Hi Steve

We had a similar fault on Ford Mondeo a while back, we changed both the rear calipers as they had siezed, but could not get a decent pedal, tried everything including a new master cylinder just in case we had pushed the pedal down to far an seals flipped over

After much head scratching it turned out that the calipers, even though they looked identical were slighty smaller, we got another pair sent up (different brand) and the calipers matched up perfect. Once on a couple of pumps and a solid pedal

Are the calipers you put on an exact match?

Peter