Hey,

I am putting this in this section because I am looking for experienced track users advice and knowledge. I am currently helping out a friend with a braking issue that he is having only under extreme driving. Read below for details and explanation.

-Car-

2007 350z Enth ( Osiris ECU )

Master cylinder has been replaced twice. New one now. Installed before the brakes. The issue started day of bbk install. Gradually gotten less but not much.

Kit.

- Stoptech -

Fronts- ST60
Rears - ST45

Fluid - Motul RBF 600


Issue- Under extreme conditions such as hard cornering or hard acceleration then sudden breaking. Basic track driving. The brakes will not function on first attempt ( 10% ) breaking power estimate. Then on second pump its back to around ( 80% ) or greater. This vehicle is mainly for auto x events so this first pump is crucial. The owner of the car is getting extremely frustrated so I decided to help.

My experience with it so far. The brakes work awesome when daily driving. Stops from high mph to low enough to pop your eyes out ( joke ). Only after 2 or three hard turns then accelerating though say 3rd gear until around 6500 rpms, then hard breaking will you get this reaction.



Whats been done so far -

1. Brakes were bleed twice regularly.
2. Brakes were power bleed completely with all new fluid.
3. Made a temp brace for master cylinder ( just to see )


What I want to try -

1. Pull abs fuse ( does not have vdc )
2. Try bleeding the brakes again ( tapping slight on rotor while for stubburn air )
3. Bleed master cylinder



Up for any more suggestions. Talked to Stoptech them selves and they really didn't seem to have an answer. Or i am just not technical to understand what they were saying. I would imagine some one else with a BBK that really pushes and tracks their car has experienced this.

 

Is the peddle itself soft on the first pump or do the brakes just lack responsiveness (the 10% you speak of)?

 

Pad knock?

http://www.stoptech.com/tech_info/wp_knockback.shtml

Try the new bracket they made to put the calipers @ the 9oclock position.

more:
https://my350z.com/forum/autocross-r...ack-issue.html

 

I'm not familiar with the Stop-Techs specifically, but this is a common issue with the Brembos we have in the car now. It's not knock back, but similar - the pistons tend to get sucked back into the caliper from negative pressure.

With the Brembos, the pedal can be very soft, but full braking is available. It's not very confidence-inspiring though and takes a lot of getting used to.

Just tap the brake pedal a couple times approaching the brake zone and you're set. It doesn't take much - just enough to push the pistons back out to the pads.

Brian

 

good question. Its not soft it feels like your pushing and some one put a stick behind the peddle preventing you from pushing it all the way down. Then on second pump it locks in the same position but with 80% or greater.





I will check those links now. Thanks.




Yeah that what he does not but its frustrating him and makes him think more about his breaking than driving the car and hitting his turns correctly.

 

Sounds like similar symptoms to ABS Ice Mode. There are some discussion here on it, but many more on other sites.

 

Probably pad knockback. Learn to tap the brakes on the straights.

 

^^ Thats what it sounds like.

 

Something I've become used to doing by now.

 

My boosted Z with stop-techs does exactly the same thing...after many conversations, bleeding, replacing the master cylinder, bleeding again and changing fluid to ATE Blue etc..I was told because I am in boost up until the point I start to brake, there is no VACUUM and therefore it takes a tap on the pedal and then reapply to get full braking power. Makes sense to me..

 

^ no because as soon as you take your foot off the gas the engine instantly goes into vacuum. The time it takes you to move your foot from off the gas to brake no matter how small is still enough time for it to have enough vacuum to work properly. Its most likely knock back, i had the same problem with other bbk during autox due to the fact that the car is cornering so hard. just my .02 best of luck.

 

Agreed with all the pad knock back comments for sho!!! Happens to all of us on track.

I just watched the Continental Tire Sports Car race I DVR'd from Road America a couple weeks back and they do the same thing coming down the straights. They give their brakes the slightest tap to re-seat everything before the braking zone.

 

Yep, I've got stoptechs and I get knockback. Simplest and cheapest solution as everyone else said is to tap the breaks. It's like learning to heel-toe. You just get use to it after a while.

 

Ok not arguing here, but just curious..knock back is caused by a floating rotor flexing left and right thus "knocking" the pad and the piston back into the caliper..right? so if I am on the brakes ( trail braking through a curve) and then hammer the throttle down a straight to the next turn..how can the issue be knockback? I still think the transition from boost to vacuum in the brake booster is the culprit.. my .02

 

I cannot comment on the whole boost thing because I am not sure on that.

I do see your point too about trail braking. When you get back on the gas though from trail braking you are still tracking out and exiting the corner. You are still putting lateral g's on the car, it just might not be as much as corner entry. Just my $.02.

I'm not trying to argue either, but I experience the same issues with pad knock back and I think all of us do. I have the track model Brembos on my car. It was way worse when I had the stock single piston calipers all the way around....WAYYYYY worse. I had an unbelievable amount of pedal travel if I didn't tap the brakes on the straights to re-seat them.

 

No. On the 350Z its caused by hub flex not a floating rotor (FYI... most floating rotors float in the plane of the hat, not laterally). The lateral loads from cornering cause the hub to flex wich causes the rotor to move out of true by a few thousandths in relation to the caliper and this pushes the pistons back into the caliper.