May 22, 2023

Transmission Repair Tip: How to Use Small Drill Bits with a Portable Drill Motor

Jim Mobley

6L80 Pump Drilling Demo Video

See how easy it is to make a vise, drill the pump and install a Sonnax PR valve.
GM 6L80 Pump Drilling Demo Video

Creating a vise from a plastic tube should make it simple and easy to drill a hole .025"–.060" without breaking drill bits.

As an example of putting this method to good use, let’s walk through the installation of Sonnax pressure regulator valve kit 104520-14K (Figure 1) for GM 6L45, 6L50, 6L80 and 6L90 transmissions.

Using this kit requires a new balance hole in the pump cover for the pressure regulator valve because of the extended land area of the much-improved Sonnax valve design. Sonnax includes a drill bit in the PR valve kit for this purpose — learn more about why drilling is key.

Figure 1 – Sonnax Pressure Regulator Valve Kit
Pressure Regulator Valve Kit_104520-14K

Setting Up a Small Drill Bit Vise

  1. Find an aerosol can such as brake cleaner. One the side of can will be a 4" red plastic tube for concentrated spraying of the contents. The tube makes a perfect small drill bit vise and will allow insertion of a small bit directly into a portable drill motor with a Jacob's chuck. Just insert tube into chuck and leave 3/8" extended by clipping the tube (Figure 2).

  2. After your tube is set up in the chuck, insert the .039" drill bit from the Sonnax pressure regulator valve kit into the tube as shown in Figure 2 and tighten the chuck down securely.
Figure 2 – Use Plastic Tube as Drill Bit Vise
Use Plastic Tube as Drill Bit Vise

Note: The hole size in tubes varies from .035"–045". For small drill bits that are on the larger side, put the drill bit in the bench vise and the tube in the drill motor chuck. Next, slightly drill a hole in the tube by running the drill chuck onto the bit until the tube fits the bit. Tubes come in many different sizes (ex. coffee stirrers), so there may be an exact fit for some larger bits, if needed.

Installation of Sonnax PR Valve

Note: Always follow the complete, step-by-step instructions when installing this kit. Click here to view instructions.

1. Inserting Checkball in Cup Plug

  1. Begin installation of the Sonnax pressure regulator kit by removing the OE retaining pin, boost assembly and small spring and save for reuse. Remove and discard the OE pressure regulator valve and large spring.
  1. Drop one Sonnax 1/8" aluminum checkball into OE orificed cup plug. Drive the checkball into the cup plug with either a 1/8" or .120"–.150" punch (Figure 3). Stake cup plug to prevent checkball displacement (Figure 4).
Figure 3 – 1/8" PunchFigure 4 – Checkball in Cup Plug
1.125-inch PunchGM 6L80 Pump Cover - Checkball in Cup Plug

2. Create Pilot Area & Drill .039" Hole

  1. Use a spring-loaded marking punch (Figure 5) to create a pilot area for drill bit stability right below the surface in the cutout above the cup plug (Figure 6).

Figure 5 –Spring-Loaded Marking PunchFigure 6 – Pilot Area
Marking PunchGM 6L80 Pump Cover Pilot Area
  1. Drill a hole using the pilot area with a drill motor and .039" drill bit at 45° angle from the cup plug cutout area into the NEW PR balance area partition (Figure 7).
Figure 7 – Drilling at Pilot Area
Drilling at Pilot Area
Figure 8 – Installing Pressure Regulator Valve Assembly
GM 6L80 Pump Cover - Installing PR Valve Assembly

Congratulations! You have successfully installed the most reliable, stable and durable GM 6L-series drop-in replacement pressure regulator valve assembly in the industry! When complete, install pressure gauge on vehicle and experience how smooth pressure responds with throttle!

This drop-in Zip Valve (Part No. 104520-14K) also is available as part of a more comprehensive Zip Kit® (Part No. 6L45-6L90-ZIP) and in an oversized version (Part No. 104520-07K) for repairing heavily worn bores.

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While Sonnax makes every effort to ensure the accuracy of technical articles at time of publication, we assume no liability for inaccuracies or for information which may become outdated or obsolete over time.