Bad brakes after installing vacuum manifold!

Ihtisham Rauf

Ihtisham Rauf

Hi, looking for some advice please.

I installed a vacuum manifold. I have a vacuum takeoff (the blue pipe) from my inlet manifold to the right hand side of the vacuum manifold. The left side of the vacuum manifold has a pipe coming out (again a blue pipe) which splits into a tee, with one side going to the crankcase and one to the brake booster.

Out of the 6 small takeoff's on the vacuum manifold, I have plugged 5 and used one for the vacuum on the fuel pressure regulator.

Everything is okay, no vac leaks, car idles nicely, but my brakes don't feel that effective when at low revs and they are really bad if I brake sharply while coasting, the pedal just feels heavy with not that much braking. At high revs, they work great.

Any ideas?

11.png
 
Chie said:
Not enough vacuum if its only taken off 1 intake runner? Just a guess
Click to expand...

Yeah you could be right there.
I have also been told the crankcase is just a breather, it doesn't need vacuum. So crankcase and brake booster shouldn't be linked together, as some of the vacuum that the booster needs, is lost to the crankcase.
Plan is to remove the crankcase from the vac system and put an oil breather filter on the end of it.
If this doesn't work, I'll go with your idea and get vac from other runners or use the individual ITB vac takeoffs.
Thanks :)
 
the offside crankcase breather (pcv valve) is connected to the vacuum system
but that pcv restricts the flow tho
 
frank said:
the offside crankcase breather (pcv valve) is connected to the vacuum system
but that pcv restricts the flow tho
Click to expand...

Ah right okay, so I'll have to leave the crankcase breather connected to the vac system. So I just need more vacuum power then like what Chie suggested, to solve the issue?

Thanks.
 
normally during closed throttle, the inlet manifold maintains a high vacuum cos all the systems plumbed into it are either:
- closed-end diaphrams (brake booster, fuel reg, carbon canister actuator) only requiring tiny volume of air to operate or
- open-end restriction-controlled ports (carbon canister purge hose, idle control valve, PCV) allowing only a trickle of gas flow but small enough to keep most of the vacuum within the manifold.

the PCV system during high vacuum mode consists of allowing outside filtered air to flow freely inside the cam/crank case via a large PCV breather port, from the crankcase through the cam cover, through the PCV valve until it reaches the important & restricted tiny port leading into the manifold.

by plumbing the large, free flowing & unrestricted crankcase breather hoses directly to the manifold with no restrictor, it's essentially created a huge vac leak so everything plumbed into the manifold including the brake booster & fuel reg will now no longer work properly.

the fix is easy,
either connect the crankcase breather back to the front of the engine cover where it goes through the PCV and restricted before entering the inlet manifold,
or fit a restrictor between the crankcase breather hose and where it joins the brake booster / vacuum manifold Tee
 
pollyp said:
normally during closed throttle, the inlet manifold maintains a high vacuum cos all the systems plumbed into it are either:
- closed-end diaphrams (brake booster, fuel reg, carbon canister actuator) only requiring tiny volume of air to operate or
- open-end restriction-controlled ports (carbon canister purge hose, idle control valve, PCV) allowing only a trickle of gas flow but small enough to keep most of the vacuum within the manifold.

the PCV system during high vacuum mode consists of allowing outside filtered air to flow freely inside the cam/crank case via a large PCV breather port, from the crankcase through the cam cover, through the PCV valve until it reaches the important & restricted tiny port leading into the manifold.

by plumbing the large, free flowing & unrestricted crankcase breather hoses directly to the manifold with no restrictor, it's essentially created a huge vac leak so everything plumbed into the manifold including the brake booster & fuel reg will now no longer work properly.

the fix is easy,
either connect the crankcase breather back to the front of the engine cover where it goes through the PCV and restricted before entering the inlet manifold,
or fit a restrictor between the crankcase breather hose and where it joins the brake booster / vacuum manifold Tee
Click to expand...

Thanks for the info Paul.
I understand what you’re saying.
On the offside crankcase breather, there is still a PCV valve there; I haven’t changed anything there. The brakes were working completely fine with this setup.

All I have done is chop the main pipe going from the brake booster to the inlet manifold, and simply plumbed a vac mani in the middle.
I haven’t changed anything regarding the PCV or crankcase breather pipe.
 
frank said:
vacuum leaking down those blanking screws maybe ihtisham ?
Click to expand...

Yeah so to rule this out, I have completely gone back to how it was before I put the vac mani in. i.e one pipe from inlet mani to a tee, with one side splitting to crankcase pcv and the other side to the brake booster. (I have had this setup since the ITB's went in, and the brakes have been fine) However, now even by going back to how things were, the brakes still don't work well!

It just seems the brakes work great for a pump or two, and then the pedal gets a bit hard. I have to keep driving for maybe around 15-20 sec, before the pedal becomes soft again and the brakes work great again. The effect is worst when coasting in neutral, after just one pump, the pedal goes rock hard.

It doesnt make sense. I have gone back to exactly how it was before I fiddled with anything and now they don't work. Maybe through the fiddling and moving of the pipes, one of the one-way valves has **** itself??



I also realised that the nearside crankcase breather sucks in air while idle.
 
yes the n/s breather is the crankcase inlet
you will only be getting 1/4 the vacuum flow from 1 runner, so it may have been borderline anyway
the only valve is the pcv, and that works 1 way in a complex way (allowing full flow at low vacuum, and restricted flow at high vacuum)
 
frank said:
yes the n/s breather is the crankcase inlet
you will only be getting 1/4 the vacuum flow from 1 runner, so it may have been borderline anyway
the only valve is the pcv, and that works 1 way in a complex way (allowing full flow at low vacuum, and restricted flow at high vacuum)
Click to expand...

Okay thanks for the info. I think I am being more critical of the brakes now that I am testing them.

I think best thing for me to do is plug that vac hole from inlet manifold and just use the individual vac takeoffs from each throttle body, so I can get the full vacuum flow rather than 1/4. And then see how things go from there.
 
Thank you to Paul, Frank and Chie for helping out.

Today, I disconnected the offside crankcase breather from the vac system and the brakes work great again. I then reconnected the vac manifold and used one of the take-off's from it to feed vac to the FPR. Brakes still work great and the overfueling at low RPM isn't as bad anymore.
 
Just one last questions guys!

Where can I connect my offside crankcase breather PCV valve? Currently I just have a pipe coming out of it and just dangling in the engine bay. (This was the pipe that was connected to my brake booster and responsible for the poor brakes.)

Can I remove that pipe completely and put a small oil breather filter on the end of the PCV valve on the cam cover? (as I have done for the nearside breather)

THANKS AS ALWAYS!
 
Either:
Plumb the PCV hose back to the ITB vacuum side using a 3mm port or in-line restrictor to retain the PCV function,

Or plumb both the (rear right) PCV breather and (front) crankcase breather to mini filters with optional catchcans


Sent from my CLT-L29 using Micra Sports Club mobile app
 

Similar threads

Ihtisham Rauf
Vacuum at Idle on 1.4 Micra
Replies
10
Views
744
Ihtisham Rauf
Ihtisham Rauf
Ihtisham Rauf
Alpha N on ITB's
Replies
6
Views
630
Ihtisham Rauf
Ihtisham Rauf
C
Brakes and exhaust manifold?
Replies
1
Views
164
smidge
smidge
C
REVERB FOR SALE (micra champion 2005)
Replies
46
Views
490
CMF_White Knight
C
C
For those interested in new vs old (how dare they even compare)
Replies
20
Views
628
CMF_turbo march-rolling shell
C
Back
Top