HOW-TO: Replacing Neutral Safety Switch (NSS, S16/3)

[nocfn]

When I had the Trans Rebuilt on the C126and E500, they both got replaced. (no it wasn't URO)

 

[emerydc8]

Again sorry to raise your heart rate !!

No harm - no foul. It's a good thing the part number was correct after all because I've had about zero luck getting Naperville to respond to any of my email inquiries. I only average about $130 a month there, so I guess that's pretty low in their give-a-$#*t priority chain.

Closed Orders
Order Number Status Order Placed Total
27974 Completed Nov 17, 2018 $20.35 Details
27828 Completed Nov 5, 2018 $151.05 Details
27498 Completed Oct 11, 2018 $18.50 Details
27013 Completed Sep 6, 2018 $66.76 Details
26916 Completed Aug 30, 2018 $43.29 Details
26547 Completed Aug 5, 2018 $269.36 Details
26201 Completed Jul 15, 2018 $20.72 Details
26199 Completed Jul 15, 2018 $125.80 Details
24944 Completed May 12, 2018 $59.20 Details
24592 Completed Apr 27, 2018 $213.02 Details
24568 Completed Apr 26, 2018 $82.85 Details
23375 Completed Mar 3, 2018 $234.66 Details
23208 Completed Feb 21, 2018 $50.32 Details
22750 Completed Jan 25, 2018 $319.68 Details
21482 Completed Nov 11, 2017 $132.35 Details
18454 Completed Jun 12, 2017 $103.60 Details
18187 Completed May 30, 2017 $100.22 Details
17665 Completed May 6, 2017 $71.28 Details
17422 Completed Apr 26, 2017 $320.30 Details
17108 Completed Apr 13, 2017 $176.19 Details

 

[nocfn]

just an FYI on Naperville - Bob tells me the business has increased, and the staffing has not been able to backfill the departures to MX tech side of the store.

Not an excuse for us to swallow, but they are working to return to the level of service we expect prior to the software changes. Calling to get an answer will be more effective as they are dealing with much demand and staff reductions. So while they all train staff on the new system, and their extensive dealer - indy network and other MB dealerships in the region, timely email response (even to me) are sadly falling thru the cracks. If you care to continue the relationship and the great ship discounts/no tax - we may have to put up with other aggravating experiences for a bit of time. Keep in mind that shipments from Germany are also depending on the data entered in the system properly over there as well. The EPC ordering system changed (ask Klink or Tom Hanson of MBUSA) for the world ordering and inter dealer communications are included. However, vote with your money - they are not the only show in town.

If anyone is able to secure a similar deal on a discounted price, free delivery and no tax - lets get it started.

 

[gerryvz]

I’ve made several recent orders with them and have had no issues. Another $500+ order is going to be put in this week.

 

[nocfn]

My only issue has been with a encapsulation panel from the fatherland recently but it took some calls.

 

[gerryvz]

Drove to Ronald Reagan Airport in stiff rain and nasty traffic this morning. On and off the throttle, high speed and low speed. Not a hint of any ASR issue. I think the new NSS did the trick.

Following up on this, I have now driven the car about 120 miles since replacing the NSS. Absolutely zero issues with LHM and ASR light coming on. The CEL lamp has also disappeared after I reset it, because the "LHM companion" Code 6 in the DM module is no longer being triggered.

This solves a persistent CEL issue I've been having for the past few years, since my NSS started acting up.

I have another spare NSS on my latest parts order, to join the spare one that I have on hand for my G-wagen's 722.3 (which is the identical NSS to that used on the E320 six-cylinder models).

Cheers,
Gerry

 

[gerryvz]

Wanted to add a few photos of my old NSS (I believe it was the original one installed on the car at the factory), in comparison with the new one, at the time I replaced it.

 

[IslandMon]

Just did this job on my 92 with 219k on the clock. I followed the how-to, pinning the switch with allen wrench and then tightening the two bolts down. No before/after measurements, and ultimately no adjustments required after a test drive.

Wish i had done this when the tranny was out of the car, would have taken 5 minutes instead of an hour!

 

[ricsim]

I would like to change mine (NSS), but as shown on this picture, i think i've to change my switch plug too.
How can i replace this switch plug ?
What is your opinion ?

 

[gsxr]

The rubber boot looks damaged, but I don't know if it's available separately. If not, I'd wrap everything in good electrical tape. Self-vulcanizing (self-fusing) rubber or silicone tape would be a better option, but given the limited space, make sure the wrap isn't so thick it interferes with the connector fully seating in the NSS.

 

[500AMM]

I picked up this particular How-To about replacing the NSS which contains most info on the topic, but the thread is in the Transmission and Driveline subforum. The How-To which IS in the How-To subforum split after post #19 and ends up about replacing the shift linkage bushing: HOW-TO: Replacing Neutral Safety Switch | "HOW-TO" Tutorial Articles
Maybe this thread should be moved over and replace/combine that thread in the How-To sub forum?

However, I am working on the starting issue on my (sold) Limited and thought I should begin with checking the NSS. I don't have any code reader so this may be a shot in the darkness. Out of curiosity I opened the NSS to have a look inside and here are some pics of the internals.

Update 29.10.2021
Some of the images are replaced

 

[500AMM]

The switch was very clean inside, I just wiped off some lube prior to taking the pics. The contact points looks fine so if the switch has any defects at all it must be in some of the components on the circuit board. I'm not familiar with electronics so I don't know what those bits are doing. Has anyone checked out something about those?

 

[gsxr]

That is an extremely simple circuit, in each position a different resistor is selected. You can measure each resistor with an ohm meter and verify the reading matches the rating (determined by the color bands). My guess is, the typical failure is dirty contacts, followed by bad solder joints. While it's possible the resistors could fail I'd think this would be relatively rare.

Thanks for the autopsy photos! I've never opened one up...

 

[Vinnie]

Out of curiosity I opened the NSS to have a look inside and here are some pics of the internals.

I was planning to do the same with mine, once it take it out. Thank you for the photos of internals! Something inside me whispers that maybe I can refurbish mine. The symptoms I'm having is that there is no difference in RPM when moving from D to N (and then to P) - they stay on 500. It's not always but becomes more frequent. However, I had not problem with starting the car, even if I switched it off when RPM were 500 in P.

As for potential problems, gxsr provided two reasons, and here are another two. There are two small contacts on the rotating arm which touch the copper sliders. Maybe they worn off with time and now do not touch the sliders all the time?

Another reason is on the very first post of the following thread:

Switching Neutral Safety Switch | Transmission and Driveline

This neutral safety switch is a truely wear and tear item. Over time, it will act up and needs replacement. Examining the circuitry, I think Mercedes engineers did a bad design by using this part. This little mechanical contact has to handle the current to activate a solenoid which then...

www.500eboard.co

It says that the contacts which you circled in yellow on your photos may finally stop working because of being worn or tarnished because of carrying high current. That might be the main reason for failure of this unit.

 

[500AMM]

Thanks for useful info from both of you!

My NSS has close to zero wear on the two contact points and that sliding contact shoe. No wear on the sliding contact plate on the circuit board either. I'll measure those resistors and if they turn out good the switch will be reassembled and goes back on the transmission.

For those who like to open the NSS - be very careful when drilling out the aluminium rivets! The drill bit quickly grabs and carves itself straight through and the hole enlarges to the drill bit size you have chosen. A soldering iron has to used to loosen two of the plug pins from the circuit board. When reassembling, apply some flexible sealant on both sides of the preshaped gasket between the two cover halves.

Update 29.10.2021
Image replaced

 

[500AMM]

Just to follow up... the NSS was not defect, but the starter was dead.

I shot some pics of the starter upper bolt challenge and posted in the starter RR How-To, post #27:

HOW-TO: M119 Engine Starter Replacement | "HOW-TO" Tutorial Articles

Hi Gang, For the last several months my starter would work on first crank sporadically. It'd always spin, but sometimes the drive wouldn't engage, so I'd hear a ZING... This never happened more than once in a row, but it did happen about 50% of my first cranks. Fear of being stranded and...

www.500eboard.co

 

[500AMM]

The resistors on the NSS circuit board are checked and I was going to verify the values against a resistor chart. I think I understand most of the chart and it appears to be a simple thing to do. All guidelines start with 1st band, 2nd band, 3rd band.... but which end do they count from when the resistor has bands evenly spread over the body?

 

[Jlaa]

The resistors on the NSS circuit board are checked and I was going to verify the values against a resistor chart. I think I understand most of the chart and it appears to be a simple thing to do. All guidelines start with 1st band, 2nd band, 3rd band.... but which end do they count from when the resistor has bands evenly spread over the body?

View attachment 130727

Of course the best way is to measure the resistance directly, but if you are not able to measure, then try to rationalize the last band first (tolerance).

Resistor Color Code Calculator - 4 band, 5 band, 6 band | DigiKey Electronics

The resistor color code calculator makes it easy to identify and select resistance and tolerance values for 4, 5, and 6 band through hole resistors.

www.digikey.com

It is pretty common to have 1% (brown) and 2% (red) tolerance …. Smaller tolerances get much more expensive so it is unlikely to have a mix of .25%, 0.5%, 1% resistors all in one board….

 

[500AMM]

Thanks, but how do I determine which end of the resistor to count from?
A friend of me checked the resistors, values shown in the image.

 

[Jlaa]

Thanks, but how do I determine which end of the resistor to count from?
A friend of me checked the resistors, values shown in the image.

View attachment 130784

You guess and do it both ways and see if it make any sense! (Especially the tolerance bands)

 

[gsxr]

I thought the tolerance bands were not the same colors as the resistance bands, so you could get an idea which is which? At least if the colors haven't faded due to age or heat.

EDIT: Nope, see post below:

 

[Vinnie]

Oh, those electronic guys are like programmers - they like to code and then code over a code. What finally makes it understandable to themselves only. Anyway - to the point - there two subtle differences, which allow to determine the tolerance band:
- it is thicker than the rest of the bands, or
- it is separated by a greater distance than the other bands.
Using the above rule to the resistors in subject, I would say that no. 1, 3, 4 and 6 have thicker tolerance band, and no. 2 and 5 have tolerance band separated by a greater distance (counting resistors clockwise, starting from the leftmost first).

 

[500AMM]

Oh, those electronic guys are like programmers - they like to code and then code over a code. What finally makes it understandable to themselves only.
Anyway - to the point - there two subtle differences, which allow to determine the tolerance band:
- it is thicker than the rest of the bands, or
- it is separated by a greater distance than the other bands.
Using the above rule to the a resistors in subject, I would say that no. 1, 3, 4 and 6 have thicker tolerance band, and no. 2 and 5 have tolerance band separated by a greater distance (counting resistors clockwise, starting from the leftmost first).

he, he....not to offend those professions, but I have noticed that myself sometimes.
But thanks for posting Vinnie, I'll follow your explanation and see how it turns out. However, since the resistors appears to be alive I'll assemble the NSS and hook it up and see what happens - it's just a "go or no-go" function with this puppy.

.

 

[500AMM]

A follow up on my NSS potential failure. The switch was not defect and is now back in the car and work as normal. I've put together some pics about replacing the aluminium rivets with M5 screws after splitting the switch.

Post #61 and #65 are updated as well.

 

[Vinnie]

Thank you a lot for sharing! This is invaluable material considering that this part is NLA, and most probably last units available somewhere will be gone soon.

 

[500AMM]

So the NSS has gone NLA as well.
That's in fact surprising due to that a vast number of cars using this part are still running. My guess is that within not more than a 10 years time are a lot of the '90 era MBs including the 036 stranded due to NLA parts. It's a disappointing fact that MB do their best to phase out the young classics.

About 10 years ago I said that the 124 cars generally will be a rare bird. Today we rarely see them on the road here in Norway and the breakers are chrushing them in a few days after arrival at their yards.

My advice is; don't just throw away replaced parts! Unless the part is totally toast, put it aside for a possible restoration or spares at a later point. I'm sure most of us doing the wrenching ourself do that already, while others may not. If people don't have the skills, tools or any interest about restoration, it is always someone else around to help out.

 

[JC220]

So the NSS has gone NLA as well.
That's in fact surprising due to that a vast number of cars using this part are still running. My guess is that within not more than a 10 years time are a lot of the '90 era MBs including the 036 stranded due to NLA parts. It's a disappointing fact that MB do their best to phase out the young classics.

About 10 years ago I said that the 124 cars generally will be a rare bird. Today we rarely see them on the road here in Norway and the breakers are chrushing them in a few days after arrival at their yards.

My advice is; don't just throw away replaced parts! Unless the part is totally toast, put it aside for a possible restoration or spares at a later point. I'm sure most of us doing the wrenching ourself do that already, while others may not. If people don't have the skills, tools or any interest about restoration, it is always someone else around to help out.

Yes all good advice there

The rising scrap metal prices mean some yards will just weigh em in now. So I now make a point of quickly salvaging everything useful off of them before they go. Aka don't hang about.

I bring all my tools and arrive early if checking for new cars that came in. That way I can pilfer them for good parts quickly, could be gone by the next weekend. I have so many w124 parts my focus is now on S class parts and the same thing applies. Whole cars headed for crushing with motors still in them FFS

 

[gerryvz]

The cars do disappear from the yards faster than a robm.uk post deleted from the forum !!

I went to a wrecking yard today in Baltimore, to get some stuff off of a 1991 300SEL sedan that I got a fair number of parts off of. A week ago, I got the passenger seat for the lower springs and seat motors/frame, the springs of which I will retrofit into my 560SEC coupe's driver's seat. I checked on Wednesday to ensure that the car was still there, and it was as of that day. Went there today and it was GONE. I think it had been there all of three weeks.

T'wasn't a wasted trip though -- there were several other cars there, including a 1983 300SD (W126), a 1990 300E, a 1996 S320, a 1988 260E, a 1976 450SL, and a 1987 300D. All new cars to the yard within the past two weeks. Alas, I didn't end up getting very much, except a LOT of good trunk badges.....

A couple of days ago I raided a 1990 560SEL at another one of the Baltimore yards that had just come in. Someone had gotten the fuel distributor, the computers and the fuel tank, but everything else was pretty much untouched.