I need a brake expert to solve this.

[pgilliam1]

First, let me tell you what I've done (all of this done about 200 miles ago):
- replaced rotors
- new pads (Hawk HPS)
- broke in rotors and pads with 50 stop/starts
- new master cylinder
- checked brake booster and check valve (both operating as should)
- checked caliper pistons for pitting (none found) all seals good
- bled system, ran car, bled again, ran car (no air found-same feel)
- bled anti-lock brake system
- no leaks anywhere
Now my problem:
After spirited drives my rear calipers, wheels and rotors are hotter than my fronts (about twice as hot - I am running 275/35/18 rear and 215/40/17 front). Is that normal? On the track, brake fade is terrible. I have to really mash these brakes hard (when I say hard, I mean I've never had to hit brakes this hard on any other car I've had) to lock them up and activate the anti-lock system. They just don't stop this car (1991 with 118K miles). I know stainless steel brake lines have been recommended, but I have never heard of anyone whose lines have actually expanded, although that is my next step unless someone can lead me in a better directon.
I like everything else about this car :smile:, except it's braking . Any help will be much appreciated. Thanks, and Happy Motoring!

 

[DocL]

I used to have the same experience as you with brake fade at the track. I tried everything short of getting a BBK. I had the calipers rebuilt. I tried every high temp brake fluid on the market. I tried most high performance pads. I had SS lines installed. And, it got even worse when I ran with Hoosier slicks. I figured out that it was probably my style of driving that heated up the brakes too much. I liked to brake late, and hard, going into the turns which resulted in heating up the system causing brake fade and cracked rotors. I even burned the piston boots once. My solution was to stop tracking my NSX. Ever since I haven't had any problems with brake fade. Problem solved for me.

 

[docjohn]

although you say you "bedded" in your pads you may have not done it correctly and glazed them and the rotor.The pads themselves may not be up to rigourous hpde.Are you using a higher temp fluid like motul 600? Could you still have air in the lines? How firm is the pedal?

 

[angus]

50 stops is not nearly enough for those pads you will need to bed them in for way longer

 

[CL65 Captain]

First off what year is the NSX?

HPS are a street pad and 50 stops is PLENTY to bed them in. I can bed in a full blown race pad like the Performance Friction PFC01s in less than a dozen stops. Takes 4-5 (60-20) to get them up to temp and then 3 high speed 90-40 and let them cool and repeate. Bedded in. That's not your problem.

If your car is a 2000+ I have the answer for you.... there is a brake proportioning valve for the rears that is not listed anywhere in the manual but I found in a parts diagram of the brake lines.

I had the exact same symptoms. Went through a entire set of rear pads on the track to the backing plate and only used less than 1/2 the fronts. Mushy brakes no matter how well I bled. Replaced the rotors, pads, lines, flushed the fluid, bled, bled, bled. Replaced the master, bled, bled, bled.

Found the $150 proportioning valve in the brake line parts diagram - replaced it and BINGO!

 

[CL65 Captain]

just noticed your car is a 1991. Doesn't have the proportioning valve.

Also Hawk HPS are not a good HPDE pad. I have never run HPS on the track, nor would I considering I can get the OEM pads to fade after 4 laps even with my brake ducting. I'm sure the HPS isn't much better.

Hawk HP+ are better, but still not "track worthy", I can get them to fade if I'm hard on them. Hawk DTC60 are good track pad for the fronts. Problem is Hawk really doesn't make a good track rear to match for the NSX. I ran DTC60s front and HP+ rear for a while. Did OK, but then I moved on to Carbotech XP10/8s. Another good choice would be Cobalt XR2/XR3s.

But your fronts SHOULD run hotter than the rears and the fronts SHOULD wear faster. My front temps are ~360-320F and rears ~280F coming off the track after my cool down lap. I have ducting front and rear. But the fronts SHOULD run hotter. So you have a problem.

 

[Daedalus]

You didn't mention anything about the shear pins or holes. Be sure the calipers aren't binding.

 

[pgilliam1]

That's exactly what I thought. I can't think of one reason, except maybe air in the front lines, and I have double/triple checked for that (OK I'll check it again). It seems most of my stopping force is coming from the rear and that's just wrong. When I checked my calpiers, all of the pistons moved in and out evenly/smoothly. I run Hawk HPS because most of my miles are on the street. These brakes really don't work that well even when they're cool. I'm using Valvoline synthetic DOT 4 now and will change to ATE Super Blue Racing DOT 4 this weekend. I also got a set of speed bleeders to help with the air possibility. Maybe that will help. Maybe I should adapt a set of BMW calipers (I miss them now). Oh, and Doc, the pedal is very firm.
Thanks and Happy Motoring!

 

[CL65 Captain]

That's exactly what I thought. I can't think of one reason, except maybe air in the front lines, and I have double/triple checked for that (OK I'll check it again). It seems most of my stopping force is coming from the rear and that's just wrong. When I checked my calpiers, all of the pistons moved in and out evenly/smoothly. I run Hawk HPS because most of my miles are on the street. These brakes really don't work that well even when they're cool. I'm using Valvoline synthetic DOT 4 now and will change to ATE Super Blue Racing DOT 4 this weekend. I also got a set of speed bleeders to help with the air possibility. Maybe that will help. Maybe I should adapt a set of BMW calipers (I miss them now). Oh, and Doc, the pedal is very firm.
Thanks and Happy Motoring!

If your pedal is firm than you probably don't have air in the lines. You can always try and gravity bleed - takes hours, but if there is any air in there it will work its way out. Open the bleeder, put a clear hose on it running to an empty bottle and let it slowly drip out. Check the reservoir every couple of hours to make sure it doesn't run dry.

 

[EdinKali]

If your car is a 2000+ I have the answer for you.... there is a brake proportioning valve for the rears that is not listed anywhere in the manual but I found in a parts diagram of the brake lines.

I had the exact same symptoms. Went through a entire set of rear pads on the track to the backing plate and only used less than 1/2 the fronts. Mushy brakes no matter how well I bled. Replaced the rotors, pads, lines, flushed the fluid, bled, bled, bled. Replaced the master, bled, bled, bled.

Found the $150 proportioning valve in the brake line parts diagram - replaced it and BINGO!

Not to hijack this thread but glad to hear you finally got that solved Captain. If I recall correctly I think I was the one who suggested looking for a stuck proportioning valve.

 

[EdinKali]

What are you using to clean the rotors? Brake Kleen? or something else?

If you are using something else, make sure it doesn't have anything in it that will leave deposits on the rotors or contaminate the pads.

Believe it or not, when I used to wrench for a living I saw things as silly as people soaking the brake pads with WD-40 to stop the squeaking.

 

[EdinKali]

Another thing to look out for is spray on tire dressing that is silicone based. Getting that on your brake rotors will cause a reduction in friction and contaminate the pads.

 

[angus]

Last time I put hawk hps on a car with new rotors , it took what seemed liike forever to get them to work , like three weeks of daily driving.

 

[CL65 Captain]

Last time I put hawk hps on a car with new rotors , it took what seemed liike forever to get them to work , like three weeks of daily driving.

yes, that is true. But if you get them up to temp and then do a few 60-20 hard stops or 90-40 you will transfer the material to the rotor. The key is to get them hot enough to begin the transfer process.

http://www.stoptech.com/tech_info/wp_bedinstock.shtml

Daily driving will eventually transfer the pad material on a street pad, but it will take a few thousand miles.

 

[pgilliam1]

You didn't mention anything about the shear pins or holes. Be sure the calipers aren't binding.

Oh Yeah I forgot, I also replaced the upper pins in the rear calipers. They were worn and loose (the holes were fine and tight with the new pins). The front pins were OK. I regreased all the pins with high-temp silicone grease. The boots were fine. The calipers seem to function fine with no binding. I took the pads out and extended the pistons out as far as possible and they look new and retract easily with no binding. I regreased the pistons as well. With the rears getting so much hotter than the fronts, there must be lack of pressure to the fronts. I just can't figure out why . Maybe they need a few more miles to bed in, but I followed Hawks procedures and have about 200 miles on them now. Happy Motoring!

 

[pgilliam1]

What are you using to clean the rotors? Brake Kleen? or something else?

If you are using something else, make sure it doesn't have anything in it that will leave deposits on the rotors or contaminate the pads.

Believe it or not, when I used to wrench for a living I saw things as silly as people soaking the brake pads with WD-40 to stop the squeaking.

I used brakeclean on the rotors when I first installed them. After that, I don't put anything on them.

 

[R13]

to reinforce what's been said to an extent. If the pedal is firm, but the car just won't stop, that isn't the fluid. If you cook the fluid, the pedal with get really mushy and eventually just go to the floor. There is some hardware problem either the pads have glazed or the rears are binding....

Since the stopping power is weak though, I'd suspect glazed/not-correctly bedded pads or something out of sorts with the front calipers. Even if the rears were dragging (which would explain the temperature bias) when you punch the pedal the fronts should still bite.

 

[goldNSX]

Are you still running the OEM calipers. Have they been revised once or so? If the calipers are 'sticky' you'll get all sort of problems.

CL65 Captain: If you say you replaced the proportional valve (which comes with the 99+ ABS) did you replace it or did you throw it out?

 

[pgilliam1]

Are you still running the OEM calipers. Have they been revised once or so? If the calipers are 'sticky' you'll get all sort of problems.

The calipers are OEM. I have checked them and regreased them and they seem to operate fine (I also drove them on the highway for several miles, got out and checked them and they were cool to the touch - which tells me there was no sticking or dragging).

I put the speed bleeders on and bled all new fluid in but the results are the same.
Let me throw another possibility in here. There has been mention here of possible problems with bedding the pads to the new rotors. The rotors I bought had a zinc coating on them to stop rust. After my first 20 or so stop/starts to bed them in, I had a lot of zinc flakes all over the calipers (this happened on both the front and rear). I called the manufacturer and they said that was "normal and of no concern". But if that zinc coated the pads (visual inspection doesn't appear to show anything foreign on the pad surface) what would be the best way to remove it (file it, sand it, grind it, etc.)?

 

[CL65 Captain]

Are you still running the OEM calipers. Have they been revised once or so? If the calipers are 'sticky' you'll get all sort of problems.

CL65 Captain: If you say you replaced the proportional valve (which comes with the 99+ ABS) did you replace it or did you throw it out?

I replaced it with a new one. I still have the old one, I was planning on cutting it apart (haven't gotten around to it) to see what's actually in there and how it works --- ie is it just a valve or is there a spring in there too, etc. Did it get clogged? Did something fail?

Also, since I now have Brembo BBK on the front and OEM on the rear I was thinking about swapping it back in and see if it would move my extreme front bias back towards the rear.

 

[CL65 Captain]

what would be the best way to remove it (file it, sand it, grind it, etc.)?

Let me drive it on the track for you. :biggrin:

 

[pgilliam1]

Let me drive it on the track for you. :biggrin:

Why didn't I think of that? Another driver probably wouldn't have all these problems - or wouldn't care (until he hit the end of that long straight !).

 

[pgilliam1]

Solution:

I took all the brake pads off and used emory cloth on a flat surface to remove any shiny/glazed surface on the pads.
I also noticed that the backing plates on the Hawk pads didn't match up to the caliper surfaces that hit the pads. I took all the backing plates off the pads (they're just glued on and pried right off) and reused the OEM metal shims/plates.
Major improvement and probably as good as I can expect. All the caliper temps are the same, nice front lockup with ABS deployment. Night and day difference.
Thanks for all the input and Happy Motoring!

 

[EdinKali]

Glad you got it sorted! You can call yourself a brake expert now.

 

[pgilliam1]

Glad you got it sorted! You can call yourself a brake expert now.

LOL, I was going over this in my sleep. I have done about 50 brake jobs and never had problems like this (I haven't used Hawk pads on NSX calipers before though). Hawk should make the backing plates cover the entire rear of the pad instead of just a little square center section that doesn't match up to the caliper. Live and Learn!