ZR51 Performance - 6-speed Manual Transmission Specialists

CLUTCH HYDRAULIC SYSTEM (CHS) - Past Actuator Cylinder "QUALITY SPILL"

In 2006, we found the cause of the problem of which many C4 ZF Clutch Hydraulic Systems were having operational problems during the last several years. As of June 2008, GM discontinued selling both the master and actuator (slave) cylinder. The slave cylinder seals have been installed backwards during manufacturing between 6/2004 thru 6/2006 assembly.

Suspect new replacement slave cylinders replaced in the last two years (6/2004 thru 6/2006) if they seem to be problematic. That is if the vehicle received the newer style ('91-'96) slave cylinder. This pertains to DOM (Drawn Over Mandrel) style cylinder bodies and does not include cast body aftermarket slave cylinders or now discontinued '89-'90 replacement slave cylinders.

Other CHS Actuator (Slave) Cylinder quality issues were the presence of burrs from orifice machining. The take-up spring, when inserted during assembly, will sometimes knock the burr loose allowing the free floating burr to possibly interfer with seal-to-bore actuation operation. This will eventually compromise the integrity of the seal and ultimately diminishing performance of the CHS Actuator (Slave) Cylinder. Corrective Action: Deburr interior of cylinder bore prior to assembly of unit during manufacturing process. NOTE: Somewhere alomg the production history of the TRW manufactured slave cylinders, this deburring process was dropped. The older cylinder assemblies all were deburred prior to initial assembly.

This cut-away of a CHS Slave Cylinder ('89-'90) has the seal oriented in the correct direction and the rubber accordian shaped boot being held in position with two barb-ring washers. Within the last year we have observed that only one barb-ring washer has been installed allowing the boot to possibly dislodge after installation pending full deployment of actuation rod. This condition is detrimental to full life-cycle longevity due to the increased possibilty of abrasive debree entering the bore-cylinder assembly. Corrective Action: Install two barb-ring washers during manufacturing of unit. 

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CHS - MASTER CYLINDER QUALITY ASSURANCE ISSUES

The TRW manufactured Master Cylinder (DOM type) has had a few quality assurance issues as well.

The plastic reservoir bulk-head barbed ridge has occassionaly been found to have a defect in shape causing the self-bleed feature of the system to become compromised.

  Symptoms produced from this anomaly range from reduced performance of clutch hydraulic system to need for repeated bleedings followed by slight reduction in performance followed shortly after bleeding. Corrective Action: Replace reservoir ensuring that bulk-head seal integrity is good. The bulk-head seal can be inverted to provide fresher sealing surface to essencial sealing surface of plastic reservoir bulk-head barbed ridge.

Other CHS Master Cylinder quality issues are the presence of burrs from orifice machining. The take-up spring, when inserted during assembly, will sometimes knock the burr loose allowing the free floating burr to possibly interfer with seal-to-bore actuation operation. This will eventually compromise the integrity of the seal and ultimately diminishing performance of the CHS master cylinder. Corrective Action: Deburr interior of cylinder bore prior to assembly of unit during manufacturing process. NOTE: Somewhere alomg the production history of the TRW manufactured slave cylinders, this deburring process was dropped. The older cylinder assemblies all were deburred prior to initial assembly.

DIFFERENT TYPES OF CHS MASTER CYLINDERS

Top: DOM type TRW manufactured. Bottom: Cast type WAGNER manufactured.

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The following Message thread was forwarded from Stan Lorence of Tom Henry Chevrolet Parts:

Received 6-7-2006

Bill,

   Thought you might find this update on the slave cylinder issue interesting.

I will continue to keep you informed. Hope it helps.

Thanks

Stan


<Stan,

Your concern has reached the person who can make a difference.

Best Regards,
John Coleman
GM SPO Northeast Region Zone Manager

----- Forwarded by John Coleman/US/GM/GMC on 06/07/2006 10:25 AM -----
To Brad Flaaen/ US/GM/GMC

Subject: Corvette slave cylinders       
                                                                          
Brad and John:  I checked with Peacy who had a little experience with C4
cars.  As far as he is aware there is no inherent problem with the clutch
slave cylinders.  This could be a quality spill by the supplier that GM is
using.
      Art Spong
      Brand Quality Manager, Corvette

Brad,
Not sure if this is your area but if not, I'm sure you would know who
should be involved.  Please advise.

Best Regards,
John Coleman
GM SPO Northeast Region Zone Manager

              
----- Original Message -----
From: Tom Henry Chevrolet Parts Department
To: Casey Rentfrow

Sent: Friday, May 26, 2006 4:50 PM
Subject: Corvette slave cylinders

Hi John,
  The following was sent to me by one of my customers, Bill Boudreau a
nationally know Corvette expert, and appears on the Corvette Forum
website. It concerns the Corvette C4 clutch slave cylinder which, in my
experience, has a very high failure rate. Nearly half of them sold over the
counter are returned to me as defective. Please visit the following web
address http://forums.corvetteforum.com/showthread.php?t=1402043  for an
explanation of the failures. These failures have been an issue for over two
years. This seemed to me to be an important enough issue that I needed to let someone
at GM know. I spoke with my parts rep Casey Rentfrow, who is always very
helpful, and he suggested that I email you the information. My customer, Bill
Boudreau, has been attempting to procure the affected seals (part number
AAD-34665237) without success. He states that they must be highly
proprietary because he has access to all the major manufacturers and they
cannot or will not supply them to him. He has asked me to approach GM on his
behalf and request that these seals be made available. After you review and
consider this information I ask that you keep me informed and "in the
loop". Thank you in advance for your attention.
Thanks
Stan Lorence
Tom Henry Chevrolet Parts

 

Received 6-12-2006:

From: Tom Henry Chevrolet Parts Department

 

Bill,

  This is the latest info on the slave cylinders.

Stan:  FYI the SPO quality group has put in a request for returned warranty
parts so they can document the concerns and root cause of the problem.  It
appears that there is a 15% percent failure rate which in regular warranty
is pretty high but for the older service parts SPO says it is not unheard
of. TRW makes the part and SPO quality has invited them in to explain the
reject or failure.  Thanks for bringing this up and if more information is
shared with me I will pass it on.

Art Spong
Brand Quality Manager, Corvette

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Send email to billb@zfdoc.com or call Bill Boudreau at (602) 319-6575.
Last modified: November 5, 2013