The brake pedal feel on my 89' 740 Turbo has really softened in the last month so I decided to bleed the fluid. I checked both the brake pads and rotor to see if they needed replacement, they didn't. So along with a patient buddy I did the tried and true old school method of pump and bleed. Started with the caliper furthest from the brake fluid reservoir and worked my way to the closest caliper. After the procedure, thinking the brakes should be nice and firm again, took it out for a quick test drive. To my surprise there was little or no difference in the feel.
Without the engine running and the servo's vacuum exhausted, the brake pedal should feel solid, firm, if it isn't, then there is air in the system, or a leak (indicated by pedal continuing to sink slowly), to test the servo, keep your foot on the brake pedal, start the engine, the pedal should promptly 'sink' a little under your foot, then come to rest again, but feel slightly spongy.
All the cars I have ever driven that are equipped with servo brakes have always had a slightly squidgy feel to the pedal, when the engine is running; some are squidgier than others, but all have had a 'solid pedal' with a 'dead' servo.
Did you or your mate observe whether or not there was still any tiny air bubbles exiting with the old fluid? There should be no air whatsoever in the exiting old fluid, even tiny micro bubbles indicate a fault, and can of course compress a lot when you press the brake pedal. If you cannot get rid of those tiny bubbles, it can indicate a faulty master cylinder.
You are also dealing with two separate circuits at each front wheel (unless fitted with ABS), did you bleed both?
With the 200 and 700 series volvo, I found that if parked on level ground, I could often 'gravity bleed' the entire system (this will NOT work for ABS equipped models, which have a special bleed sequence), just by opening the opening the caliper nipples, a transparent exit tube allowed me to check for air; one man job, no worries. This method, however, does not prove the health of your master cylinder, and any sludge buildup in the system may not be removed with the old fluid.
If all seems well with the hydraulic system, I believe, although I'm not sure that certain types brake of pads (if not all types) can give a 'dodgy' pedal sensation, if they have been overheated and become glazed, also, new pads take a short while to begin to feel 'normal', but neither of these conditions would appear to apply to you, so I'm otherwise at a loss!
Did you use clean, fresh fluid from a sealed, unshaken container? Was all the old fluid flushed out until it ran clean? On the front callipers there are two nipples, both of which need bleeding.
If all that was done OK, check all the flexible pipes to see if they balloon when an assistant presses the pedal.
Are there any leaks anywhere?
If everything else seems OK, suspect the master cylinder is failing.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.