Vacuum Bleeding a Shock

WARNING: ALWAYS WEAR EYE PROTECTION. I’ve had suspension fluid sprayed in my eyes and it sucks. It can happen even if you do everything right.

Degas the Suspension Fluid 

Suspension fluid has a lot of dissolved air in it, and before bleeding this air must be removed for two reasons:

• Dissolved air makes the oil more compressible.
• It allows the oil to absorb any small air bubbles left after bleeding.

Fill the vacuum bleeder reservoir no more than halfway with suspension fluid. Close the compressed air valve, open the vacuum valve, start the vacuum pump and run it to -30 in of Hg, then close the vacuum valve and turn off the vacuum pump. The the fluid sit in vacuum for 15-30 minutes. The vacuum can then be relieved by slowly opening the compressed air valve.

Bleed the Damper

NOTE: These bleed instructions are for bleeding a reservoir shock with a bleed port and an IFP. Although the basics of the bleed procedure are the same, the details for other damper architectures are different, so be sure to familiarize yourself with those before bleeding. 

Preparation

• Service/rebuild the damper and assemble it without suspension fluid.
• Connect the appropriate bleed adapter to the bleed port on the shock, and position it so it’s the highest point of the damper.
• Install the IFP and the reservoir cap retaining clip. It is very important the IFP be retained inside the shock during the bleed process.
• Fill the vacuum bleeder reservoir no more than halfway with the desired suspension fluid.
• Set your compressed air regulator to 45 PSI.
• Connect the compressed air source to the vacuum bleeder.

Bleed

1. Close the compressed air valve, start the vacuum pump, and slowly open the vacuum valve. Once there’s a good vacuum, close the vacuum valve and turn off the vacuum. Be sure to close the vacuum valve before turning off the pump.

NOTE: What look like bubbles under vacuum are actually pockets of vacuum and will collapse during the pressure phase of the bleed.

2. Verify the vacuum valve is closed, and slowly open the compressed air valve. Oil should start flowing from the reservoir into the damper. Once the pressure is stable, cycle the damper several times by hand. It can also help to tap the damper to dislodge any bubbles.

4. Repeat steps 1-2 several more times (I usually do 5 cycles) to help insure all the air is evacuated from the shock. Any small bubbles which remain will be absorbed by the degassed suspension fluid.

5. Close the compressed air valve, and use the pressure relief valve to release the pressure.

6.  Disconnect the air compressor, open the compressed air valve, and set the IFP depth. The excess oil will be pushed back to the vacuum bleeder reservoir.

7. Disconnect the vacuum bleeder from the bleed adapter, then remove the bleed adapter and close the shock's bleed port.

8. Install the reservoir cap and pressurize the reservoir to spec.