Bench Bleeding the GM QTU Master Cylinder

Problem: Ineffective bench bleeding causing air to enter hydraulic system



Cause: Air left in the no-pressure areas of master cylinder migrates to pressure areas once master cylinder is installed.



Solution: QTU master cylinders can be bench bled using a combination of pressure or vacuum bleeding on the secondary end and RFI on the primary side. Conventional bench bleeding requires a 15 second pause between each single stroke of the master cylinder. using the methods described here the process can be done in under 5 minutes. Here are the steps involved:



1. Place master cylinder in vise so that the master cylinder body is in a level position.



2. Install bench bleeding kit supplied with master cylinder. Route rubber hose from secondary master outlet to master reservoir.



3. For primary side use RFI injector hose assembly (adapter, connector, tubing, in-line coupler) instead of bleeder kit hose.



4. Prepare the RFI injector for pressure bleeding. Install universal port adapter on output side of gun. Attach injector input hose to new fluid supply (prime gun).



5. Fill secondary half of reservoir to 1/2 full level with new brake fluid making sure to keep secondary master output hose submerged.



6. Use needle nose vise grips to push master cylinder piston in 1/8 inch and hold in that position making sure to clamp against the snap ring. (See figure 82.1)



 Figure 82.1



7. Place injector inside secondary reservoir against vent and replenishing ports. (See Figure 82.2)



 Figure 82.2



8. Push fluid through master cylinder using slow steady strokes until only fluid passes from secondary outlet (approximately 4 strokes).



9. Release vise grips allowing master to return to rest position. Move master cylinder to an angle position (as it would sit on vehicle / top of reservoir level).



10. Use UPA (Universal Port Adapter) to perform RFI bleeding on primary outlet of master cylinder. (See Figure 82.3)



 Figure 82.3



11. Push fluid into master cylinder's primary outlet using slow steady strokes until only fluid escapes from quick take up valve (approximately 8 - 15 strokes). Be aware of geyser from quick take up valve.



12. Remove hose from master cylinder primary outlet and let gravity bleed until only fluid passes from master cylinder primary outlet.



13. Attach bleeder kit hose to primary outlet and route to reservoir. Master cylinder is now ready for installation.