After replacing any clutch hydraulic components, air will have been introduced into the system, and this will prevent proper functioning of the clutch mechanism, so it must be bled. Start by carefully topping-up the fluid reservoir in the dash with fresh fluid. Unlike the brake hydraulic system, the clutch evidently cannot be bled simply by pumping the pedal; the air bubbles will only compress and expand instead of being forced out, so Volkswagen specifies that a vacuum-pump-actuated bleeder be used. The Haynes manual states one CAN use the usual bleeding techniques, so who knows? I’m also told that one can simply leave the rear of the van raised and the bleeder screw left open overnight, allowing air bubbles to work themselves out, but I have not tried this method, and remain dubious.
I purchased a vacuum bleeder pump kit which can be used for both clutch & brake hydraulic systems, as well as testing vacuum hoses.
- Atop the slave cylinder is a bleeder screw, protected by the rubber dust cap. Remove the cap, loosen the screw 1/2 turn, and attach the hose of the vacuum bleeder, according to the bleeder kit’s instructions.
- Actuate the bleeder pump several times, until fluid begins to flow through the tubing and into the bleeding reservoir. NOTE: If the hydraulic fluid has not been changed in recent years, it will be dark or nearly black, indicating contamination by dirt and water; this is perhaps what caused your components to fail in the first place. Volkswagen (and most other auto manufacturers, for that matter) recommends brake/clutch fluid be replaced every two years, as outlined here.
- Continue drawing fluid until it is clear of dirt, moisture, and air bubbles, periodically pausing to check the level in the dash reservoir and adding fresh fluid if necessary. Do not allow this level to fall below the ‘MIN’ indicator, or air will again be introduced into the system, and you will have to start bleeding all over again.
Remember, you’ve got about 10 feet of 3-4mm line to bleed, so this may take a full 12 oz. bottle or more.
- When satisfied all the air has been bled from the system, tighten the slave cylinder bleeder and replace the dust cap. Fire up the engine and see if you can engage/disengage the transmission. If the gears clash or refuse to engage, you probably still have air in the line; re-bleed and try again. If all seems well, drive down off the ramps and take her out on the road to run through all the gears. You may find that within a couple hundred miles of driving over the next few weeks, the gears will begin to complain. This probably means you still have some air bubbles lurking in your line, so bleed again until it works right.
Check with your local municipality regarding the proper disposal of your used brake fluid. Mine requested that I add it right to my used motor oil and recycle it all together. Others may prefer that you keep the brake fluid separate from other automotive fluids and dispose of it as a hazardous material.
Even if you have failed during this process to keep the fluid level in the reservoir topped-up, as long as you haven’t depressed the brake pedal air should not have been introduced into the braking system, so the brakes will not need to be bled. However, if the fluid is more than two years old, and since you’ve already gotten your tools dirty and probably stained your pants, now would be a good time to bleed your brakes.