Brakes on old international d1510

Have just acquired d1510 international and brakes require large effort to depress pedal .any ideas on where to start

Hello Guido,
If that is with the motor running, I think the first thing to look at is clearance between brake pedal linkage and body, then see if the brake booster is working. Is master cylinder filled to correct level with CLEAN brake fluid? Check that brakes are adjusted properly.
After that, maybe pull drums off and check for worn-out linings, broken springs, stuck cylinders, etc.

I will be working with owner of D1510, 6 cylinder, today and will ask him about brakes and your V8 question.

As they say in the classics (or is that in old newspapers) watch this space!

Happened on my C1600. It was a collapsed flexible brake line.

Easy to tell if the booster is working.......shut off the motor,and push the brake pedal down slowly four or five times,pedal should get much harder to push as vaccuum is lost.....you should hear the booster whistling too,as air goes in or comes out ,or whatever.......If the booster isnt working,first check the vacuum,if Ok its likely the small slave piston is stuck.......even if you get the booster resleeved,they dont do the slave cylinder in the booster casting.