Another Day at the Orifice - Transmission Digest

Another Day at the Orifice

Modifying orifice size in valve body separator plates has been practiced as long as automatic transmissions have been in existence. From performance upgrades to attempting to fix problems caused by valve-body wear, opening up orifices can provide positive effects – but can just as easily cause unforeseen problems. To avoid unwanted results, it is necessary to know when to drill, what size to drill to and when not to drill.
Another Day at the Orifice

TASC Force Tips

Author: Brian Wing
Subject Matter: Opening orifices or not
Issue: Details of drilling

A small change in diameter can make a big change in area

TASC Force Tips

  • Author: Brian Wing
  • Subject Matter: Opening orifices or not
  • Issue: Details of drilling

A small change in diameter can make a big change in area

Modifying orifice size in valve body separator plates has been practiced as long as automatic transmissions have been in existence. From performance upgrades to attempting to fix problems caused by valve-body wear, opening up orifices can provide positive effects – but can just as easily cause unforeseen problems. To avoid unwanted results, it is necessary to know when to drill, what size to drill to and when not to drill.

Increasing clutch feed orifice size is a proven way to improve clutch engagement time and firm up shift feel. This helps with otherwise lazy-shifting transmissions, hardworking commercial applications or units modified for performance use. But all too often when a feed orifice is enlarged, the hole is drilled too big and the change in shift feel is far greater than intended. This often results in harsh shifts, which many customers do not like and view as a nuisance. When other orifices are enlarged in an attempt to overcome leaks or other problems, it can cause a host of issues such as pressure fluctuation, converter drain back, noise, pump damage, etc.

You can navigate the minefield successfully by understanding why some orifice modifications have better alternatives and how orifices are commonly drilled too large as a result of incorrect calculation. When considering modifications, avoiding these pitfalls will help you bring a smile to your customer’s face.

In a nutshell

Separator-plate orifices are precisely sized holes that restrict fluid flow, reducing the speed of the oil in a given circuit. They work in tandem with valves and checkballs for timing purposes and to prevent valve fluctuation. For example:

• On the feed side of clutch and band circuits, a restriction serves to control the gear application to prevent harshness.

• On the balance end of pressure regulating valves, a restrictive orifice is needed to dampen pressure pulses from the pump that would otherwise cause the valve to move erratically and buzz audibly.

Common mods & side effects

Balance

As regulator valve bores wear over time, the increased leakage past the balance end of the valve is too much for the orifice to flow, and the valve only strokes partially – or not at all. This positions the valve in a high or max pressure position. Opening up the orifice to flood the balance end in an attempt to overcome this leakage is something that has been widely performed. From AFL and solenoid modulators to TCC, mainline and secondary pressure regulators, builders have had mixed results with this practice.

The reason for such inconsistent results is that enlarging the balance orifice makes a BIGGER leak in an effort to mitigate a problem caused BY leaking. The extra volume might overcome the effect of the balance leak and get the valve operating closer to its proper range (for a while), but we are simply sending more oil volume into the leaking area to be exhausted. This causes the pump to work harder, which can lead to wear or damage. In addition, now that some of the precise control variables designed by the OE engineers have been altered – the valve/bore tolerance from wear, coupled with the balance feed change – there can be unexpected problems with proper valve return, valve vibration/buzz and/or unstable pressure (Figure 1). Multiply that across other bores in a tired valve body and you can see why it doesn’t always seem to work, or why it seldom seems to produce fully repeatable results.

Line to lube

On units with lube issues, line-to-lube modifications of one sort or another are necessary. But drilling too large or enlarging the plate orifice when a valve body modification has already been made can allow converter drain back.

TCC

TCC exhaust orifices control how fast the converter releases; it is a common practice to enlarge them so that TCC apply is quicker due to diminished resistance to flow of the release oil. But the converter exhausting too fast can cause harsh lockup precisely because of that diminished resistance. Similarly, drilling to bypass the converter clutch backpressure valve on Ford 5R55W/S/N units can cause harsh lockup because resistance to exhaust of release oil has been reduced.

Actuator feed limit

Another widespread practice is to enlarge the solenoid feeds in GM units as a Band-Aid for low AFL pressure. AFL pressure is typically equal to line pressure until approximately 110-120 psi. Opening these feeds may result in a small drop in line pressure and can cause the solenoids to flood and partially close.

Performance

Chrysler 46/47/48RE units often bind up when over-enlarged direct-feed holes are used in tandem with a performance servo.

With any of these modifications, it is possible to induce temperature-related problems such as normal feeling operation when cold, but adverse operation as the unit comes up to temperature.

As shown by these examples, there are factors involved that make the effectiveness of enlarging orifices to repair problems a hit-or-miss proposition. For most issues, a more effective and repeatable repair is to recondition the bore and install an oversized valve. This seals off leaks to restore normal operation; it does not create new leaks to Band-Aid others. Modifying valve control generally results in shift quality that will not meet customer expectations; do it right and reserve your drilling for performance mods.

Drilling orifices the smart way

When enlarging orifices, it is very common to drill too large because diameter often gets confused with area. A small change in diameter can make a big change in the area of the hole the oil flows through. For instance, it is easy to think that enlarging a 0.070″ clutch feed orifice to 0.100″ will provide good results. That is approximately a 43% increase in diameter, but a 104% increase in area! Drilling that large will often result in timing problems, harsh shifts, rattled teeth and possibly broken components.

If you wish to enlarge clutch feed orifices, the following guidelines will help you determine what drill-bit size corresponds with a specific percentage increase in orifice area so you are less likely to cause problems when making common performance modifications. When tuning a transmission, experience has shown that a 20% increase in area yields a subtle yet noticeable change in shift feel without causing harsh shifts that generate customer complaints. Since the flow rate increases proportionally to the area increase in a clutch apply circuit, the clutch will also apply 20% sooner. We could analyze the mathematical formulas involved, but I’d rather just cop a cheat sheet (Figure 2). Use this chart to determine drill diameter for any increase in orifice area that you think best suits the vehicle you are working on.

Let them sing your praises

As you can see, some mods are better left unperformed when a proven, targeted repair exists. While the over-enlargement of orifices continues to be a common error for some, you now have the key to avoid going too large and causing adverse effects. Knowing when and how much to modify orifices will give you a higher success rate that your customers will absolutely love you for.

You May Also Like

Trying to Stop the Wheel Hop on Ford Edge with 6F50 Transmission

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a

The 2014 Ford Edge SEL with a 3.5L engine (figure 1) and a 6F50 transmission can also be equipped with an AWD system. This would include a Power Transfer Unit (PTU) attached to the transmission with a rear driveshaft going to the Read Differential Unit (RDU). The RDU comprises a differential assembly along with a viscous coupling assembly controlled by an Active Torque Control (ATC) coupling solenoid. The system is designed to monitor vehicle conditions continuously and seamlessly adjust torque distribution between the front and rear wheels. When it is functioning correctly, there should be no perception of this taking place when launching or driving the vehicle. 

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Related Articles –

ab60
GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – TASC Force Tips: Hydraulics Fundamentals: Check Valves – Shift Pointers: Mazda Sensitive to Pressure – Transmission Testing & Repairs:

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

Other Posts
GM 9T series: Critical wear areas, vacuum test locations

Sonnax has provided the following guide on critical wear areas and vacuum test locations for the GM 9T series of transmissions. Technicians working on these models should find this guide helpful. Related Articles – Solving a 4L60E acceleration shudder puzzle – The transmission repair industry: Globally integrated – Shift Pointers: A 10R140 with a classic

TASC-Tip-1400
The torque converter can of worms: Lockup and aftermarket programming

Lockup torque converters have been around now for some time. They came into production around the time when fuel mileage demands were put into effect by the government, and the auto manufacturers needed to do something to better connect the fluid coupling (torque converter) of the automatic transmission to the motor. By doing this, OEMs

tascfeature-1400
Watch out for high pressure in GM 8L45, 8L90 valve bodies

Hey now! Oh boy, do I have a fun failure to share with you and warn you about today! Related Articles – Shift Pointers: Where’s that fluid leak coming from? – Multitasking: Sorting out multiple issues with the same vehicle – Chrysler RH/RE late shifts and high pressure Have you encountered a crack in the

Shift of the shaft: Diagnosing Chrysler 48RE manual shaft issues

The TorqueFlite transmission has been around since mid-to-late 1950s. There have been many changes surrounding the manual shaft and rooster comb through the years. This transmission shaft controls the position of the manual valve that directs oil for the gear ranges, but it also is used for a Reverse light control as well as Park/Neutral