'79-300D - Sticking Solenoid - How easy to replace?

[DieselPop]

Thanks to a previous post and help in this forum I was able to figure out that my starter-solenoid has started to stick. It has trouble engaging and starting, and once it does, it has trouble disengaging and lets the starter motor spin like crazy.

So... provided I can source just the solenoid... how difficult is this to replace for a home mechanic, jacking the car up in the driveway?

Anybody out there done this project?

[t walgamuth]

That sounds like a problem with the bendix not the solenoid.....but if you are going to all that trouble may as well change them both. While its out I would have an expert look at the main motor brushes as well, or look at them myself.

The good news is that benz diesel starters are extremely rugged and seldom need to be removed.

The bad news is they are a triple b!tch to get off with the extra brace, etc.

[kerry]

I've replaced starters in about an hour so it's not that hard in my opinion, if you have the right tools. Jack up passenger side of the car and use about 3' of extensions with a universal socket and a big breaker bar to go up alongside the transmission to break the top bolt free. Starter drops out thru the steering mechanism. My recollection is that wheels have to be turned to the stop in one direction or the other to get it out.

[t walgamuth]

Originally Posted by kerry

I've replaced starters in about an hour so it's not that hard in my opinion, if you have the right tools. Jack up passenger side of the car and use about 3' of extensions with a universal socket and a big breaker bar to go up alongside the transmission to break the top bolt free. Starter drops out thru the steering mechanism. My recollection is that wheels have to be turned to the stop in one direction or the other to get it out.

IIRC, it is the extra brace on the nose that is tough.

[kerry]

I don't remember that brace on the one I replaced. It was a 77. Perhaps it did not have it.

[DieselPop]

In all of these posts you guys are talking about removing the whole starter...? Is that what I have to do to replace the solenoid?

When I was trying to stop my starter from reving like crazy after the engine was started and then also stopped, I rapped hard on the solenoid with the end of my breaker bar, which is visible from the top of the engine...

Why can't I just replace the solenoid from the top? It seems visible enough from the top and under the exhuast manifolds and such?

Also.. what is a bendix?

I've thought that perhaps it is my key switch giving the problem, but then why was I able to solve the growling starter thing by rapping on the solenoid/starter?...

All the input I am grateful for - thanks.

[t walgamuth]

I don't believe it is possible to remove the solinoid from the starte with it on the car.

The bendix is the mechanism which engages and disengages the starter gear from the flywheel. When working correctly it will fling the gear to the rear of the car on the sliding shaft it rides on on the starter. When the motor starts the faster turning flywheel then flings it back toward the front of the car disengaging the starter from the flywheel.

Mercedes may not call it a bendix since that is an american company, but they all work very similarly I believe.

[DieselPop]

So.. provided I can take out the whole starter unit including the bendix and solenoid, would it be possible at all to service these items to get them back in running order, or are they all sealed up and impossible to get into?

It seems like something is just sticking, so if I could oil/grease it, it might all work as designed again for another 20 to 30 years?

[tarnbarn]

Removing the starters from a 123 body is easy with an OM616, but a bit harder with the OM617; 1 more cylinder= much less room against the bulkhead (firewall for yanks)
I've gotta say that I find the starters/solenoids to be a weakness. Maybe it's just the age our vehicles are at...

[oldiesel]

When you get the starter off you may find that the bendix drive and the shaft it slides on are just gummed up,clean it well and use no grease or lubricant on it as those things collect dirt and crap and can cause the problem you are having. There is a plunger inside the solenoid that is pulled in by magnetism that also can get gummed up and sticky cleaning that is a bit more work and the same caution applies there ,no lube just clean.
With luck you can cure your problem with no money spent! Don

[DieselPop]

Before I go pulling the starter out, which sounds like a bit of a challenge, how can I rule out the ignition switch as the culprit in this thing?

Is it possible that if the starter/solenoid is not getting enough current, it could exhibit these sticking symptoms?

[dude99]

you could start it by bridging the terminals under the hood for week and if it still sticks while doing this you know its not the ignition switch. It does sound like a bad solenoid though. Definitely have the starter replaced\rebuilt while you in there though. Getting it out your first time is a b**ch. took be 2 days the first time. After that I had it down to less the 30 minutes.

[Rich1Merc]

Here is my experience and what I did to overcome the worst nightmares of starter removal. DO NOT USE IMPACT WRENCHES FOR THIS JOB! If you need torque, use long breaker bar , if you need more torque, use pipe on end of long breaker bar. If you have stuck bolts like I did, doing the job on the ground is not conducive to applying a lot of torque on your breaker bars. Oh...it helps if it is your wife's car...she assisted with this job and paid for her own parts!! What a country!
On a lift, you can really apply your body strength to the tools.
Also, don't even think about removing the starter until you have eliminated :
LOOSE CABLES AT STARTER and each and every wire ring terminal in the circuit. Corroded ring terminals, defective neutral safety starter switch.
Make a jumper to jump 12+ volts to the correct starter solenoid energizing wire. ON my car it is the white wire. This is the wire that goes to the back of the solenoid and is a small ring terminal with a small phillips head screw. If you jump 12+ volts to this terminal directly (or to where it terminates on the fender) and still no click or reaction from the solenoid or the starter, then and only then replace the starter. The extra effort is well worth not having to to this PITA job.


First of all, this is not a hard job. It only gets hard if you have seized starter attachment screws..especially the top one which is difficult but not impossible to get to. If you strip one or both of these screws the job gets even more difficult, but not impossible. 5 cylinder Turbos leave you very little room. My 240D 4-Speed has lots of room under there.

Process: A few days before I de-greased that area of engine and transmission housing. Less grease and dripping crap in you face and on your arms..takes 10 minutes. To remove starter: Removed battery negative cable. disconnected starter motor harness from terminal block on passenger wheel housing. Turned steering wheel left to stop. Jacked up car on right side, blocked under wheel,under chassis in two places, blocked 3 wheels front and rear.
Removed passenger side end of the steering stabilizer. Loosened the lower 10mm 8.8 cap screw with aid of PB blaster. Normal amount of rust and seizing.

Top cap screw rusted in place so I needed to put BP blaster or liquid wrench around the bolt to get it in where it is needed. Takes 2 minutes to drill three small holes along the bolt, which only can be done from above for this top starter bolt.

Takes a few minutes to do the following: Removed battery, battery tray, exhaust heat shield, air cleaner housing. Going in from above with 12" long jobbers drill. Drilled 1/8" hole x2 in the bell housing until it hit the stuck bolt. Did one more hole in the ear of the starter motor which is where the threaded end of the stuck bolt was. Added PB blaster, added a little heat.
Tried again: Not even a creak or budge! The universal joint makes things worse.
Since the bolt just declared nuclear war on me there was only one solution.
Go in straight by drilling a 1 1/2" access hole in the passenger footwell. (see photo) Remember: the object is to remove the seized bolt and not to preserve the stupid design of the car! This takes less than 5 minutes and will save you many gray hairs and stripped out screws. BE CAREFUL drilling. I used a 1/8" drill to approximate the location of the desired hole. There is a plastic shield between the body and the transmission and its filler tube. Once you find the right spot which leads directly into the socket of the screw, then use the hole saw attachment on your drill motor. Go carefully since you don't want to drill into the filler tube. The plastic shield will not cut through on the first pass. You have to put the drill bit back through the hole and just lightly touch the plastic shield to make the hole in it. Even if you are slightly off center, this is 100% better than the standard way to attack the screw.

With a straight shot at the top cap screw no luck. More torque, then VOILA@! stripped 10mm screw! (See photo) Time for BOo Hoo, coffee, regroup.

Made a manly easy out (see photo) from my fathers aviation easy out hammered into a 12 pt 1/2" deep socket 1/2"drive. This managed to do the job after trying 10 minutes.

With stuck bolts you just have to keep on trying. Time is not important anymore since you still have to remove the starter screws. The starters weigh approx 27 lbs, so be careful not to let it down on your face!

I used a $2.59 NAPA HEX HEAD 8.8 screw for the top position. Everything went back together easily. USE LOTS OF ANTISIEZE compound. I used antioxidizer on the ring terminals. Plug the hole with either a chassis plug from NAPA or auto finisher supply store, use duct tape, or use a metal plate + sealer and pop rivets.Any of these is easy to remove next time. Put the carpet back and your are done.
Per the recommendation of others on this forum, I bought a BOSCH reman. The $72 core return shipping charge from NY to Arizona was approx $33 on FED EX and is insured for $100. Better than USPS.
When reinstalling, it helps to have someone guide the harness up through the engine compartment while your are getting a hernia pushing the starter up into place. Other than that it is a piece of cake!

[JWJ]

You'd have thought MB would have provided holes in the footwell/firewall to the starter bolts - considering the pain with the 300D.

What did you plug the created hole with?

[Rich1Merc]

I was not able to find the exact plug at NAPA or AutoZone. I'll just make a patch for now with duct tape, and if I can find a thin sheet of steel, I'll make a steel patch with body sealer to make it watertight. Two steel poprivets ought to suffice.
There will not be any water splash there since it is tucked way up between the transmission shield and pretty much behind the engine.

I'll post a photo of the patch when I am satisfied with the job.