What does the check valve do in the braking system?

Just had my STi brake booster/master cylinder installed, and now when I accelerate hard, I can hear a «new» sound coming from where the booster is, kinda like a «pssssshhhhhhhhhhh» that's not the same as the turbo or blow off valve.

 

The shop said they didn't need the check valve that's referred to in the master cylinder walkthrough on here.

 

Could it be it?

There's a valve in the soft rubber hose from the manifold to the booster - they fail every now then, but is not super common or anything.

Can this be indicated with A/F Learning #1 being large?

 

I am curious about the check valve as well. I thought it was the piece that mates the hose to the booster (the nipple).

the brake booster operates on vacuum. the check valve prevents it from being pressurized.

 

you need the check valve.

without the check valve try slamming on the brakes in full boost

 

and if you actually do this, make sure you don't actually have to stop...

without the check valve try slamming on the brakes in full boost

 

and if you actually do this, make sure you don't actually have to stop...

 

Ok, in other words, it doesn't brake?

There is a vacuum line connecting the booster and the manifold. Without the check valve the booster will see the manifold pressure, you will not be able to depress the pedal.

Well, maybe this is my issue. Whenever I'm at full boost, if I want to press the brake pedal as quickly as possible following the moment I let off the gas, the pedal is very tough to depress, it takes a split second before I actually can.

Who the hell are you taking your car to??? they're a bunch of retards for taking the valve out; esp in a boosted car! Wonder what other things they think you "don't need". "sir you only need one pad on a caliper cos the piston will make up for the gap"

New shop I just «tried», specializing in Subies. My other tech changed careers.

 

They did a decent job of fixing my fubar'ed ignition cylinder, installed the master cylinder/booster in the estimated time, adapted some rear lines to fit the STi calipers... seriously, they did a good job, but I specifically told them «what about the check valve?», and they said they were fine, didn't need one.

 

I figured they were gonna re-use the one from the LGT, but I think it's internal, I don't even know what it looks like.

 

But after boosting the other day and trying to brake, I was like «whoa!!!» for like 0.25 seconds. That's 0.25 seconds too long.

are we all talking about the same valve in the line going to the booster? Is there any other check valves in the vacuum or even hydraulic system?

are we all talking about the same valve in the line going to the booster? Is there any other check valves in the vacuum or even hydraulic system?

 

Yes we are. I ordered the STi hose from the dealer that has the STi check valve in it.

 

I'll try to find out how to install it.

Yes we are. I ordered the STi hose from the dealer that has the STi check valve in it.

 

I'll try to find out how to install it.

 

k just wanted to make sure I understand the situation correctly.

Still curious if a failed one will show up in A/F Learning #1 A like a vacuum leak does. Any ideas?

 

OP, it's a straightforward install. Trace the old one to the manifold and swap it out.

Thanks. Do I insert it closer to the manifold, or booster?

doesn't matter where it goes, it just needs to face the right direction. Nissan has an external one that you can install by cutting the hose in the middle and sticking it in either end. The cosworth manifolds come with it and I used to have the part number around.

All right, thanks man.

 

I know that the direction is written somewhere on this forum in the brake booster swap walkthrough.

you need to be able to blow through it into the manifold. you shouldn't be able to blow through it into the booster.

 

and I think there is an arrow printed right on the hose.

you need to be able to blow through it into the manifold. you shouldn't be able to blow through it into the booster.

 

and I think there is an arrow printed right on the hose.

 

You are right. It says « eng. -> ». pretty straightforward.

All right, I cut open the STi brake hose, removed the bullet-shaped STi check valve, and installed it in the LGT brake booster hose.

 

I lubed the valve a bit to ease the installatiojn, but should've lubed the inside of the hose, since it wouldn't go very far (it's a VERY tight fit).

 

Anyway, I had enough hose length left to securely install it on the booster.

 

No more lack of braking power under boost!

 

And absolutely no congratulations to the shop...

Awesome! Glad it was an easy fix

Fifty percent of auto technicians graduated in the bottom half of their class.

Fifty percent of auto technicians graduated in the bottom half of their class.

 

As obvious as it is, it's scary!

Fifty percent of auto technicians graduated in the bottom half of their class.

 

As obvious as it is, it's scary!

lol i think he's joking around. what he says is true. but it's also true of every other profession. think about it.

Once you take into account the licensing exam for MD's and bar admittance for JD's it's not always the case. But it is interesting to think about it like that. There are a lot of under qualified people out there making important decisions.