question about brake fade
08-30-2011, 11:35 AM
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question about brake fade
2003 Track edition. About 45,000 miles. Brembos with Hawk HPS pads. Pads are about a year old with maybe 4 autocrosses and a weekend of HPDE on them. Brand new ATE super blue brake fluid. Car is stock, and I was running on Yokohama Advan ao48's, which only had one autocross and the HPDE on them.
At the autocross this past weekend (about 45 seconds per lap) by the 4th or 5th run of the first session, my brake pedal became very soft. I really had to give it increasing pressure to slow down.
Could it be my brake lines expanding? I just find it hard to believe that the rubber is that soft and the fluid is heating up that quickly. If I didn't flush my brake fluid properly, and there was air in the lines, wouldn't I notice even when the fluid is cold? I don't think I want to install stainless steel lines because that will take me out of the stock SCCA class (I think).
Any ideas/suggestions?
Thanks in advance for any input.
At the autocross this past weekend (about 45 seconds per lap) by the 4th or 5th run of the first session, my brake pedal became very soft. I really had to give it increasing pressure to slow down.
Could it be my brake lines expanding? I just find it hard to believe that the rubber is that soft and the fluid is heating up that quickly. If I didn't flush my brake fluid properly, and there was air in the lines, wouldn't I notice even when the fluid is cold? I don't think I want to install stainless steel lines because that will take me out of the stock SCCA class (I think).
Any ideas/suggestions?
Thanks in advance for any input.
08-30-2011, 12:01 PM
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2003 Track edition. About 45,000 miles. Brembos with Hawk HPS pads. Pads are about a year old with maybe 4 autocrosses and a weekend of HPDE on them. Brand new ATE super blue brake fluid. Car is stock, and I was running on Yokohama Advan ao48's, which only had one autocross and the HPDE on them.
At the autocross this past weekend (about 45 seconds per lap) by the 4th or 5th run of the first session, my brake pedal became very soft. I really had to give it increasing pressure to slow down.
Could it be my brake lines expanding? I just find it hard to believe that the rubber is that soft and the fluid is heating up that quickly. If I didn't flush my brake fluid properly, and there was air in the lines, wouldn't I notice even when the fluid is cold? I don't think I want to install stainless steel lines because that will take me out of the stock SCCA class (I think).
Any ideas/suggestions?
Thanks in advance for any input.
At the autocross this past weekend (about 45 seconds per lap) by the 4th or 5th run of the first session, my brake pedal became very soft. I really had to give it increasing pressure to slow down.
Could it be my brake lines expanding? I just find it hard to believe that the rubber is that soft and the fluid is heating up that quickly. If I didn't flush my brake fluid properly, and there was air in the lines, wouldn't I notice even when the fluid is cold? I don't think I want to install stainless steel lines because that will take me out of the stock SCCA class (I think).
Any ideas/suggestions?
Thanks in advance for any input.
08-30-2011, 12:29 PM
#4
There is NO way your fading cause of heat on an AutoX.
On a side note, HPS suck. Id almost say OEM Nissan pads are better. HP+ is the way to go for autox if you can deal with the beat up on your rotors.
The tape on the line is a good idea... never thought of that.
It is pretty stupid that lines are illegal for stock class. I checked and its only legal for cars mfg before 92. You would think for safety reasons maybe. If the lines are expanding, I'm sure you can pick up a take off set from someone who upgraded for cheap.
Give it a good bleed too. May be a bubble.
On a side note, HPS suck. Id almost say OEM Nissan pads are better. HP+ is the way to go for autox if you can deal with the beat up on your rotors.
The tape on the line is a good idea... never thought of that.
It is pretty stupid that lines are illegal for stock class. I checked and its only legal for cars mfg before 92. You would think for safety reasons maybe. If the lines are expanding, I'm sure you can pick up a take off set from someone who upgraded for cheap.
Give it a good bleed too. May be a bubble.
08-30-2011, 12:34 PM
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Well given that the car is almost 9 years old, and the generally violent nature of autoX braking, I would look at the brake lines. Easy test to see if it the brake lines, is use some thin strips of painters tape. wrap one layer, and only one layer around the brake lines. go drive it, and see if the painter's tape is torn. If not, It might be time to flush the fluid. generally people state that brake fluid is only good for 90 days due to its nature of absorbing water, which lowers its boiling point.
08-30-2011, 12:36 PM
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There is NO way your fading cause of heat on an AutoX.
On a side note, HPS suck. Id almost say OEM Nissan pads are better. HP+ is the way to go for autox if you can deal with the beat up on your rotors.
The tape on the line is a good idea... never thought of that.
It is pretty stupid that lines are illegal for stock class. I checked and its only legal for cars mfg before 92. You would think for safety reasons maybe. If the lines are expanding, I'm sure you can pick up a take off set from someone who upgraded for cheap.
Give it a good bleed too. May be a bubble.
On a side note, HPS suck. Id almost say OEM Nissan pads are better. HP+ is the way to go for autox if you can deal with the beat up on your rotors.
The tape on the line is a good idea... never thought of that.
It is pretty stupid that lines are illegal for stock class. I checked and its only legal for cars mfg before 92. You would think for safety reasons maybe. If the lines are expanding, I'm sure you can pick up a take off set from someone who upgraded for cheap.
Give it a good bleed too. May be a bubble.
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08-30-2011, 01:03 PM
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2003 Track edition. About 45,000 miles. Brembos with Hawk HPS pads. Pads are about a year old with maybe 4 autocrosses and a weekend of HPDE on them. Brand new ATE super blue brake fluid. Car is stock, and I was running on Yokohama Advan ao48's, which only had one autocross and the HPDE on them.
At the autocross this past weekend (about 45 seconds per lap) by the 4th or 5th run of the first session, my brake pedal became very soft. I really had to give it increasing pressure to slow down.
Could it be my brake lines expanding? I just find it hard to believe that the rubber is that soft and the fluid is heating up that quickly. If I didn't flush my brake fluid properly, and there was air in the lines, wouldn't I notice even when the fluid is cold? I don't think I want to install stainless steel lines because that will take me out of the stock SCCA class (I think).
Any ideas/suggestions?
Thanks in advance for any input.
At the autocross this past weekend (about 45 seconds per lap) by the 4th or 5th run of the first session, my brake pedal became very soft. I really had to give it increasing pressure to slow down.
Could it be my brake lines expanding? I just find it hard to believe that the rubber is that soft and the fluid is heating up that quickly. If I didn't flush my brake fluid properly, and there was air in the lines, wouldn't I notice even when the fluid is cold? I don't think I want to install stainless steel lines because that will take me out of the stock SCCA class (I think).
Any ideas/suggestions?
Thanks in advance for any input.
1) If you left air in the lines you would probably not notice so much when cold although the pedal might not be as firm. Having said that, I don't think you could heat the fluid up enough in autocross to boil the fluid and make a noticeable difference in pedal pressure.
2) I doudt very highly it is the brake lines that caused your problem. I assume as they have gotten older they probably expand a bit more but I could not imagine you would notice that much of a difference this time.
3) I don't think the pads would be your issue if you have been running on them for more than just this event but my recommendation for auto-x is HP+ (rotor aggressive) or carbotech ax6 pads.
My recommendation would be as follows. Check the fluid level and inspect the system for leaks (i.e. a bleeder screw that is not fully closed). If no leaks, pull off front calipers and inspect the pistons and seals around pistons (don't remove pistons, just look at them). You are looking for scratches or knicks to the pistons or seals that are cracked. If they look good, make sure the pistons retract properly (push them back in as if you were putting on new pads). I have seen calipers that need to be rebuilt where the piston will not retract enough and keeps the pad in contact with the rotors (producing extra heat and causing fluid boil). Bleed fluid and then change to a more aggressive pad.
If you do all this and everything looks fine but you still have the issue, could be a master cylinder going bad.
Just my thoughts
Last edited by jnathan68; 08-30-2011 at 01:07 PM.
08-30-2011, 01:06 PM
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Probably just air, considering you bleed the brakes the night before. A small air bubble turns into a large bubble with very little heat added to it.
08-30-2011, 01:21 PM
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Questions for you: did the brakes start out firm on the 4th and 5th sessions and get softer toward the end of the session or were they soft the entire run? Also, how do the brakes feel on the street after the autocross?
1) If you left air in the lines you would probably not notice so much when cold although the pedal might not be as firm. Having said that, I don't think you could heat the fluid up enough in autocross to boil the fluid and make a noticeable difference in pedal pressure.
2) I doudt very highly it is the brake lines that caused your problem. I assume as they have gotten older they probably expand a bit more but I could not imagine you would notice that much of a difference this time.
3) I don't think the pads would be your issue if you have been running on them for more than just this event but my recommendation for auto-x is HP+ (rotor aggressive) or carbotech ax6 pads.
My recommendation would be as follows. Check the fluid level and inspect the system for leaks (i.e. a bleeder screw that is not fully closed). If no leaks, pull off front calipers and inspect the pistons and seals around pistons (don't remove pistons, just look at them). You are looking for scratches or knicks to the pistons or seals that are cracked. If they look good, make sure the pistons retract properly (push them back in as if you were putting on new pads). I have seen calipers that need to be rebuilt where the piston will not retract enough and keeps the pad in contact with the rotors (producing extra heat and causing fluid boil). Bleed fluid and then change to a more aggressive pad.
If you do all this and everything looks fine but you still have the issue, could be a master cylinder going bad.
Just my thoughts
1) If you left air in the lines you would probably not notice so much when cold although the pedal might not be as firm. Having said that, I don't think you could heat the fluid up enough in autocross to boil the fluid and make a noticeable difference in pedal pressure.
2) I doudt very highly it is the brake lines that caused your problem. I assume as they have gotten older they probably expand a bit more but I could not imagine you would notice that much of a difference this time.
3) I don't think the pads would be your issue if you have been running on them for more than just this event but my recommendation for auto-x is HP+ (rotor aggressive) or carbotech ax6 pads.
My recommendation would be as follows. Check the fluid level and inspect the system for leaks (i.e. a bleeder screw that is not fully closed). If no leaks, pull off front calipers and inspect the pistons and seals around pistons (don't remove pistons, just look at them). You are looking for scratches or knicks to the pistons or seals that are cracked. If they look good, make sure the pistons retract properly (push them back in as if you were putting on new pads). I have seen calipers that need to be rebuilt where the piston will not retract enough and keeps the pad in contact with the rotors (producing extra heat and causing fluid boil). Bleed fluid and then change to a more aggressive pad.
If you do all this and everything looks fine but you still have the issue, could be a master cylinder going bad.
Just my thoughts
08-30-2011, 01:22 PM
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I completely flushed the system and replaced the fluid the night before. Maybe you are right. I could have messed something up since the calipers have two bleeder valves. I haven't found a write-up on how to bleed the brakes using both bleeder valves. Thanks.
08-30-2011, 01:26 PM
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On my stoptechs, I bleed the outside one first on each caliper and then close it and bleed the inside one next.
08-30-2011, 01:29 PM
#14
Your pads might be starting to taper due a piston issue. I was going to say pad knock back, but you said it didn't start until the 4th or 5th session. That is assuming you weren't putting around the first three which I don't see why you would. I don't think heat is an issue either in a 45 second auto-x session.
09-01-2011, 05:41 AM
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i just went back a re-read the first post, it might be pad knock back as well.
As you state the later the runs the more prone this is to happening. Well AO48s do take a bit a time to heat up, and as violent as AUTOX can get, you very well might be inducing pad knock pad, I do it all the time on my AO48s.
not sure how good you are with your left foot, and I know AUtoXs are very busy with inputs, but if you can "prime" the brakes either with your left foot befor ethe braking zone, or give them a quick hard pump and then get into your braking zone with the second application of brakes.
Be careful with your timing, the Z does not talerate being WOT and hitting the brakes, she'll dive into limp mode for sure. So play with the timing and give it a shot.
I would be curious as to your rotor choice as well.
As you state the later the runs the more prone this is to happening. Well AO48s do take a bit a time to heat up, and as violent as AUTOX can get, you very well might be inducing pad knock pad, I do it all the time on my AO48s.
not sure how good you are with your left foot, and I know AUtoXs are very busy with inputs, but if you can "prime" the brakes either with your left foot befor ethe braking zone, or give them a quick hard pump and then get into your braking zone with the second application of brakes.
Be careful with your timing, the Z does not talerate being WOT and hitting the brakes, she'll dive into limp mode for sure. So play with the timing and give it a shot.
I would be curious as to your rotor choice as well.
09-01-2011, 08:00 AM
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i just went back a re-read the first post, it might be pad knock back as well.
As you state the later the runs the more prone this is to happening. Well AO48s do take a bit a time to heat up, and as violent as AUTOX can get, you very well might be inducing pad knock pad, I do it all the time on my AO48s.
not sure how good you are with your left foot, and I know AUtoXs are very busy with inputs, but if you can "prime" the brakes either with your left foot befor ethe braking zone, or give them a quick hard pump and then get into your braking zone with the second application of brakes.
Be careful with your timing, the Z does not talerate being WOT and hitting the brakes, she'll dive into limp mode for sure. So play with the timing and give it a shot.
I would be curious as to your rotor choice as well.
As you state the later the runs the more prone this is to happening. Well AO48s do take a bit a time to heat up, and as violent as AUTOX can get, you very well might be inducing pad knock pad, I do it all the time on my AO48s.
not sure how good you are with your left foot, and I know AUtoXs are very busy with inputs, but if you can "prime" the brakes either with your left foot befor ethe braking zone, or give them a quick hard pump and then get into your braking zone with the second application of brakes.
Be careful with your timing, the Z does not talerate being WOT and hitting the brakes, she'll dive into limp mode for sure. So play with the timing and give it a shot.
I would be curious as to your rotor choice as well.
Rotors are stock. I have really, really, really been fighting the urge to start upgrading the car. I know once I start, it will snowball, and I'd rather just buy a different car.
THANKS FOR THE INPUT, EVERYONE!
09-01-2011, 09:23 AM
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So pad knock back may be the effect of a problem with my caliper piston? I'll take a look the next time I get the car on the lift.
Rotors are stock. I have really, really, really been fighting the urge to start upgrading the car. I know once I start, it will snowball, and I'd rather just buy a different car.
THANKS FOR THE INPUT, EVERYONE!
Rotors are stock. I have really, really, really been fighting the urge to start upgrading the car. I know once I start, it will snowball, and I'd rather just buy a different car.
THANKS FOR THE INPUT, EVERYONE!
but the concept is as follows: the brembos are a floating rotors verses a floating caliper. This floating rotor can deflect inside the caliper and push the pads back into the calipers.
I have found the stickier the tire the worse it is, the two piece rotors do it more than one piece, in my experience, I think the stock rotor is the best one for the OE brembo fitment, IMO. I think it is just the nature of the beast.
The upshot, if you really cannot deal with the knock back and want to change and stay in class, pick up some 06-08 base model brakes. They are just a fuzz (0.4") less diameter and almost the same size pads as the brembo, but they are floating calipers which doesn't suffer knockback near as much, as in 90% less, beacuse as the rotor deflects in the caliper, the caliper slides with the rotor. you can stay in class because it is OE and SCCA yack yack and some rules lawyering, it is actually less hardware than what you have.
Hope that makes sense.
09-01-2011, 09:41 AM
#18
So pad knock back may be the effect of a problem with my caliper piston? I'll take a look the next time I get the car on the lift.
Rotors are stock. I have really, really, really been fighting the urge to start upgrading the car. I know once I start, it will snowball, and I'd rather just buy a different car.
THANKS FOR THE INPUT, EVERYONE!
Rotors are stock. I have really, really, really been fighting the urge to start upgrading the car. I know once I start, it will snowball, and I'd rather just buy a different car.
THANKS FOR THE INPUT, EVERYONE!
Pad knock back is caused by what LightningGuy said. The rotor will push on the pads during cornering and push them back into the caliper causing a longer pedal...and yes it does get worse with stickier tires because you are pushing more lateral g's in the corners.
Like LightningGuy said, a tap on the brake pedal before a braking zone will set them against the rotor again and then when you do you braking it should feel good again. If that does not fix it then it is something else. I have used the tap on the brake pedal technique many times to re-seat mine coming down a straight away. I've seen a lot of the Continental Tire guys do it too.
09-01-2011, 10:54 AM
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No. I was saying the pads might be tapering because of the piston possibly going out.
Pad knock back is caused by what LightningGuy said. The rotor will push on the pads during cornering and push them back into the caliper causing a longer pedal...and yes it does get worse with stickier tires because you are pushing more lateral g's in the corners.
Like LightningGuy said, a tap on the brake pedal before a braking zone will set them against the rotor again and then when you do you braking it should feel good again. If that does not fix it then it is something else. I have used the tap on the brake pedal technique many times to re-seat mine coming down a straight away. I've seen a lot of the Continental Tire guys do it too.
Pad knock back is caused by what LightningGuy said. The rotor will push on the pads during cornering and push them back into the caliper causing a longer pedal...and yes it does get worse with stickier tires because you are pushing more lateral g's in the corners.
Like LightningGuy said, a tap on the brake pedal before a braking zone will set them against the rotor again and then when you do you braking it should feel good again. If that does not fix it then it is something else. I have used the tap on the brake pedal technique many times to re-seat mine coming down a straight away. I've seen a lot of the Continental Tire guys do it too.
09-01-2011, 04:33 PM
#20
Is it safe to assume that this is a new issue with your brakes - you have not experienced this before?
Can knock-back just 'start up'.. ?
It sounds like he has a fair amount of experience with auto-x, hpde.. if this didn't occur before (with same tires, pads, fluid..) why would knock-back start now?
Can knock-back just 'start up'.. ?
It sounds like he has a fair amount of experience with auto-x, hpde.. if this didn't occur before (with same tires, pads, fluid..) why would knock-back start now?