The Starter System                                                                                                                                                                     7/07 - R. Kwas

General, and Terminology:  The electric starting assembly fitted to vintage Volvos, commonly referred to a "Starter", is really a combination of two important parts, consisting of a SOLenoid and a one Horsepower electric Starting Motor (SM).  The Bosch Starter design is a quality, series wound, (field coil is in series with armature) DC motor.  The SM spur gear has 8 teeth, and the flywheel ring-gear has 80, so the torque advantage the SM has over the engine (10:1) is significant.  Later permanent magnet/planetary-geared types are fit/form/function interchangeable...the SMs on these are noticeably smaller in diameter, due to the absence of bulky field coils...they also sound different, due to the higher RPMs of the actual motor and planetary gears, but these are also highly reliable as their forbearers from what I've seen.  Avoid mechanical shocks, like hammer strikes, to these, as this can demagnetize the ultra-powerful field magnets...then it’s no longer a starter but a good doorstop or buoy anchor...the factory is probably the only one equipped to remagnetize the assembly at that point.  

Starter Assembly, showing the earlier style SOLenoid. 
The newer SOL has a different form but is the same functionally.  Source:  GPC's Site

Normal Function, Electrical and Mechanical:   One important function of the SOL is as an electrical contactor to switch the significant starting currents.  It does this with two dedicated High Current Contacts (HCC).   As power is applied to the SOL coil, the ferrous armature is moved due to the magnetic field created.  This causes the attached bridging contact to complete a connection across terminal 30 (terminal to which battery cable is connected), and an unnumbered output terminal connected directly to the SM by way of a short hop-over cable (the hop-over cable (5) Is often without insulation, but a rubber grommet keeps it from making contact with the SM case as it enters).  Later versions also had an additional small disconnect terminal, by which the fuel injection system could also be imformed when the engine was being cranked.  Individuals who have, or intend to convert their IGN system to a solid state module (Pertronics or Allison/Crane) can also connect one input of the diode "ORing" cable to this point in order to get power while cranking.  This is required because terminal 54 of IGN Switch (the other input to the ORing cable), which would normally be supplying solid state IGN module, is disconnected from power during cranking (LINK to IGNITION and Armored Cable article), in order to shed other loads, which allows the battery to have the least additional load and give the best chance of starting. *By “OR-tying” these two power sources, it is assured that the IGNition electronics are continuously supplied.


Detailed Starter System diagram, showing control and high current paths,
assembly internals, and the way the SwEm Start Switch Upgrade comes into play. 

**  What's the big deal about the Braid?  The there is nothing sacred about a braid other than its fine wire strands are better able to cope with the movement and vibration without being damaged. 


In-Situ:  A well charged battery and clean tight connections along the (high) current path are a prerequisite (ALWAYS, when troubleshooting electrical equipment, but more-so when troubleshooting high-current electrical equipment) ...and this includes the chassis-to-engine strap which also carries the substantial starting current as can be seen in the Diagram above.  Poor/loose connections cause voltage drops under the substantial load current...then things don't work so good...and the electrical current seeks the easiest alternate path...which might be through the throttle linkage or chock cables...then you can get some really weird secondary effects... but all bad! 

Bypass the IGN switch and apply power directly to energize SOL, and in turn SM.  A "remote starter switch" connected between the big bolt, terminal 30, and the smaller quick disconnect control (terminal 50) works well for this...a much less elegant (but equally effective in a pinch) technique uses any conductive tool between these two adjacent terminals (like a big screwdriver...but I wouldn't use my about the right tool for the job)...this makes big sparks and one needs to be ready for the engine movement when starter engages...  A remote start switch is preferable because it allows for the troubleshooting steps which follow, without big sparks in the engine compartment (big sparks scare onlookers, pets, and can ignite stuff!).  A remote starter switch with its spring loaded electrical clips isn't bothered by the rockin' anda rollin' of the engine either. 

Additional Safety Reminder:  Gearbox should be in neutral, handbrake applied, and IGN OFF (prevents starting).  Lunging cars scare wives and neighbors ("...maybe you should let that nice mechanic at Joe's Garage fix your car, dear")!

Since the SOL is directly connected to SM, this should normally result in a clack, and the SM immediately turning over the engine, as both work correctly...but if there is no clack, SOL is not being activated due to an external electrical problem (not getting power from IGN Switch), or an actual SOL failure exists (rare but not impossible!). 

A clack not accompanied by the SM turning the engine over on the other hand suggests a HCC problem OR a problem with the SM itself.  A simple way to determine which one to suspect is to measure if voltage is being routed through the high-current-contacts and being applied to the SM itself.  A voltmeter on the short uninsulated cable stub which hops from the SOL (output terminal), to the SM while energizing SOL will tell a lot...if battery voltage is measured, but no action from SM results, the SOL is working as expected, but the SM is suspect.  If on the other hand, SOL clacks when activated but no voltage is detected, the HCC is suspect.

X-Ray view of the Starter Assembly from the green factory manual, showing high starting
and low IGNition switch current paths, also the mechanical function of the pivot linkage...
SOL pulls, pinion gear is driven in direction away from SM to engage ringgear.


Removed from Vehicle:  Operation of a starter can be checked off a vehicle by establishing similar operating connection as when in the vehicle.  A set of battery jumper cables may be used, but smaller gauge test wires 16-14ga. will do fine, since the SM will not be operating under load, and will therefore not be drawing typical high operating currents which necessitate really heavy wire found in the vehicle.  A negative connection must also be established from starter housing to battery negative.  Be aware:  The high starting torque is capable of twisting it out of ones hands if you are not ready for held in a vice or simply on the ground with a foot securing it is a good idea!  When activating, the solenoid should clack, apply power to SM, and spur gear should spin and also advance, along its shaft, and away from the motor body (to engage ring gear when installed), when released, the spur gear should return to its unenergized position.  Any excessive slop should be investigated and repaired as necessary. 

Note:  Do not apply power for more than a "touch-test" as an unloaded series-wound motor can "run away" and self-destruct! 

The two through-bolts which hold the endplates can be removed in order to gain access to the internals and to check the brushes.  If length of brushes is such that brush-springs (28)are down to the holders, brushes should be replaced.  PN for springs is:  906983

Normal Function, Mechanical:  In addition to the electrical non-magic happening when the SOL is engaged, it must also perform a very important other mechanical function, that is, to connect the SM to the flywheel.  It does this by a simple pivot linkage.  As the SOL armature is pulled to connect the HCC, it also moves one end of a lever.  The other end of this lever simultaneously engages the SM driven gear with the flywheel ringgear.  After the engine has started and the flywheel's ringgear speed exceeds the SM spur gear, an over-run mechanism, which only allows the SM spur gear to engage the ring gear when flywheel speed is slower than SM speed, disengages the SM's spur gear from the flywheel ring gear.  

Mechanical Problems:

High Mileage Issues:  With the high margin build into all the Starter components, the assemblies are quite reliable, but, eventually, even a brick wears out.  If a starter has more that 200,000mi. on it, and along with it an unknown number of prolonged cranking sessions which were necessary to bring the engine to life in frigid ski area parking lot for instance, a removal and inspection might be a good idea! 

Typical symptoms of wearout problems:

Brushes wear, so starters then have been known to develop "dead spots".  (This is where MG drivers would apply several calibrated blows from their (required on-board equipment) brass hammers...often with success...Lucas equipment often works like that...even when new!...your result with Bosch equipment is likely to be quite different and more rewarding...see above!).  

HCCs carbon up and become intermittent (see above) a pretty rare case, I had a contact actually become detached from its mount, and bridge between battery terminals and chassis...YEAOW!...this made for an instant engine shutdown due to voltage collapse, smokeshow from under the hood as oil and dirt burned off the ground strap at the chassis, also the temp gauge heading instantly for the sky, as electrical current coursed along every possible path (including the metallic capillary tube of the temp sensing system, and probably also the throttle linkage for all I know)...and me scrambling, trying to get under the hood to disconnect the battery..."steppin' anda fetchin' like my hair was on fire and my a** was aketchin' " (with apologies to Charlie Daniels). 

Pivot or over-run mechanism wears or loosens causing gear engagement or disengagement problems.  (often characterized by a noticeably different sound while cranking or releasing...your car is talking to you...are you listening?)

Starter Replacement Notes:  Later starters had threaded mounting holes to eliminate the nuts, but these were metric threads...they can be used but require drilling out the threads.


* This connection, or the diode ORing cable are not required if a SwEm Start Switch Upgrade (always a good idea!) is installed.  


Related Links:


Related Story:

Bosch Starter:  I'm not suggesting that they used the same Starter at LeMans, but it's definitely from the same house!  In researching Bosch Starters, I remember that Jaguar won LeMans in '88 because the leading Porsche ran out of fuel because of a communication problem with the pits...after running out of fuel, it was driven back to the pits ON THE STARTER AND BATTERY, making it quite possibly:  The first hybrid Porsche!  ...and I think this speaks pretty highly of the Bosch starter!

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This article is Copyright © 2015.  Ronald Kwas.  The terms Volvo, Bosch, Pertronics or Allison/Craneare used for reference only.  I have no affiliation with any of these companies other than to try to keep their products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here.  The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, at the readers discretion.  As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles! 

You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source.  If you don’t, you’re just a lazy, scum sucking plagiarist, and the Washington Post wants you!  As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor and probably wise-a** comment. 


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