VOLVO 850 1983. When I brake the car keeps on moving especially when I am reversing. When the car is moving there is tap sound especially when I am turning the car it sounds very loud.

Is the knocking sound when the car is moving or sitting still as well? Does the grinding sound happen just as you put the car into reverse or does it keep grinding?
These transmissions are very problematic, especially if they are not properly maintained. The most likely candidates are a cracked flywheel or a broken drum inside the transmission. Either way, it sounds like the transmission will have to be removed to pinpoint the problem.

Is it just in reverse? Are your rear brakes drum or disc?

sounds like you have bad wheel cylinders. or the brake hardware is bad.

sounds like an axel bering-bring it by a parts place and ask someone-ther preatty good at helping

It sounds like you have a stone lodged in one of your wheels.They can lodge themselves between the brakes and backing plate
.Possible solution ,try reversing and slam on the brakes .This has worked for me several times. Good luck

your problem lies in the internal parts of your transmission which are the clutch linings, they are already worn out and starts to slide.

Check the front and rear transmission mounts on the transmission.Excessive play will make the car bang when it is put in gear,especially reverse.Put the hood up and have someone watch the engine movement in forward and reverse.Make sure they stand to the side of the car. With your foot firm on the brake ,give it a quick push and release on the gas pedal that takes the rpm up to 2800 to 3000 rpm.If the engine moves more than 1/2 inch,suspect the mounts.
I have seen this before.
Also volvo have a software upgrade for that car.
Our shop had one that had the "check transmission".lit up.
After volvo upgraded the software it was fine.
The cost was 90 dollars.
That is a "Dealership only" information.
The power steering can be noisy as well.
Drain the power steering system and add synthetic fluid.
You will be amazed at the difference.

removedisc/drum check to make sure linings are secure on shoes bonding can fail this will cause brake to lock make sure shoes are secure on backplates hold down clips can go weak also make sure pull off springs are not weak loosen hand brake adjuster fit drum adjust up shoes on adjuster wheel till brake locked then back off so wheel spins freely re-set hand brake cable

Sounds like your vacuum assist brakes diaghram has sprung a leak. Pull the hose to the assist and plug it with a bolt or something. Then try it.

The only thing I can think of is something got stuck in the caliper , rock or some other goofy thing.Good luck