Tilton brake bias valve incompatible with ABS ?
07-14-2014, 06:22 PM
#76
Rennlist Member
Nope.
With ABS active (as stock) :
I don't run this way much anymore. Not really sure which end was getting it worse. After switching to race compound pads it took only 3-4 hard laps and the peddle went to the floor. A non-scientific walk around the car suggested all 4 calipers were roasting. "PORSCHE" lettering on fronts went from white to brown. (see photo) Wish I had some pressure transducers to place in the lines. (I also changed to rebuilt calipers with no effect)
With ABS deactivated (fuse pulled) :
The brakes now stay cooler but bias goes so much to the front that it is nearly impossible to threshold brake on anything but billiard table smooth tracks.
Edit: Some background info. Years ago I never noticed the problem with street tires, semi-metallics or Hawk HPS. When I started running DOT Race tires with Hawk Blacks it began to slightly occur, although I wasn't aware that it was ABS related and just assumed the calipers were old. So they got rebuilt. (fronts new actually)
Modified car more and got faster... began running full race pads (Hawk DTC, CL RE6, etc) this is when I could no longer keep the brake under me. Tried new cooling ducts, etc. No help. Finally resorted to pulling ABS fuse. This "fixed" one problem only to reveal the bias issue.
With ABS active (as stock) :
I don't run this way much anymore. Not really sure which end was getting it worse. After switching to race compound pads it took only 3-4 hard laps and the peddle went to the floor. A non-scientific walk around the car suggested all 4 calipers were roasting. "PORSCHE" lettering on fronts went from white to brown. (see photo) Wish I had some pressure transducers to place in the lines. (I also changed to rebuilt calipers with no effect)
With ABS deactivated (fuse pulled) :
The brakes now stay cooler but bias goes so much to the front that it is nearly impossible to threshold brake on anything but billiard table smooth tracks.
Edit: Some background info. Years ago I never noticed the problem with street tires, semi-metallics or Hawk HPS. When I started running DOT Race tires with Hawk Blacks it began to slightly occur, although I wasn't aware that it was ABS related and just assumed the calipers were old. So they got rebuilt. (fronts new actually)
Modified car more and got faster... began running full race pads (Hawk DTC, CL RE6, etc) this is when I could no longer keep the brake under me. Tried new cooling ducts, etc. No help. Finally resorted to pulling ABS fuse. This "fixed" one problem only to reveal the bias issue.
07-22-2014, 08:43 PM
#77
Pro
Mark,
One was the track I was doing most of my running/testing at was our local track here in Pittsburgh. Used to be called BeaverRun, now called PittRace. This is a short "point & squirt" track that is extremely hard on brakes because the surface has a lot of grip and there are 2 longish straights followed by heavy breaking with little time between them for cool down. A recipe for heat soak. But in three 3 laps? In a 911?
What I didn't realize until later is that on "real" tracks such as Watkins Glen and Mid-Ohio, the ABS could be left engaged with little to no problems. On these tracks the brakes could be cooled between hard application points.
So what was the deal at my home track?
I must admit that I've never done the proper engineering analysis to determine the exact root cause of failure at the home track. I've just stopped driving hard there.
But with ABS engaged there is definitely a bias change and there is definitely a fluid fade / heat soak issue that doesn't occur at longer tracks. Without it engaged I get approx twice the track time before the heat soak start to degrade the system.
I don't race the car (just DEs) so I don't have data aq. toys and pressure/temp senders to determine the cause. If this ever starts happening at any other tracks maybe I'll get off my butt and start logging everything and determine the real cause.
One was the track I was doing most of my running/testing at was our local track here in Pittsburgh. Used to be called BeaverRun, now called PittRace. This is a short "point & squirt" track that is extremely hard on brakes because the surface has a lot of grip and there are 2 longish straights followed by heavy breaking with little time between them for cool down. A recipe for heat soak. But in three 3 laps? In a 911?
What I didn't realize until later is that on "real" tracks such as Watkins Glen and Mid-Ohio, the ABS could be left engaged with little to no problems. On these tracks the brakes could be cooled between hard application points.
So what was the deal at my home track?
I must admit that I've never done the proper engineering analysis to determine the exact root cause of failure at the home track. I've just stopped driving hard there.
But with ABS engaged there is definitely a bias change and there is definitely a fluid fade / heat soak issue that doesn't occur at longer tracks. Without it engaged I get approx twice the track time before the heat soak start to degrade the system.
I don't race the car (just DEs) so I don't have data aq. toys and pressure/temp senders to determine the cause. If this ever starts happening at any other tracks maybe I'll get off my butt and start logging everything and determine the real cause.
