Brake Clunk Upon Initial Press

[m3f_BlackHawkRacing]

I recently pulled and ended up rotating my front pads (left to right, right to left) in an effort to even out some of the taper. After re-assembling and bleeding the calipers, I took the car for a test drive and noticed a single, mild yet audible, clunk when I depressed the peddle.



This took me by surprise so I released and hit the peddle again. Nothing. Next light (less than a 1/4 mile), same thing happens. Clunk on initial press but nothing if I repeat. I circled the block and pulled back home to re-check all my torques; all of the bolts were where I originally tightened them to.



I then took the car on another drive and did a few pulls to make sure they still performed well. No issues (full breaking power and good pedal feel) yet the clunk still exists if I wait a little bit between peddle touches.



Anyone have any ideas?



Also, rattle clips are still in place.

[m3f_tykluss18]

"I've never heard of someone rotating brake pads, and that won't likely be good for the calipers" - My Dad (27 years as a brake R&D engineer)


I would put them back the way they were. If the clunk goes away leave them how they were initially and don't rotate pads anymore. If the problem doesn't go away after you switch them back then you caused something while you were disassembling and reassembling them.


If you still want to leave them "rotated" then I would read how to properly bed them to the rotors and do that. Then see if they still clunk. If they still clunk my guess is that there is some slight caliper flex (but I didn't consult dad on that one).

[m3f_BlackHawkRacing]

I've done it several times before and never had an issue, it's simply to even out the taper you get from sliding calipers. Trying to make them last as many events as possible. Also, I re-bedded them after the reinstall.


But your dad's point/advice is noted. EDIT - Although thinking about it can you ask him to elaborate how it would be bad? It's just like using a set of used pads. You don't know which side the PO had installed where and with things like a BBK, pads often fit in any corner. And for clarification I didn't swap them inside for outside ect. I put the outside driver side pad on the outside passenger side pad and ditto with the inside pad.

[m3f_englishtom1596q]

your brake pads wear specifically with the rotor. When you "rotate" them the wear patterns no longer match causing them to wear differently again. By doing this you're reducing the contact patch of the pad to rotor because they are no longer matched and decreasing your brake effectiveness.


If your getting tapered wear then your calipers aren't sliding properly. you clunk is probably the pad rotating from it sitting like l/ to ll against the rotor. the square cut seal is holding the piston out and probably the reason you don't hear it on a second brake application.

[m3f_Solaris99]

A lot of people have to rotate pads to get more life out of them for track events. I sure do with the Wilwood calipers. My inside pads will be paper thin on the leading edge while the trailing edge has 75% left. Until you up your game with expensive calipers that have differing piston sizes, this is a fact of track life.

[m3f_BlackHawkRacing]

your brake pads wear specifically with the rotor. When you "rotate" them the wear patterns no longer match causing them to wear differently again. By doing this you're reducing the contact patch of the pad to rotor because they are no longer matched and decreasing your brake effectiveness.



If your getting tapered wear then your calipers aren't sliding properly. you clunk is probably the pad rotating from it sitting like l/ to ll against the rotor. the square cut seal is holding the piston out and probably the reason you don't hear it on a second brake application.

Correct me if I'm wrong but Isn't that the point of bedding? To leave a transfer of material and match the grain pattern of the pad to the rotor. That's why I have to re-bed them when I switch btwn track and street pads.



Also, while that might to true for street cars, the taper is very common among track cars, which this is.



But your last comment brings up a good point. I did find another thread with similar issue to mine. What ending up happening was the piston side pad wasn't grappling the piston well and would move slightly while the car wasn't on brakes but then get reset upon the pedal being depressed. Going to check it out

Until you up your game with expensive calipers that have differing piston sizes, this is a fact of track life.

Truth. Considering going AP in the spring but it's such a large initial outlay. Which wilwood are you running? Trying to justify the AP but Massive had a good price on a front BBK untilizing the SL6R caliper.

[m3f_the-git]

It is called pad knock back.

First issue could be the swapped pad having and presenting an incorrect profile to the rotor...too much space on one portion due to the dissimilar wear patterns.

Second issue might be a worn component in the front suspension causing a vibration.

the vibration may encourage piston retraction.

the rotor may have an uneven wear across its surface...tends to "hammer" the pad/piston away from the rotor surface.



m

[m3f_Aavi]

are you getting the clunk at low speeds? you get one sold clunk/jarring/thud once you brake and then you dont feel it later.


If this is the case - check your brake pad backing plate, it might have separated from the pad material, i had this issue when i had an E36 M3/4/5

[m3f_Solaris99]

Truth. Considering going AP in the spring but it's such a large initial outlay. Which wilwood are you running? Trying to justify the AP but Massive had a good price on a front BBK untilizing the SL6R caliper.

These are the Superlite 4R that are used in the UUC kit. The previous owner had put these on and I think it is the UUC kit. Other than the taper, I've had no issues with them.