Help with violent shaking when braking pls

[Estoril]

I'd be surprised if spring clips were a cause. I'll be interested to see if pads are tapered at the outboard edge. Of course make sure pad ears are fully seated and not binding. For a street car, I'd just stick with Zimmerman blanks. Drilled rotors buy you nothing and are more prone to cracks.

I *think HF sells a dial gauge IIRC. Might be able to borrow one from a retail shop with a program. Make sure the hub face is fully clean with zero corrosion or crud. Same for rotor inner mount surface. Same for caliper pins straight, no significant rub marks and clean. I know you know most of this - just reminders.

[eacmen]

Casting a vote for uneven pad deposits. Dial gauge should see it.

Historically for me however doing an aggressive brake bed in usually fixes it. Sounds like you've done this already.

The 996 calipers are 6pot? Maybe you have a seized piston causing uneven pressure of the brake pad on the rotor?

If you're feeling adventurous you can bolt just the rotor to the rear wheel hub and take a flat block with sandpaper to the rotor faces while the engine is running and in gear. Its ghetto but it can work in a pinch if you dont have access to a rotor lathe.

[SQ13]

Think I found the culprit. The difference is about 9-9.5-thousandths of an inch. Photos were taken before I started taking things apart, but cleaning mounting surfaces, pins, etc didn’t change it. Shining a very bright light on the rotors allowed me to get a better visual of the surface, and I believe the reason why the outer portion of the ring is more shiny and consistent is bc the pad deposits have worn off more than the center.

The 996 calipers are four piston. The pistons and seals, hardware, pads, and rotors looked fine and measurements for pads and rotors were near new. This was a freshly rebuilt setup that was installed shortly before the collision fwiw. Given that the rotors are fresh, should I just have a shop resurface them? Or throw on PFC 11s and do a few hard stops (been meaning to buy 11s for a while now lol)?

What are the non-drilled options for ZCP fronts, just Girodisc and PFC?

[Estoril]

I'd do a full bedding by the Zeckhausen procedure with PFC-11s , if your weather allows it (and assuming you actually need the -11s).

[eacmen]

Ideally find a shop with a brake lathe and have them turned. Should be cheap.

hawk blue pads are the go-to to remove pad deposits. never tried pfc11 for this purpose, they aren't cheap pads

[bigjae46]

Ideally find a shop with a brake lathe and have them turned. Should be cheap.

hawk blue pads are the go-to to remove pad deposits. never tried pfc11 for this purpose, they aren't cheap pads

Shops won't want to turn drilled rotors since they tend to destroy the cutting tips which will turn the job into a profit loser. The edges of the holes aren't very nice to the tips.

[Slideways]

Shops won't want to turn drilled rotors since they tend to destroy the cutting tips which will turn the job into a profit loser. The edges of the holes aren't very nice to the tips.

This ^

Abrasive hawk blue or track pads will do the job in a few stops.

[SQ13]

Well fuck my life then I guess lol. In that case I’m going to grab the PFC11 fronts since I need them for the track anyways (have the PFC11 rears from when I ran StopTech C43 F/996 R setup).

F and R pads should be an easy 15-20 min swap, and if following the Zeckhausen guide doesn’t help then I think the next step would be to buy Girodisc fronts and Centric rears.

[Slideways]

Well fuck my life then I guess lol. In that case I’m going to grab the PFC11 fronts since I need them for the track anyways (have the PFC11 rears from when I ran StopTech C43 F/996 R setup).

F and R pads should be an easy 15-20 min swap, and if following the Zeckhausen guide doesn’t help then I think the next step would be to buy Girodisc fronts and Centric rears.

Track pads are abrasive when they are not bed in. Bedding in will transfer pad material to the rotor.

[heinzboehmer]

Yes don't bed them in. Drive the car around town with the brakes cold until they really start squealing. That's when the existing pad material on the rotor has been removed.

[SQ13]

Yeah, sorry I was referring to this article where they mention removing deposits using track pads. Will try to clean the surface during the abrasive/cold period and report back.

https://www.zeckhausen.com/catalog/index.php?cPath=6446_6444

Didn’t know that squealing indicates that the rotor surface is clean and ready for bedding lol. That’s good to know.