Knocking brakes

[Sycostang67]

I figured I would throw this problem at some fresh eyes.  I have a 1967 mustang, I recently did a front disc brake conversion on it with slotted rotors and 4 piston calipers.  On the first test drive, there was a knocking sound right away when applying the brakes.  Upon investigation I had misread the directions and put the rotors on the wrong sides.  Swapping them made the sound go away instantly, however it came back a few days later.  This time I swapped the pads around and once again the sound was gone but came back a few days later.  I have isolated the sound to the passenger side, at which point I swapped the pads on that side, inner vs outer.  The  noise went away and came back after a few days.  This time I removed the pads, beveled the edges and swapped them again.  The same thing happened, no sound then it came back.  I have a 4 page thread going on my mustang forum, apparently a few other people are having this problem as well.  I even have the gentleman who sold the kits trying to help out as he said he's never had this complaint until recently.  The sound can be felt through the pedal and is loud enough to echo off buildings.  It's only present when applying the brakes and the frequency will slow down with vehicle speed.  I've included a video of it happening.  Any ideas you guys might have would be appreciated.

 

 

[Mopar1973Man]

Personally I'm not a fan of slotted rotors. I would have the rotors checked for run out. I'm going to guess the rotors are deforming at the slots where there are the thinnest and weakest. Little heat and now the knocking starts. Changing rotors and pads are disturbing the problem to go away for a short time. If it is possible to get standard non slotted rotors I going to bet the problem will be gone.

[CTcummins24V]

I had this happen on the Dodge this spring. Caliper was hitting the wheel weights only when brake was applied.

[Sycostang67]

Well I just ruled out the wheel weight, I only have one and it doesn't come anywhere near touching the caliper.  I guess I will take the rotor in and have it turned just in case.  If that doesn't work then I guess I will have to blow an extra $200 on some flat rotors. 

[Royal Squire]

I would be talking to the seller especially if its not just you having this problem 

[Sycostang67]

I have, he's trying to help as well.  It's just that he's sold hundred of these kits with no issues but suddenly 5-6 people are just now having problems.  We are all trying some different things to see if we can fix it or find the cause. 

[Royal Squire]

Is he willing to send you another kit?

[Sycostang67]

I wouldn't want him to send me another kit, I'd rather find the defective part and have him send me a new one of those.  Since it's a group of people who have recently purchased this kit, I'm wondering if something from the supplier is messed up.  Hoping we can get this figured out before anyone else has to go through it. 

[Mopar1973Man]

I'm still on the bet it the rotor are either cracked in the slots and deforming as they heat up causing the knocking noise. Again you'll have to pull the rotors and have them check for runout and cracks. Even if the runout is good you could still have a crack that only deforms with braking heat causing the knocking noise. You could have him send a set of rotors but being slotted they will most likely do the same thing again. 

[Sycostang67]

It will happen even if the rotor is stone cold though.  I live on the corner, I back out of the driveway, pull forward 20' to the stop sign and it's already knocking.  I was thinking of having the rotor turned to make sure it's flat and I can look for cracks as well. 

[Mopar1973Man]

Then it should show up runout if you have them checked now then.

 

If you want to see quality brakes do a search for "Brembo Brakes". I know it's way beyond your price range as well as my own but you'll see what REAL drill and slotted rotors look like. Not the cast rotor you most likely got now that are going to be prone to issues. 

 

 

Edited September 6, 2018 by Mopar1973Man

[Sycostang67]

I just decided to order some new non-slotted rotors.  I'm getting tired of pulling the wheel every 2-3 days to change something.  Hopefully that will fix it and I can enjoy my car until winter. 

[Sycostang67]

I replaced the side that was knocking with a non slotted rotor, knock is currently gone, will continue driving to see if it stays that way.  If does then I will swap out the other rotor as well.  The car isn't pulling either way so I didn't see an immediate need to change the other one yet.  If this doesn't work I can at least return one rotor. 

[Sycostang67]

I haven't had anymore issues with the knocking and I have both non slotted rotors on now.  We surmised there must have been some kind of fluke in the machining process.  Dennis, the guy who sells these kits says he orders 2000 rotors at a time and has only had 8 people experience this problem.  He offered to send me new rotors or reimburse me for the ones I had purchased.  As I am tired of taking the wheels apart, I opted for the reimbursement.  I could probably get the other rotors turned and use them but the car works so I am happy for now.  

[Mopar1973Man]

11 minutes ago, Sycostang67 said:

could probably get the other rotors turned and use them

 

I would have those rotors checked for cracks and runout before machining or thinking of using those rotors. I'm betting the slotted rotors either cracked or they are not machined true at all or both.