Starter rebuild issue... - PeachParts Mercedes-Benz Forum

Shern · #1 10-04-2019, 11:44 PM

Been having intermittent issues with my starter and decided to attempt a rebuild.
Found a solenoid on eBay for pretty cheap but later realized that the part number did not match exactly what was on my starter -despite the part coming up for my 240D on multiple sites. Figured maybe the part number was superseded at some point or another...

Solenoids

The new solenoid had a slightly longer spring on the piston and a different anchor mechanism though both had a similar level of resistance.

I installed it and attempted a bench test.

When I apply 12v, the gear (bendix?) spins, but it does not move up and down. Isn't this the point of the solenoid? Otherwise, the brushes were good, the commutator (?) I scrubbed up with a nylon scouring pad to bring the brass color back, and everything else seemed to move freely.

I'm boggled. Ordered a rebuilt bosch unit from Napa just in case but jeez that feels like a waste... this seems like such a simple device (all magnetic field, and few moving parts).

What am I missing here?

Sugar Bear · #2 10-05-2019, 12:44 AM

Yes, that is the point of the solenoid.

Are you applying the voltage to the starter motor directly or through the solenoid? It has to go through the solenoid (large + bat lug and small lug) to kick the bendix drive out.

The other situation I've encountered is that sometimes the 12V test power supply isn't strong enough to kick the bendix drive out, but enough to spin the motor. Be certain the power source is known to be good such as a functioning battery in another vehicle.

I don't know if this can be done on a Bosch solenoid but on Delco Remy's one could open the solenoid and flip the contact disc over to have a new clean connection, in case you needed to use the old solenoid.

Good luck!!!

ah-kay · #3 10-05-2019, 02:17 AM

There are 2 coils in the solenoid, one pull, one hold. It may help. It is quite simple once you understand.

Check out #13 in this link

Expert with starter or solenoid.

97 SL320 · #4 10-05-2019, 06:27 AM

This setup should have a hook ( starter side ) and eye ( solenoid side ) attachment that moves the starter gear. Make sure this was hooked together during install.

When testing, are you applying 12 v + to the solenoids battery terminal then jumpering 12 v + to the small trigger terminal? If you are applying 12 v + to the wire leading into the motor, the solenoid never gets a signal to pull in.

Shern · #5 10-05-2019, 09:56 AM

To test, I'm clamping negative from battery to body of the starter, and positive from battery to terminal of the starter. I have not been using the small ignition wire on the starter however... which I've read should also be given 12v.

In the sequence above, as soon as I touch the negative cable to the battery it whirs up (and sparks on the battery of course).

I know I'm doing something wrong here.

Mike D · #6 10-05-2019, 10:03 AM

You are activating the starter winding and not the solenoid. As Sugar Bear mentioned you need to activate the solenoid at the same time as the motor winding. Secure the assembly because it WILL "kick" quite a bit.

Starter rebuild issue...-mercedes-benz-starter-replacement-change-011.jpg

Shern · #7 10-05-2019, 10:07 AM

Ah, thank you. One further question: The is the tip of the solenoid meant to clip onto the armature an any way? It appears to just slide in there (with a lot of pressure to overcome the spring) and then get screwed on.

Additional question... In all the bench test videos I've seen, the battery is fully connected to the starter, while the starter lays dormant. It is then actuated by jumping the ignition wire. On my starter, as soon as I connect the negative terminal to the battery, I get a huge spark at the battery and the starter whirs up. This cannot be right...

Diseasel300 · #8 10-05-2019, 10:42 AM

See MikeD's post above. There are 2 big posts on the solenoid. The lower one is what the motor terminal connects to. The battery + terminal connects to the other. In this configuration, nothing should happen. To activate the starter, use a heavy piece of wire and jumper the battery + terminal to the small terminal. The solenoid should pull in, the motor should run, and the Bendix assembly should be flung out to engage the ring gear.

The armature of the solenoid free-floats. It shouldn't be greased either, wiped with oil is fine, but don't grease it. It's usually only held in place by the rubber boot on some designs, or only by tension against the Bendix fork on others.

Shern · #9 10-05-2019, 11:08 AM

Quote:

Originally Posted by Diseasel300

See MikeD's post above. There are 2 big posts on the solenoid. The lower one is what the motor terminal connects to. The battery + terminal connects to the other. In this configuration, nothing should happen. To activate the starter, use a heavy piece of wire and jumper the battery + terminal to the small terminal. The solenoid should pull in, the motor should run, and the Bendix assembly should be flung out to engage the ring gear.

The armature of the solenoid free-floats. It shouldn't be greased either, wiped with oil is fine, but don't grease it. It's usually only held in place by the rubber boot on some designs, or only by tension against the Bendix fork on others.

This is the way I've been wiring it. Although as soon as I connect the negative to the battery I'm getting a spark and the starter whirs up.

Diseasel300 · #10 10-05-2019, 11:45 AM

You must have the armature in a bind or forced in its engaged position. When the solenoid pulls in, it closes a set of contacts to engage the starter motor. If you have the armature forced back in its engaged position, it's just like being pulled in.

ah-kay · #11 10-05-2019, 11:54 AM

Put the starter on the bench and do the following. Report what you observe.

1) Test Pull in coil - connect the trigger terminal to +12, the starter STUD ( where the thick cable goes ) to ground. The gear should pull in OK. Basically the starter motor coil ( very low resistance ) is used to ground the coil when unit is installed in the car.

2) Test Hold in coil - connect the trigger terminal to +12, starter casing to ground.

3) If both work as expected then connect 12v to small terminal AND stud. Starter should pull and spin.

Good luck.

Shern · #12 10-05-2019, 12:57 PM

Ah-kay --I'll follow this and report back.

Some terminology I'm unclear on however.
When you're saying the gear "pulls in" -isn't that the default state?
The gear is pulled in and away from the ring gear. When it gets power, it's supposed to extend out and catch the ring gear thus driving it to ignition.

My gear is not extending. It appears to be stuck in its retracted state.
It's spinning, yes, but it's not extending.

Diseasel -- I'm not sure what you mean. If I have this right, the armature is the arm that connects the solenoid to the shaft of the starter which is what articulates the gear when the solenoid extends/retracts. At the moment it's fully retracted. Why would that be causing a spark?

ah-kay · #13 10-05-2019, 01:07 PM

Quote:

Originally Posted by Shern

Ah-kay --I'll follow this and report back.

Some terminology I'm unclear on however.
When you're saying the gear "pulls in" -isn't that the default state?
The gear is pulled in and away from the ring gear. When it gets power, it's supposed to extend out and catch the ring gear thus driving it to ignition.

My gear is not extending. It appears to be stuck in its retracted state.
It's spinning, yes, but it's not extending.

My bad. The solenoid pulls in. When the solenoid pulls in, the lever attached to it 'extends' the bendix/ring gear. Check step (1). A lot of the times, the pull action is not working is because the starter motor is faulty, not the pull solenoid. The carbon brushes are not touching the armature well to make the pull circuit. I think your problem is the starter motor carbon brushes, solenoid rarely go wrong.

97 SL320 · #14 10-05-2019, 01:24 PM

It sounds like the solenoid plunger ( piston ) isn't engaged into the fork that moved the starter gear. When the solenoid is improperly installed, the plunger becomes compressed bridging the internal contact feeding power to the actual motor at all times.

See attached pic

Original pic
https://www.autozone.com/repairguides/BMW-318-325-M3-525-535-M5-1989-1993-Repair-Information/Engine-Electrical/Starter/_/P-0900c1528004a133

Shern · #15 10-05-2019, 01:28 PM

I'm an idiot... I figured it out.

I had not installed the solenoid properly. I was following Stretch's starter teardown (which is great) but neglects to mention how the solenoid plunger sort of clips onto the armature.
I had mine jammed in there and then bolted it shut. I'd been wondering how this thing was supposed to articulate... You basically slide the thing in until it clips.

Unbelievable...