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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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suddenly starter motor wont engageViews : 2290 Replies : 39Users Viewing This Thread : |
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Feb 13th, 2019, 18:54 | #11 | |
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There could always be a first time though. |
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Feb 13th, 2019, 19:08 | #12 | |
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It's a common enough occurrence here, usually a gummy residue on the plunger causes the sticking and it works both ways as well - it can hold the starter pinion in once the key has been released, as well as preventing the plunger sliding towards the contacts and mechanically pre-engaging the drive pinion before completing the circuit to the starter motor and switching to the hold-in coil from the pull-in coil. Usually cleaning the plunger with brake or carb cleaner/thinners restores normal operation.
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Feb 13th, 2019, 19:11 | #13 | |
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It depends on climate, starter location and starter design. Certainly not impossible. The solenoid is grounded through the body of the starter and the brushes play no part in this. This can easily be shown by connecting a 12v feed to the solenoid ignition switch and grounding the solenoid body. You could have badly worn brushes or no brushes at all in the starter yet still engage the solenoid.
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Feb 13th, 2019, 19:34 | #14 | |
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As you can see, the current through the pull-in coil in the solenoid runs through the brushes and armature - only when the solenoid is completely in does it run through the hold-in coil direct to earth. That image was picked at random from an image search for "pre-engaged starter solenoid circuit" so wasn't picked for it's "unique" arrangement - this is arguably the most common arrangement on the pre-engaged starter.
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Feb 13th, 2019, 19:51 | #15 | |
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The solenoid can absolutely 100% be operated without the main starter being energised in fact the main starter can only be energised if the solenoid has been activated in the first place to bridge the permanent live feed to the brush pack. Without independent solenoid operation, the brushes receive no voltage.
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Feb 13th, 2019, 19:58 | #16 | |
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I've stripped and reconditioned thousands of starters and alternators in my time, some by the side of the road to get a breakdown sorted (obviously they weren't fully reconditioned) and i know this is how almost all of them are wired - do an internet search using the same terms as i described above - you will see this is the case.
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Feb 13th, 2019, 21:03 | #17 |
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The solenoid is grounded via the starter body to the engine block which in turn is connected to the battery negative terminal directly via an engine strap in the bay or like on mine via an engine strap to the chassis then another strap back to the battery in the boot.
I can't make it any clearer so I'm happy to agree to disagree.
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Feb 13th, 2019, 21:11 | #18 | |
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Yes, there is an earth return path from the solenoid coils through the starter body - but which solenoid coils? The pull-in coil, hold-in coil or both?
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Feb 13th, 2019, 21:34 | #19 | |
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Here is a solenoid being operated disconnected from any starter. No brushes present or needed https://youtu.be/bTj_lVMmgX4
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Feb 13th, 2019, 21:48 | #20 | |
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The pull in winding is as shown in Dave's diagram and earths via the main motor circuit ie through the brushes. A hold in winding (lower current) operates in parallel and is earthed directly. When the solenoid contacts close the pull in winding has an equal voltage at each end and so stops operating. The hold in winding continues until the circuit is de-energised. |
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