Root cause of brake problems?

[dquarasr2]

OK, so back in late 2007 I had posted about the problems I was having with cracking rear rotors.

I traced the problem to pad wear. Inboard pads were wearing much more toward the outer edge of the rotors compared to near the hub.

So, considering the inboard pads were torquing the floating calipers on the slide pins, the outboard pads were contacting the rotor only near the centers, which resulted in uneven heat and subsequently, cooling, cracking the rotors.

I've also looked at my front rotors, and they're a mess as well, surface cracks mid-pad contact area. I was getting the same wear pattern on them as well, with a similar uneven heating then cooling.

I've since replaced the offending rear rotors with new units and in street usage, with new Hawk HPS street pads front and rear, seem to be wearing normally.

So, the real question remains, why, in track usage, are the calipers torquing on the slide pins and causing uneven wear on the inboard pads? Again, the pads wear at least 50% quicker and at an angle, wearing progessively more towards the outer edge of the rotors.

Is this something technique can remedy (poor heat management), is this a function of the stock calipers (flex), or are parts failing and need to be replaced?

Thanks to Prime again.

 

[RP-Motorsports]

Does it seem to be worse on the rears? If so, get a brake bias control, and just dial out the rears a bit. One dissadvantage of 99% of OEM brake systems is they are built for street use. At track conditions, you really need a 4 piston minimum, and the leading edge piston needs to be smaller than the trailing edge piston, so as to get exact even pad wear. With equal sized 4-pots, 2 pots, or the worst singe pot calipers, they will bite hard at the leading edge, and wear out uneven.

In your post you mentioned them wearing out towards the outer edge of the rotor. That is really odd. They usually wear uneven from leading to trailing, not from top to bottom. It could be that the pads are not seating correctly into the caliper due to a burr, rust, dirt, etc. If it is just the rears, I would dial out the bias, or replace the system. For the best idea, buy the Stoptech kit.

 

[Peter Mills]

Lubricate the slide pins. The high heat of track braking burns off the lubricant so the pins bind causing the inner pads to constantly contact the rotor causing excessive heat. With constant pad contact, which is similar to using your parking brake when you come off the track, the heat built up at the pad rotor contact spot will crack a rotor. Last year I wrote an article in NSX Driver about this problem. Do yourself a favor and read it.

OK, so back in late 2007 I had posted about the problems I was having with cracking rear rotors.

I traced the problem to pad wear. Inboard pads were wearing much more toward the outer edge of the rotors compared to near the hub.

So, considering the inboard pads were torquing the floating calipers on the slide pins, the outboard pads were contacting the rotor only near the centers, which resulted in uneven heat and subsequently, cooling, cracking the rotors.

I've also looked at my front rotors, and they're a mess as well, surface cracks mid-pad contact area. I was getting the same wear pattern on them as well, with a similar uneven heating then cooling.

I've since replaced the offending rear rotors with new units and in street usage, with new Hawk HPS street pads front and rear, seem to be wearing normally.

So, the real question remains, why, in track usage, are the calipers torquing on the slide pins and causing uneven wear on the inboard pads? Again, the pads wear at least 50% quicker and at an angle, wearing progessively more towards the outer edge of the rotors.

Is this something technique can remedy (poor heat management), is this a function of the stock calipers (flex), or are parts failing and need to be replaced?

Thanks to Prime again.

 

[MvM]

One dissadvantage of 99% of OEM brake systems is they are built for street use. At track conditions, you really need a 4 piston minimum, and the leading edge piston needs to be smaller than the trailing edge piston, so as to get exact even pad wear. With equal sized 4-pots, 2 pots, or the worst singe pot calipers, they will bite hard at the leading edge, and wear out uneven.

I am by no means a brake-expert but would like you to clarify on your comment that you would really need a 4-piston caliper at minimum.

Is this because the OEM calipers use sliding pins and two pistons on only one side of the rotor (the inside side).
And then this versus race-oriented calipers which use fixed calipers with pistons on both sides? With the reasons being that the race calipers are better able to distribute the pressure on the pads correctly ?

I am fully aware that the NSX OEM-calipers use unequal sized pistions, but I would have to check my used pads to see if I might have the same phenomenon.

 

[NSXDreamer2]

I once had that binding problem at the track and then stupid me, when i installed the pads, I didn't turn the piston back to "+" position. and of course the end result is burning pads and rotors and seized sliding pins.

I had hair line cracks all over my front rotors when using with pather plus pads in only one session.. however that rotor survived more than 20 track days and still going. No problem at all. Those surface cracks doesn't hurt anything.

 

[nsxtasy]

I think the root causes have already been noted above.

Just to provide another data point, on my '91 NSX with stock calipers, brake cooling ducts in front, and 12K+ actual track miles:

Brake pads - My brake pads wear evenly - side to side, top to bottom, outer pad vs inner pad, both front pads and rear pads.

Rear rotors - I have never experienced any cracking in the rear rotors. I think I have replaced them once, due to thickness reaching the minimum spec. Given the number of track miles, my rear rotors basically last almost forever without any problems.

Front rotors - Over time, stress cracks start to form on the front rotors, and they eventually develop cracks serious enough to require replacement (I try to replace them when you can feel the cracks with the edge of your fingernail and/or when they're at least half an inch long). This typically happens after 800-1200 actual track miles.

I used to have problems with excessive shudder in the front. Since reviewing the technical white papers on the Stoptech website, I religiously bed my brakes any time I change rotors or pad compounds, and since then I have not had any problems with shudder.

HTH

 

[dquarasr2]

I think the root causes have already been noted above.

Just to provide another data point, on my '91 NSX with stock calipers, brake cooling ducts in front, and 12K+ actual track miles:

Brake pads - My brake pads wear evenly - side to side, top to bottom, outer pad vs inner pad, both front pads and rear pads.

Rear rotors - I have never experienced any cracking in the rear rotors. I think I have replaced them once, due to thickness reaching the minimum spec. Given the number of track miles, my rear rotors basically last almost forever without any problems.

Front rotors - Over time, stress cracks start to form on the front rotors, and they eventually develop cracks serious enough to require replacement (I try to replace them when you can feel the cracks with the edge of your fingernail and/or when they're at least half an inch long). This typically happens after 800-1200 actual track miles.

I used to have problems with excessive shudder in the front. Since reviewing the technical white papers on the Stoptech website, I religiously bed my brakes any time I change rotors or pad compounds, and since then I have not had any problems with shudder.

HTH

I'm somewhat at a loss to explain things.

I tried to bed them in correctly; I started with new pads (Cobalt GT-Sport) and new rotors, so there wasn't a compatibility problem or dealing with old pad deposits. I bedded them in best I could on the street, then at the first track event with the new pads I heat cycled them a few times before I really abused them, and on that first day by the afternoon sessions they got better and better, and by the end of the day I was getting really good braking performance. But then later on the second and subsequent track days the performance degraded and I started cracking rear rotors (all the way through to the inside of the vents), and getting some weird, um, colorations on the fronts, including surface cracking and pad deposits.

I was conscious of the rear's nub positions. I had the calipers rebuilt (hmm, I wonder if that was done poorly?!?), including good lubrication of the slide pins.

If I were to go at this again, I'd again start over, this time with new calipers, and again new sets of pads and rotors (I did trash the pads due to the uneven wear).

But since I've decided to retire the car as a track rat, I likely won't bother. I was just trying to figure out why some many here on Prime beat the poop out of their brakes and have no problems, and why I had so many problems.

Like I had originally questioned, I would like to find out if my technique (too much heat), the original design (too much caliper flex) or failing parts (bad or underlubricated slide pins) caused the uneven pad wear.

When I talked about this with non-NSX experts (Cobalt), I was advised that it sounded like classic case of caliper flex. It just might be that the first times I went out with the NSX I heat soaked the calipers, got a little flex, then initiated the wear pattern that from then on continued to get worse.

I'm disappointed in that I thought the NSX was designed for this kind of use. While I understand it's faster (higher brake zone approaching speeds) and heavier than my Miata, I didn't expect them to be problematic.

Thanks to all that provided data points.

 

[L8apex32]

+1 to caliper slide pins not being lubricated or caliper not working correctly

-1 to caliper flex - many (hard) track miles with no rear brake problems

 

[RP-Motorsports]

including surface cracking and pad deposits.

Like Ken Said, after a few events (10 full days) you will start to develop surface cracks. If you don't, then you are not a fast driver. :biggrin:
Also for me (fast driver :wink: ) I get pad deposits after every single event. This wears off after about a week of street driving, and then the rotors are shiny again. If you are religiously good with slowly heating up your rotors on the warm up lap, cooling them down on the cool-down lap, not holding your car with the brake pedal in the false grid, and no e-brake etc, you should not get a warp. The NSX is better than most cars with even pad wear due to the size of the pads. They are fairly long.

Also in order to use the oem system as an advanced driver, you must at the minimum use Motul 600 with a fresh flush, and a decent pad (Hawk HP+) or better. S.S. lines are not needed, but only can help. Cooling ducts are not needed, but again only will help. I used to have ducts on mine, but ripped them off during a off-track excursion @ Gingerman. I never put them back on, and the brakes are ok without them, a little fade/soft pedal if there is an early braker in front of me, causing irregular heavy braking on my part.

 

[velo-ct]

Did you pull the caliper pins out and look at them? They can wear to the point where there are flats that can allow unwanted movement so even if well lubed and not binding you can have wear issues. New pins solves the problem.

 

[dquarasr2]

Did you pull the caliper pins out and look at them? They can wear to the point where there are flats that can allow unwanted movement so even if well lubed and not binding you can have wear issues. New pins solves the problem.

Yes, I looked at them and they looked ok. I can only hope they actually are.