How to set up new brake shoes on volvo 850,they keep jamming when traveling forward but not reverse,

The rear suspension has no drive parts as your car is a FWD, front wheel drive. There are parts on the wheel axles which have bearings and also Brakes.
If you have rear disc brakes, the inner part of the rotor has a drum for Emergency brakes and these linings often peel off their brake shoe. The loose lining can get ground up in the turning rotor hub. The Emergency brakes are pinned to the brake backing plate and can clunk when the shoes shift. If you have rear drum brakes the shoes may be out of adjustment or worn out leaving room to rock as vehicle direction changes.
Bearings, excess play can cause noise. Suspension brackets, bushings within the mounts for these components can wear out. When parts are moving in 1 direction a "set" is grooved into the rubber parts. Changing direction of travel will unseat the part and make noise.
Traveling sound. You may be hearing a sound you suspect is in the rear of the car, but is actually a cradle mount around the Firewall. Sound travels through metal.
You need to get the rear wheels off the ground and check for play in all the components. For the cradle mounts, have someone ride the brake pedal and shift the transmission forward and backward to see if noise is generated or excess play is seen.

DO NOT DRIVE THIS CAR! Your brake pads/shoes are worn beyond reason. There is a good probability the disks/drums are damaged as well. STOPPING is way more important than GOING. Get this car repaired before you cause property damage, injure yourself or others. The TAP sound you report is probably your car warning you of this condition, as if not being able to stop was not enough.

Have your repair shop come get the car with a tow truck ... do not attempt to drive it to the shop.

This is a very dangerous condition.

Thanks for your question @ FixYa.com

is it manuel or automatic? sounds like internal trans gear problem. gonna have to bite the bullet and take it to transmission shop

Yes, the brake shoe clearance has to be set at the minimum and the brake edges should be chamfered (angled) where it contacts metal in either direction, the shoes get hung in reverse if they are loose because of the movement of the entire brake assy, and they kind of get cocked & locked until you apply the brake. Once the brakes are adjusted correctly, there is no room for them to lock.

Try & pull up a hair on the handbrake lightly when this happens & it should remove the bind by centering the shoes within the drum.

Minimum brake clearance is the cure. Sometiimes if parts aren't replaced, the fit isn't perfect due to the lip remaining which prevents intalling the part at minimum clearance.

good luck

Remove the brake drum and check the brake shoes. I had a similar problem with my 99 Sportage. The brake shoe separated from the backing and was jamming the brake drum. A new set of brake shoes fixed the problem.

remove panel at back of centre console you will see adjusterjcheck first if hand brake shoes can be adjusted in drum like on the 850 with wheel off and torch revolve disc if there is a an adjuster use this before adjusting cable

Forward Braking
The actuating force for the wheel brake is generated during braking of the towing vehicle, as the trailer tends to overrun and
pushes the drawtube in. This force is transmitted to the expander devices in the wheel brakes via the overrun lever, brake rod,
compensator and brake cables.
As a result, the brake shoes are pressed against the brake drum. The resulting friction from contact of brake linings and drum
produces the required braking.
On releasing the brake on the towing vehicle, the drawtube returns to its original position and the brake shoes are released from
the drums by means of the tension springs.
Auto-Reverse
During reversing the drawtube is pushed in and the brake shoes press against the drum (as in forward braking).
When the trailer wheels are in reverse, the reverse rotation, combined with the friction generated from drum and lining contact,
causes the sliding shoe to slide on its carrier towards the adjuster.
This displaces the sliding shoe radially inwards away from the drum. The drawtube may then travel fully to its end stop without
applying further force to the brake shoes and the trailer can be reversed without any difficulties.
Changing direction from reverse to forward travel results in the drawtube being pulled out, allowing the sliding shoes to be
returned to the forward braking position by means of the tension springs.
From this guide which contains more information also.

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.

I would first bleed the brakes again -- maybe there is still a small amount of air still in the lines. If this doesn't work and there is no visible leak, I would have to suspect the master cylinder is "leaking by" internally. A new one shouldn't be failing already, but it's happened before.

Check you transmission fluid level and if it's not your transmission, I'm thinking that your brake shoe lineing in the rear brakes may have separated and is jamming up aginst the drums when your trying to back up. Sorry can't halp you with any more, good luck and start with that and hope it help's.