[HeroofTime]

Hello everyone,

I'm extremely interested in buying an S420 that I've recently found. It has very low miles, but I'm trying to figure out what issues these cars have before I go jumping in head first. Currently, my Volvo is sitting in the transmission shop because the torque converter is shot. This is the second time it's went into a transmission shop in almost exactly 40,000 miles which is ridiculous.

Most importantly, what are all of the common issues that a 1995 S420 would have?

Other questions that I'm curious about...
• Is there a big difference between the 4-speed and 5-speed transmissions? I have read that the 1996-1999 models received the upgrade, but is it an upgrade in terms of reliability?

• How many wiring harnesses need to be replaced? Is it only one that runs along the fuel rail or more? What is the typical cost of all wiring that needs to be replaced on a 1995 S420?

• Is the W140 platform the very last example of Mercedes' "perfectly" engineered car?

Thanks for any and all help guys. I'm very serious about this purchase and would appreciate a little bit of your time greatly!

 

[HeroofTime]

I greatly apologize for double posting, but I forgot to mention a couple things about myself that should help you guys decide whether or not I should purchase the vehicle. I also do not see an edit button for the original posting.

I do nearly all maintenance work myself on the cars at home. My father helps too at times, for he used to be a mechanic. I work on everything outside of engine and transmission overhauls. The 1995 S420 I am looking at is not equipped with electronic suspension which is a plus in my book. I may sound like I hate to do maintenance, but it's vehicles that have inherent problems with their engine or transmission that I hate.

Thanks again for any and all help!

 

[Thom_7]

Hi there -- welcome to the forum! Everyone here is a big help, so if you do end up purchasing one of these cars, you'll find this forum a great resource. So anyway, to answer your questions:

1. As far as the transmission goes, there's no real difference in terms of reliability between the four and five speed that I'm aware of. These transmissions are basically bulletproof if maintained properly. Generally speaking, if an issue does arise it tends to be at around 100k-150k miles or so, and usually manifests itself in the reverse gear going bad, requiring a rebuild. But even that isn't the end of the world, as rebuilt transmissions can be found for $1500, usually with a warranty.

If you're looking at a car and want to roughly determine the state of the transmission, just shift it from park into reverse and drive. If it takes two seconds or more to engage the gear, chances are it'll need a rebuild within the next 20k miles. If it takes between 1-2 seconds you have more time. Under one second and the transmission is solid.

2. The wiring issues are present in a few components, however the upper harness is the most critical. It costs around $700. I don't believe there are many cars currently operating which haven't had the harness replaced yet, as it's a well-known issue which greatly impacts the functionality of the car -- but of course check anyway. Next after that is the ETA or electronic throttle actuator, which also will need to be rebuild due to wiring issues. This is another well-known issue that will leave the car in limp mode when it goes bad. Rebuilt ETA runs about $300. Then you have the lower harness, which rarely goes bad and operates the alternator and starter, along with a few ancillaries. This would be more of a preventative maintenance item, unless you're seeing weird oil temp/press readings. I believe a lower harness runs ~$500 but I could be wrong. And finally the wiring can also affect the power/folding mirrors, the mechanism of which will also need to be rebuilt. This is a comparatively minor issue, and if necessary will probably cost in the neighborhood of $500 to repair as well, if I had to guess.

3. Most people agree that the W140, particularly the pre-facelift examples, was indeed the final model produced according to the 'old' Mercedes engineering standards. The engineers ran the show back then, and very little attention was given to cost, if it meant a sacrifice in quality.

As you mentioned, the S420 will not have the hydraulic suspension system which was standard on the 500 and 600 models. While it's true that it offers and improvement in ride, it also is an order of magnitude more expensive to maintain. Not that it's unreliable -- it's really quite good -- but when it does require attention, it can get expensive fast, especially compared to the standard setup.

Hope this helps, and let us know if you have any more questions. I'm sure someone else will chime in here if I missed anything.

 

[HeroofTime]

Awesome! Thanks for the detailed response.

I forgot to ask about the W140 and rust. Is it an issue at all? I live in northwest Ohio where they salt the roads often when snow inevitably hits us. The car I'm looking at is from Florida and has absolutely no rust now, so I'm worried about the future if anything. I plan to keep this car for a very long time, hence why I'm worried about major maintenance down the road! I really hate rust, so it's a big no-no for me.

Lastly, are the wiring harnesses serviceable by someone you'd call a home mechanic with shop tools? Thanks again.

 

[Thom_7]

The upper harness has a lot of plugs, but it's really a no-brainer for anyone who can keep track of what plug goes where; couple of hours of work, tops. There's really no trick to it beyond that. I don't even think you need tools.

I have no idea how accessible the lower harness is, but I don't think it's too difficult of a job either.

As for the rust, it's not really an issue. Sometimes rust can happen on the body panels where the lower plastic cladding meets the sheet metal, but it takes some neglect for that to occur. The undercarriage isn't really an issue, but if you're worried, there's always undercoating. Structurally though, I've never heard of one of these cars rusting away unless it's been abused.

 

[HeroofTime]

Thank you Thom_7! I keep having small questions coming up in my head as the days go by before I go and see the car this coming Sunday.

Is there a lot of room to work underneath the hood when performing repairs? What about the rest of the car?

I have been doing research about the audio system, but I can't seem to figure out how many speakers the 1995 S420 has. I believe I was reading somewhere that the earlier W140s had fewer speakers than the later ones. If I were to ever swap the speakers out of it, I would like to upgrade 7 or 8 speakers versus 14 speakers. In other words, I'm trying to keep things as simplistic as possible.

Is the 4-speed transmission technically less problematic than the 5-speed transmission because of the electronic 5th gear controller? In other words, are those controllers prone to failing? I don't understand how the 4-speed and 5-speed transmissions differ entirely, so I'm going off of what I've previously read the past couple days. Also, does the 5-speed transmission have issues with the reverse failing like the 4-speed does?

Was the paint process changed at all during the W140's lifetime? If so, would rust accumulate more or less on the earlier W140s versus the later W140s? I ask this because the late 90's Mercedes-Benz vehicles were plagued with rust issues no matter how much one had cared for the vehicle's paint (specifically the W210s, which is what I base this information off of).

Lastly, (I hope I don't get hate for this) are there any performance parts for our W140s? Specifically for the S420, 4.2L V8? I am not looking at creating a howler that can be heard around the corner. I prefer to get a little more oomph out of my cars while maintaining sleeper status and that is all.

Please forgive me for asking so many minor questions, but I would like to know what I'm getting myself into before dropping 10K. I think I should be all set if you could help me out with this last batch of questions. Thank you very much!

 

[Thom_7]

The Bose Beta audio system has eleven speakers; four along the rear deck, two in each door, and one nondirectional tweeter behind the rearview mirror. The earlier cars did not have fewer speakers, but they did have a different amplifier/crossover setup I believe. Best advice is to leave the audio system alone. It still sounds great even by today's standards, and it's a MAJOR undertaking to replace the speakers and amplifiers. They're all nonstandard sizes, so new mounts need to be fabricated to accommodate modern speakers without making a hash of it. It's not impossible by any means, but it's very expensive to do properly and end up with a better final product than you started with.

Some owners have upgraded the head unit (but even that comes with some complexities), and there are a few other options to get AUX and Bluetooth functionality on the stock unit as well. But to be honest, you'd have to spend big $$$ to build a system that sounds significantly better than stock. Not recommended.

I'm not a transmission expert by any means (one of our other moderators, MAVA, is the resident expert on transmissions), but from what I do know (and having owned both) there is very little reliability difference between the 4 and 5 speed boxes, and yes reverse is prone to fail first on both of them. As for the technical differences, perhaps MAVA can jump in on the conversation and help out there.

As far as the paint goes, I believe that Mercedes in general went to a lighter, more eco-friendly paint by the end of the 1990s, so that would presumably include the W140. I don't have any information to back that up either way though. Bottom line is that everything will rust under the right conditions, but the W140 is not known to be 'plagued' with rust either. Keep the car clean and waxed, and don't allow salt to sit on the finish for too long. Only advice I can give on that.

In my personal experience, the paint on the W140 is impressively resilient. Even neglected Mercedes paint can come back with a good cut and polish. I wouldn't worry about rust too much unless your car is going to be sitting outdoors all winter and you don't have the time/resources to keep it waxed and give it a wash every few days to get the salt off.

Performance parts... not so much. Back when these cars were new, all the big tuners (AMG, Lorinser, Brabus, Carlsson, etc.) produced parts for the M119 engine; superchargers, cams, exhausts, heads, etc., but these parts are extremely rare today. You can probably still find a performance exhaust easily enough, but anything else is going to be next to impossible -- plus you're looking at a 420, which was the mid-range engine to begin with. I think all the performance parts were made for the 500 and 600. Nobody buys a mid-range engine option and then spends big money on performance parts, when there are two more powerful engines available right from the factory.

 

[MAVA]

Welcome to the forum Hero,

The S420 is a great mix of a car as you get the V8 power with out having the rear hydraulic shocks, and the tandom power-steering pump, but you loose those hydraulic shocks that permit you to carry that additional weight, and compensate the ride height, but the feature I love the most on the S500, and S600 is the on-fly-switch-control of the ambient-carbon scrubber. That feature is way to cool when on the highway passing through very smelly cattle farms, or smelly diesel exhaust. This carbon scrubber works in about five seconds. Filters all this smelly air .

The +96 cars trasmissions have a longer life, yet the is roughly double life. The +96 cars have an electrical shift plate that is a consumable part, and that last 150k to 200k miles, and DIY mechanic can replace it in a few hours. Plus you gain the fuel economy of that fift gear which can give you a highway mileage of 24 to 26mpg.

The 92-95 transmissions run a little hotter in temperature, and are known to lose reverse gear, or get a chattering reverse. Some lose forward. This can happen around 100k miles to 150k miles.

No real harness issues on +96 cars, and no distributors/ignition cables to deal with.

The Audio is best on +94 cars. The 92/93 is some weird audio system, yet I have repaired both styles of radios and amplifiers, and the fidelity on the amps is on the +94 cars. Much better system. To put an aftermarket is a sin on these cars...

Martin

 

[BrianA77]

Hi,

I have owned about a dozen older Mercedes (w123, w116, w124, w126) since the mid 1990's, many of which I did much of my own work. I have had my '97 s420 for about a year. I am not an expert mechanic by any stretch of the imagination. My car was well maintained but had 137k miles when I got it. During the past year, if my experience is anything to judge by, I had to replace the purge valve solenoid, injectors, plugs, fuel pressure regulator, motor/transmission mounts, blower motor regulator, cabin temperature sensor, steering gearbox, idler arm bushing.

As preventive maintenance, I replaced the thermostat and heater t-hose on firewall, as well as the sepentine belt. Next oil change, I am replacing the upper plastic timing chain rails, cheap parts know to fail on this engine at higher miles and trash an otherwise perfect engine.

Others may disagree, but I would try to get as new as possible with the updated wiring harness and later transmission. I chose 1997 because it had these updates and was also before the addition of xenon headlamps ($$$) and had the simpler, less expensive cupholder design. The AC evaporator, buried in the dash, is a huge problem on these cars, which I do not know if ever resolved. Make sure the AC works before you buy one.

The w140 is probably the most comfortable Mercedes I have ever owned. If just floats down the highway.

On the flip side, I have found this car the most frustrating one to wrench of all the ones I have owned. Except for basic stuff like oil and air filter changes, it is overall horrendous. Especially if it involves anything that has to be accessed underneath, as there will likely be the subframe or suspension part in the way. The dashboard is like a jigsaw puzzle. Despite its size, I have found accessibility dismal. This may not seem like a big deal, but I have found that an inaccessible bolt can double the time I spend doing something. It is the ultimate mental torture-seeing something you can appear to access but realizing that you have to take apart a dozen things to get to it.

There are plenty of parts aftermarket. I have found, however, that getting any major parts from the dealer less viable. Seems like even basic parts can be a few times what you pay in the aftermarket. Also, even basic washers, o-rings, bolts are no longer stocked at my dealer which can become an issue if you are in the middle of a repair and need something quickly. And, in my area (northeast USA), forget about any chain auto parts store having much, if anything for this car.

Brian
'97 s420

 

[glepore]

I agree that the stock audio system is very good. It doesn't have the deep bass of some more modern systems, but the bass it does have is very clean and without boom or exaggeration. The imaging is excellent. It could use higher quality tweeters, but overall you'll like it. I have done modern Kenwood headunits in my 90's Benz's. Easy to do, plug and play as preamp output is high enough. For $150 plus install you get Bluetooth (major plus if you do nav) aux and usb, and best of all some great dsp that allows you to adjust digital delay to each speaker to clean the imaging up perfectly along with 13 band eq.

Lighting-I went to led headlights on my car which lacked zenon (early 96 coupe). They work very very well, but have a downside-incurable rfi on fm. Even the good bulbs do this, oem's spend a lot of time and energy curing theirs. I just stream local radio as needed to avoid, as the rfi doesn't interfere with the audio system, its an fm only problem.

I really loved my former 420 sedan. I would confirm that the engine is sludge free, as they're not kind to long or neglected oil changes. My car required a motor swap due to this from prior owner abuse.

A common issue is worn suspension, these cars ride and handle very very well, but suffer from the weight and all of the bushings in the suspension will begin to need attention at around 100k.

One thing to be aware of-Mercedes is beginning to end parts support for these cars-for example, I recently needed a fan for a 97 r129, and its nla. Others are reporting this for random electronic parts. The v8's are common enough that parts stock should last, and there's the used part market, but Benz's reputation of supplying parts for its older cars "forever" isn't true any longer, particularly for some of the computer modules etc.

 

[jal1224]

Glepore, what led bulbs did you buy for your coupe?

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[glepore]

Glepore, what led bulbs did you buy for your coupe?

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H4 HB2 9003 PHILIPS LED 192W 19200LM Headlight Beam Bulbs 6000K White High Power | eBay

 

[jal1224]

Thanks.

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[HeroofTime]

We purchased it! Thank you for the information that everyone provided for me. I've carefully read everyone's replies and taken notes.

I'm looking forward to engaging in more topics here in the W140 forums. I will be creating a new thread about it with a link to a video of it.

 

[glepore]

Welcome and congrats.