Thump from front brakes sometimes when leaving a stop sign or stop light...

[rothsean]

Any idea what would cause a thump when I go from a stopped position with the brakes held (like at a red light) and start driving. It is a quick thump at brake release/movement...

Thanks,

Sean

[rdarlington]

I get that with a clutch press/release sometimes.

[Jonathan]

Caliper piston sticking maybe? Have your brakes been rebuilt recently (or do you know what their condition is?)

[vwdmc16]

Do you feel the thump or only hear it? Can you feel it in the pedal or the floor of the car?

[Doogie]

I'm thinking that when you come to a complete stop, then let off the brakes, the pads are still 'firm' to the rotor. When you give a bit of gas, the rotational force of the rotor 'breaks' the bond and they pad and rotor separate, giving you the clunk your hear.

I imagine air in the lines could cause that? (When you release the pedal, the plunger in the brake Master Cylinder pulls backwards, and the hydraulic fluid "sucks" the brake caliper pistons back off the rotors. If you have air in the lines, that air could prevent the "sucking action" that would pull the pistons back off the rotors.)

It could be a simple flushing/bleeding of the lines, or a replacement of the Front Calipers. (Rebuilding them is also very very simple)

Anyone want to confirm my theory? (I'm not a hydraulic specialist, but my brother is! :-)

Doogie

[jmettee]

Check to make sure your jack in the front compartment under the hood is secure. That is a common source of clunking in the front end.

Other than that it could be possibly a loose shock or less commonly a loose bolt in the front suspension somewhere. I doubt it would be something in the brake system, but you might want to check all the bolts on the calipers upfront.

[vwdmc16]

Hey thats right, I had a strange banging noise too under braking a few years ago, after two days of looking under the car I found I had left a small tool box in the trunk.


Doogie's idea is possible that there is a stuck caliper, But not from an air bubble. The retraction of the brake fluid isnt what pulls brake pistons back into the cylinders, it's the square cut rubber o ring around the piston that is deflected and pushes the piston back that minute amount it needs to move. Just the same calipers can stick if they are filthy or corroded. I had an old VW beetle with discs and the one wheel would stick when the pads got down below 3-4mm, the pistons were corroded on the base and the wouldnt slide back against the rubber seals when pushed that far. The quick and cheaper solution was just installing new thick pads sooner than needed so the good part of the piston was against the seal (instead of rebuilding with new pistons) but I was just 16 and had no money for new brake calipers.


Always check for simple stuff first like loose objects. Can you have someone else ride with you and narrow down the source of the noise?

[David T]

Hey thats right, I had a strange banging noise too under braking a few years ago, after two days of looking under the car I found I had left a small tool box in the trunk.


Doogie's idea is possible that there is a stuck caliper, But not from an air bubble. The retraction of the brake fluid isnt what pulls brake pistons back into the cylinders, it's the square cut rubber o ring around the piston that is deflected and pushes the piston back that minute amount it needs to move. Just the same calipers can stick if they are filthy or corroded. I had an old VW beetle with discs and the one wheel would stick when the pads got down below 3-4mm, the pistons were corroded on the base and the wouldnt slide back against the rubber seals when pushed that far. The quick and cheaper solution was just installing new thick pads sooner than needed so the good part of the piston was against the seal (instead of rebuilding with new pistons) but I was just 16 and had no money for new brake calipers.


Always check for simple stuff first like loose objects. Can you have someone else ride with you and narrow down the source of the noise?

Although the noise may seem related to the bakes because that's when you hear it, it may have nothing at all to do with the brakes. It could be a bad ball joint, sway bar bushings, the list is really too long to give you an item-by-item list. Someone has to do a thorough inspection under the car. Loose pads make more of a clicking noise. Maybe a bolt is loose or missing for one of the calipers. Maybe loose lug nuts. Just a few guesses.

[DMC5180]

Do you have general location as to where the sound is coming from? I have thump when releasing the brakes does not tell us much.

Does this sound only occur as you begin to accelerate from a stop? Manual or automatic?

possibilities include:

Loose object in trunk area

Loose caliper mounting bolts

Broken Transmission mounting bracket

Failed upper front shock mount (spax w/ thin backing washers)