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