No brake assist!

[WorkInProgressK]

As the title states I don't have any brake assist on my 240sx.

This is the setup:

-Jdm front stock brakes (altima discs, stock caliper),
-Rear stock caliper and discs,
-Manuel transmission booster with stock 7/8 master,
-Pads are Hp+ at every corner,
-Replaced the check valve which work( flow towards the engine) and replaced booster with another used one.

Engine: SR, 264 cams, gt2560r and a super huge intercooler( no flame it came with the car!).

There is no kink in the vacuum line going to the booster and I am attached to the 90deg fitting on the intake manifold (just like in my silvia)

Is it possible that the engine is not building enough vacuum? I remember seeing my gage telling me 20 mmhg in vacuum and I know my silvia runs at 65-70 at idle, but its a stock engine.

The engine is also freshly rebuilt, so the piston ring haven't sealed yet?

Anyway I am just lost with this car. Any input is appreciated!!!

[logr]

It is building enough vacuum if it runs.
Check vacuum at booster. No vac, no help.

[Def]

Sounds like you might have a big vacuum leak.

Does the pedal firm up when you pump it with the engine off?

[WorkInProgressK]

The pedal is always firm. I never have that transition feeling. Usually a pedal sinks by 1/2 inch on start up(if your firm on the pedal). Mine doesn't. And I know that my other does...

Vacuum leak wise. When the Throttle body is close the vacuum lines are: the brakebooster line from the back of the intake manifold, the FPR(tb facing), the pcv valve(right next to and a line that goes to the wastegate actuator, recirc and my boost gage. Pretty much 4 holes right? Am I forgetting something?

[Def]

The stock mani has tons of lines for the PCV system. One of the main reasons I eliminated mine. I'd go over everything with a fine tooth comb, but it definitely doesn't seem like you're getting vacuum on the booster.

Maybe get another vacuum gauge and hook it up and see. Even with big cams you should see about -11 to -13 in-Hg at idle. Rings should seat pretty quickly (like a matter of minutes) to pull a reasonable vacuum. Things might improve slightly over the next couple of hundred/thousand miles, but it won't be a really drastic change over the first few minutes of running-in.

[Matt93SE]

20mmHg is near zero for vacuum. My Maxima engine pulled 20in Hg at idle and 26-28in Hg (675mmHg) off throttle at higher rpm.

1. that's a lot of cam. couple be a cause of low vacuum.
2. vacuum leak. poke around and see what you can find as mentioned above.

[logr]

If you have a vacuum leak the car will run lean and fast(idle) and you would still have enough vacuum to run a booster. Did you physically check for vacuum at the booster? It sounds like you are not getting vacuum to the booster.

[WorkInProgressK]

Ok double checked every thing. With my stock Sr I am getting an avg of 25 inchhg with the camed Sr i am getting 20inchhg( it was inch not mm my bad). Now with my stock sr I have a auto brake booster so its maybe because of that I see a huge difference.

I checked the intake manifold, the tube going to the booster and found a little flow reducer (which i removed). I noticed a little gain but i still need to stomp it to stop the car, mind the discs are rusted, but the pedal feel is still as if I didnt have any assist.

I browsed around google and big block guy who use stoopid huge cams usualy add a reservoir for their Bb. I guess if i can fab something up cheaply, it is worth the try.

[Tower240sx]

you have more than enough Vacuum (as i suspected, no one reads in mmhg) 20inhg is plenty

I would believe you have the check valve in backwards,

It's the little black nippled barrel that clips into a firewall bracket behind and above the valvecover, put it in backwards and you build boost in the booster...which coincidently makes it an UN-booster

Ask me how I know...no wait don't

[Def]

Yep, more than enough vacuum, you don't need a reservoir. Hell, at this point I'd take the check valve OUT and run a hose barb in there really quickly just to test if the booster works (do not boost it like this, or drive it very far, you'll lose assist as you give it throttle).

[WorkInProgressK]

Tower, my silvia has a boost gage with mmhg :P but the car is from the land of the rising sun. But the valve is not backwards that's for sure(replaced and checked 15 million times.... I even tested it with my mouth............). Maybe I am just used to the brakes with the auto booster. We will see when I break in my brakes.

[Def]

My pedal with a 1" MC is *SUPER* stiff with an S13 manual booster on it. It does firm up a little when it's off(to where there's essentially no movement when pressing on the pedal after cycling it a few times, which is normal). But even with the engine running it's pretty damn stiff.

[WorkInProgressK]

So the manual booster doesn't really assist much. It was the worst behind my dads miata and I believe his doesn't work.

[Tower240sx]

hmmm....all my cars have been auto conversions so I've never driven on a manual booster car, can it really be that much different?

I always felt the brakes were a little over-assisted, but I also thought the auto vs manual booster was a myth

[McCoy]

I have the auto booster with the 1" Z32 BMC. The pedal was fairly stiff with the Z32 setup and I do notice a bit more travel/softness with the wilwood setup, but nothing that really concerns me. I've yet to drive an S chassis with a manual booster yet...