Why Do I Drill the Pump? Preventing Excess 6L80 Series Line Pressure with a Drop-In Sonnax PR Valve

This content relates to two discontinued Sonnax parts: pressure regulator valve kit 104520-14K and oversized pressure regulator piston kit 104520-07K. These kits required drilling the pump, and Sonnax now offers equally effective repair options that eliminate that extra labor: drop-in kit 104520-15K and oversized kit 104520-16K.

Here in the Sonnax Tech Center, we get a lot of calls about our drop-in GM 6L45, 6L50, 6L80, 6L90 pressure regulator valve 104520-14K asking, “Can I install the valve without drilling into the pump?” and “Why do I need to drill?” The answer is simple: combined with the improved Sonnax valve, drilling ensures you’re making an effective repair that keeps line pressure at OE specifications. Here’s a little background about this valve to help shed more light on the situation.

During our research, we found several areas of the bore that commonly wear and need to be addressed. It is common for the balance end of the valve to wear into the casting, resulting in high line pressure, harsh shifts and overheating due to insufficient cooler/ converter lube flow. We also found wear at the outboard spool causing the converter feed pressure to decrease, resulting in low line pressure. Wear at both ends of the valve causing both high and low line pressure unfortunately doesn’t even out, and pressure can be erratic if both sides are worn badly enough.

During design of a drop-in PR valve, Sonnax engineers found it necessary to lengthen critical spools to increase stability and prevent future wear. Since fluid introduced into the bore under pressure can cause the valve to side load and increase bore wear, annular grooves were added to one end of the Sonnax valve to help the fluid surround the valve evenly. This centers the valve in the bore, preventing side loading and unnecessary wear (Figure 1).

OE vs. Sonnax Pressure Regulator Valves

After redesigning the valve, we needed to ensure the proper amount of balance oil was introduced back into the circuit to stay consistent with OE performance. That’s what prompted the additional step of drilling a 45° hole through the adjacent channel: drilling provides balance oil to the valve while in regulating position. If the Sonnax valve is installed without drilling, the result will be excessively high line pressure.

Figure 2 – Drilling the Pump to Restore Circuit Balance Oil

Watch this quick video where I show these parts in detail and the simple, step-by-step drilling process.

If you are installing an older version of Zip Kit^® 6L45-6L90-ZIP that includes PR valve 104520-14K and decide you don't want to drill, purchase Sonnax pressure regulator valve kit 104520-15K separately. It's an easy, effective drop-in repair (no drilling required) for a common wear area that can contribute to a handful of problems. The 104520-15K valve is included in current versions of the Zip Kit.

Andrew Jessiman is a Sonnax product support representative. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax technicians.