Substitution: Fan Hydraulic System Bleeder

One relatively expensive and difficult to locate fitting is the bleeder valve assembly (Fig. 178, Item 3 & 4) on the line charging the fan clutch.  This assembly consists of a TEE, PIPE 4730-01-473-8047 [4730014738047], and a bleeder screw 4820-01-473-3580 [4820014733580].

The purpose of this bleeder is to ensure all air is removed from the hose leading to the fan clutch 2930-01-168-7870 [2930011687870]. Although we have since applications where the hose threads directly into the solenoid, this can be considered an upgrade to those situations. Overall,  it is generally better practice to purge air from the system at the highest point. Even if you bleed the system using the quick-coupler near the fan clutch as a bleed point, any air remaining in the hoses or fittings from the solenoid to the fan clutch may still likely travel to the highest point.

The pipe tee itself appears to be a common 1/4″ NPT Street Tee, however the perpendicular hole is instead threaded to accept a bleeder screw.

Our solution is to actually use a regular brass 1/4″ Street Tee with a specialized 1/4″ fitting incorporating a bleeder screw.

1/8″ NPT bleeder screw adapters are extremely common and easily located on eBay and Amazon. However, we wanted to avoid using a 1/8″ to 1/4″ bushing.  We were able to locate a  1/4″ NPT bleeder adapter, although it is not specifically marketed as 1/4″.  The CTA Tools 1235 Brake Bleeder Screw Repair Kit, 3/8-Inches is actually a repair fitting intended for defective brake bleeders on calipers such as Brembo and others.

As the hydraulic pressure used in the fan system is only 100 to 150 p.s.i., we feel comfortable that fittings designed to handle brake fluid pressures (800 to 2000 p.s.i (applied pressure)) should be more than sufficient.  In this application, we intend to machine the fittings so that the bleeder adapter sits as low in the fitting as possible, and will post pictures after machining.

Leave a Reply

Your email address will not be published. Required fields are marked *