Clutch - Cable Actuated, Notes  

Feb  2016  R. Kwas,  up-dates ongoing

 

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Background:  Late 120 and 1800 as well as all 140 models replaced the earlier Hydraulically (push) activated Clutch mechanism with a Cable (pull) mechanism.  While this got rid of the hydraulic system, where leaks or failed seals may have been perceived as a weakness (with a failure, driver would loose Clutch control), it replaced this with a mechanically actuated Cutch system that was not without weaknesses of its own (a failed Clutch Cable would instantly also loose Clutch control).  And early versions of the Clutch Throwout Fork are known to develop a cumulative stress fault which also resulted in a somewhat slower, but nonetheless loss of Clutch control, (failure was not instantaneous and symptoms gave some warning)...the ultimate failure of either system would instantly render the Clutch Pedal into a footrest, so there is really not much difference in the failure modes. 

These are my notes on the Cable Actuated Clutch. 

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Two known Failure Modes
Adjusting Clutch Fork Free travel

The other end of the Cable

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Source:  Genuine Classic Parts GPC site. 

 

Two known Failure Modes of the Cable(18) operated Clutch:

If symptoms of lack of Clutch disengagement occur when Pedal is depressed, it should be determined if Cable OR Throwout Fork is failing: 

Check Clutch Cable:  Check for amount of travel the Clutch Cable imparts to Throwout Fork when Pedal is depressed fully.  It should be greater than about an inch (author invites specific cornfirming info!).  If less than this, cable may be stretching on the way to complete failure.  Once cable starts stretching, strands have already begun to fray (through abrasion at unlubricated points of contact with sheath) and it will soon fail completely and need replacement...they don't get better by themselves(!), that is why a well lubricated cable is important, and so lubing a replacement cables before installation and while it is fully accessible, is much simpler and preferable!  It is no fun job, but I believe it is a worthwhile service to lube even an installed cable with an unknown history to maximize its' service life.  I recommend graphite containing grease or Anti-Seize, thinned and forcefed into the upper sheath-end until it comes out the bottom!...that will serve to minimize friction at cable to sheath contact points (it will obviously not repair any wear which may have already occurred, but should slow down new wear)!    

While checking Throwout Fork action, is also a good time to check correct clutch free-travel adjustment.  Proper checkout and repairs should be made ASAP and not put off! 

Failed Clutch Cable: 

Not a very detailed picture, but note the rust either side of the break.  It is for this reason I like to lube the cable with graphite containing grease.  Rust occurs if moisture precipitates out inside the sheath.  As the cable then moves under use, the rust particles abrade the wire strands and wear is exponential. I'm certain this would be less and possibly totally eliminated with graphite present.  My suggestion:   Lube your Clutch Cable, particularly a new replacement cable, before installation! 


Picture of failure area of a failed Clutch Cable. 
A solid core wire and damaged wire strands due to rust and abrasion (and lack of lubrication!)are apparent. 

 

Clutch Throwout Fork(31):

The mechanically actuated Clutch system has a further weakness which develops after time (Cumulative Fatigue issue).  The Throwout fork (also:  Withdrawal Fork, Item 31) was of a formed sheetmetal design.   Fractures would develop at an inside corner where the "C" section had a shape change to clear the Bellhousing.  Force concentration at this Stress Riser results in eventual failure.  Symptoms of this are a decreasing Clutch action as Pedal is depressed, and inability to be able to adjust for an adequate Pedal function within the adjustment range.  These symptoms are not unlike when cable is stretching in preparation to failing.  That is why it is important to determine which of the two common failure modes is occurring.   

Check Throwout  Fork:  After moving Dustboot (Item 35) at Bellhousing, inspection of trouble area of Fork is possible. If sufficient cable action is observed at the end of the cable, the motion may be lost as Fork bends, so motion and force is not applied to Throwout Bearing and Pressure Plate to release friction disc and allow it to slip. 

Clutch Throwout Fork Weakness and Failure:

The original Fork may develop fractures after long-term service.  These fractures can develop at the Stress Riser located at a corner in the Fork needed to clear the Bellhousing (or anywhere along the stressed area, see below!) .  A combination of the corner being too sharp, the material being too thin, and working against the repeated counter force of the Pressure Plate, means the formed sheetmetal Forks of the early design suffers from Cumulative Material Fatigue.    

Typical view of a failing, fractured Fork during inspection.


View along Clutchfork(31) after removal of Dustboot(35).  At Green, direction of tension from Clutch Cable.  At Orange, Stress Risers at notch for clearing Bellhousing edge at Blue.  At Red, a fracture has developed as a result of Cumulative Material Fatigue

Thanks to Tom H. for providing another picture of a failed Fork.  He measured the material thickness as 0.125". 


Fracture has occurred at Reds, inboard and nowhere near the Stress Riser notch, so I guess it can occur anywhere in the Orange area. 

Replacement Forks are made of a heavier gauge sheetmetal which stands up to the task (and possibly the inside radius at the Stress Riser has been increased, although it looks pretty abrupt in the CVI picture below).  As another option, a failed Fork could be repaired/reinforced.


Picture of replacement Clutchfork 677431-9 from CVI.  These are of a heavier gauge formed sheetmetal which seem to stand up to the forces better over the long haul.  Corner at Orange, is the Stress Riser and area of weakness of the original design is highlighted. 

This picture of an ebay offering:  "NEW OLD STOCK GENUINE VOLVO  CLUTCH RELEASE FORK"  appears to be of the thinner sheetmetal (to be confirmed, Author invites input!): 

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Notes on Repairs: 

A failed Clutch Cable can be replaced without a major procedure.  After unhooking top end from Pedal and extracting remains of the failed Cable it can be laid next to (pre-lubed!!) replacement cable and (Inside) adjustment nut brought to a similar adjustment position before installation which is, as they say, reverse of removal.  (Outside) adjustment nut and final Free Travel Adjustment will be made once cable is installed.  Broken/separated area of failed cable can be inspected, including under a magnifying glass to get a good idea of the failure mode.  

A failed Fork needs engine to be separated from Bellhousing in order to be able to replace it...a much bigger job!  Throwout and Pilot Bearings, and even state of Clutch Friction Disc and Flywheel and Pressure Plate surfaces should receive a critical inspection at that point as well.  

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Reference Information:  

Adjusting Clutch Fork Free travel:


These instructions from Factory Green Manual reference other Figures not shown here.  Adjustment nuts are Item 30 above.  

 

Application List for the 1212189 Clutch Fork by Volvo vehicle models and production years (the 122 application is not even shown, but is similar to '68 140):

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Repairing a failed Fork:  Failed Forks can also be repaired and reinforced, by welding, to make the "C" section of the Fork an "O" section.  The added plate shown below would be in tension so would heavily reinforce the weak Stress Riser area. 

Concept Drawing (quite simplified, and not even showing Stress Riser), but the viewer should still get the idea!

 :

 

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The other end of the Cable:  


 

Link to thread Clutch Pedal Return Spring:  http://www.volvoforums.org.uk/showthread.php?p=2287957#post2287957

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From a popular reference source: 

Stress Riser:  https://en.wikipedia.org/wiki/Stress_concentration

Cumulative Material Fatigue:    https://en.wikipedia.org/wiki/Fatigue_%28material%29

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Links: 

VOC thread ['73 Clutch Cable]:  http://www.volvoforums.org.uk/showthread.php?t=245092

VOC thread [Clutch Cable or other issues]:  http://www.volvoforums.org.uk/showthread.php?t=240799&highlight=Clutch+fork

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External material sources are attributed.  Otherwise, this article is Copyright © 2016.  Ronald Kwas.   The term Volvo is used for reference only.  I have no affiliation with this company other than to try to keep is 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 and future! 

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 donít, youíre just a lazy, scum sucking plagiarist, and the Boston Globe 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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