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.

does anyone have any crude ??? any guess ?

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

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)

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.

This.

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

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

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.

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

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