Volvo Air Assist Clutch

Volvo Air Assist Clutch

12/31/2013

From Sibernut (Ron):
 

THE HARD-CLUTCH-PEDAL FINAL SOLUTION

The clutch in my 2000 Volvo 610 has been extremely hard since I have had it.  It has been to a Volvo dealer, and the mechanic said it was the hardest he had ever felt.  Although I have an Autoshift, my wife had a hard time with it.  I myself have had the "shaking knee" in heavy constant traffic stop & go.  There has to be a better way.  Volvo dealer said to replace the clutch for $2G, but would not guarantee it would be easier than now.

I experimented with several air cylinder assists to the stock hydraulic slave cylinder with no luck.  The air cylinder made the clutch easy, but it would not release *proportionally* to the clutch pedal being released.  Most times it would release suddenly at the top of the pedal travel like a drag race.  Others have successfully used an air cylinder with a manual switch to release the air, but I wanted something that performed like stock.

Here is the description of the work I performed, with pictures showing the procedure.

  •  
    I spent some time digging and reading all kinds of Volvo literature, and I have found a solution.  I discovered that Volvo actually makes an air assisted hydraulic slave cylinder, it is part # 1671953, called a "clutch servo".  WABCO also makes the same thing part number 9700511920.
     
    BUT - this is/was only used on Volvo transmissions, nothing else.  In particular, it was used in an HDT on a Volvo trans 14 speed VT 1414.  I have found many similar clutch "servos" on other Volvo transmissions in Medium trucks also.  If you do a salvage search for all heavy Volvo transmissions, you may see them in a picture like I provided.  I have no idea if the specs are the same as the part number I have.  You may find one in a salvage yard like I did, but many yards will not sell them separately (if they even know what it is).  Mine cost me $125 plus shipping, but I have found several suppliers in China that say they will supply one brand new for about $40 plus shipping of $60.  (I'd rather spend my money in the USA, and not have it fail or try to kill me.)
     
  •  
    This is the servo I purchased from a salvage yard. 
  • I removed the Volvo slave cylinder from the clutch cross-shaft arm, and compared the travel of the stock cylinder with the travel of the air servo unit.  To utilize the full travel of the new servo to the clutch, the arm needed to be approximately 3" long from CL to the yoke attaching point.
  •  
    The arm was modified by extending it 3"  and mounted on the shaft one spline counterclockwise from stock to match the actuating rod angle from the much larger cylinder.
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    The other side of the clutch arm.  Nothing permanently was done in case I need to return to stock. 
  •  
    A bracket was fabricated to suspend the air servo from the bolts to the bellhousing.
  •  
    The servo and parts ready to go.

    A second brace was extended to the bottom of the transmission for stiffening of the support.
  •  
    The yoke rod from the prior slave cylinder fits perfectly (!) inside the threaded end on the air servo.  This yoke also provides some adjustment once the servo is installed, just like stock.  (Note the air servo must have some allowance for slight movement at the pivot on each end to align properly over the travel of the arm.)
  •  
    The extended arm mounted back on the clutch shaft.
  •  
    The servo attached to the clutch arm.
  •  
    The hydraulic (blue) line and the air line (green ) attached.

    I ran the air line directly from tank #1 since that gets pressure before the others, and I wanted the clutch to get it ASAP. 
  •  
    The servo hangs down lower than the stock unit but is still higher than the front axle.
  •  
    The servo from below/

The clutch actually works easier with no air than the stock setup did, so it is "fail safe".  The entire setup probably cost me less than $200, but I had most of the materials needed.  It would be possible to set up a belcrank assembly under the truck to mount the servo parallel to the frame.  But the front axle is much lower than the servo and a belcrank would be more parts to fail, etc.

Although I expect this modification to perform well, I always try to leave myself an "out".  Nothing I have done will prevent me from returning the entire setup to stock easily.  I'm carrying the removed parts with me, and I estimate I can reverse it in less than 1 hour plus bleed time (on the servo, not me).

(And speaking about bleeding the cylinder - I have come up with a foolproof relatively quick & easy solution to bleed them with only one person.)

Here's hoping I have made it easier for those with the same hard clutch to fix theirs.  The guy I drive for part time owns 5 Volvos, and he said this pedal is much easier than the one that has an "Easy Pedal" clutch installed.

Real world road test - I ran this setup for approximately 250 miles, in traffic and over the road.  It performed flawlessly, and I'm very pleased with the result.  I'll make a small adjustment to raise the engagement point of the pedal, but it works fine as it is.  For those of you with an Autoshift, you know that complete disengagement of the clutch and application of the brake is critical to it "finding" a gear.  This setup is better in that regard than stock.  Good luck, and relax in the stop & go traffic.