Soft brake pedal on a track (HR)
#1
New Member
Thread Starter
Soft brake pedal on a track (HR)
So at the last track day I noticed that the brake pedal was getting soft after a few laps. It was getting firm again after pumping a little bit and it's back to normal when I drive the car daily now.
No problem with braking on a track though after pressing the pedal hard. The braking force was the same, it's just that I didn't have that initial bite/pedal resistance/fluid pressure. It was a rather cold day (10 degrees C) so I don't think it was overheating. No leaks either.
The rbf660 is 4-5 track days old and I have Stoptech SS brake lines.
What is causing it and how can I fix it? New pump? How often do you guys change the brake fluid in your track cars?
No problem with braking on a track though after pressing the pedal hard. The braking force was the same, it's just that I didn't have that initial bite/pedal resistance/fluid pressure. It was a rather cold day (10 degrees C) so I don't think it was overheating. No leaks either.
The rbf660 is 4-5 track days old and I have Stoptech SS brake lines.
What is causing it and how can I fix it? New pump? How often do you guys change the brake fluid in your track cars?
Last edited by GodISmE; 10-30-2016 at 07:01 AM.
#2
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MY350Z.COM
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What you're describing as having a soft pedal is likely air in the brake system. To prevent this, I bleed the brake system before every weekend. It doesn't have to be a full bleed, just 10-15 seconds at each corner (both nipples) with a pressure bleeder. RR, LR, RF and LF to make sure the brake fluid gets cycled through and past the hottest part of the system. I also think using Ti shims on each Brembo caliper helps reduce the impact of the heat. If the pedal feels spongy during the weekend, I'll rebleed the system again, but there may be a learning curve as well. At the SCCA Runoffs, I had a soft pedal during the last qualifying session when one of my crew members bleed it alone. After I used the pressure bleeder, the brakes were strong and consistent once again.
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RobPhoboS (03-21-2017)
#3
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If you have bleed the brakes and still have soft pedal pressure, bleed them again but have the motor running. I'm not sure why this works but it does. I don't know if its a function of the brake booster or possibly the ABS block electronics doing its thing, but it works.
I normally do a quick bleed before every event. About .5 liters worth of fluid. I also bumped down to RBF 600 from the 660 since its a third of the price and I dont mind flushing it so much.
I normally do a quick bleed before every event. About .5 liters worth of fluid. I also bumped down to RBF 600 from the 660 since its a third of the price and I dont mind flushing it so much.
#4
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MY350Z.COM
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If you have bleed the brakes and still have soft pedal pressure, bleed them again but have the motor running. I'm not sure why this works but it does. I don't know if its a function of the brake booster or possibly the ABS block electronics doing its thing, but it works.
I normally do a quick bleed before every event. About .5 liters worth of fluid. I also bumped down to RBF 600 from the 660 since its a third of the price and I dont mind flushing it so much.
I normally do a quick bleed before every event. About .5 liters worth of fluid. I also bumped down to RBF 600 from the 660 since its a third of the price and I dont mind flushing it so much.
By bleeding the brakes on a regular basis, it has the added advantage of ensuring the total volume of brake fluid stays fresh over a season.
#6
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I've never heard of this as a brake bleed technique. Are you using a pressure bleeder, or the two man brake bleed method? If it's the latter, it might make sense by engaging the brake booster.
By bleeding the brakes on a regular basis, it has the added advantage of ensuring the total volume of brake fluid stays fresh over a season.
By bleeding the brakes on a regular basis, it has the added advantage of ensuring the total volume of brake fluid stays fresh over a season.
I'm also wondering if the bleeder port is actually the highest point on the rear calipers and it just took a ton of pressure and flow to get it out.
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RobPhoboS (03-21-2017)
#7
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I do like 2 pumps out of each bleed port after every track weekend. The fluid in the caliper is the most damaged from heat, I get rid of it
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#8
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Thread Starter
I will try to bleed the brakes then, I've never done this actually.
I would prefer to do it myself (if necessary with a friend to help). Is there a kit that I can buy and a diy video applicable to 350z or something that you could recommend?
If I cooked the fluid though, how would I know if the symptoms are the same? Should I change it now? How to avoid it going forward?
I would prefer to do it myself (if necessary with a friend to help). Is there a kit that I can buy and a diy video applicable to 350z or something that you could recommend?
If I cooked the fluid though, how would I know if the symptoms are the same? Should I change it now? How to avoid it going forward?
Last edited by GodISmE; 10-31-2016 at 06:55 AM.
#9
Can you get this over there?
https://www.motiveproducts.com/colle...-prong-bleeder
Screw it on, pump it up to the recommend PSI, and then open each bleeder screw one at a time. Done. There are plenty of videos on Youtube on how to do it. Definitely worth the money.
https://www.motiveproducts.com/colle...-prong-bleeder
Screw it on, pump it up to the recommend PSI, and then open each bleeder screw one at a time. Done. There are plenty of videos on Youtube on how to do it. Definitely worth the money.
#10
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For those saying the car needs to be on that might help, I don't know.
However, the FSM states that you either need to disconnect the negative battery cable or unplug the ABS control unit. There is obviously some power still on the system that the FSM wants to be removed. I've always unplugged the unit and never had any problems with air left after using a Motive Power bleeder.
However, the FSM states that you either need to disconnect the negative battery cable or unplug the ABS control unit. There is obviously some power still on the system that the FSM wants to be removed. I've always unplugged the unit and never had any problems with air left after using a Motive Power bleeder.
Last edited by jledford; 10-31-2016 at 10:06 AM.
#11
New Member
Thread Starter
I read about this Motive power bleeder some time ago. If this thing does the job and only costs 60 bucks then great!
I still do not know if I actually have air in the system or if I just cooked the fluid. How would I know? Would the pressure be back to normal - like it is now - when daily driving the car if it was air? On the other hand, if this only happened during my fifth event, maybe the fluid has more water in it now and is easier to get cooked? How does it work?
I still do not know if I actually have air in the system or if I just cooked the fluid. How would I know? Would the pressure be back to normal - like it is now - when daily driving the car if it was air? On the other hand, if this only happened during my fifth event, maybe the fluid has more water in it now and is easier to get cooked? How does it work?
Last edited by GodISmE; 10-31-2016 at 10:06 AM.
#12
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For those saying the car needs to be on that might help. The FSM states that you either need to disconnect the negative battery cable or unplug the ABS control unit. There is obviously some power still on the system that the FSM wants to be removed. I've always unplugged the unit and never had any problems with air left after using a Motive Power bleeder.
#15
Who knows. The vibration of the engine running could have knocked the bubble loose???
I've read to use a rubber mallet and to drive down a bumpy dirt road to knock the air bubble loose. I have to admit, the dirt road thing seemed to work. Could have been a coincidence though.
I've read to use a rubber mallet and to drive down a bumpy dirt road to knock the air bubble loose. I have to admit, the dirt road thing seemed to work. Could have been a coincidence though.
#16
New Member
I tap with a mallet when using the Motive... and its seems to help. The bubbles are really tiny making them very difficult to see. Another tip is to close the nipple, tap with the mallet several times then open the nipple quickly. Seems the surge of fluid sucks the trapped air out a bit easier. I've also had the brakes be a little soft right after bleeding but then firm up after daily driving for a few days so the bouncing thing might be helping as well.
#17
Registered User
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I use Russell speed breeders and they work great and you can use without help. I bleed mine every time I go to the track. 4 or 5 pumps per corner before and after when I change my pads from street to track.
http://russellperformance.com/mc/speed-bleeders/
http://russellperformance.com/mc/speed-bleeders/
Last edited by 06platinumG; 10-31-2016 at 08:45 PM.
#18
I tap with a mallet when using the Motive... and its seems to help. The bubbles are really tiny making them very difficult to see. Another tip is to close the nipple, tap with the mallet several times then open the nipple quickly. Seems the surge of fluid sucks the trapped air out a bit easier. I've also had the brakes be a little soft right after bleeding but then firm up after daily driving for a few days so the bouncing thing might be helping as well.
Ever since then, I've had no issues. The pedal is nice and firm.
#19
New Member
Thread Starter
I bled the system but still the same problem from the second session onwards today. Althouh it did get better later on... or maybe it was just me learning and getting used to pumping the brakes on straights using my left foot
Anyway, time to replace the fluid with rbf600 but that's for next season
Anyway, time to replace the fluid with rbf600 but that's for next season
#20
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MY350Z.COM
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What fluid are you running now?