Brake fluid leaking from pistons/seals normal?

[Hanakuso]

I recently bought the Essex Sprint AP Racing kit and I'm not sure if brake fluid leaking from the seals/piston is normal on race calipers. I bedding in my pads a couple days ago and took them out to inspect the pads. I noticed a small amount of fluid around the pistons on all 8 (4 on each caliper). It's also on the back side of the pads. I cleaned them off and next day drove around for 30 minutes and noticed some came back.

I also noticed a clicking noise coming from the driver side that is being caused between the pad and rotor. I did notice it has gone away slightly after bedding in.

[King Tut]

No. While they don't have dust boots, the seals in the piston bore should not be allowing any brake fluid past. How is the brake pedal feel? Have you noticeably lost any brake fluid? Is there a chance it is brake grease from the installation of the piston and seal?

[Hanakuso]

Originally Posted by King Tut

No. While they don't have dust boots, the seals in the piston bore should not be allowing any brake fluid past. How is the brake pedal feel? Have you noticeably lost any brake fluid? Is there a chance it is brake grease from the installation of the piston and seal?

Brake pedal feel is good. It hasn't faded or anything noticeable in decreased feel. At most maybe 1mm in the brake fluid reservoir has been lost but nothing else. I kind of doubt it's brake grease. I did not apply any grease myself and the actual fluid seems to be much more "fluid" then "grease". It's definitely not water tho

[JRitt]

Your caliper seals are not leaking. When AP assembles the calipers, they use brake fluid as a lubricant. The seals are coated in brake fluid and slid into the bores, then the pistons are coated in brake fluid and slid into the bores. In fact, they are actually soaked in brake fluid for a while. As a result, there's a little residual fluid on them when they're first installed. It will burn off, show up a little on the pads, etc. as you've seen. This is completely normal.
If a piston seal was leaking:

1. You'd likely not see it on 8 pistons unless every piston bore, seal, or piston was defective. The odds of that happening on any caliper is highly unlikely, and on an AP Racing caliper, infinitesimal. All calipers are pressure checked by AP at both high and low pressure before leaving the factor, and we inspect them at Essex as well.
2. If a seal was toast, you'd see more fluid than the tiny little ring on the back of the pad. It would leak steadily.
3. Your pedal would not be hard if the calipers were leaking. A hydraulic brake system is a closed system, and brake fluid does not compress. If the pedal goes down, it means one of two things A) there is a leak somewhere in the system, or B) there is gas/air in the system that is compressing. If the pedal is rock hard, you don't have a leak or air in the system.
4. Your fluid reservoir would clearly drop. If you actually did see any lowering of the volume of fluid in your reservoir, it was likely that the pads wore down a little, and you're pushing more fluid out into the lines as the pistons extend further.

No need to worry, you're fine.:happy0180:
Another common occurrence is for people to think their bleed screws are leaking. When you bleed your brakes, there is always a little brake fluid remaining in the tip of the bleed screw. If you don't blow that fluid out with compressed air, brake clean, etc., it will dribble out many times when you get the brakes hot...down onto the side of the caliper. Then it looks like the bleed screws were leaking...happens all the time.

As for the clicking noise...likely either: Pad clicking against J Hooks, pad moving back and forth in caliper a little bit. Just keep tabs on it and let us know how it is after the pads have settled in a bit.

[Hanakuso]

Thanks for the explanation! I had a feeling they used some type of fluid beforehand but it's reassuring to know the truth now.

I believe i found out my clicking noise is coming from a combination of the rotor having some dents on the outer edge, the j-hooks, and the pads are slightly loose. I inspected it carefully and the rotor or wheel isn't hitting anything it's not suppose to.

[CSG Mike]

Originally Posted by Hanakuso

Thanks for the explanation! I had a feeling they used some type of fluid beforehand but it's reassuring to know the truth now.

I believe i found out my clicking noise is coming from a combination of the rotor having some dents on the outer edge, the j-hooks, and the pads are slightly loose. I inspected it carefully and the rotor or wheel isn't hitting anything it's not suppose to.

Mine does the same thing. Unnerved me, but after double checking everything, I just accepted it as normal, and never looked back.

[Dave-ROR]

Mine clicked in reverse and the occasional bump only that I've noticed and it was just one pad moving a little. Mentioned the noise in my review too

[JRitt]

Below is a pic of the seal in an AP Racing CP8350 caliper (the ones used in our FT86 competition systems). You can see how close they are to the end of the piston bore. The little lip between the end of the bore and the seal, and the edges of the piston sometimes have a little fluid on them after the seals and pistons are installed. That's what appears on the pads.


As for the clicking, the J Hooks can sometimes have a little extra NVH vs. a plain disc or straight slots, but they also have superior bite and better heat distribution. From our website:

When you cut a slot or drill a hole in a disc you impact heat transfer. The area around the slot or hole acts as a cool spot when the disc heats up, which is not ideal. Ideally, heat is distributed uniformly around the disc so it can be hit with the cooling air that is pumping through the disc, radiate outwards away from the disc, etc. Cool spots create stress risers and increase the likelihood of the disc cracking. They also cause the face of the disc to distort unevenly, leading to uneven pad deposits, vibration, and judder.

Benefits
During exhaustive R&D testing, AP's J Hook design was found to create a constant pathway of evenly distorted material on the face of the disc. The hooks are spaced out as evenly as possible both around the circumference of the disc, as well as from the inside edge (where the hat attaches) to outer edge, with a slight overlap to promote even heat distribution/distortion. In addition to reducing cracking, the even heating of the disc also helps provide an even transfer layer of pad material on the disc when you bed them in.

Additionally, the J Hook slot pattern produces a greater number of leading edges for the pads to bite into vs. a traditional curved slot pattern. While this may lead to slightly more whirring or scraping noises from the discs when applying the brakes, the benefits of more even heat distribution, less propensity to crack, cleaner pad material transfer during bed-in, and more bite far outweigh the slight increase in NVH for the serious enthusiast.