Brake pressure drop while down shift

sawill629 · 06-09-2013, 01:44 AM

I have my used 09 370Z sport 6MT for 6 mths 35k. Does any one have this symptom or any advise ? Thanks in advance.

Change all fluid before the track day
fornt Hawk DTC 70 rear DTC 60
power slot (slot) rotor F/R ( no brake cooling duct )
SS brake line
OEM suspension
CB exhaust / test pipe
front camber arm

When I am at the local track day ( mission raceway). squeeze the braking under high pressure (like 70%) downshit while release the clutch. I can feel the brake pedal pressure drop down a bit. while the pedal drop the car wasnt slowing down as it should be ( could be scary ). No matter under S-mode or not still the same. try to breed the brake and do another test. still the same. normal daily driving or light pressure under track condition (50%) brake feel like normal. I guess thats not ice mode since the pedal being soft instead of being hard. I dont feel ABS kicking the pedal. any advise ???

another question is while I am testing the brake for the 2nd time I do 8 laps ( 2 laps warm up 6 laps more aggressive in total 16mins ) after that I am doing a cool down lap. I experience my first brake fluid boiled which i am using Motel RBF600 already.( my lucky day). no brake. sponge on pedal. I know different track and brake skill will total affect the temp of brake fluid which I have been doing this race track for 10 yr. with my previous STI I have no problem at all for a full 30 min. Do you think brake cooling duct will help ?

Please forgive if I am making story long.

sawill629 · 06-12-2013, 03:03 AM

does anyone have any crude ??? any guess ?

Alstann · 06-12-2013, 08:23 AM

Maybe when the car revs up during downshifting, the brake vacuum assist is stronger, causing the pedal to drop slightly? My guess.

Chuck33079 · 06-12-2013, 08:38 AM

I'd check the brake booster and the vacuum hoses. As far as your other question, brake cooling will help. Titanium pad shims should help as well.

DEpointfive0 · 06-12-2013, 01:09 PM

Quote:

Originally Posted by Chuck33079

I'd check the brake booster and the vacuum hoses. As far as your other question, brake cooling will help. Titanium pad shims should help as well.

Can we go 1mm shims? (So 2mm total per brake caliper)

Chuck33079 · 06-12-2013, 01:10 PM

I'm not sure. I've ordered a set of the thinner ones, but they're not getting installed until it's time for new pads.If they didn't fit, shaving the pads wouldnt be too hard.

Sh0velMan · 06-12-2013, 03:01 PM

Quote:

Originally Posted by Alstann

Maybe when the car revs up during downshifting, the brake vacuum assist is stronger, causing the pedal to drop slightly? My guess.

This.

edit: nevermind, re-read the OP. You're boiling your fluid. Titanium shims, ducting, etc.

Rusty · 06-12-2013, 04:06 PM

Quote:

Originally Posted by DEpointfive0

Can we go 1mm shims? (So 2mm total per brake caliper)

Quote:

Originally Posted by Chuck33079

I'm not sure. I've ordered a set of the thinner ones, but they're not getting installed until it's time for new pads.If they didn't fit, shaving the pads wouldnt be too hard.

I installed the .5mm shims.

D1346 Titanium Brake Heat Shield Shim for Nissan 370Z Infiniti G37 [TS-T-D1346] : Hard Brakes - Titanium Brake Backing Plates, Brake Shims, Brake Heat Shields

sawill629 · 06-14-2013, 01:09 AM

thanks for all the input. will check brake booster and vacuum host.
titanium shim will be a good idea. cooling dust will be on as well.
I have order the brake master cylinder already. Will put on soon. Hope that will solve the problems.

Alstann · 06-15-2013, 10:10 PM

Quote:

Originally Posted by Sh0velMan

This.

edit: nevermind, re-read the OP. You're boiling your fluid. Titanium shims, ducting, etc.

I think the first time, since he didn't boil the fluid the first outing, my theory may still hold true.

The second time though, totally agree with you Shovel. ^^

06-09-2013, 01:44 AM	#1 (permalink)
sawill629 Base Member Join Date: Sep 2012 Location: vancouver Posts: 14 Drives: 09 370Z Rep Power: 12	Brake pressure drop while down shift I have my used 09 370Z sport 6MT for 6 mths 35k. Does any one have this symptom or any advise ? Thanks in advance. Change all fluid before the track day fornt Hawk DTC 70 rear DTC 60 power slot (slot) rotor F/R ( no brake cooling duct ) SS brake line OEM suspension CB exhaust / test pipe front camber arm When I am at the local track day ( mission raceway). squeeze the braking under high pressure (like 70%) downshit while release the clutch. I can feel the brake pedal pressure drop down a bit. while the pedal drop the car wasnt slowing down as it should be ( could be scary ). No matter under S-mode or not still the same. try to breed the brake and do another test. still the same. normal daily driving or light pressure under track condition (50%) brake feel like normal. I guess thats not ice mode since the pedal being soft instead of being hard. I dont feel ABS kicking the pedal. any advise ??? another question is while I am testing the brake for the 2nd time I do 8 laps ( 2 laps warm up 6 laps more aggressive in total 16mins ) after that I am doing a cool down lap. I experience my first brake fluid boiled which i am using Motel RBF600 already.( my lucky day). no brake. sponge on pedal. I know different track and brake skill will total affect the temp of brake fluid which I have been doing this race track for 10 yr. with my previous STI I have no problem at all for a full 30 min. Do you think brake cooling duct will help ? Please forgive if I am making story long.

06-12-2013, 08:23 AM	#3 (permalink)
Alstann Track Member Join Date: Oct 2011 Location: South Florida Posts: 882 Drives: 12 PW 370z 6MT Sport Rep Power: 14	Maybe when the car revs up during downshifting, the brake vacuum assist is stronger, causing the pedal to drop slightly? My guess. __________________ 2012 Pearl White 370Z GReddy Twin Turbo

06-12-2013, 08:38 AM	#4 (permalink)
Chuck33079 A True Z Fanatic Join Date: Nov 2011 Location: Houston Posts: 12,265 Drives: 2011 370ztt Rep Power: 29538	I'd check the brake booster and the vacuum hoses. As far as your other question, brake cooling will help. Titanium pad shims should help as well. __________________ 2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

06-12-2013, 01:10 PM	#6 (permalink)
Chuck33079 A True Z Fanatic Join Date: Nov 2011 Location: Houston Posts: 12,265 Drives: 2011 370ztt Rep Power: 29538	I'm not sure. I've ordered a set of the thinner ones, but they're not getting installed until it's time for new pads.If they didn't fit, shaving the pads wouldnt be too hard. __________________ 2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

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06-12-2013, 03:03 AM	#2 (permalink)
sawill629 Base Member Join Date: Sep 2012 Location: vancouver Posts: 14 Drives: 09 370Z Rep Power: 12	does anyone have any crude ??? any guess ?

06-14-2013, 01:09 AM	#9 (permalink)
sawill629 Base Member Join Date: Sep 2012 Location: vancouver Posts: 14 Drives: 09 370Z Rep Power: 12	thanks for all the input. will check brake booster and vacuum host. titanium shim will be a good idea. cooling dust will be on as well. I have order the brake master cylinder already. Will put on soon. Hope that will solve the problems.