Tips for your W126 - PeachParts Mercedes-Benz Forum

bhatt · #1 03-06-2006, 09:01 AM

Hi all,

Thought it would make sense to start a thread for new W126 owners with some of the little-known and useful tips for this model.

Perhaps we could later do this for other models and make them stickies or put them in a separate forum. If someone could put together a W140 one, I'd be grateful!

W126 tips & secrets
-300SD air cleaner rattling: check the rubber mounts below it. Search the forum for more info

-W126 tach erratic: loosen the small cap under the hood (on the fender) and put a rubber o-ring from a garden hose inside. Then re-screw the cap and it should fix the problem. If it happens again, replace this part (called a "tach amplifier")

-W126 rear heat vent blowing COLD air: This is normal. The heat comes from under the seats. This vent is a 'fresh air vent'. Make SURE it's shut off all the way in winter --- slide it to closed, then keep pushing hard until it 'clicks' into the off position. You'll see what I mean when you do it. If it doesn't click off, it will leak cold air.

-300SDL noisy engine: run synthetic oil. HUGE difference

-300SDL not enough power: check the turbo boost switchover valve (search forum)

-300SDL maintenance: run Diesel Purge through the system once a year.. big improvement! Change 2x fuel filters and your air filter at the same time

-W126 cruise control: the amplifier under the dash dies. It's by the parking brake pedal and is held in by a 10mm bolt. Either take it apart & resolder connections OR send it to be rebuilt (about $150-200). Can't do both-- if you resolder, they will NOT accept it as a core.. decide first!

-W126 trunk leaks: If it's leaking from a "hidden" spot into the trunk wells, check three areas: 1)tail light can leak water in from the seal 2)antenna grommet can be bad and will leak 3)rear window gasket can leak in bottom corner. Hope it's not #3 as this means there is rust under the gasket in this area (common) and needs to be cut out & fixed. It's worse than you can see as it's hidden by the gasket. Get in trunk & have someone spray with hose to find the leak.

-W126 rear seat: easy to remove- find two tabs (may be colored red) at bottom of rear seat cushion. Push both tabs toward each other, lift front edge of seat and pull out. Seat back comes out by removing a few 10mm bolts at the bottom, then pull bottom away from car and lift straight up. WATCH out that the metal tabs on the bottom don't scratch the car on the way out!

-W126 erratic fuel gage OR low fuel light not working (diesel): Remove rear seat, remove large plastic cap and disconnect wiring for fuel sender. Use large socket (46mm?) to unscrew fuel sender. Use rag as it is full of fuel and will drip! Take off nut at bottom and remove metal tube. Clean CAREFULLY so you don't break any of the fine wires. I use brake cleaner and it works fine. Reassemble and fuel gage will work. If not, replace.

-W126 back end of car steers itself: your subframe mounts are old. They can be easily replaced by making a tool out of threaded rod and some bolts, and using a couple of shop jacks. Spray the bolts 2 DAYS BEFORE with PB blaster and the job will be 100x easier! Search forum for more info on replacement

-W126 fuse for trunk light and memory seats keeps blowing: the wiring harness near the trunk hinge flexes all the time, and the wires have shorted. Pull the wires and electrical tape them, and you'll be fine.

-W126 window won't move, but motor runs: search forum for my post on "sliding jaw". This can be replaced for $5 and does not require any rivets if you use a bolt & nut like I did. Need to take off door panel, but it's an easy job otherwise. MB window regulators and motors almost NEVER fail.

-300SDL vacuum pump: if you have 150,000+ miles on your car, replace it NOW. If it fails, it WILL take your engine with it. Costs about $300 and is 1/2 hour to replace it.

-W126 voltage regulator: Look at back of alternator, remove two flat screws with stubby screwdriver. Pull out (comes out at an angle, doesn't pull straight out) and look at the length of the brushes (two rectangular rods with curved tips). 1" = brand new, 1/4"=dead on roadside. Judge how bad yours are and replace. They're $15 and well worth it. Even if you don't replace it, buy a spare for the trunk.

-300SDL glow fuse: This will strand you if it fails, is easy to replace with just a screwdriver. Costs $1. You will feel like an idiot if such a simple part leaves you stranded. Buy two NOW. Replace your current one and keep the other as a spare. These fuses look good but have microscopic cracks, so just replace the one in there now.

-W126 fuses. Replace them ALL before troubleshooting electrical problems. See above -- they look good but are NOT! I've had them fall apart in my hands even though they looked fine when in the fuse box. They're cheap -- buy a set and replace them all NOW and you'll be fine for 10 years!

Hope this helps.. feel free to add to this list if I left anything out..

Neal

Brian Carlton · #2 03-06-2006, 01:02 PM

Neil, that's a great list. We need to keep it going.

I'll add just three:

- Brake fluid reservoir is divided into two chambers........front and rear. Very difficult to see the fluid level in the rear chamber because front chamber wraps around driver's side. Look at reservoir from passenger side to determine fluid level in rear chamber. Rear chamber is about 1/5 the size of front chamber and any slight leak in the rear system will cause all the fluid to be lost very quickly.

- Problems with the cruise amp can also be interrelated with the actuator. If the actuator is old and draws excessive current it will take out your remanufactured cruise amp. So, if you are going to spend the money to replace the cruise amp, make sure you send in the actuator for a "tuneup" as a minumum.

- On the older vehicles (pre-86), the auxiliary water pump will take out the CCU if it draws too much current (getting old and tired). Add a 1 amp fuse inline with the pump........or simply disconnect the pump. You don't need the pump unless it gets brutally cold and you are travelling at very low rpm's.

Hatterasguy · #3 03-06-2006, 01:52 PM

I will expand on some of your SDL points:
For the vacuum pump inspect it first, if it has 4 screws on the cover you are fine. If the cover is smooth that is the old type with exposed bearings. If it lets go it will cause the timing chain to snap, and you are looking at a rebuild.

If the engine is noisy it is probably the lifters, run a good quality synthetic oil and see if it helps. If it doesn't replace the lifters.

Doing a diesel purge once a year is overkill, and IMHO I would not do one on a diesel with a fresh set of injectors. You can cause more harm then good.

W126 front end clunk:
Could be a few things, but the tie rod ends and guide rod mounts are very commen.

W126 rear end clunk:
Check the sway bar links, they make lots of noise!

bhatt · #4 03-06-2006, 02:01 PM

-W126 locked out of trunk: if the trunk linkage becomes loose & sloppy, you can't open it by pushing the button. Take a 2x4 about a foot long and hold it so one tip is on the trunk button. Whack the other tip with a hammer (seriously). The trunk should pop open. Make SURE the lock is unlocked first (you can lock & unlock the drivers door to make sure it is in the unlocked position). This won't work if something else is wrong with your trunk. Now pull off the top plastic cover and pull back the carpet. You can adjust the linkage from here. Make sure it works before closing the trunk!!

-W126 rear brakes: Make SURE you keep on top of the pad thickness. Once you're down to about 20% pad or less, the pads will cock themselves in the caliper diagonally. Then the caliper siezes. You will know this happened when you pull the pads and can't push the piston back into the caliper. It's time for a rebuilt caliper at this point. I'd change the rear pads (they're cheap and last for yeras!) when they're down to 35-40% just to be safe.

-W126 parking brake light stays on: There was a recall for the parking brake cable on this car. It involves removing the entire cable from the pedal to the rear brakes, including a ton of labor. Here's the easy fix: Put a wire tie around the parking brake pedal arm (near the top) and clip one end of a spring (from Home Depot) to it. Clip the other end under the dash to keep the pedal pulled up. Everything works as normal, but the little bit of slack in the pedal is eliminated, so the light will stay off.

-W126 dripping ATF: Most likely this is the ATF lines going to the radiator (transmission cooler). Replace these lines if they're dripping -- you just need a crowsfoot wrench. You will know they are leaking if there is any ATF on the outside. You can find these easily by looking at the bottom of your radiator (look from under the car) and find two hoses that look like they have a "spring" covering the outside. It looks like a hose with a piece of wire wrapped around in a coil-like shape. You'll see what I mean.

-300SDL glow plug replacement: pull off the intake FIRST. Makes the job much easier. Careful around the injector lines - these are fragile. While in there, replace the following items: 1) intake gasket (both ends - there is a large one and a small oval one), 2)shutoff valve (easy to do while you're there) 3)replace ALL glow plugs.. sucks to have to do this job again in 6 months! Remember all plugs are the same age, so if one goes the other 5 aren't far behind.

-300SD rough shifting between 1st & 2nd gear: This is NORMAL. It is called the 'neck-snapper' shift by many in reference to the feeling you get when it shifts

There is a bowden cable that can be adjusted to soften it, but the tradeoff is between long transmission life <--> soft shifts. By softening it, you'll shorten the transmission life. Careful doing this if your transmission is old and hasn't been rebuilt.

-300SDL trap oxidizer: Look under the hood (passenger side) for a large metal thing that looks like a football that is plumbed into the exhaust system. You'll see it immediately if you have one. If you do, go to the Mercedes Dealer and they will replace it, along with your exhaust system and possibly even your turbo if it's bad. Search forum for more info. If you have trouble with the dealer denying knowledge, keep bugging them or try another dealer. Be assured this IS covered by a recall and it's still in effect if you car has the trap ox in it. Note that your car (or car you're potentially purchasing) has most likely NOT been to a dealer in the last 10 yrs! Many "dealer maintained" SDL's on eBay still have the Trap Ox

-W126 hood pad: Buy a new hood pad but be CAREFUL how you install the new one. Search the forum -- there is a special 3M glue and you MUST scrape off ALL the old gunk first. If not, you'll be doing the job again in 2 weeks. Make sure to do it right the first time!

-W126 battery: The MB battery is made by Interstate and this is the best battery for the car. Try an Interstate before buying anything else for this car!

-W126 tires: Many opinions here, but Michelins have always been EXCELLENT for me on a number of these cars. One tire expert told me to remember the phrase "Michelins on Mercedes" because that's all they recommend after years of being in the business.

-Clunking from front end going over bumps: Check your brake support bushings (search forum for info). These are common problem areas on the W126. If they haven't been replaced, you will be changing them for sure.

-W126 windows or seats not working: The switch is dirty. Clean it out with contact cleaner or similar (TV tuner cleaner from Radio Shack works also). Most times the switch is just dirty. Keep working the switch back & forth while cleaning.

-W126 radio scratchy noise in some speakers: The fader (roller dial in the center console) corrodes a bit. Roll it back and forth as far as you can in each direction. I do this about every 3 months and the problem never reappears.

Neal

bhatt · #5 03-06-2006, 02:03 PM

Brian,

Thanks for the additional points.. hadn't thought of those.

Hatterasguy,
Good points. Had forgotten to check the vac pump for bolt heads before replacing. Thansk for the comments.

If anyone else has items to add OR finds any errors or changes to what has been posted so far, feel free to add them. I'm trying to make this a useful thread or sticky for everyone who is new to these cars. There is a ton of knowledge out there, and I know 5+ years ago I would have LOVED to find it all in one place when I bought my first W126!

Neal

bhatt · #6 03-06-2006, 02:13 PM

-W126 wipers: Use the original MB wipers (or buy a set if you have aftermarket blades). Some members have had great experiences with Anco blades, but I find the MB ones to work perfectly. You only replace the rubber in these blades (search forum for instructions on swapping blade rubber) and keep using the same blade "frame".

-W126 smearing windshield: After trying a ton of things (bending wiper arms, new wiper blades, scrubbing windshield w/glass stripper, etc, etc.) I found a solution. Put about 6 drops of dishwashing soap into the washer reservoir with each gallon of washer fluid. Use a "degreasing" detergent like Dawn or one that says it "cuts grease" on the label. Works perfectly (don't worry, there are no suds with this little soap). Keeps my nozzles from clogging and keeps the windshield clean.

-300SDL vacuum pump: There are 2 types of gasket for the vacuum pump (one with a "dam" and one without) and there may be a basket installed that has to be removed. Search the forum for instructions -- depending on model year & engine number, the instructions and parts needed to do the job differ.

-W126 stereo installation: Do NOT screw an amp to the rear wall of the trunk like you can do in many other cars. The fuel tank stands up (rather than being under the trunk) and is directly behind that wall. Diesel+amp screws=fuel smell in trunk. Gas+amp screws=BOOM!

bhatt · #7 03-06-2006, 02:23 PM

W126 rim care: These wheels are PAINTED silver, they are not clearcoated "aluminum rims" like on other cars. So treat them like you would the rest of the paint on your car -- don't spray or use anything on the rims you wouldn't feel comfortable using on the hoood! I have found a 1/2 bottle of full strength Simple Green and a brush will get off 90% of the dirt. Spray GENEROUSLY on cold rims and brush. Spray again and wait 5-10mins, then hose off. If they don't look significantly better at this point, nothing will help much and you're better off repainting them.

W126 tire "bouncing" at highway speed: You are driving down the road and feel a wheel "bouncing" off the ground back and forth. Steering shakes and it's really scary. Slowing down makes it go away. The problem is 99% wheel balance. These cars are sensitive to wheel balance and will behave like this until the wheels are balance properly. Get someone with a Hunter wheel balancer -- ther is a special model of Hunter that works REALLY well (search forum for info). Or try someplace that specializes in Porsche racing, high performance MB/BMW, etc, etc. Or try calling around to MB/BMW/Jag dealers to see if they have one.

Want to trade my MB for a BMW: Don't do it. Been there, done that. Huge mistake. Expensive parts, not as logically constructed, not as durable. Yes, they're more fun to drive but how many 1981 BMWs (or even 1991 for that matter!) do you see on the road? And how many W126's? See what I mean?

What color diesel W126 should I buy?: Here's a tip I heard somewhere -- "Buy a color your grand kids like because they'll most likely be driving the car for a good portion of their life". Seriously. I have a black on palomino one and could drive it for most of my natural life if I wanted to. Will certainly get bored of it before I die.. and I'm in my 30's

Bulb out indicator is on, but all bulbs are working!?!?!: Check the two bulbs that light up your rear license plate. They are on the same circuit and will set off the indicator. You never notice them, but if they are burned out, the indicator will come on. Also check the taillights, as there are two tiny "marker lights" in the outboard corners of the car (ie. furthest away from the license plate). Look at both taillights when on and see if they look different (one has a light were the other doesn't)

Neal

Neal

Hatterasguy · #8 03-06-2006, 02:31 PM

The MB battery does not seem to be made by the company that makes Interstate batterys. Compare and OE and Interstate side by side they are very different. The OE weighs more.

If the parking brake lights stays on because the pedal will not come all the way back up here is how you fix it:
Underneath the car their is for lack of a better term what I call a "cable spliter". Just follow the drive shaft back and look up you will see it, towards the rear. One cable runs up front to the pedal, then two others are connected to it and those lead to the parking brakes. This "cable spliter" (whatever) rusts up and can get jammed. Pull it down and clean and grease it. After this is done you can adjust the cables as well. The pedal will be tight and the parking brakes will work very well.

W126 parking brakes are little drums on the inside of the rear discs. Like all drum brakes they do wear over the years and require cleaning and shoe replacment to work correctly.

At this point in the game the newest W126 is 15 years old. Any original rubber brake line is bad, replace them as you do brake jobs.

The rear wall of the trunk is right against the fuel tank, so don't screw into it. But you can remove it by taking out a couple of screws and mount anything you want on it with some rivits or bolts.

Check for rust under the rear window, these cars love to rust their.

WARNING FOR NORTHERN CARS!!!!
If your car sees salt roads inspect the rear steel brake lines above the subframe. They are out of sight and out of mind, but the salt sits up their and rusts them badly. I have had to replace a lot of brake lines on both of my W126's.

W126 shocks:
You cannot use the "bounce test" on these cars. Unless the shocks are completly blown out they will not bounce. But the ride will be gone long before that. Check the shocks for leaks, if they are leaking replace. Also 100k-150k is about all they are good for. Bilsteins are the best shocks to use.

bhatt · #9 03-06-2006, 03:14 PM

In under 8 hours, we have a HUGE encyclopedia of W126 tips & tricks. Let's keep adding to this list.. If you come across something in your W126 that could help a new owner, potential new owner, or even something new you want to share with people who have owned these for years, DEFINATELY add it to this thread!

Thanks especially to Brian and Hatterasguy so far for their excellent contributions!

Neal

PS.. Now, will someone start a W140 thread like this one? I know about Bose amps, wiring harnesses, and evaporators but I'm sure there is a TON of stuff I don't know about those cars..

Randy · #10 03-31-2006, 02:42 PM

Be Certain to check the area in the cowl for leaves and any thing else which can be flammable. There are parts in there which can start a fire!

The fuse terminal for the high climate-control blower can overheat when the blower is run on High a lot; it turns loose, and can get against something in the bottom of the fuse box, and it is hot enough to melt through insulation on wiring in the bottom of the fuse box and give a few amps to some other circuit (in my case, it was the outside temperature indicator which was fried, emitting a great cloud of smoke inside the car, etc.). There was a service bulletin, to replace this fuse with a remote-mounted fuse. My car never got it.

I hope these help someone.

gmercoleza · #11 03-31-2006, 02:47 PM

Can someone do this for the W124? Can these be made into stickys?

vstech · #12 03-31-2006, 08:12 PM

my 82 300SD has a problem with belts needing to be tightened.
the repair can be startling! ok first, the pair of altenator belts are the innermost belts, so of course they are the thinnest and most likely to need tightening... great design! (anyone know of a serpentine kit for the old turbo diesels?)
before you losen all the bolts to adjust the belt tension, OIL THE ADJUSTER BOLT WITH PB BLASTER!!! the special bolt that tightens the belts is very thin, and any rust...

45.00 bolt replacement! also, make sure you losen ALL THREE bolts that mount the altenator. they are 17MM they all losen from the back of the alt, and if you forget one...

45.00 bolt replacement! (anyone know where to get reproduction bolts for less?) two are through the alt. the third is on top of the bracket that holds the alt. only need to losen it a bit.
ok, now if you need to replace the belts... and who dosent? you will need to loosen and remove the AC belt and the PS belt. the ac has two bolts through it from the back of the compressor, they are 19MM I find the best way to get at them is with a 1/2" "breaker bar and a 6point shallow socket. a rachet will not fit between all the lines up there, and the top bolt can't be reached with a open end. then back off the adjuster nut... don't lose it. my car had someone break off the adjuster bolt on the PS pump, DON"T OVERTIGHTEN THE ADJUSTER BOLTS!!! the PS adjuster bolt is threaded into the soft aluminum body, it breaks easily.
oh, and I don't know how well this will hold up over time, but the injector return lines are hard to find. my local lawnmower repair shop stocks a clear fuel line that is the same id. real low cost solution to a leaking return line!

John

Matt L · #13 03-31-2006, 09:50 PM

Quote:

Originally Posted by vstech

oh, and I don't know how well this will hold up over time, but the injector return lines are hard to find. my local lawnmower repair shop stocks a clear fuel line that is the same id. real low cost solution to a leaking return line!

John

Hard to find? The local MB shop had the line in stock for the '83 we have here. Cost about $11 for enough to replace them all.

Monomer · #14 03-31-2006, 10:12 PM

Quote:

Originally Posted by vstech

my 82 300SD has a problem with belts needing to be tightened.
the repair can be startling! ok first, the pair of altenator belts are the innermost belts, so of course they are the thinnest and most likely to need tightening... great design! (anyone know of a serpentine kit for the old turbo diesels?)
before you losen all the bolts to adjust the belt tension, OIL THE ADJUSTER BOLT WITH PB BLASTER!!! the special bolt that tightens the belts is very thin, and any rust...

45.00 bolt replacement! also, make sure you losen ALL THREE bolts that mount the altenator. they are 17MM they all losen from the back of the alt, and if you forget one...

45.00 bolt replacement! (anyone know where to get reproduction bolts for less?) two are through the alt. the third is on top of the bracket that holds the alt. only need to losen it a bit.
ok, now if you need to replace the belts... and who dosent? you will need to loosen and remove the AC belt and the PS belt. the ac has two bolts through it from the back of the compressor, they are 19MM I find the best way to get at them is with a 1/2" "breaker bar and a 6point shallow socket. a rachet will not fit between all the lines up there, and the top bolt can't be reached with a open end. then back off the adjuster nut... don't lose it. my car had someone break off the adjuster bolt on the PS pump, DON"T OVERTIGHTEN THE ADJUSTER BOLTS!!! the PS adjuster bolt is threaded into the soft aluminum body, it breaks easily.
oh, and I don't know how well this will hold up over time, but the injector return lines are hard to find. my local lawnmower repair shop stocks a clear fuel line that is the same id. real low cost solution to a leaking return line!

John

I'm sure you can find the proper replacement bolt at a industerial fastoner store.

I've found a steady supply of 1 1/4-8 NC shcs, I'm sure you can find one yourself.

joes87sdl · #15 04-01-2006, 01:31 PM

The belt shock,makes a raddle sound at idle.Need to remove the fan to get the lower bolt out.Also the engine mounts need changed if car shakes to much at idle.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode