123 300d starter R&R question - PeachParts Mercedes-Benz Forum

chev · #1 05-19-2006, 03:51 PM

My '78 300D (146K) has acquired a starting problem: the selenoid click. I measure 12v to the large boot-covered connections on the selenoid, but when an assistant turns the key, I do not measure voltage on other, adjacent, large connector feeding power from the selenoid to the starter motor.

1. Am I correct in the assessment that the selenoid is done for?

b. Are these available? I haven't seen listings anywhere...

III. What's the proceedure for removing the starter on this babe? My MD CD manual says nothing about the proceedure; it looks like it has to come out the bottom, but there sure isn't much room. And how does one get to the hidden mounting bolt(s?) on the top?

iv. If the entire starter must be replaced (selenoid not servicable/no parts) are the rebuilt starters available at Fastlane, Bosch rebuilt or should I care?

I have to repair this quickly. I find myself waiting 10 seconds after turning on the ignition on my gasoline powered car.

Motorhead · #2 05-19-2006, 06:01 PM

Try the starter by going from the battery side of the solenoid to the small terminal on the solenoid. If the starter works every time that way then you need to put in a "Hard start" relay. I had to do that with my '77 240D several years ago. Let me know as I can give directions on how to wire the relay.. It's an easy job. Chris

phidauex · #3 05-19-2006, 06:07 PM

Some places sell just solenoids, but if the solenoid is going, the rest of the starter isn't far behind. Sounds like solenoid is your problem. Power is getting to it, but since it isn't actuating, power isn't making it to the motor. Have you tried whacking it with a metal rod a few times and then trying it? If it works a few times after getting a good whack, then its definately the solenoid.

The starter has four mounting bolts. There is a bracket on the front of the starter (front of the engine), that has two small bolts that go into the block. Undo these first, but leave the bracket attached to the starter.

The other two bolts are 10mm allen bolts through the bell housing, a bottom one, and a top one. The bottom one is pretty easy to get to, but the top one can be a pain! My recommendation: Get a good, new 10mm allen socket. Put it on a 3 inch extension, then add a wobble joint, then a 12 inch extention, then your ratchet (preferably 1/2" size), then feed the whole assembly up from the side of the transmission, and to the bolt. Its a hassle, but it does work. Make sure your socket seats deeply in the bolt before trying to turn it, its easy to strip!

Once you get them out, the starter can be navigated through the suspension components without disassembly. On my turbo wagon, I had to turn the wheel all the way to the right, then it would slip through in front of the steering components. Its heavy, so be careful.

When you reassemble, use antiseize compound on all the bolts, TRUST ME.

I'd recommend a Bosch rebuilt starter. Fastlane has them. They aren't super expensive, and have the best reliability, it seems. I've got a Beck Arnley in my car right now, and its been doing well, but who knows how long it'll last.

peace,
sam

Motorhead · #4 05-19-2006, 11:18 PM

In the 37 years owning and working on german cars, I have never had to buy a rebuilt starter. I have pulled them out and usually had to clean and ck the brushes. I have had to replace two solenoids. I have installed a BUNCH of hard start relays on VW's 6 and 12 volt and several Mercedes. I have a starter out of a '79 300SD with over 300,000 miles on it when the car got wrecked and it is still in good condition. Bosch electricals, especially their starters, are near bullet proof.
If you want to spend $155.00 (fastlane) for a Bosch rebuilt, plus freight, plus core charge, plus freight to return the core,

then go for it.

You can wire up a hard start solenoid for about $25.00

I thought THIS site was about REPAIRING our cars.

The back of the starter comes off easy, a solenoid is about $35.00. Check it out first, then if it is worn out, replace it.
The relay setup takes the CURRENT load off of the ign switch and directs a shorter, higher amp capacity circuit to the starter solenoid. It has worked 99% of the time

MY $.02 worth

Samuel M. Ross · #5 05-20-2006, 01:03 AM

I'm not sure you verified with your meter that the solenoid is receiving 12v from the ignition key switch. I guess your "click" might be interpreted that it is, but such assumptions are how we can go wrong. Verify with your VOM that the solenoid is receiving 12v [the smaller terminal connector]. If not, then there is a problem elsewhere.

If/when you remove the starter, you might find a problem fishing it down through the steering parts even if you do turn the wheel to the right [I rec you plan to remove the wheel from the getgo!]... so you might face removal of the "Idler" section of the steering which is not too difficult... and be sure to inspect it closely for wear although I wouldn't expect any of it to be a candidate for replacement if it only has 146K unless it has been whacked with something kicked up from the road or damaged by bottoming out! If it needs anything, I think it's likely to be only ~$35-40!

Sam

P.S. - I just replaced the starter on my '80 300D

chev · #6 05-21-2006, 03:31 PM

Wow, guys, thanks for all the replies.

Phidauex- first, I really almost fell on the floor reading your sig! Eventually I'm seriously considering using biodiesel. I've a couple friends doing it using wvo. Boy, do they look smug.

Sam- I think you're correct about the idler needing to be removed. I can't imaging getting all that stuff out with the steering gear in the way. I suspect that the different years and models of the 123 have differing clearances between the exhause, frames , and steering gear.

Per Motorhead's suggestion, I jumped the 12v from the "hot" side of the starter to the solenoid's low current wire and obtained the same loud click from the solenoid/Bendix (louder because I was down there with it!) but still no action from the starter motor. I guess a 100% check on this would be to jam a big screwdriver between the two large connectors, and amid a shower of sparks, the starter motor should turn (I haven't tried this, but if I were stuck on the side of the road I would)
This car's been a daily LOCAL driver, so it gets a lot of stop and starts for the mileage. Wouldn't supprise me if the solenoid's the problem. The starter motor has never sounded slow or like the bushings are worn out. At first I thought it was a weak battery. (Two years ago I replaced the alternator with a rebuilt, and more recently a new Interstate battery (which accepts a charge and all cells float a hydrometer to GOOD). A few months ago I suddenly started getting the charge light warning staying on weakly again, until the revs are up.
I'm guessing I've got a bad diode in the alternator, but I've got no idea where to look for parts to rebuild either the starter or the alternator. I used to do the alternator diodes fairly regularly in the 70's on Dodge vans. Now it's harder to find parts. Motorhead, if you know a supplier for Bosch repair parts, I'm nuts enough to try to repair rather than replace this beast.

I recently helped a friend with his Toyota van starter which had the same symptom I now have with the starter. When we got his starter out, I disassembled the selenoid/bendix and found the contactors were burned away 1/4" or more, which was just beyond the "throw" of the selenoid. Back in the really hungry days, we'd have brazed more metal on and slapped it back in for another xthousand miles. We looked for a bendix for it but weren't able to locate one. He went for the Autozone "Lifetime" starter. I wonder if you die under the car, on your back, taking out the old one for the third time, do they still honor the warranty...

Anyway, am I correct in the understanding that in this system, all the solenoid is doing is taking low current 12v through the ign switch, actuating the bendix, which engages the starter gear to the ring gear, and simultanoeusly actuates a high current solenoid which simply applies 12v from the large connector on the assembly to the adjacent large connector (with the heavy pigtail) into the starter motor itself?

After years of owning this car, I finally won an Ebay auction for the factory chassis and electrical shop manual. Two days later this problem came up. I'd guess there's more on this topic in that manual. I couldn't even find a reference on the cd version.

Again, thanks for the suggestions. My wife tells me to "get rid of that old thing, and get a new car." I'd seriously consider it. If only I could find a clean '84 300D with 140K....

t walgamuth · #7 05-21-2006, 03:41 PM

before any of the above (very good) proceedures, i would check carefully all battery connections and grounds. including the engine to chassis strap. and sometimes on an old car an auxiliary ground from the neg on bat to one of the starter mounting bolts will do the trick.

tom w

Motorhead · #8 05-22-2006, 12:56 PM

chev. It sounds like you DO need to pull the starter. I would try the connect between thr two BIG lugs on the solenoid to see if the starter motor itself is good. The motor should just spin as you don't have the solenoid to engage the starter drive. It isn't a big deal to replace the solenoid. BEFORE you buy a replacement solenoid, take the back off of the starter and ck the brushes.
1) to see if they are worn down real low
2)look to see if the brushes could be stuck in the brush holders.

On your alternator, The regulator removes from the back of the alternator. It has two screws to remove it. You do not have to remove the alternator to service the regulator. Chances are real good that the brushes are worn out and that usually causes the alternator light to stay on.

Samuel M. Ross · #9 05-22-2006, 02:59 PM

however I would not be making any high amp connections using a large screwdriver while underneath the car. You are going to be taking the starter out anyway so you should wait to trial test the starter once you have it out, after you have disassembled it, cleaned it, and made the judgement call about the brushes [where they binding, are they large enough to reuse]... and then after you reassemble it, then if you need, you can benchtest it more safely with jumper cables off of your battery.

I recently went through this with the starter on the 80' 300D and found the brushes were almost gone and they were the type you had to use a high wattage iron/gun or brazing torch to remove/install. So I turned my unused new solenoid back in to a complete rebuilt starter... ~$140 through my local independent VW/foreigh parts store where I have been doing business for years!

I sounds like you have all the help you need on your alternator.

Chou,
Sam