thx..
my last mechanic said this too & pulled the square mutipin thingy..
it's fine for me since I'm a good driver & only driving very local at traffic speeds in LA..
so no rain (usually) or snow.

Re-reading your advise, sorry but just to be clear...

So you're saying by loosening the master cylinder from booster and it rolls AND brakes normally then it's the booster that needs replacing?
BUT if it still has the problem with brakes active then it's not the booster.. or still could be?
Sorry ...

Sweet!
The booster is not very expensive..
but the ABS Hydraulic unit is very expensive.

I'll probably buy one of these from rockauto.com
https://www.rockauto.com/en/catalog/volvo,1990,740,2.3l+l4+turbocharged,1288414,brake+&+wheel+hub,power+brake+booster,1884
I think this is the right one for ...

THANKS so much for reply!!!!
(I've taken this to 3 mechanics and had 3 different replies.
last 1 said he put it on lift and it was all wheels.)

Hmmm, a few questions, I hope you don't mind..
+ Have you heard or seen this behavior before, odd it only does it after warming up?
+ Will this loosening ...

I have a very old 1990 Volvo 740 SW Turbo with ABS…
(also called a 2.3L L4 SOHC 8V TURBO).

It generally drives great,
the problem is after driving for 15 mins or so and after things warm up
the brakes start to activate on their own (argh)!
Only slightly at first but gradually more and more ...