Valve-Body Bore Preparation - Transmission Digest

Valve-Body Bore Preparation

We’ve all been there. You get your bench set up to clean and inspect the valve body, pull the first retaining clip – and then it happens. The first bore you touch ends up having either a stuck end plug, valve, sleeve or – worse yet – all the above. Fast-forward a few steps and, what the heck, how did that O-ring get torn? Why do I always end up with sticking valves on the way back together? The thing to keep in mind is that most valve bodies use aluminum castings that can dent, scratch and develop ridges very easily. Once this occurs, it can quickly lead to damaged components and lost time trying to repair them. The best place to start in avoiding this scenario is to understand why it happens.

Valve-Body Bore Preparation

TASC Force Tips

Subject: Preparing valve-body bores before reassembly
Essential Reading: Rebuilder, Diagnostician
Author: Tory Royce

TASC Force Tips

  • Subject: Preparing valve-body bores before reassembly
  • Essential Reading: Rebuilder, Diagnostician
  • Author: Tory Royce

We’ve all been there. You get your bench set up to clean and inspect the valve body, pull the first retaining clip – and then it happens. The first bore you touch ends up having either a stuck end plug, valve, sleeve or – worse yet – all the above. Fast-forward a few steps and, what the heck, how did that O-ring get torn? Why do I always end up with sticking valves on the way back together?

The thing to keep in mind is that most valve bodies use aluminum castings that can dent, scratch and develop ridges very easily. Once this occurs, it can quickly lead to damaged components and lost time trying to repair them. The best place to start in avoiding this scenario is to understand why it happens.

Causes

With valves, bore wear is logical because of the movement involved when they are hydraulically actuated. Pressure-regulation valves and those with PWM controls tend to wear more rapidly because of the continual oscillation involved. But how does a seemingly “stationary” component like an end plug wear? There are several ways this can happen.

Often end plugs are used as a spring stop. Even though they are not intended to stroke in the bore, valve forces are transferred through the spring, causing movement of the plug. A similar action can occur if the end plug is used as a stop for the valve itself. Some valves also may have a passage on the outboard end that applies varying amounts of hydraulic pressure at the end plug, causing it to oscillate. On top of all this, end-plug-to-bore clearances often can be larger, causing a loose fit initially that only gets worse over time.

Damage inflicted by the rebuilder from removal techniques is another problem. Care must be used during disassembly to avoid bore and component damage from the improper use of tools. Let’s discuss some methods of preventing these occurrences.

Disassembly tips

End plugs: Some OE end plugs come from the factory threaded (Figure 1) to accept a bolt or slide hammer. If you have threaded plugs, use them to your advantage to aid in the removal process. If this feature is not provided, another option is to drill and tap your own set of threads for the same purpose.

Valves: The trick with a stuck valve is to concentrate on the face of the spool, staying away from the edges or outside diameter. Dents and scratches on these surfaces can wedge the valve even further and quickly lead to irreversible bore damage. Dental picks (Figure 2) with blunt edges work great for this, because they won’t cause nicks like a pick or screwdriver often can. In the event the valve is severely stuck, compressed air and a wet-air-test plate can be used to push it out of the bore.

Another option is to fashion a tool from a tube, threaded bolt etc. to use as either a punch or a method of attaching a slide hammer to the end of the valve. This will typically damage the valve but will at least keep the bore intact.

Sleeves: Sleeves often will have a protruding stem that can be used as a point to grasp with pliers (Figure 3). Work the sleeve back and forth carefully to prevent contacting the outside of the sleeve or bore surface.

Once you are ready to put things back together, there are a few techniques that can be beneficial during the reassembly process.

Assembly tips

  • Always inspect the bore opening for nicks and ridges. These imperfections often can be difficult to see but can be identified by dragging a pick down the edge of the cast-in chamfer (Figure 4).
  • If necessary, a small-diameter flap wheel chucked in a miniature die grinder can help smooth ridges. A non-abrasive tool such as a radial wire brush also can work great for de-burring the bore for O-ringed sleeves (Figure 5).
  • When installing O-rings, roll the plug or sleeve on a flat surface to size. This will help prevent cuts and tears. Lubricate the O-ring(s) for best results. Products such as Sonnax Slippery Stick (Part No. O-LUBE), P-80 rubber lubricant or a 50/50 mixture of STP oil treatment and ATF will make the installation much easier.
  • Finally, cleanliness is your best friend. Always clean bores of any unit debris on disassembly as well as after using a radial wire brush, flap wheel or emery cloth. Failure to do so can result in sticking of the components you have worked so hard to repair. Soft-bristle bottle brushes in various diameters (Figure 6) used in a cleaning tank work well for this. Dry the cleaning fluid off with a blow gun and recheck for particles of debris.

Encountering a dilemma or two during a valve-body rebuild is a normal part of the transmission world, but learning to adapt as these situations arise is your best defense. I hope that implementing these tips into your repair practices will result in more-consistent results, less rework and quicker turnaround times.

Tory Royce is a Sonnax technical-support specialist and a member of the Sonnax TASC Force® (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians. E-mail Sonnax Tech Support at [email protected] or call 800-843-2600.

©Sonnax2013

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