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1973 450 SL
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2,091 Posts
Discussion Starter #1
Over the last 6 weeks or so, I have had a rough running when cold problem. I did not bother with my breakout box / multimeter / oscilloscope thinking it was a sticking AAV. The symptom persisted with a rebuilt AAV so I had to dig further. In retrospect, one clue to the problem was a worsening symptom - car would not run well after it warmed up.

I pulled my distributor and found a badly soaked pulse generator (trigger points). The lower pair was so oil soaked, I could see a liquid film when I manually opened the contacts. I installed a working spare, installed the distributor, reset the timing and the problem is gone. I think the lower distributor bearing is worn to a point where oil is weeping into the cavity where the trigger points live. It could also be that I did not use the right kind of grease on the cam pads. I need to find a better product for this.

A little research on https://oldtimer.tips/en/d-jetronic/tc tells me these trigger points are the latest in the production series and include plastic shields to protect the contacts. I had never disassembled these before so I thought I'd give it a try and document what I learned. Disassembly is necessary in order to clean the lower pair of contacts.

First step is to de-solder the wires from the connector; necessary to remove the connector and gain access to the two Phillips head screws that hold the trigger mount plate to the body of the assembly.

PG Cleanup & Adjustment (1).jpg

I had to walk the connector body out of the slot prying at both sides

PG Cleanup & Adjustment (4).jpg

PG Cleanup & Adjustment (5).jpg

Next, remove the screws and carefully lift the plate from the body. If you hold the assembly with your fingers around the leaf springs, it is easy to wiggle it up and off the body. The wires from the lower pair are routed through the large hole in the plate.

PG Cleanup & Adjustment (6).jpg

PG Cleanup & Adjustment (7).jpg

At this point, use a pick to remove the circlip and fiber washer that holds down each rubbing block and plastic cover. I had to use the pick to lift the plastic cover off the adjustment tabs because they fit pretty tight - easy to break these if you don't lift them straight up from both ends.

PG Cleanup & Adjustment (10).jpg

Right lower side clean, left lower side next . . .

PG Cleanup & Adjustment (11).jpg

PG Cleanup & Adjustment (12).jpg

I used Norbert's adjustment tool to set the gap at .5mm or .02". I experimented doing this with and without the plastic covers in place. There is a little play in the plate mount. Research taught me to push the plate as far towards the curved piece then tighten the screws. Any gap adjustment done before mounting will require readjustment after mounting so might as well assemble everything then make gap adjustments at the end. I used a small bent needle nose pliers pushed up against the plastic cover - careful not to break what you just cleaned.

PG Cleanup & Adjustment (15).jpg

Finally, slide the connector back into place and solder the wires. Be careful not to let the solder iron touch the connector body like I did (upper right). I will look for a product to replace the rectangular seal on these trigger points

PG Cleanup & Adjustment (16).jpg

If this symptom repeats, I will look for oil on the replacement trigger points installed in my car, install this set in a spare distributor and send the leaking distributor out for a rebuild by Cardone.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,626 Posts
I have no horse in the race...but this thread is already screaming:

STICKY
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,768 Posts
Good work Brad. It's impossible to clean those plastic covered points. But then, I guess it should not be necessary!

I had a brand new set of trigger points. I think they have the plastic covers too. Before I installed them, I once checked them with Norbert's tool and found that the gap was not same as that in Norbert's instructions. I told him about it, but I think he decided to stay with his number? For life of me, I can't find the numbers or the correspondence with Norbert. It may not make any difference anyway.

There is a spiral on distributor shaft appears to be there to catch oil leaking into the lower bearing and then push it back down into the crankcase. There are two bearings/bushes in the distributor - an upper and a lower with a gap between them. can't recall, but you would think there should be an oil seal somewhere.
 

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1973 450 SL
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2,091 Posts
Discussion Starter #4
Graham,

I forgot about that spiral oil bleed - maybe the contamination came from using the wrong grease. Oldtimers talks about using a high temp grease. I went to Autozone yesterday and was not sold on any of their products. I'll figure this out and post what I learn.

I had a look at some oscilloscope readings I took on a set of trigger points 5 years ago. The scope I used has a statistics feature that might give me some duty cycle info I can convert to duration in terms of degrees. I want to make a comparison of the installed triggers against these I just cleaned and adjusted. This graphic on Oldtimers provides an outline to channel assign the output.
 

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1973 450 SL
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Discussion Starter #5
The Service Manual specifies Bosch FT1V4 grease for distributor cams (specifically at the rubbing block of the ignition contact points). Can not find a different specification for the trigger points but the idea is the same. This Bosch product appears to be NLA in North America. D-Jet enthusiasts at TheSamba.com recommend SuperLube as a substitute:

https://www.napaonline.com/en/p/NCB21030

I will give it a try.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,768 Posts
The Service Manual specifies Bosch FT1V4 grease for distributor cams (specifically at the rubbing block of the ignition contact points). Can not find a different specification for the trigger points but the idea is the same. This Bosch product appears to be NLA in North America. D-Jet enthusiasts at TheSamba.com recommend SuperLube as a substitute:

https://www.napaonline.com/en/p/NCB21030

I will give it a try.
That grease contains PTFE (Teflon). Not good for conductivity if it gets on points. But then, I am not sure the silicone greases are either?

This looks like another option - Those British car guys should know :)

https://www.bpnorthwest.com/points-lube.html

https://www.summitracing.com/int/parts/smp-sl2/overview/

Look at price in Canada! (but good picture to read label) https://www.amazon.ca/Standard-Motor-Products-SL2-Lubricam/dp/B000JKDAR6

I haven't lubed those points very often. I just checked my spare distributor. Cams are coated with grease :thumbsup: What I noticed, was that the felt pads that are supposed to spread the grease and perhaps prevent it getting thrown off are impossible to inspect without totally dismantling the distributor, They are opposite the opening where the trigger points are inserted. Maybe a dentists mirror would help.
 

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1973 450 SL
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2,091 Posts
Discussion Starter #7
I bought and used the product referenced in post #5. I applied it directly to the lower distributor shaft where the trigger points ride, to the corners below the rubbing blocks and to the felts on the trigger points. I did reach back to feel the felts were intact behind the distributor shaft but as you said, very difficult to access.

The trigger points pictured above are back in service; inspected 4 other spares and 5 spare distributors. I noticed it is easy to convert between the two types of distributor caps on these distributors. All my spares have a larger vacuum element with a single port. I'm guessing the weights on the mechanical advance are different, possibly the springs that govern them.
 

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W212 E350 vanagon
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75 Posts
Hi Brad, Hi Graham

I just noticed your postings here.

Maybe I can answer some questions...

The grease Bosch FT1V4 is the same used for greasing ignition points. Therefore you can use ignition points grease. Take care the grease you use doesn't absorb any oil, doesn't contain copper or graphite components. Just tough high-temperature grease.

Graham, I don't remember what you found out / told me about the gap you measured at the new unit.
But: Even new units have quite often not been ajusted very exactly. In most cases you will do the job much better than the factory did...

Using my tool, the points will work at a gap between 0.004 in <less = points opening no longer> and 0.04 in <more = points closing no longer>.
The gap of 0.5 mm (0.02 in) is the median and allows the highest tolerance the unit in positioning or the distributor-camshaft could have.

The pic shows the point in the fully opened position at operation when having been adjusted to 0.04 in.

Graham, please check your tool. You got one of the first I shipped overseas - maybe it has a diameter of 24 mm. I revised this after having 'discovered' the points units with the plastic hoods I hadn't seen before. If so, please tell me...

Regards
Norbert
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,768 Posts
Hi Norbert. I am about 1500km from home at present and not back until April. So cant measure tool until then.

I did use your tool to adjust my two sets of old trigger points and they worked.

Eventually, I installed my new set, just because I had them!

As we have discussed, the exact setting is not so important. Seems that if the points stay closed for an arc of say 110 to 140deg, then the points work fine. But when adjusting, adjust to the low number to allow for future wear of rubbing blocks.

When that arc gets higher (over 150deg?) on one or all pairs of points, some owners (including me!) have had over-rich problems. Hard to explain, but perhaps points start to bounce causing incorrect firing of injectors? Or maybe ecu receives incorrect engine rpms (that also come from same points). Adjusting back to 110-120deg usually eliminated the problem.

Regardless of reasons, it makes sense to adjust points with your tool to your gap and/or the arc we sometimes use for checking wear. Then the points should be good for a while.

It is hard to do the adjustment without your tool! I always recommend it! Maybe post your contact info again so others can get one.
 

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Hi Graham,
I wish you have a good time...

It would be interesting to connect an oscilloscope to trigger points with a very high arc.
I think this is when the gap is around zero, the points will flutter because the distributor-camshaft does some fluttering, too. This will cause extra pulses when the corresponding opposite side flutters, too - because then the ECU-internal flip-flop is being resetted and the extra pulses can occur. This can't happen when only one point is near zero - the flip-flop-reset is needed to generate the next pulse.
Same can occur when the gap is too high...

One more: Volker <oldtimer.tips> as I by myself had trigger units for service (even with the original repair set installed by a professional) with the upper points-carrying-sheet not installed correctly or with the bolts underneath the soldering points not having been tightened enough.
When the upper sheet can move, the whole unit cannot work correctly because the points-unit-adjustment is realized by the fingers at the bottom of the main corpus.
Check this out!
You have to unsolder the leads to tighten the bolts correctly.

Regarding my tool: I am a hobbyist, it's not my professional business to sell the tool. Users can contact me by PM. I will send them a figure they can produce the tools using a lathe and the instruction - or I send them the ready-produced tool after I have received a payment of 20.00 US$$ via PayPal. Contact me by PM...

Regards
Norbert
 

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1973 350SLC
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14 Posts
Hi guys. New to the forum. 1973 350slc.
Can someone explain how the trigger points are actually adjusted using Norbert's guage.
Also, I have had mine apart completely, cleaned and re-assembled but can't get a clean open/closed resistance reading. This is before they are even re-connected to the base plate. Any clues?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,768 Posts
Welcome to yet another Djet owner!

Do you have Norberts instructions? (I have attached copy that I had saved). It's a bit trial and error, but basically you have to bend the plate that one side of points is attached to.

After doing this and reassembling in distributor, I would do the rotation check (covered in several places here and on Peachparts Vintage). Check the angle that the points stay closed for. We have found that if it is in the 100-140 deg range the points work well. Lower angle the better, so they don't wear out fast. This will tell you if you have similar adjustment on all 4 sets.

Regarding resistance. You measure from center pin to each of the other pins. Resistance should go from zero to infinity as the points open and close. Make sure points are actually opening and closing and that points are fully inserted into the distributor.

PS: Someone will tell you sooner or later to fill in your CP at top of page (user CP). Lets us know where you are in the world. 350slc presumably a Euro car?
 

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1973 350SLC
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Many thanks, MBGraham.
I do not have a tool so will contact Norbert to get one.
I also would rather have a new set of trigger points. I live in the Canary Islands so no Bosch centre. I have sent an email to Bosch but no reply as yet.
 

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1973 350SLC
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Hi again.
OK, the full story.
A previous owner (or his workshop) has replaced the trigger points but completely wrecked the wiring.
I have dismantled the whole thing but cannot get one of the points to give a clean open/closed signal. This is before they are assembled back in the distributor. I am searching for some resistance path.
Also, to make things worse, one of the wires has broken off the contact. Any thoughts about how this can be repaired would be useful.
I am looking into sourcing a new set but Bosch won't sell to me directly so, in the meantime, I want to try and fix these.
 

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1973 350SLC
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Me again.
So I have repaired the wiring the best I can.
With the contact set on the bench, I have checked continuity of the 4 leads against the central return. All go open circuit when I depress the contacts.
2 show 000.0 when closed but 2 show resistance of 000.2ohm and 000.5ohm.
I don't want to put them back in unless they are 100% so I am now looking for a new set. Bosch won't sell to me direct. There isn't a Bosch service centre where I live. Does anyone know of a reliable internet source that I can try?I haven't tried the MB dealer - should I?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,768 Posts
The resistance could be due to points not being aligned (touching is just one small place). Or perhaps a cold soldered connection on wiring. Or dirt or oil between points.

Not sure if new sets are even available. Bosch did come out with a retrofit kit. Requires soldering. I don't know where best to get them. Maybe SLShop in UK or sls in Germany? But they do cost an arm and a leg

https://www.sls-hh-shop.de/main/en/mercedes-280-500sl-c-r-c107-/07-a-b-d-jetronic-efi-components/07-b-d-jet-efi-components-350-450sl-c/rep-kit-jetronic-pointers-v8-p-10622

I have heard that other Djetronic cars from late 60s/early 70s use the same points. One owner said he bought VW points off eBay and that they would fit. Can't confirm that, but perhaps you have a local VW dealer?

Sometimes a good used set can be found. Takes some searching.

I would try and fix the ones you have!
 

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1973 350SLC
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14 Posts
Many thanks for the help.
I checked with MB yesterday. They can get them......... for 840€!!!!
SLS HH have them on order.
I have found a new set in UK for £400. As I intend to keep the car, I will order them.
I have tried to send Nordfisch a message about getting his tool but, as a newbie, I can't yet.
One thing that you definitely need with these cars is patience!!!!.
 

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W212 E350 vanagon
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Hi oldgaffer,
I noticed your reply to the thread now and will send you informations by PM.

It will not be neccessary to replace the points set - save the money.

I know and own the VW / Porsche units, too. They are almost completely different and the only part you could use is the 'Pertinax' arm with the spring and the points that are mounted to it. But the wires are too short and you would need two of the VW sets because they only have two points mounted on.

Graham, you own an earlier version of the tool and posted an earlier instruction.
You can use your tool, it is o.k. and works for you - but I redesigned it some years ago.

Regards
Norbert
 

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1973 350SLC
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14 Posts
Many thanks Norbert.
I have worked on it again today. I have managed to get them opening and closing cleanly.
The closing "dwell" is around 150 degrees so I need to adjust them.
The biggest problem is that a previous owner has removed the soldered plug and replaced with an external plug so the wiring was bad. I am searching for an original plug with the lead that I can splice back into my loom.
Thanks again
Chris
 

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1973 350SLC
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Norbert.
I have just tried to send you a message but cannot as I am a newbie.
I have sent you a PayPal transfer.
You now need my address.
We will get there somehow!!!!
Regards
Chris
 
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