Car: 1991 940GL sedan with ABS. Girling single piston calipers on the front and ATE calipers on the back.

I had been having trouble with long pedal travel and a lack of braking power - sometimes requiring more effort than I thought reasonable to stop the car. Also, the pedal could be pumped several times quickly and the pedal travel would have reduced. Also, if the brake pedal was pressed REALLY hard a few times while standing still, the pedal travel would be reduced and the brakes would feel stronger for a few days after.

I replaced the Master Cylinder with a new ATE unit (same as original) and thoroughly bled the whole braking system making sure there was no air in the system. For about a fortnight, the brakes were great - they felt strong, less pedal travel. I thought I had solved the problem.

Yesterday I discovered the same problem was back again. I was pretty annoyed - just blew $200 for nothing??? Brake hoses on the front are 4 years old and about 3 months old on the back. Front calipers are also about 4 years old. Rear calipers appear to be original.

Could this be a faulty caliper? Is there potentially air still in the lines? Any other possible causes? I'm at a loss to explain this.

Any advice would be greatly appreciated.

Regards

Brad