new brake behavior Q's

[p00t]

I just installed pbr semi-metalic pads and brembo blank rotors all around on my 93 240sx w/o ABS. i put new nissan shims and clips on and im positive I've installed everything correctly. all lines were bled with fresh dot 5.1 brake fluid. But this is my first time with new brakes and rotors so here are some Q's.

1. I followed pbr's recommendations for bedding in the pads. you do 10 slow stops from 30-40 mph with 20-30 sec imbetween stops. Then you let everything sit overnight and you should be done. When I first started out the pedal pulsed alot, felt rough, and required alot of pedal pressure to stop. I am pretty sure this is normal for fresh pads.

So I followed the bedding in precedure, the feel of braking was a bit better, but not much. i felt the calipers afterwards, and they were barely warm. outside at night (when i was bedding the pads in) its been like 30-40 degrees, so its pretty damn cold.

the next day i did some normal driving and then a few moderate stops from 60-65mph. it seemed to help more then when I did the bed-in proceedure. but there is still a slight pulse in the pedal and the pads sound alittle noisy (rough). outside temp was about 55 degrees.

My intuition is telling me I'm just not getting the brakes hot enough to bed in properly, since i can always touch the caliper afterwards, but maybe im wrong. Maybe this is normal behavior, and it just takes awhile to break them in? The PBR break in guide says to go easy on them for the first 150 miles of use, is this brake behavior going to get progressively better and be completely gone by 150 miles?

2. It seems like the brakes work alot better at highway speeds then speeds under 20 mph (with the same applied force). Im assuming this is just the nature of semi-metalic pads or is it cause of a problem that I might have mentioned in #1? My old pads behaved almost in reverse to how these are behaving :dunce.

**If you have any "new pads n rotors tips" please feel free to share

THANKS!

[NISTECH]

when you say the pedal feels like it has a "slight pulse" Does it feel like you have warped rotors? if you know what that feels like. When I do brakes; once reassembled I pump the brakes to set the pads against the rotor before I even drive it. then once out on the road I get up to 40 or 45 mph and slam on the brakes in an attempt to lock them up. At this point they wont due to impurities on the surface of the pad the car will slow gradually during this application. I regain my speed and slam on them again depending on how much build up there was on the pad it may actually lock up this time or at least have a better response to the pedal request. after that application I head for the freeway. Drive about a mile with no brake application (to allow the pads and rotors to cool down)then exit ,on the off ramp I give it another heavy brake application but not as hard as the first 2 usually this one feels like a normal brake application. once back at the dealer the brakes are functioning as normal. This process is called burnishing.

[Grant@tirerack]

It may take longer to build up a transfer film onto the rotor surface if it's that cold outside. The break in procedure needs to generate enough heat to leave a thin film of compound on the rotor surface. If it is not a complete film all the way around the rotor, the pads will grab-slip, grab-slip, as the rotor spins and you put pressure on the pedal. That will cause the pulse you feel in the pedal.

[Q45tech]

Most don't understand that this transfer film is what stops the car because a virgin rotor will only have a coefficient of friction of iron/cast iron ~~~0.25 vs the pads which can be 0.33-0.45. depending on temperature.

We usually warn new pad turned rotor customer that unless they break in correctly the full friction may take 300- 500 miles to achieve.Guess what 999 out of 1,000 stare blindly at you not understanding what you are talking about.

[p00t]

NISTECH i mean that you can feel it in the pedal, the car does not feel like it is slipping then grabbing. you can feel a very slight pulse in the pedal, but when you have been driving around for a bit it is almost gone, i assume its only there when its cold.... But braking at low speeds is still weak.

I hope its not possible that i got a defective rotor or anything. I do have the old rotors at the ready however.

I only have access to the car on the weekends usually so there has only been 15-20 miles put on the new pads and rotors. And from what you guys have been recommending I guess i will put forth a considerable effort to get these puppies heated up friday, and I'll let you know how it goes.

Grant what would be an ideal temperature for the bedding in to occur? For example should the rotor be glowing hot, too hot to touch, or just hot when u touch it (but you can leave you hand there for a bit). If I can gauge how hot it should be then maybe i can do some test runs and feel the rotor afterwards (getting progressively harder braking with each run).

Thanks!

[Q45tech]

The optimum friction coefficient [the point at which it begins to nose over and decline] in MM pads is around 500-550F [a single 120-130 mph to zero stop].....each full ABS stop from 60 mph to zero will heat the rotor about 120-150F from ambient......probably bettter to do multiple 60-30 stops.........8 or 10 in in 15 minutes should work.

Measure the rotor temp with an IR thermo gun.

It won't glow until around 1500F [1145 C melt temp] by then everything will have been destroyed....."should the rotor be glowing hot"?

[NISTECH]

No I can tell you from experiance it should not be glowing hot. WARNING: Never drive a tow truck as hard as you can with the PTO brake engauged. the above mentioned melt down WILL occur.....lol

[Grant@tirerack]

If you can touch the caliper right after driving like you said, they are not hot enough. When the pads slip and grip on the rotor it will give you that slight pluse in the pedal you are feeling. The forces on the pad will pull it ever so slightly sideways in the caliperand that movement will be transfered to the piston, through the fluid behind the piston, through the brake line and m/c, and to the pedal. A lot of times folks mistake this for a warped rotor.