1988 Volvo 740 brakes have stumped the mechanic

My old Volvo has an intermittent problem of the front brakes dragging. The drag gets harder and harder, until, once, I could only drive at 20mph. I have replaced the pads, rotors, calipers , hoses and now my mechanic says” maybe it’s the master cylinder” But it doesn’t show those classic symptoms of pedal going to floor or feeling spongy. If anything, it feels hard when this occurs. I keep asking about push rods and boosters but I’m always told it isn’t that. What’s left? Mechanic says time to dump it but this last round of repairs has cost close to $1400. and I hate to give up on my old trusty wagon

It sounds like your mechanic is stumped. I’d bite the bullet and take it to a Volvo dealer.

It may very well be the master. I had the same problem on an old Nissan. Firm pedal but the front brakes dragged. The car didn’t have much power so it was noticeable.

If it’s the original master I’d just change it on principle.
Everything with rubber or plastic elements is suspect at that age.

Try disabling the ABS to see if it has an effect.