Just got new front brake pads and rotors on 1995 blazer. When braking, there is an ''air-like'' sound....pssssssh, when you push down on the brake. Needs further bleeding? Should we take back to mechanic? Please advise and thanks!

if you put new pads on with out resurfacing the rotors and the rotors are not smooth then until the pads wear to match the grooves your not stopping with full friction surface

air in the system wont make the brakes grind,you have done some thing wrong there.

Look through the openings in your front wheels and look at the front rotors-are they gouged up? You are probably running metal-to-metal, pads to rotors.
Chances are real good your rotors will have to be replaced along with new pads, but if you catch it early enough you might be able to have them machined, although nowadays that is hardly easy to get done and the savings usually is not as significant as it once was.

your booster diaphram has torn. replace booster and let us know if you have questions.

Rear disc brake pads offer better performance and are not as affected by moisture like conventional brake shoe style brakes are. Rear disc brakes are similar to front disc brakes. The main difference is that rear disc brake systems must incorporate the emergency brake system. There are two methods widely used for the emergency brake with rear disc systems. The first system is a brake shoe inside the brake disc that is actuated by the emergency brake lever. The second is a screw style actuator inside the brake caliper. When activated the brake pads are forced into the brake disc and held tightly by the emergency brake lever.
READ COMPLETELY BEFORE STARTING
Step 1 - Identify Rear Disc Brake Components
Rear disc brake assembly includes; rear brake disc, rear brake pads, brake caliper mount and a caliper mounting screw. (Note: Some vehicles do not have the rotor mounting screw.)
Step 2 - Removing the Rear Brake Caliper Mount Bolts
To replace rear brake pads and rotors the rear brake caliper needs to be removed. First loosen the rear brake caliper mount bolts and remove them. Turn counter clockwise.
Step 3 - Lift Rear Brake Caliper from The Caliper Mount
After the caliper mount bolts have been removed, gently lift the brake caliper from the caliper mount. Inspect the caliper slides; they should move freely in the caliper mount. Remove rear brake pads and hardware.

Step 4 - Removing Caliper Mount Bolts
With a socket wrench or other appropriate removal tool, loosen the rear brake caliper mounting bolts. Remove bolts and lift the caliper mount and remove it from the vehicle. Remove the retaining screw from the disc mounting hole. Tap the rotor gently to release any rust that has accumulated between the rotor and bearing hub. Lift brake rotor from wheel hub holding on tightly, using both hands. You do not want to drop the rotor.

Step 5 - Removing Rear Brake Rotor
Remove the retaining screw from the disc mounting hole, tap the rotor gently to release any rust that has accumulated between the rotor and bearing hub. Lift brake rotor from wheel hub, hold on using both hands and do not drop.

Step 6 - Install New Brake Rotor
Check the new rotor against the old brake rotor to make sure they are the same size. Clean the mating surface on the wheel hub before the new brake rotor is installed. Reinstall rotor retainer screw.
Step 7 - Reset Rear Brake Caliper
Before new brake pads can be installed, the rear brake caliper must be reset. The reset tool winds the piston back into position so the new brake pads will fit. This style of brake caliper will not compress with a clamp tool; it can only be reset with the proper reset tool.
Step 8 - Reinstall Rear Caliper Mount and Install New Rear Brake Pads
After the caliper has been reset, reinstall caliper mounting bolts and make sure the bolts are tight. Then match up the old brake pads to the new brake pads. They should be exactly the same except, of course; the old ones will be worn out. Check the new brake pads for proper fit and install any brake hardware that is required.
Step 9 - Remount Rear Brake Caliper
Reinstall the brake caliper, align brake pad hardware and reinstall caliper mounting bolts. (Note: align the rear peg of the brake pad to the groove in the caliper piston.) Recheck and retighten all caliper and caliper mount bolts. Bleed brake system to relieve any air in the system. Before driving the vehicle, push the brake pedal down and let it up slowly. This operation forces the brake pads to travel to the brake rotors. DO NOT DRIVE VEHICLE until proper brake pedal operation resumes. When test driving vehicle listen for any unusual noises during the operation of the brakes.
WARNING! Always have the vehicle under inspection on level ground, in park with the emergency brake on. Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when anyone is near the battery or engine. Always have an operational fire extinguisher close by, obey all first aid instructions in the event of an injury. Never stand in front or behind a vehicle when cranked over or running. When engine is cranked over keep hands and clothing away from rotating components. Never move a car without proper brake pedal operation.

have you had problems getting pressure to the rear brakes before? if yes it is proportion valve problem if no try to sequence bleed the entire system starting with tire left rear, right rear, left front, right front. do the sequence 2-3 times.

Small rapid vibrations will sound like a squeal, like chalk on a black board! There is a product that is placed on the bake of the brake pads that will absorb this vibration. You can use silicon in a tube or gasket silicon in place. Nick name is "brake spooge"

you need to have new pads and rotors installed,the rotors is where your vibration is coming from

Sounds like air is still in the brake lines, the air sound that you hear is the power assist, but the brake pedal needs to be "high and hard".

if the pedal goes to the floor, that is not good. Sometimes, when pumping brakes for bleeding purposes, the master cylinder gets damaged, as the piston goes past it's normal "travel zone" and gets damged on deposits.....

Now, with that being said, if everything was perfect, brakes are typically not as firm after replacement, due to differences in new pads/shoes and old rotors and drums. Pedal to the floor, however, is never okay.

Doc

have you checked to see if the vaccum hose from the intake to the booster is connected properly with no cracks or damage to hose?