My 1990 Volvo 760 turbo has a problem. The brakes are sometimes hard to depress (although they work). When this happens, there are accompanying problems with sluggish acceleration and difficulty with the automatic shifting. What’s happening?
You have a vacuum problem
I suspect you have a vacuum leak, possibly a broken vacuum hose/fitting
A competent shop (not necessarily a Volvo shop) should be able to handle this
Ask the mechanic to check for a vacuum leak in the brake power booster diaphram too.