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W126 1990 500SE W126 1991 300SE
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Discussion Starter · #1 · (Edited)
Dating your Voltage Regulator
This is an approximate date of manufacture for Bosch Voltage Regulators. The list is compiled from entries later in the thread, and can be used as a guide to check when your VR was last replaced. Of course, if your part could have been replaced recently with an old stock part, so this check will not be 100% reliable. You will need to read the 3 digit number on the front of the VR under the 'Made in' text. Please reply to the thread with your info, and I will add it to the list.

YearCodeSerial
19900621-197-311-023
19911621-197-311-022
20156301-197-311-023
20206561-197-311-028
20216601-197-311-028




I've had some issues with my 1990 500SE, and have been meaning to change this part for a while. For anyone who doesn't know, the alternator has a little device screwed into the back of it, called the voltage regulator. This part has two brushes that contact the rotating alternator. Anyway, these brushes wear down over time, and when they're gone, or almost gone, the car will stop working. Apparently, before the car stops working, there can be indicators of short brushes, such as electrical issues. Here's a good thread on the subject, and MBL recommends 80k miles as the replacement interval.

Everyone says that it's an easy job to replace this part.....just two screws to remove, pull the old one out, pop the new one in, and you're good to go. Not so for some people!
2697882

There is not enough room to get a tool onto the lower screw. More accurately, there is no tool small enough to fit between the oil filter housing and the lower screw. The clearance is just over three quarters of an inch, or about 20mm. I showed the car to a few people, including a mechanic and the Snap-On guy. All of them insisted that the only way to replace this part was to remove the alternator. Hardly a quick roadside fix then! Notice also, that the lower screw has been slightly rounded by someone's previous removal attempt. :mad:

Well, I am obviously in the minority here, because across the forum people are changing this part without any fuss at all. I wonder if it is to do with the car being a V8, being RHD, being a UK car, being Gen2, or some combination of these? It surely can't be that all V8s are like this? Otherwise I would have expected this issue to have come up on the forum more often - I could only find one other brief reference to having to remove the alternator.

Strangely the workshop manual does not show, anywhere, how to remove the alternator! I did manage to find a tutorial on this at Pelican Parts, but still, it would be a headache for sure. So, I decided to make my own tool for the job:
2697883

2697884

2697885


So, I hunted around for a 1/4" box end, which was not easy to find! But this one from Britool is inexpensive and readily available on eBay. I then chose the screwdriver bit that fitted most snugly into the screwheads. This turned out to be a posidrive which is strange, as the screws appear to be Phillips. I don't think it's right to recommend using a Posidrive bit on a Phillips screw, but it was the best fitting bit, and so that's what I went with. As you can see, the depth of the tool is under 16mm, and will fit nicely. I used JB Weld to fasten the bit to the box end.
2697888

I took this photo later, to show how the tool fits (new VR already installed).
The tool is quite short, but this is not a problem, as there is very little space to move, and it would be impossible to turn a long tool very much at all. The main difficulty here is making sure to get enough downward pressure on the screw, but there is just enough room to get a finger between the tool and the oil filter for this purpose. I removed the oil housing cover, but it made hardly any difference at all.

So, the car has 125k miles on it, and I'm pretty sure this job has never been done. Here's how the old part looked, compared with the new one:
2697889

2697890

Looks like I just made it!!! So, I urge everyone to check this part and get it changed. Apparently the minimum recommended brush length is 5mm. The old one has 2.6mm & 5.13mm left on it - probably ok for another half a mile or so. 馃槀 According to Greeney's book, the wear pattern should also be checked, as this can indicate alternator issues - not in this case luckily. The new brushes measure 11.54mm & 11.47mm, and I intend to check them after 5000 miles to see how quickly they are wearing.

Fitting the new VR is not as easy as it seems. It needs to be put into place with the brushes pressed all the way down! For this, I used a piece of tape, but I have since read the excellent recommendation of using a cable tie!

Well, after carrying out this headache of a job, I decided to do the same on my 300SE, which doesn't have the clearance problem. I took some better pictures this time.....
 

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W126 1990 500SE W126 1991 300SE
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Discussion Starter · #2 · (Edited)
So on the 1991 300SE, there is no such issue with clearance....you can get any screwdriver you like on there!
2697891


So, the first step is to disconnect the battery, and I highly recommend a battery cut-off, which makes this so easy:
2697893


You should also use some penetrating fluid on the two VR screws, as they are exposed to the elements, and can get corroded. Be sure to use a snugly fitting screwdriver, and apply as much downward force on the screw as you can before turning. Once the screws crack free, they can be undone by hand quite easily. Note, the voltage regulator is spring loaded, so if you have a problem fastener, remove that one first, because as one screw loosens, it puts more pressure on the other screw. Be gentle removing the VR from the hole, although unless your brushes are new, it should come out quite easily.
2697894

The old VR had 6.4mm & 5.94mm of brush left on it, so a pretty good time to replace - this car has just under 96000 miles on it. Note, both my cars use the same VR part number, but I don't know if this is the same for every W126.

Voltage Regulator - 000 154 36 05 - 拢42 from MB
Screws - 000 990 75 21 - 拢1 each from MB

When putting the VR back in, I definitely think the cable-tie method is best, but I did it with gaffa tape:
2697896

The disadvantage with this method, is that it can be tricky to remove the tape afterwards. I did it by making sure I only used enough tape on the back edge to hold the brushes down for a few seconds...just enough time to get the part in place, and then the brushes would release. But the idea is to get the part in place, and while holding it firmly against the back of the alternator (because it is against a spring) put each of the screws in and tighten them a few turns by hand, then remove the tape.

2697897

And I must admit, on this car, it really is quite a quick roadside job! Mind you, I don't think it's necessary to carry a spare one around with you, as the interval is so huge between changes. I would simply check it every so often to measure the wear.

With this one, I took the added step of checking the battery before and after, which I thought might be interesting to do.
2697902


I have no idea why the voltage would be lower after fitting the new VR!! Any ideas?
 

Registered
1989 300SE 239k miles
Joined
2,538 Posts
Feel this. Though my car鈥檚 the 300, so access was easy. I used a zip tie to hold the brushes in. It was a super pita, and I was worried if I used tape, the tape would stay between the brushes and the alternator.

As for your tool, good ingenuity. I bought a 1/4鈥 ratcheting box end wrench for those screwdriver pieces. State-side, at least, I鈥檝e found the bits to be 1/4鈥. And using a ratcheting wrench makes things much easier for unscrewing.

I have to add, I stupidly did not initially disconnect the battery and got a nice ZAP!

As for why the new part is a lower voltage, I鈥檇 say: Everything today is more efficient than 30 years ago.

Great write-up. I particularly enjoy the engine differences.
 

Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
Joined
5,171 Posts
Nice work. I don't remember difficult access to my Gen2 560. Maybe I removed the alternator belt and moved the alternator to the end of its travel? Certainly not difficult to remove the alt, though. Just two bolts and the electrical, no?
 

Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
Joined
5,171 Posts
That's what they say about the voltage regulator 馃槀 馃槀
Haha! Yeah, usually easier said than done. I went one step further once and just installed new brushes in my old regulator. Much easier to install a whole regulator.
 

Registered
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1,156 Posts
I've had some issues with my 1990 500SE, and have been meaning to change this part for a while. For anyone who doesn't know, the alternator has a little device screwed into the back of it, called the voltage regulator. This part has two brushes that contact the rotating alternator. Anyway, these brushes wear down over time, and when they're gone, or almost gone, the car will stop working. Apparently, before the car stops working, there can be indicators of short brushes, such as electrical issues. Here's a good thread on the subject, and MBL recommends 80k miles as the replacement interval.

Everyone says that it's an easy job to replace this part.....just two screws to remove, pull the old one out, pop the new one in, and you're good to go. Not so for some people!
View attachment 2697882
There is not enough room to get a tool onto the lower screw. More accurately, there is no tool small enough to fit between the oil filter housing and the lower screw. The clearance is just over three quarters of an inch, or about 20mm. I showed the car to a few people, including a mechanic and the Snap-On guy. All of them insisted that the only way to replace this part was to remove the alternator. Hardly a quick roadside fix then! Notice also, that the lower screw has been slightly rounded by someone's previous removal attempt. :mad:

Well, I am obviously in the minority here, because across the forum people are changing this part without any fuss at all. I wonder if it is to do with the car being a V8, being RHD, being a UK car, being Gen2, or some combination of these? It surely can't be that all V8s are like this? Otherwise I would have expected this issue to have come up on the forum more often - I could only find one other brief reference to having to remove the alternator.

Strangely the workshop manual does not show, anywhere, how to remove the alternator! I did manage to find a tutorial on this at Pelican Parts, but still, it would be a headache for sure. So, I decided to make my own tool for the job:
View attachment 2697883
View attachment 2697884
View attachment 2697885

So, I hunted around for a 1/4" box end, which was not easy to find! But this one from Britool is inexpensive and readily available on eBay. I then chose the screwdriver bit that fitted most snugly into the screwheads. This turned out to be a posidrive which is strange, as the screws appear to be Phillips. I don't think it's right to recommend using a Posidrive bit on a Phillips screw, but it was the best fitting bit, and so that's what I went with. As you can see, the depth of the tool is under 16mm, and will fit nicely. I used JB Weld to fasten the bit to the box end.
View attachment 2697888
I took this photo later, to show how the tool fits (new VR already installed).
The tool is quite short, but this is not a problem, as there is very little space to move, and it would be impossible to turn a long tool very much at all. The main difficulty here is making sure to get enough downward pressure on the screw, but there is just enough room to get a finger between the tool and the oil filter for this purpose. I removed the oil housing cover, but it made hardly any difference at all.

So, the car has 125k miles on it, and I'm pretty sure this job has never been done. Here's how the old part looked, compared with the new one: View attachment 2697889
View attachment 2697890
Looks like I just made it!!! So, I urge everyone to check this part and get it changed. Apparently the minimum recommended brush length is 5mm. The old one has 2.6mm & 5.13mm left on it - probably ok for another half a mile or so. 馃槀 According to Greeney's book, the wear pattern should also be checked, as this can indicate alternator issues - not in this case luckily. The new brushes measure 11.54mm & 11.47mm, and I intend to check them after 5000 miles to see how quickly they are wearing.

Fitting the new VR is not as easy as it seems. It needs to be put into place with the brushes pressed all the way down! For this, I used a piece of tape, but I have since read the excellent recommendation of using a cable tie!

Well, after carrying out this headache of a job, I decided to do the same on my 300SE, which doesn't have the clearance problem. I took some better pictures this time.....
a pliers with sharp teeth will do the job .the new regulator will go in , just push it up against the spring loaded brushes . you are making way too much out of this .
 

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1985 MB 500sel (Euro)
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740 Posts
Jeez, just when I think I am finally caught up, youse guys spring another "must do" fix on me. but thanks, will follow up.

Lucky Mike, as long as you are here, since I read your tip on slightly releasing the pressure on windows that are fully closed, I have become obsessive about doing so. but does the the same hold true for when the window is fully down?
 
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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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Jeez, just when I think I am finally caught up, youse guys spring another "must do" fix on me. but thanks, will follow up.

Lucky Mike, as long as you are here, since I read your tip on slightly releasing the pressure on windows that are fully closed, I have become obsessive about doing so. but does the the same hold true for when the window is fully down?
That is an excellent question. I don't know but would assume that the same holds. Even if the effect is small, every little bit helps on these old cars, eh? We so rarely roll ours down that I haven't given it much thought.
 

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W126 1990 500SE W126 1991 300SE
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Discussion Starter · #10 ·
a pliers with sharp teeth will do the job .the new regulator will go in , just push it up against the spring loaded brushes . you are making way too much out of this .
Which job do you mean with the pliers? Undoing the hard to reach screw? And then use pliers to tighten up the new screw?

I did see a forum post from someone who had tried fitting the VR by just pushing it in. The brushes broke off, and he had to buy another one.

Maybe if you've done a lot of these, or have a better idea of what the alternator looks like inside, then you'd be confident/skilled enough to get the VR in there without preholding the brushes down. But I don't have that experience.
 

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Which job do you mean with the pliers? Undoing the hard to reach screw? And then use pliers to tighten up the new screw?

I did see a forum post from someone who had tried fitting the VR by just pushing it in. The brushes broke off, and he had to buy another one.

Maybe if you've done a lot of these, or have a better idea of what the alternator looks like inside, then you'd be confident/skilled enough to get the VR in there without preholding the brushes down. But I don't have that experience.
the pliers will get hold of the screw head to remove and back in .also there is a ratchet short blade screw driver that is available , it come in 2 flavor , flat of phillips . has using tape , if you dont force the regulator in , you wont have a issue .never broke one out of a hundred or more .
 

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W126 1990 500SE W126 1991 300SE
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Discussion Starter · #12 · (Edited)
the pliers will get hold of the screw head to remove and back in .also there is a ratchet short blade screw driver that is available , it come in 2 flavor , flat of phillips . has using tape , if you dont force the regulator in , you wont have a issue .never broke one out of a hundred or more .
If you've done a hundred or more, that would be why it seems like nothing to you! :)

I wasn't able to find any tool that would fit there, do you have a link by any chance?

In hindsight, it would have been better if they had used allen head bolts for the 500SE I think. That way an allen key would probably fit in there.


EDIT: Actually I did buy this tool last summer, hoping that it would do the job. It could be the type that you mean. It did not fit. I also forgot to mention that when I made my own tool, I had to cut the screwdriver bit in half, because it would have been too long otherwise.
 

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W126 1990 500SE W126 1991 300SE
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Discussion Starter · #13 ·
I might as well post the pictures from last summer. This will give a better idea of just how tiny the clearance is.
A standard screwdriver bit would just about fit in there, meaning that it would be impossible to undo the screw even slightly, as there would be no room behind the bit for it to move out.
2697979


Then a comparison of the bit size with the tool that I got:
2697980

2697981

So, obviously no way for that tool to fit in there.

And here's what I had to do to the bit:
2697982

2697983


So, while I agree that it's a pretty easy job to do on the M103. On the other car, with that much clearance, it's really awkward. Using a pair of pliers might have worked. But there is also little room for making lateral turns. The only possible way to do that with pliers, would be from underneath the car. It would also be tricky to put the new one with pliers, as the washers could easily be deformed.
 

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I think Alain is saying you don't need to zip tie the brushes. I too have done dozens at least by just angling the thing into place. I will admit, though, that most of the cars I worked on afforded much better access.

Often (not always) if you remove the adjustment bolt and take the drive belt off you can pivot the alternator to a much better position for access.
 

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If you've done a hundred or more, that would be why it seems like nothing to you! :)

I wasn't able to find any tool that would fit there, do you have a link by any chance?

In hindsight, it would have been better if they had used allen head bolts for the 500SE I think. That way an allen key would probably fit in there.


EDIT: Actually I did buy this tool last summer, hoping that it would do the job. It could be the type that you mean. It did not fit. I also forgot to mention that when I made my own tool, I had to cut the screwdriver bit in half, because it would have been too long otherwise.
craftsman number 4117 is the flat blade tool , the phillips one must be one number up or down .always look at tools at stores , some screw drivers kits have short angle ones in at time .when you put the regulator in , you go in a angle , then go straight , dont force , it will go in .a plier will unscrew the bad screw .craftsman number 4116 has 2 blades , a flat and phillips .kobalt brand also [ lowes ] .
 

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Discussion Starter · #16 ·
craftsman number 4117 is the flat blade tool , the phillips one must be one number up or down .always look at tools at stores , some screw drivers kits have short angle ones in at time .when you put the regulator in , you go in a angle , then go straight , dont force , it will go in .a plier will unscrew the bad screw .craftsman number 4116 has 2 blades , a flat and phillips .kobalt brand also [ lowes ] .
Well, next time I do one, I'll be a bit braver and try getting it in there without cable-tying the brushes. Thank you for the craftsman details. I had a look online, but as you say, it's definitely better to see them in a store. Still, anything that takes a standard length bit will not fit there. If they have a shorter bit, then there's a chance.

I'm surprised that others haven't had a car with the same setup. Can anyone confirm which of our W126s have this limited clearance?

As a side note, for anyone buying a VR. MB have changed the packaging this year, but I'm not sure if there was any change to the part. I have 5 VRs on hand here, and there is a clear chronological progression for the 3 digit number printed under the 'Made in Hungary' text.
2698031

2698032


The first picture shows the VR I bought last year, which came in the box pictured on the left. And the VR numbered 660 was bought last week, and came in a narrower box, which incidently is not wide enough for the part. I expect these are renumbered after some revision is made? Anyway, I noticed that the VRs I bought last week had much stiffer brushes then the one from last year. That is, the springs loading the brushes were much firmer. I don't know what effect, if any, this will have.
 

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1991 500SEC Euro, 1987 560SEC Federal
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Well, next time I do one, I'll be a bit braver and try getting it in there without cable-tying the brushes. Thank you for the craftsman details. I had a look online, but as you say, it's definitely better to see them in a store. Still, anything that takes a standard length bit will not fit there. If they have a shorter bit, then there's a chance.

I'm surprised that others haven't had a car with the same setup. Can anyone confirm which of our W126s have this limited clearance?

As a side note, for anyone buying a VR. MB have changed the packaging this year, but I'm not sure if there was any change to the part. I have 5 VRs on hand here, and there is a clear chronological progression for the 3 digit number printed under the 'Made in Hungary' text.
View attachment 2698031
View attachment 2698032

The first picture shows the VR I bought last year, which came in the box pictured on the left. And the VR numbered 660 was bought last week, and came in a narrower box, which incidently is not wide enough for the part. I expect these are renumbered after some revision is made? Anyway, I noticed that the VRs I bought last week had much stiffer brushes then the one from last year. That is, the springs loading the brushes were much firmer. I don't know what effect, if any, this will have.
Hey there Martin,

My 560 & 500SECs have the same limited clearance you display in the pics.. That bottom screw can be a PITA totally. Cannot agree more.
Last time I did that on the road parking lot I had to use a mini vise-grips to crack it free....

Use the stiff springed version. 100 yeares ago, I replaced my original Bosch with a 'made in Germany' Kaeler unit and it only lasted 40K miles before giving out one fine day in the wilds of New Hampshire.
It was a big $ tow home that day.

When I got my Bosch unit from FCP I checked the brush tension against the Kaeler regulator. Though the brushes were hardly worn, the brush tension was less than half that of the Bosch.

Bosch went in and no troubles 8[?] years later..

M
 

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OOHH THE MEMORIES that come back from reading this post :oops: 馃槰 馃槻 On our infamous Memphis Road Trip in the formerly owned 300SE. We had stopped in Birmingham for a pit stop and that's where the troubles started, the radio started acting up then we lost the A/C and climate blower, making it to Tupelo before the fuel pump finally gave out. It hadn't been long since I had replaced the VR but the symptoms pointed to it. Long story made short, we had to abandon Sadie at the Loves Truck Stop for a day until we could get back down there with a new alternator to replace the factory unit that was eating regulators.

Fast forward to today, I now carry a spare alternator, VR, fuel pump relay, KLIMA relay, and EZL(?) ignition module just in case as well as an assortment of the various fuses and a set of the old belts
 

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1991 500SEC Euro, 1987 560SEC Federal
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OOHH THE MEMORIES that come back from reading this post :oops: 馃槰 馃槻 On our infamous Memphis Road Trip in the formerly owned 300SE. We had stopped in Birmingham for a pit stop and that's where the troubles started, the radio started acting up then we lost the A/C and climate blower, making it to Tupelo before the fuel pump finally gave out. It hadn't been long since I had replaced the VR but the symptoms pointed to it. Long story made short, we had to abandon Sadie at the Loves Truck Stop for a day until we could get back down there with a new alternator to replace the factory unit that was eating regulators.

Fast forward to today, I now carry a spare alternator, VR, fuel pump relay, KLIMA relay, and EZL(?) ignition module just in case as well as an assortment of the various fuses and a set of the old belts
Hah

Along with the factory tools, I carry a new fuel pump relay, a spare MB gas can, a cell phone, a AAA card, and a National Parks Lifetime Pass.

Weeks long road trips we take the SUV..
 

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Yes, Ursula came with the factory tool kit, Sadie did not, and I carry a basic tool kit on over night road trips. Day trips are usually to the Doctor or down to my son's house so "rescue" isn't but a phone call away
 
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