GodISmE

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?

dkmura

iTrader: (64)

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.

armt350z

iTrader: (6)

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.

dkmura

iTrader: (64)

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.

CK_32

iTrader: (1)

Sounds like air or cooked fluid. Did you bleed them after your track days?

armt350z

iTrader: (6)

I use a motive power bleeder. I was chasing an air bubble in the system for a while and ended up turning the car on and pumping the brake pedal with the motive unit still hooked up and finally got the bubble out from the rear right caliper.

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.

terrasmak

iTrader: (8)

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

GodISmE

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?

JBJ

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.

jledford

iTrader: (1)

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.

GodISmE

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?

jledford

iTrader: (1)

To add to this the FSM also has a different order than most people for bleeding: RR, LF, LR, RF

03threefiftyz

iTrader: (25)

Use the Motive all the time....love it.

armt350z

iTrader: (6)

I know it doesn't make sense why it matters if the car was on, maybe its a coincidence. But the last bit of air that was trapped only came out when I bled with it on.

JBJ

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.

JMII

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.

06platinumG

iTrader: (1)

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/

eye-5

When I first did my Brembo conversion, despite re bleeding, the pedal was a little soft. I engaged ABS a couple of times and within a couple of days the pedal firmed right up. I bled with a motive power bleeder. The ABS module might have something to do with it.

Ever since then, I've had no issues. The pedal is nice and firm.

GodISmE

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

terrasmak

iTrader: (8)

What fluid are you running now?