This is weird, so stay with me here.

Here is the problem. When running my slicks (ET streets) I have no brakes after being in boost. At the end of the 1/4 mile it takes a good 2-3 sec to get my brakes back. I have no pedal, as in it can't be pressed in.

This is only on my ET streets. It has never happend on my street tires and it happens every time on my slicks. It's not a fluke thing, I have ran my slicks down the track many times.

I think it has to be a vacuum thing. It's not mechanical.

As far as I know the only vacuum source the brake booster uses is the large one comming off the top of the manifold. There is a check valve in that line so the brake system doesn't loose vacuum when the manifold does.

One woud think that maybe the check valve is bad and when I am in boost the brake system loses vacuum. But if that was the case it would happen on street tires too.

I have thought of a couple theories but they dont' make sense.

 

Sounds kind of scary to me

 

Definitely weird.. Is there anything catching on the brake lines etc?

 

but arent you in boost for a longer time than on the streets? do you ever run full boost for 12sec on the street?

Weird issue though, see if you can swap out that part with some one elese for a track day

 

Very odd. It may not strictly be related to the tire selection even though it appears that way. I'd still look at that check valve as the prime suspect until you can positively rule it out. Mardi might have a point with the length of time at full boost?

 

yeah that was def scary seeing you run down the track, and than coming around and saying you didnt have breaks... yikes, hopefully you can figure this out mike

 

Got ABS?......

 

Have you ran street tires at the track recently? If not, try to emulate what you do at the track on street tires(same psi etc..) and see if the problem persists; if not, then it may be vacume. Is your brake fluid level the same?

 

Nismo-
Nothing catching on the lines. That was my first thought

Mardi-
Since I have been turbo I have probably 50 1/4 miles passes on street tires and 20 on the ET streets. Has never happend on street tires but every time on the ET streets. It's not hit or miss, it's been every time on the ET streets. I can go from street tires and have no problems to the ET streets 10 min later and no brakes.

I probably do see more boost for a longer period of time on the ET streets, but it's gotta be an insignificant amount for what were talking about.


Dandy-
Like I said, it has been 100% tire dependant so far. also, I took the ET streets out on a deserted road and after being in boost thougjust 1st and 2nd I had no brakes.


Icey-
Yes, I have ABS. Come one this is an Infiniti not a maxima!


Sleeper
I ran street tires and the ET streets back to back at the track 2 weeks ago. Only happend on the ET streets. Never the street tires.

 

Just pulling this out of my ****, but if you change the size of the wheel/tire dramatically or front/rear bias or tire/brake grip, maybe the ABS can activate?

Although, you would see the ABS light flash, so I doubt that's it.

 

It's a possibility, but it's not like it's the abs activating. I physically can not push the brake pedal in. After 2-3 sec the brakes come back.

 

Maybe it's an air pocket in the lines. When you launch on the track the car is at a certain angle degree wise (thrust angle)maybe that could cause the problem. Again slick profile maybe different from daily runners (tires and rim), angle with air pocket. Just a guess.

 

thats exactly what i was gonna say....its your abs sensor having seista....mine does it on the street all the time after my brake swap

 

Air in the lines causes a spongey feeling. The brake booster causes hard pedal. Certainly weird though.

 

I take it you have a boost gauge. I would plumb it in on the brake booster side to monitor behaviour of what's going on there. you might want to consider running two check valves in parallel if you find that vacuum is indeed being lost.

 

dam that is wierd! Hope you get that steight!

 

Brilliant! it the brake booster check valve leaking a common problem on boosted cars? Ive often wondered but never checked. It the check valve on a turbo supra better made to deal with this than on a NA one?

 

Actually, it is something I have suspected for a while now but never really checked. My variable intake manifold sometimes suffers from not opening even though the AEM switches the valve. Can't say I have run into the brke problem though. That IS serious! A supra one would probably work better .. I actually thought about that too when I typed the last response. Supras, boosted DSMs etc might work better .. but need to diagnose it first.

 

Pull the check valve and check to see if it works...

It took me several tries to find one that would really hold pressure and not just "slow" the flow down.

 

Does it do it on a hard and soft launches on the ETs?

 

Thanks for all the reply's guys. Sorry I have not responded, been working.

Of course the check valve is the first thought. But it just doesn't make sense that it would never happen on street tires and only on the ET streets. That is the part that's got me. I have stayed in boost plenty long on street tires compared to the ET streets.

I have pulled the check valve a few times already, and the simple blow test shows that it works, but that doesn't prove that it doesn't fail me sometimes. I have had a check valve with my MEVI set up that would work off and on.


The idea of the hard launch on the ET streets causing the check valve to act up is a decent theory, but I have done alot of runs on both tire sets and have launch hard and soft on both. Still, only happens on the ET stretts.....and happens every time on the ET streets

The only way to test any fixes I make will be to put the ET streets on and do some driving. Will replace the check valve and let you all know what happens. It will be a little bit before any testing is done, I am in the midst of a move right now