I changed the front brake pads on my parents' Chevy 1500 Express van yesterday and they seem to work fine now except for a thump that you can hear and feel when you step on the brake pedal. I didn't open up the line to compress the piston, just used a C-clamp to push it back into the caliper, so I figured I didn't need to bleed any air out of the line. Everything is on tight and appears to be normal. I've replaced brake pads many times before and have never had this problem.

 

Now days with antilock brakes , your not spouse to push the brake fluid back into the system but open the bleeders to compress the caliper , the newer, the bigger the problum , but the clunking sounds like somethings not rite , try spining the wheel by hand and have someone touch the brakes to see where the clunk is coming from .

 

Thanks John, I'll give that a try.

 

The advice on not compressing the caliper without opening each corresponding bleeder is all to often overlooked. It both forces the dirt from the caliper back into the front antilock valves, but it can also jamb the valves and burn out the controller. On a Chevy that is $925 just for the part, then add an hour labor minimum.

Once you have done the old C-clamp routine without opening the bleeder you will need to have the system bled using a power bleeder. You want two things to happen, the caliper to be washed clean and all the particles of crud you forced back into the ABS valve to be expelled.

The thump you describe is likely not related to either of the above though. I would expect the piston in the caliper has worn the cylinder a bit tapered and is snapping and causing the pads to lock and shift when you depress the brake. Also, carefully check your wheel bearings, if they get worn or loose you can get the entire disk assembly and hub shifting when you nail the brakes.

 

How did you tighten the wheel nuts? Try jacking the vehicle up, loosening all the wheel nuts, give the wheel a good shake and then just snug the nuts up. After you have snugged them up, tighten them in two stages by going to opposite nuts.
If you tighted the nuts in the wrong order, you could have inadvertanly warped the rotor.

 

Mexstan - Yep, lug nuts were tightened correctly (it's so much better only having to worry about 5 per wheel as opposed to 8).

RCW - Thank you for the comprehensive reply. I had my cousin help me bleed a little fluid out today and the pedal does feel a little firmer. The clunk is also lessened. My dad also said that it has done that before from time to time. And that's what it's doing now: intermittent. Doesn't do it every time you use the brakes, just once in a while.

If it has been doing it for a while, I'm glad it's nothing I did, but I'm going to tell my parents to have it looked at. The van has 69k mi on it and I think it's still the original brake fluid. The stuff is black.

 

Another thing to check.
Did you lube the back of the pads where the caliper touchs and the caliper slides with some silicone. Did you replace the caliper hardware? If you bought the GM pads they would come with all of the replacable dustcovers and such.

 

being a GM i would check all the steering linkage and the ball joints, they have a tendency to wedge and not look bad but jack the truck up and take a bar or pipe and pry up on the tire and see if you get any movement. also on the crack the bleeder screw loose when compressing caliper piston, unless the ABS is operating at the time you compress the piston none of the solenoids or dump valves are open. therefore no sludge can enter into the ABS unit, GM uses Kelsey Hayes and they do not allow back flow through the unit. the only time you have a hard time bleeding is if the master has been replaced and the prime in the ABS unit is lost, then you have to a Scanner or laptop to cycle the ABS solenoids and dump valves while pressure or vacuum bleeding to purge out all the air. Just finished brakes class and have done dozens of those jobs before.

 

Sounds like Chop might be on to something.
Loose front end components?
Remember when working under a vehicle use jack stands
DONT trust the jack especially if you are prying around with a bar.