everything is changed from the coil to the spark plugs. Except for the ignition unit.
I am running out of ideas. What other check or suggestions to find the snag. It just stop and stalled. I have been trying to fix it by changing the obvious.
Nick...any suggestion?
Thanks for your support.

Best regards GAB,😊
August 30, 2015
  Followup from the Pelican Staff: I will return to my earlier question, have you confirmed the coil is being triggered? - Nick at Pelican Parts  
GAB Comments: Nick
My coil did not spark , ihavechangedit. I will be purchasing a condenser. Because mine going to the distributor is burned and broken...I don't think that it is working right ?
Well I have changed a lot of the electrical however I am not sure that I will be right. The car just stopped working and I could not get it going.
All you help is greatly appreciated.
Cheers. Gab
July 25, 2015
  Followup from the Pelican Staff: Let me know if the condenser fixes it. - Nick at Pelican Parts  
Gab Comments: Hi very interesting comments.
My 390 SL 1985. Won't start. It looks like no sparks from the coil ,I have bought a new coil and distributor and cap new wire set and spark plugs. I figure that it was time to change all that. I also realized that my condenser wire looked burn and the part that goes to the distributor is crack and a piece came off the back.
I will buy a new one and change it. Do you have any other advice if it still won't start?

Just asking...thanks
Also I live in WasagaBeach Ontario canada do you know a very good mechanic for vintage MB?
July 12, 2015
  Followup from the Pelican Staff: Does the coil have power and is it being triggered? - Nick at Pelican Parts  
BigCrazyMike Comments: Yep mechanical injectors. What a PITA. I mean EVERYTHING lined up perfectly. Both cams, balancer, distrib, etc.
Than it hit me, so I opened each injector while cranking it over and it started to start. So I had to disconnect the coli wire to keep it from starting until all the injectors were bled out.

Lifts might now be fully pumped up yet, still making noise and smoking. When I had the heads off, I put a lot of oil into each cyl to keep them from rusting out.

If you'd like, I'll keep you apprised of the situation.

Shal ' aam Aleichem
AAPiY
Mike
December 12, 2014
  Followup from the Pelican Staff: Thanks for the follow up
- Nick at Pelican Parts
 
BigCrazyMike Comments: This comment is directed to Nick.

Hey man, this is Mike. I've been working on that 1980 MB 450 SLC. Well I got her started.
I re-checked everything, all timing marks lined up perfectly on both cams, distributor and balancer.
The reason why it wouldn't start is I needed to "bleed" the injectors something the Haynes repair manual failed to mention.

it runs, but I believe I need to re-adjust the valves because the heads were shaved .005" and the rocker's are clacking away like crazy oil is coming outta the oiler's w/o any problems. However, the manual states that "after 1976 the engines are equipped with hydraulic rocker arm pivots. With hydraulic pivots the only adjustment to be made requires a special gauge."

What is this gauge, is it a dial indicator or something different?

It would seem that prior to '76 they were a lot easier to adjust.

Shal ' aam Aleichem
AAPiY
Mike
December 11, 2014
  Followup from the Pelican Staff: Hey Mike, mechanical injectors - RIGHT. Been a while and that didn't pop into mind. Glad you got it going.

Are the lifters pumped up? I am not 100% sure what they tool looks like. It may just be a specially bent wrench to access fasteners, you will likely need angled feeler gauges. - Nick at Pelican Parts
 
BigCrazyMike Comments: "I would think it is more than a few degrees off, maybe 180° off. "

But I never turned the engine over after I shut everything down before I pulled it apart.
Before I took it apart, I made sure it was on TDC on the compression stroke. The valves #1 cyl were closed and the rotor was pointing at #1 and the timing mark was dead on at the balancer.

Ok, I'll check everything once again.

Oy-vey.

Shal ' aam Aleichem
AAPiY
Mike
November 20, 2014
  Followup from the Pelican Staff: Thanks. Keep me posted. - Nick at Pelican Parts  
BigCrazyMike Comments: I'll check the compression tomorrow, but I don't understand it ran good except for the head gasket last year.

As far as the timing, I've turned the distributor from lock to lock and it "almost" started, but wouldn't. I've even moved the plug wires over one in each direction.

The plastic cover that goes over the distributor wire that goes to the control box crumbled off completely and I'm wondering if its shorting out some? I taped it up, but maybe?

I've been a mechanic for 42 yrs and this vehicle is really perplexing to me.

Could being one or two degrees off on one of the cams make a big difference? When I put the sprockets back on one was ever so slightly "off". I mean, hardly a hair off. So close its not off but is.

I appreciate your help and I'm sorry if I'm being a pain, but like I stated this car first MB I've ever did any serious work on is very perplexing to me.

Shal ' aam Aleichem
AAPiY
Mike
November 20, 2014
  Followup from the Pelican Staff: I would think it is more than a few degrees off, maybe 180° off. I would start with timing and compression. You say spark and fuel are good, that is all that is left. - Nick at Pelican Parts  
BigCrazyMike Comments: I have a customer with a 1980 450 SLC. last year I needed to remove the heads blown head gasket. I had the heads checked out at a local machine shop.
It took the customer some time to get the funds to have the heads shaved, so the car sat for a while.

The engine ran w/o any problems last year except for the blown head gasket. However, I replaced both gaskets, followed everything procedure in the repair manual and now the engine will not start.
I checked to make sure everything is correct, I had a friend "bump" the engine while I had the #1 plug out and my finger over the hole. It hit the compression stroke and I used a socket to turn the engine a few inches more to get it on TDC. I removed the cap and the rotor was indeed facing the mark I'd put into the distributor.

i checked for spark and I do indeed have spark at #1 plug. I checked all plugs, re-gaped them all.Its getting fuel. In fact I sprayed starting fluid into the intake and it will not start.

Before I removed the heads I did mark the cam's, chain and sprockets and re-installed them to the correct position.

Most of the pollution junk had been removed by whomever owned the vehicle previously and most of the vacuum line were rotted out. I replaced all of them. The rubber sleeve on the throttle valve housing was all rotted out as were the 8 rubber connections on the plenum.

I don't understand why after replacing everything it won't start? Can I by-pass the ignition control box temporarily and hook up the distributor wire direct to the coil to see if the box is bad?

Shal ' aam Aleichem
AAPiY
Mike
November 20, 2014
  Followup from the Pelican Staff: If you h ave spark and fuel, compression must be your issue. Check engine compression and mechanical timing. - Nick at Pelican Parts  
justin Comments: Hi, this is very helpful, thank you! I am looking for the condenser wire mentioned above for my 1985 500 SEL. Can't find it anywhere, any suggestions? Thank you!!
August 16, 2014
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
 
24k Comments: love these posts on 560 del
May 25, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Tom Comments: Unbelievably helpful.
Thanks very much!
April 1, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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