Confirm my starter solenoid diagnosis - PeachParts Mercedes-Benz Forum

AUDIBLE · #1 09-19-2012, 01:37 AM

After a couple hours in 100 degree heat city driving, the mighty 300SDL refused to re-start after a short stop. The starter motor whirred like crazy, but no solenoid click and no gear engaged with flywheel, so she no start.

Tow home.

Charged the battery overnight for good measure. Next morning, isolated the solenoid and applied 12+v, and she clicks. Pulled starter, put 12+v to the solenoid and she shoved the gear forward. Put the starter back in, she whirred like crazy, but no solenoid click and no gear engaged with flywheel, so she no start.

To try to eliminate low voltage as a cause, I took a heavy jumper cable and applied battery voltage directly to the pin on the solenoid, same result, no click, lots of starter motor.

Apparently, no matter how it behaves out of the car, the solenoid seems bad, and must be replaced?

But there doesn't seem to be much in there except a magnet, coil and spring. If it clicks and shoves the gear forward when out of the car, why not when it's installed?

Love to hear any comments.

Many thanks!

Stretch · #2 09-19-2012, 02:46 AM

It does seem crazy that something as simple as a coil should not work. They are indeed very simple things. My guess is that there's either a loose connection at the posts on the solenoid; that some how or other the coil has gotten burnt out; the electrical insulation is duff; or that it is just gunked up with junk and physically can't move any more. Have you been having any nasty turbo oil leaks on that side of the engine?

Here's a thread that might help you remove the starter motor (your turbo is in the way)

PeachPartsWiki: Starter Motor Replacement

Here's a thread that shows some pictures of the starter motor and solenoid in bits

PeachPartsWiki: Starter Motor Rebuild

ah-kay · #3 09-19-2012, 03:04 AM

It is a 300SDL. The starter is NOT on the side of the turbo.

The solenoid MUST click in order for the starter to whir like crazy. If the starter motor spins but the pinion gear is not engaged then it is possible that the contacts are bridged between the solenoid terminals inside the solenoid. That is contact is made without the solenoid coil pulling it.

Good luck.

Stretch · #4 09-19-2012, 03:32 AM

^^^^

Oh %^&^& I read that all wrong - sorry about that. The links I posted probably won't help.

vstech · #5 09-19-2012, 07:50 AM

Yup, if the motor whirrs when you turn the key, the solenoid is doing it's job. the problem lies elsewhere. you could have stripped teeth on the ring gear, or the starter bendix...

NJ300sdl · #6 09-19-2012, 08:21 AM

Might be bad ground. Use jumper cable to test.

Tubularfab · #7 09-19-2012, 11:32 AM

I had a chevy starter in a jetboat that I was sure was having a problem kicking the bendix out. It would just spin up fast and not engage. Turned out that the one way clutch in the bendix was shot - the gear was engaging but the shaft was free spinning inside the pinion gear. The clue was that if you held the key on long enough it would suddenly engage and turn the engine over a few times than spin up again.

So - are you sure the pinion is not engaging?

Diesel911 · #8 09-19-2012, 12:49 PM

Post #7 is likely.
Burred or worn Teeth on the Ring Gear can do the Same.

AUDIBLE · #9 09-19-2012, 01:15 PM

Thanks for the many thoughtful replies. The teeth on starter gear are smooth and intact, show no damage. Hadn't considered that the bendix gear could be coming out but not holding. Will update as soon as I get the bugger out again and taken apart. Isn't the starter rebuild tutorial just excellent? Great folks here, tell ya what.

thanks
Bruce
s

vstech · #10 09-19-2012, 01:44 PM

Quote:

Originally Posted by Diesel911

Post #7 is likely.
Burred or worn Teeth on the Ring Gear can do the Same.

Hey! I said that in post #5!!!
#7 described the issue in more detail though.

AUDIBLE · #11 10-13-2012, 08:35 PM

I opened up my dead starter with the great OM617 starter rebuild instructions in hand, to discover that the two are not very similar. The one from my 300SDL had a complex and crappy plastic reduction gear setup, which I couldn't find a kit for. The local alternator/starter guy said that parts for it were more than a new one, so he sold me a new one for $100. cash.

Since I took pictures thinking I'd rebuild, I thought it would be interesting for people to see them.

When I got the brushes end out of the housing, the brushes were a crumbled mess, floating around the armature. It all comes apart in a similar way to the OM617 starter, until you get to the splines on the end of the armature.

Here's the gear on the end of the armature, just pulled out of the housing that it inserted into.

When I took the metal plate off, it looked like this inside. You can see in the center where the splines went. That's a shattered plastic ring with gear teeth between the reduction gear setup and the starter housing.

Here's the same part with the shattered ring cleaned out.

Here's what the ring's pieces looked like.

Here's the part cleaned up a bit. The thin plastic covering shown here clamps on top of a metal housing holding the three reduction gears. Behind this presumably is the bendix gear/spring that engages the flywheel.

Not as useful as a rebuild tutorial, but kind of interesting.

Stretch · #12 10-14-2012, 03:28 AM

Wow very different - first time I've seen pictures like that. Thanks for posting.

layback40 · #13 10-14-2012, 06:20 AM

Quote:

Originally Posted by Army

Wow very different - first time I've seen pictures like that. Thanks for posting.

Army,
Thats a planetary inline reduction. Very common in cars from about 85 on. Most cars on your side of the pond have them.

97 SL320 · #14 10-14-2012, 08:25 AM

The starter in my 97 E320 is similar and has a metal ring gear.

This Bosch starter is used on lots of USA cars, ( 80's Chrysler products with a 3.0 Mitsu V6 until they went to the Nippondenso starter come to mind )