rezanourai

I've been running stock rotors + pagid RS29 yellows for some time. Third set of rotors now & second set of RS29s. I typically swap back and forth between a clean set of rotors I keep for street use + oem pads and old abused rotors + pagids for track use. The last time I swapped back to my track set up, I noticed the pedal sunk to the floor more and required really standing on it to stop the car, and even then the pressure felt all over the place. I bled the brakes afterwards and it helped a little, but not a ton. Figured the master cylinder was bad and took it to the dealership since I still had a bit of warranty left. They agreed it was probably the master cylinder and they replaced it. Brakes felt better, but still the pedal travels more than I remember. Car stops fine now just that I have to push the pedal further.

Took it to WRLS this past weekend and the brakes performed just fine for 2 days. Pads are down to about 4-5mm and on the way home again the pedal travel seems way too far. Any ideas on what's going on? Is this just how track pads feel when they get low? I don't recall this issue with my first set of Pagids, but to be fair the first time I did RS29s in front and stock rears. This time I have RS29s at all 4 corners.

In any case, the rotors are pretty shot (cracks connecting holes) so I ordered a set of slotted rotors and am going to try RSL1's in front this time, but I'm worried that something else could be the issue. I suppose I could swap back to my street set up and see if the problem goes away (they I know it's the pads). I think I'm also going to do a full flush of the fluid & replace with fresh Motul 600 (running ATE gold right now) in case I still have air in the lines or if air got into the ABS module.

I guess I'm just looking to see if some pedal feel changes are "normal" with track pads and what others are experiencing. Car is a 2012 Carrera S.
Thanks!

2BWise

Are the pads tapered?

Does it feel the same when you put new track pads on it?

TXE36

Pedal travel should not change. As the pads wear, they automatically adjust. The squared piston seals ensure that the pads only just pull off the rotors. As the pads wear, more fluid is retained in the calipers, maintaining that small gap. There is enough reserve in the MC reservoir to supply the extra fluid over the pad's life. Thus the pedal travel should not change.

Sometimes with pads, sometimes the pedal effort required for a certain decel rate will change, but it should not change a lot. In my experience, the biggest change is from temp. With PFCs, I can tell when they "turn on" on the track as when they get up to temp, the pad grip goes up correspondingly. However, the pedal travel does not change perceptively.

IMO, long pedal travel is indicates fluid is boiling or something is leaking somewhere.

-Mike

Thundermoose

I have found that some track pads struggle on street due to lower operating temps compared to track temps.

jdistefa

Sounds like you have air in the system.

Also, Pagids should go in the garbage at 1/3 thickness.

Pads can also become sintered/glazed over time.

mj951

And that combo often eats rotors.

ProCoach

fatbillybob

This^^ could be issue but you have to look at the system overall. It might just be marginal for the track and your driving style. You can do everything wrong and be fine if your system has lots of headroom. In your case you need to find answers. So I would do is everything right. That means new rotors and new pads and new fluid. No air in the system is a given. Pads need to be properly bedded and rotors properly seasoned. Do not use other kinds of pads on these rotors. You need to check wheel bearings and hubs!!!! Use only slotted rotors on track. If you want a street and track set fine but do not drive home swapping your street pads on your track rotors. Know that if you see 4mm on the outside pad there is pad taper on the outside pad that will mean you may have more or less than 4mm. The inner pad runs hotter and you will have less pad than the outside. Less pad thickness means less stopping ability because brakes are all about managing heat. The more marginal the system the newer pad you need to run just like the 1st laps of a Hoosier dot-R tire is magic. Pad taper kills pads and when severe makes for poor braking. Some setups just taper. That is why there are 1,2,3,4,piston calipers to reduce taper. Some calipers flex and old calipers flex more. That makes for more taper and worse braking. Consider using the next higher heat range pad if you are destroying the ones you got now. Destroying pads will also destroy rotors. Use templix indicator paint on your rotors/caliper to help you determine if the pad you selected is in the right heat range. Can you duct cool air to the brakes? This should give you a good start.

jdistefa

^ Ton of excellent advice here. Sometimes the internet works

rezanourai

Thanks! I haven't pulled the wheels off since I've been back from this past weekend (the car is not a daily driver). I will pull them off and take a look around. The last time I looked:
1. bearings and hubs looked okay
2. rotors were cracked, but not too bad (cracks not connecting holes). I don't use the same rotors with other pads. When I swap to street pads, I swap the rotors as well
3. the pagids are pretty low. I had not heard that you shouldn't run them below 1/3rd before, so maybe that is a big part of the problem?
4. I will check for tapering. I didn't notice much when I put them on, but will check now that I put 2 more track days on them. WRLS is fairly brutal on brakes too coming into turn 2
5. I suspected boiling the fluid, but wouldn't that go away once the fluid cools down? If not, then that could be it. I'm running ATE gold Dot 4, but going to switch back to Motul 600 with this next brake job. Don't recall ever having trouble with the Motul 600
6. can rubber brake hoses be an issue? Are steel braided worth it?
7. I am switching to slotted with my next swap (just ordered them). I have been running stock (well, Sebro instead of OEM brand to save $$) drilled rotors. Maybe the Sebros aren't as good as OEM? or maybe drilled just isn't as good. Looking forward to switching to slotted.
8. When I looked at pads when I put them on, inner & outer were both around 5-6mm. It's possible that this last trip out I wore the inners. Will inspect again when I pull the wheels off next.
9. I am moving to a new compound up front (higher friction & higher heat).
10. Will look into ducting

Thanks for all the pointers! I'll take pictures of the rotors & pads and put them up here when I get them out. Hopefully this weekend, but have to check with the boss to see if she has plans for us first.... might be in a couple of weeks

One more thing. I noticed the yellow pagids start to turn slightly orange/rust colored. Is that any indication they are getting way too hot? I'm starting to think i'm down under 1/3rd and they just aren't handling the heat well. Will measure when I get them out.

rezanourai

A couple of additional questions that came to mind:
1. I've heard it's possible to get air into the abs module when pushing the caliper pistons back in during a brake job. How can I tell if that happened and how do I fix? Will a normal brake bleed fix that? Somebody mentioned a possible solution is opening the bleeder valve at the caliper while pushing the pistons in instead of the usual opening of the reservoir. Any truth to that?
2. How can I tell when calipers are done for and need to be rebuilt or replaced?

Sorry for the 1000 questions, but trying to learn

TXE36

Cracked rotors won't cause long pedal travel unless the friction surface has departed the car. You will just get a thud-thud-thud that you can hear and feel in the brake pedal when the rotor cracks through.

If the system is sealed, pushing pistons back should not introduce air anywhere in the system. The reason for cracking the bleeders when doing this to to keep from pushing crap from the calipers back into the system.

The a nice way to bleed/swap fluid is with something like a Motive power bleeder. In looks like a garden sprayer can with a fitting to connect to the master cylinder reservoir. It applies pressure (and can add fluid) at that point and you just open each bleeder until done. I don't know about P-cars, but I've filled both BMW and Jaguar brake systems that have been completely drained during brake hose service and never had a problem - ABS and all.

Unless they are old, rubber brake hoses are not a problem. After having a Jaguar factory SS line fail and nearly having a quality aftermarket SS line nearly fail on the race car, I'm not big on SS hoses.

The brakes on a modern Porsche are generally very good - you should not be having issues with long pedal travel. It may just be air, but get to the bottom of it as something ain't right.

-Mike

fatbillybob

Agreed ^^^^^ I have never done the open caliper bleeders to push back pads just because it is a messier job. I also keep brake fluid in all my cars fresh to avoid problems. I might open the caliper bleeders and push the pistons in if the master cylinder fluid just looks really nasty with many years between service. But I might not even bother and just rebuild the calipers on an unmaintained system like if I bought a old used car with unknown history and I want to put it back into service.

I'm lazy and fluids are cheap. So instead of going 5 years on my 5 year extended life antifreeze and having to pull block drains when flushing I will drain a system at 2.5 years without going at the block and refill. Instead of waiting until brake fluid is dark and have to drain a system dry to refill it I will annually suck the master to near top of cylinder ports refill with new fluid and bleed. Some do the ATE blue and gold thing and that's fine but I think the DOT has outlawed blue. I like the firm pedal you get with new rubber lines or stainless braided lines. I always go stainless on my performance cars but only use DOT stainless braided lines like those from Stoptech. It is much harder to get a stainless line to pass the DOT tests because the DOT tests are designed for rubber. If you got a DOT stainless line I think those superior to any rubber line. On my racecar I change those after 2 years regardless.

Agree air still in the OP's system is low hanging fruit to go after.

fatbillybob

On #1 I really can't see that being a problem especially since you are going to bleed your brakes after pad change anyway. If not please make that a regular habit as best practices.

On #2 I just do it every 2 years on racecar or if I let a car sit like your garage queen pristine 60's 911S. A car that sits needs just as much maintenance as a car that races. Machines don't like to sit. But in general you can own a daily driver for 100k miles and more and never have to rebuild. Caliper spreading is something you diagnose as an option of last resort. You and your buddies racing the same setup will all start to see the problems or increasing pad taper as the caliper ages out. Then one day you change the caliper and voila only the crappy pad taper you had when new. There is always some pad taper.

Yeah I'm not a big fan of running pads to the backing but I have just like I have been cheap running tires to the cords. I should be better with my words. The goal of brakes is to throw off heat. The initial heat is from rotor and pad contact. The heat capacity of the pad is best when it is thick. As you thin the pad there is less pad to absorb and dissipate the heat. When thin the heat is dissipated into the metal pad backing and transfers to the pistons and then the caliper and into your fluid. Fluid boils and you loose the pedal. There is just less of that with a thicker pad. None of this matters when you have extra room in your brake package but all of this matter like what fluid is used when your system is engineered just enough. So maybe one solution is to replace the pads at 1/3 left. Maybe you can go lower if you use SRF high temp brake fluid. Maybe you can duct cold air to the brakes?

Here is what happens when you go to far on your pads. The heat breaks down the binder that glues the pad to the back and a piece of pad chunks off. While you have more airflow with the pistons extended and big airgap behind the pad backing you have less pad for heat capacity.

fatbillybob

Sorry pic did not post. I'm too dumb to figure it out