Austin-Healey - Bleeding the Clutch - ‘Hanging on the Hose’ Method
This method has worked well for me for many years. It’s easier to do if the ‘extended upper slave cylinder bolt modification’ has been done, for obvious reasons.
Here is what I do:
If the slave cyl. and / or slave hose are being replaced, first temporarily mount the cyl. to the bellhousing and install the hose in order to properly orient the hose so that there are no kinks or twists when the job is done. (No need to install the pushrod yet)
Now remove the slave cyl. mounting bolts and let the cyl. hang free on the hose. Bottom the piston (all the way forward) in the bore - I use a screwdriver, anything handy. Open the bleed screw (well opened) and fill the centre part of the reservoir with the selected brake fluid and allow the fluid to seep into the plumbing by gravity until a drip or so of fluid is seen at the bleed screw. This can take awhile, depending on whether or not the master cyl. has been pre-bled - usually time for a beer or two. Keep the reservoir topped up while working on the beer.
When brake fluid drips from the bleed screw, close it - permanently - and top up the reservoir. Now stroke the clutch pedal steadily by hand to the floor and back up - gently. The pedal should stroke 3- 4 times before the slave piston fetches up against the circlip. The pedal will stop suddenly and unmistakably when this happens - care needs to be used here - the force generated is tremendous, and the circlip can be easily blown out of the cyl. causing a great mess.
Now, from under the car, hold the slave cyl. with one hand so the the hose outlet is facing upwards. The idea here is to get the air bubbles in the cyl. gathered right at the hose opening, poised for the next step. With the other hand, firmly push the piston to the bottom of the bore. The volume of the slave cyl. is enough to clear all the air right into the reservoir where they will rise to the top and be gone.
I usually repeat the procedure 3 - 4 times to be sure that no air is left anywhere in the system. It doesn’t hurt to tap on the body of the slave cyl. - just before the piston is pushed - to assist in dislodging air bubbles that may be clinging to the walls of the cyl. This seems to be especially helpful with DOT 5 silicone brake fluid, which I use but find a bit harder to bleed. When no more bubbles appear on the surface of the reservoir, the system is bled.
Now bolt the slave cyl. in place on the bellhousing and install the pushrod. Sitting in the driver’s seat, work the clutch pedal a few times to pump the piston out to it’s working position, and to be sure that everything feels ‘comfortable’. Now is the time to do the final top up of the reservoir. (If it’s done sooner, it could overflow with all the piston pushing).
This method is a bit of extra work but is cleaner (and uses less fluid!). It can be done with the tunnel cover removed, or still in place on the car (with the bolt modification) - a great advantage if you happen to own a BJ8! It helps to involve a family member or friend to watch for bubbles at the reservoir as you push the piston home each time. I’ve never had to re-bleed a clutch using this method, as long as no other difficulties (bad seal, etc.) are revealed, and as long as care is used.
Works for me!