I thought running a lower temp pad in the back will "increase" rear bite, as rear doesn't get loaded as heavily under braking, so if you use the same temp range pad all around, the front would be in the right temp range, while the rear doesn't come up to temp.

Is my thinking incorrect?

For one thing, rears can run hot because they are smaller and typically don't get as much cool air over them, and often they are not ventilated (though they are on the FD). But anyway, most track brake pads have a wide enough range that you should be in the high-coefficient range even if the rears are a bit cooler.

Carbotech XP10s have remarkably good bite even when stone cold, they don't have to get too much heat in them to be in optimal range.

For XP24 Carbotech site mentions that they aren't recommended for the street due to dust and noise and the heat required for them to work properly. They don't mention heat being an issue for street use for the XP8, 10, 12, and 20, just the dust and noise.

I also agree to first confirm that there are no mechanical issues. I have a similar brake setup in my FD: Brembo BBK front (Hawk DTC 70), 929 MC, ABS removed, 99 rear rotors, Wilwood calipers (Hawk DTC 60) and a proportioning valve for the rear. 18 x 10.5 with 285/30/18 Hoosier R6.

Similarly to Fritz, I get a little lock up now and then. You can hear an example at the 4:10 mark in this video.



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Good luck sorting this.

Guy

Great stuff with the NSX! Expect no quarter, give no quarter :D

I needed to stagger compounds on my FC. And my rear brakes come off the track much hotter than the fronts. But I do have an adjustable prop valve. With the OE the prop valve, I ran the same pad all around.

The car gets a little rear wheelhop occasionally when I brake too late in certain situations. With DTC 60s all around the car wanted to lock the rear wheels too early, even when I dialed out rear brake. Switching compounds was a huge improvement instantly.

Yeah, my FC always wanted to swap ends braking. Especially over bumps where the heavy/bindy rear suspension would cause hop (I made the mistake of using poly bushings and never fixed that).

I actually liked that fact that the FD would brake nice and straight with some front bias after I put the 14" front brakes on.
It felt nice and safe braking down from 120mph into the bumpy narrow braking zone (if you cross the crown you wreck) on the local hillclimb.

I adjusted the FD chassis to oversteer slightly, so once you are off the brakes turning in you are steering with throttle input and countersteer- on low speed turns.
The big rear spoiler helps settle the rear at speed so it feels stable once over 90mph or so.

I have a feeling the OP is struggling to find a best line through a double apex turn or struggling to turn in as late on a certain apex as he would like.

Video?

thanks everyone for your help, we will check the hard lines, try the abs delete/prop valve, perhaps even change the rear brake compound to match the front.

don't have a recent video, but here is the video from a year ago, when i first got the car.
this is the old brake setup with brembo gt front, stock mc, stock rear, carbotech xp10 front/xp8 rear. I wasn't trail braking much in this video, the pedals were very mushy (stock mc), just straight line braking and coasting it into apex.
Also had a badly setup oil catch can vent, half way through the lap the windscreen started filling up with oil splashes (hood is vented), that problem has since been fixed with damian's catch can method (works really well !!).

track is buttonwillow cw 13, time is 1:56
First time out in a big car in 5 years, so abit rusty :)

here's another video in an Toyota ae86, no abs, about 90hp (lol yes..), really easy to brake in this car

The stock size 15/16 MC should not cause the brakes to feel mushy. Think of it this way, a larger MC such as the 1" 929 will push more fluid per given amount of travel. The stock MC should actually provide more travel thus more feel to properly modulate the system.

These cars are getting older and it's possible that the MC itself could be leaking on one of the circuits thus giving a bias issue. Same with the prop valve and abs pump etc... Any sticky caliper pistons?

Verify everything mechanically is 100% before making any drastic changes.

Didn't see any lock up but did see some trial braking.

In the 1st corner or at about the 18 second mark it looks like you are leaning into the corner a bit and heavily trail braking :scratch:

Nice vids :icon_tup:

its hard to see in the video , but I'm actually braking quite early and coasting into the apex

[QUOTE=Brekyrself;12155718]The stock size 15/16 MC should not cause the brakes to feel mushy. Think of it this way, a larger MC such as the 1" 929 will push more fluid per given amount of travel. The stock MC should actually provide more travel thus more feel to properly modulate the system.

These cars are getting older and it's possible that the MC itself could be leaking on one of the circuits thus giving a bias issue. Same with the prop valve and abs pump etc... Any sticky caliper pistons?

Verify everything mechanically is 100% before making any drastic changes.[/]

I need to have pedal pressure (a hard point ) to modulate the brake, the stock mc with big caliper doesn't hsve that hard point .

@ Brekyrself

What you have stated is simply not accurate. The smaller mc requires almost no effort to lock a wheel and results a sinking pedal ( to fill the big pistons of the bigger caliper). The bigger mc keeps the pedal high, and the harder push required makes it easier to modulate .

Imagine it takes 30 lbs of force to lock a wheel ( which is barely pushing the pedal). If you are barely pushing It is hard to push a little less . And the pedal will sink with a bbk. If it takes the equivalent 60 pounds to push to lock a wheel, it is easier to push 45 pounds from 60.. Any factory built racecar and any high end gt Porsche will have a rock hard pedal that doesn't move and requires some extra strength compared to most cars.

Gotcha!

That's a super busy track that I know zip about so it's very difficult to judge any damn thing LOL

Anywho good luck with the braking issues :icon_tup:

You are correct it is easier to modulate pressure vs pedal throw however I was trying to make the point a 15/16 mc should not exactly feel mushy compared with a slightly larger 1" mc. Even taking in consideration the larger front calipers. There could be something mechanical at play at which the original poster mentioned needing to make sure everything is 100%.

Take a look at the attached xls doc another member made to see different pressures etc... with different mc sizes.

I think I might find it easier to modulate with more leverage, less effort, more pedal travel. Thinking of swapping a 15/16" MC back into my FD (Stoptech ST40 front/RZ rear brakes) as with the 929 1" mc the pedal feels a bit too stiff and wooden...

I went through this with my 240Z, I swapped in a 15/16" 280ZX mc, didn't like it, reverted back to stock 7/8" mc, found that much more to my liking.