Boy, does this bring back memories!

Given the extreme humidity in my climate (NJ coast), I try to make a point of flushing brake and clutch fluid in my car at least every two years. The first time I did it on my Volvo, I had the exact same problems that you did: air seemed to be getting into a sealed system -- far more air than should be able to enter via the threads around the bleed screw. I too was using a vacuum bleeder. After about six hours of screwing with it, SOMEHOW I got the pedal pressure back. I closed everything up and was done with it.

I've since bought a pressure bleeder, which I documented in a web page as being THE solution for flushing or bleeding hydraulic systems. I can flush the brake lines in either of my cars in about 15 minutes with that thing. Literally, fifteen minutes. What a great tool! On my little Mazda RX-7, it works great for the clutch hydraulics, too.

But when I tried to flush the brake and clutch hydraulics again, just a few months ago, I had the same problems -- this time, with the pressure bleeder. (The last time was with a vacuum bleeder.) Again, I spent hours trying to get air out of the system.

The more I worked on it, switching among my available resources -- a pressure bleeder, a vacuum bleeder, and a friend's left foot, for the classic two-man method -- the more I became convinced that there's something about the S70 clutch master cylinder and / or fluid reservoir that allows air into the line whenever pressure or vacuum bleeding methods are used.

On a whim, I decided to try gravity bleeding the clutch system. I left a clear nylon hose attached to the slave cylinder bleed screw, put the other end into a glass bottle, and openned the bleed screw. The pressure bleeder was not attached, and I left the fluid reservoir cap off so that I could monitor and top off the fluid level. After about 15 minutes, there were no more small bubbles of air coming out of the bleed screw, so I closed it up. Interestingly, I had pedal pressure, but only after pushing the pedal down about half-way through its range of travel. Barely enough to shift with, but at least I could move the car.

Going on another hunch, I decided to take the car for a brief ride, thinking that any air that's still in the system might actually work its way up the line and back to the reservior during a little driving. Sure enough -- full pedal pressure was restored before I got around the block.

As I've now dealt with this clutch bleeding problem twice on this car, I decided to verify my solution by creating the problem again, with the pressure bleeder, and fixing it with another gravity bleed. Sure enough, the pressure bleeder could be used to quickly introduce a stream of bubbles into the lines, with the accompanying lack of pedal pressure. In fact, the pedal went to the floor and wouldn't come back up. Pressurizing the system to about 20 psi, with the bleed screw closed, would allow the pedal to come back up and the master cylinder piston to expand to the "pedal-up" position. It still wouldn't disengage the clutch, as there was still air in the line from having pressure bled the system, but the pedal was up. After another 20 minutes for gravity bleeding, the system was fully operational again.

It seems that the solution for 70-series clutch hydraulics is to do a gravity bleed. Add pressure to a closed system with a pressure bleeder, if the master cylinder piston has collapsed because you applied pedal pressure to an unsealed hydraulic system or if you had air in the lines.

I have a web page on this matter, that I haven't updated since discovering the gravity bleed solution. Tim, please let me know how this solution works for you, and I'll update my page accordingly.

--
Jim Rothe, '99 S70 T5M,
http://www.jimrothe.com/volvo/index.html

This happened to me when I flushed the fluid in my clutch/brakes (I did
the clutch at the same time). Just a tiny amount of air seems to cause
the pedal to drop limp to the floor. I re-did it using a new drain line
(the hose end had become a bit flared from use on the brakes and did not
fit tightly on the clutch end) and I was very careful to made sure no air
entered. I also used a power bleeder and only opened the drain nipple a
small amount. Second time I got it right.

Here is the link to the power bleeder that works well:

http://www.motiveproducts.com/

You might be able to do it with two people the old fashioned way BUT I have my doubts. I'd use a pressure bleeder as I've done before but you won't have access to one so why not just have it towed to a dealer or shop that has Volvo experience and be done with it? The car's been down for how many days already and you're not gaining.
There's a good reason why it lost its fluid (if that's the cause) so that needs attention, not just a matter of bleeding the slave cyl.