Odd brake sound

[rogus]

I recently changed one of my front disc brakes on my 81 elky. Afterwards, while the car was still off the ground I spun the tire by hand and heard a scraping sound. It wasn't a continuous scraping sound but only at one spot as wheel went around. I would think this would mean that the disc was warped at one spot. Otherwise the scraping noise would be continuous as the wheel went around.

Am I right thinking this or is this normal right after replacing discs and pads?

 

[SS_Malibu]

Not normal. I'd pull it back off and reinstall everything checking it carefully. Compare it to the other side that is not rubbing.

 

[rogus]

Not normal. I'd pull it back off and reinstall everything checking it carefully. Compare it to the other side that is not rubbing.

Thanks. I wanted to double check with someone before tearing this back apart

 

[78Delta88]

Check the backing plate. If that got bent during install, it will create the scraping sound like you mentioned.

Either way, pull the wheel and spin the rotor and inspect for contact issues.

Did you turn the rotors to true them up?

 

[ssn696]

If stock rotors and calipers, did the car sit a long time? There could be a pitted spot where moisture got between the pads and rotors.

If Blazer knuckles and packaged hubs, make sure there is no dirt, rust or debris between rotor hat and the hub.

 

[rogus]

Check the backing plate. If that got bent during install, it will create the scraping sound like you mentioned.

Either way, pull the wheel and spin the rotor and inspect for contact issues.

Did you turn the rotors to true them up?

Thanks. The backing plate didn't even occur to me. The rotors were brand new, right out of the box, so having them turned hadn't occurred to me either.

 

[rogus]

If stock rotors and calipers, did the car sit a long time? There could be a pitted spot where moisture got between the pads and rotors.

If Blazer knuckles and packaged hubs, make sure there is no dirt, rust or debris between rotor hat and the hub.

Thank you. The vehicle did sit for awhile before changing the pads and rotors - would moister still be a problem?

 

[69hurstolds]

Used discs always have a degree of runout/warpage on them due to heat cycling when using the brakes. Even though they might look ok, you should resist just slapping new pads on and calling it a day. Get them trued, as mentioned as long as there's still enough meat on the discs. There is a minimum thickness for the discs. Factory discs have a minimum thickness of 0.980" after turning with a discard thickness of 0.965". Runout is max 0.004". If aftermarket discs, consult the manufacturer. Sometimes min. thickness is cast into the part somewhere.

Truing will take out any high spots, and minimize any pulsations felt in the brakes when stopping. You do not want to get to the point to where you start to step on the brake and you feel a ton of shuddering. Truing the discs is designed to take the slightest amount of material off just to get them to a point where they run straight, aka "true". Turning trues the discs as well, but usually you're taking a slightly bigger bite to refinish the entire surface a certain amount to get rid of grooves, etc.

 

[rogus]

Used discs always have a degree of runout/warpage on them due to heat cycling when using the brakes. Even though they might look ok, you should resist just slapping new pads on and calling it a day. Get them trued, as mentioned as long as there's still enough meat on the discs. There is a minimum thickness for the discs. Factory discs have a minimum thickness of 0.980" after turning with a discard thickness of 0.965". Runout is max 0.004". If aftermarket discs, consult the manufacturer. Sometimes min. thickness is cast into the part somewhere.

Truing will take out any high spots, and minimize any pulsations felt in the brakes when stopping. You do not want to get to the point to where you start to step on the brake and you feel a ton of shuddering. Truing the discs is designed to take the slightest amount of material off just to get them to a point where they run straight, aka "true". Turning trues the discs as well, but usually you're taking a slightly bigger bite to refinish the entire surface a certain amount to get rid of grooves, etc.

Thank you. These are brand new discs and brake pads though.

 

[69hurstolds]

Check your runout. If it's greater than 0.004" you probably need to true them up. Even brand new rotors can have slight issues. Key is, a slight drag like that might be caused by 0.002" runout for example, so it may not be a big deal.

Here's only ONE video of many showing you how to check it.