I have a 87 dodge dakota, 3.9 carb. It has a new booster and master cyl. but still runs like **** when you put it in gear and the brakes are still wierd acting and seems to still be getting air in the lines somewhere even though we have bled them several times.

that's odd ,try disconnecting the vacuum hose at the booster chamber and see if they release,had a truck do that once,the master cyl.seal at the booster failed and the brakes were applied.

the reason may be : the brake booster is lack of pressure.

It's the master cylinder, Theresa. It will need replacing, because the internal seals are not holding against pressure.
It is not a job for just anybody, but somebody with some experience in bleeding the master cylinder and then bleeding the individual wheel brakes could do it. It's a procedure for getting all air out of the system after replacing parts.

You sure you have the correct booster
Or use the same rod
You should not have to bleed anything,you
didn't open the brake system
Now you need to bleed all 4 corners,never
the master,that is a myth.

Ever consider the engine has to be running for
the booster (vacuum remember) to work,
and you can not bleed the brakes without
the engine running as you have to have
someone push the brake pedal thus the booster

the rear brakes shouldn't be apart if your pumping
the pedal,now you screwed up the brake switch position

use a flare wrench and remove the two brake lines
then remove the the two nuts that hold it to the fire wall
then remove.
then remove the master cylinder reservoir because your
going to have to put it on the new one
drain out any brake fluid from it
in stall the reservoir on the new master cylinder
now you'll have to prime the new master cylinder
put the master cylinder in a vise and put brake fluid into it
now place your fingers over the two holes that the brake line go into
use a large phillips screw driver and push the piston in and out about 10 times
but do it slowly. make shore to keep your fingers over the brake line holes .
now install it back in
remember to bleed your brake system when your done

Master cylinter is shot is my first thought. if it has been replaced with a referb.. replace it again. make sure you bench bleed the master cylinder before putting it on.. if it's new, you have a ton of air in the lines.. bleed the pass rear first/ drivers rear/ pass front/ pass rear.. FYI your brakes/ tires should never lock up, you have ABS.

did you bleed the master cyl. before or during installation? bleed brakes in proper order?RR LR RF LF? does it have a power booster between master cyl.& firewall?check for vacuum to booster.when ABS isn't working you should still have brakes.suspect power booster diaphram.

always bleed front driver side first, front right,left back
right back.
make sure you always have oil in the master

have you checked the power booster and the master cylinder> what about the wheel cylinders> have you looked at them to see if theres a leak somewhere?

master cylinder maybe or the brake lines going to the back of the truck, but most likely the master cylinder, check to see if you see any brake fluid on the front of the brake booster or any paint peeling off the brake booster