Ok, so I was at the track yesterday and I experienced a weird brake pedal feel/actuation anomaly. Ok let's go over some basics: Calipers: OEM, JCW in the front Rotors: OEM smooth surface Pads: XP10s in front, XP8s in read Lines: Stainless Fluid: Motul RBF600 and fresh Temps: Definitely hot ~94F, towards end of last session. So maybe, 10% of the time I experienced a brake pedal that seemed high and hard. So I would have to use more pressure to get through this 'spot' and then the pedal and brakes would work normally. So for a split second when I would go to throw out the anchor I did not have much to work with, sometimes when this happened I would end up just braking a little deeper and I would have to brake much harder to catch-up. One time however, it sent me off track for a little gardening. :mad5: Anybody ever experience anything like this? Do I just need to bleed them more, like between sessions, or what? Of course they work fine on the street and almost all of yesterday on the track. Also, when the pedal was 'high and hard' there was no notchiness or anything like that, it was still smooth. Brake booster going out? When you boil the fluid at the caliper, does this cause a hard pedal or a mushy pedal? I have not touched them yet since yesterday's track adventure, but if I get some air in the line I guess I just boiled the fluid.
From your description it is difficult to understand what was going on. If you are having brake issues there is normally one of two scenarios that you will encounter. The first is a hard pedal, but the car doesn't slow down as expected - this is they symptom of brake pad fade. The second is either too much pedal travel before the brakes "engage" or the pedal goes all the way to the floor. In both the increased travel or the case of the pedal going all the way to the floor, there is very little resistance against the pedal. This is symptomatic of boiling your brake fluid. My experience with boiling your brake fluid, is that once they cool down the pedal normally returns to normal for street driving. The danger is once you heat them up again, the air will come out of solution again and you will experience a softer pedal once again.
Well, a little extra brake bleeding can never hurt. I guess one thing to try is to bleed them after a session the next time I feel the weird pedal.
It could be pad kick-back, on hard corner exit flex in the wheel bearing or rotor run-out can press the pad back, so the next need for the brake, extra pedal movement is required to set the pad. The test for this is to tap the pedal a couple of times before the spot where you are experiencing odd pedal feel and then apply the brake, if that cures the issue, it's time to replace the front wheel bearing and/or the rotor.
One bit of evidence of the higher temps is a simple one. After each session as per norm, I check the tire air pressures and adjust. This is the first time that I was NOT able to use my bare hand to remove the metal valve cap, it was just too incredibly hot. I have never heated the wheels up as much as I did yesterday, it was crazy.
I still have a Genesis Technologies Brake Temperature Paint kit that I'm willing to share for only cost of shipping. The Brake Temperature Paint delivers the widest temperature range in one bottle. Temperature readings ranging from 0° to 671°+ Celcius (0° to 1239° Fahrenheit) are displayed over a six color change from cold to hot. The bottle features a Metal Cap with a Horsehair Brush for quick and easy application on any surface, such as rear end housings, transmission cases, brake rotors or exhaust pipes. Packaged in a plastic carrying jar, the bottle also features brake temperature color code guide on the bottle for quick temperature reference. Simply apply paint evenly to a clean, grease free surface, allowing to dry to touch, and to remove used paint off of surface, use a disposable towel or rag and wipe off remaining paint material
If you bring it to the F1 party this afternoon I would love to borrow it. I am running a time trial at Hallett on June 12th. I will give it a test "drive".
Well that was a backhanded compliment if I ever saw one. And no, I was definitely not driving like a sissy yesterday.
I would also guess it was a pad getting pushed back off of the rotor while turning. To test this do a tap dance on the brake pedal as you are going down the straight and see if you can get the pad to reseat itself before the turn. Not heard of it happening on our cars, but real common on heavier cars.
I am aware of that possibility, but it just does not seem to fit this situation. Especially on my 23K mi. car. Unfortunately for further testing, I may be done with HPDEs until it cools down a bit here in TX. So, I think I will just flush the system, give it a good inspection, put the street pads and wheels back on and limit the stress to some spirited street driving for a few months. I do not see any opportunities for the tap dance test any time soon, but I will definitely keep this in my repertoire. Thanks for the suggestions guys.
Was the pad "smearing" on the rotor? Easiest way to check pad fade. Based on my experience and conversations with some time trialers on stock calipers, XP12 front is the way to go.
I think Scott and others might be right. The extra push you are needing to go thru (rather than a smooth push the pads up against the rotors) may be caused by the pad getting a little cockeyed and sticking a bit. The high and hard bit you have to push thru is pushing the pad back in line with the rotor. When you do the bleed, see if there is any evidence of one of the front pads sticking. If yes, remove the problem area with a wire brush (dirt, accumulated hot brake dust, etc) or file (metal from manufacturer error or whatever else might be the case). This "push back" of the pad from the rotor seems to occur at higher brake temps. If your track has a bunch of hard braking before this "issue", maybe look for a way to increase cooling air to the caliper. Hope that helps. Pat
Yes, thanks for the input. Imminently, I will be bleeding and changing the pads back to street and so I will be giving everything a thorough inspection and I will definitely be specifically looking for any signs of a pad that spent some time being ****-eyed.
Well, it looks like big brother does not like my language. I guess you can't say c-o-c-k-eyed around here.