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Location:
Terrigal
Registered:
May 2002
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Remote brake booster problem.
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Tue, 27 April 2004 04:27
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Hello, i'm trying to assist a friend fixing a problem with their brakes.
They have installed a remote brake booster due to space issues (needed to make way for a turbo).
Now when you connect the large vacuum line to the booster, it actually makes it harder to press the peddle down - actually almost impossible. If you disconnect the vacuum line the brakes work but of course are not assisted.
I'm assuming he has got something arse-end about but I have no experience with remote boosters so hoping someone can give me some clues?
From what I can see.. 2 lines come out of the master cylinder, go into a T-piece that joins the lines into 1. This 1 line goes into the remote booster, then 1 line comes out that goes back to a T-piece for the front and rear brakes.
Cheers
Joel
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Remote brake booster problem.
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Tue, 27 April 2004 06:33
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Hmm dunno if ive missed something, maybe im not following... your saying the brakelines??? come out of the original master for front and rear lines then join in to one line at T piece ( this alone doesent seem right to me but then im no expert either ) then they got ot the booster??? im assuming you mean to the remote master???
then only one line comes from the remote master then splits for front and rear???? ( again this dosent sound right to me )
or perhaps you are referring to the vacume line in which case im completely stumped as to why youd have two lines 
My expectation would be this.....
you have a master at the pedal with a single line going to a slave at the back of the remote booster? which pushes the booster and therefore the remote master. the remote master should have two lines coming off it ...
one for the front brakes that goes to the proportioning valve
and one for the rear brakes going to the proportioning valve
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Remote brake booster problem.
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Tue, 27 April 2004 06:45
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hmmm..
so you've removed the first booster totally?
and you then connected the vac line that originally went to it.. to the remote booster..
and when the lines connected, the brakes get "reverse boosted" (for want of a better term)
hmmm...
first thought that came to mind was that the one way valve in the vac line is connected arse-about, so when you get boost, you are actually pumping up the booster, so it pushes against your foot, rather than helping it....
connect the line, do what you did before (when it didn't work) then take the vac line off and see if it's actually got positive pressure in there?? can you put a boost gauge between the brake booster and the one way valve?? that would rule it out pretty quickly...
as for connections, you might be able to get away with just having the front brakes boosted, and leaving the original rear brake line alone... if they just happen to be sized right (unlikely) then you may have good bias...
actually, i prefer ira11y's way 
Cya, Stewart
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Location:
Terrigal
Registered:
May 2002
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Re: Remote brake booster problem.
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Tue, 27 April 2004 07:05
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Hmm i'm going to have to double check everything here..
But from what I remember when I traced the brake lines around the place...
The original booster is removed, so now a master cylinder is bolted directly to the firewall/peddle.
There is 2 brake lines from the master cylinder, front & rear. These go into a T piece which changes it to 1 line, this one brake line goes into the remote booster cylinder (slave i'm assuming?), then a brake line comes out of the cylinder and goes back into a t piece to get the lines to the front and rear.
This setup might be totally wrong, and no offence to my mate if he reads this, IT PROBABLY IS!
I originally thought it was the one way valve in the vacuum line also. He was complaining about brakes, I took it for a drive and felt like the booster was not working. So checked the 1 way valve and it was backwards. So I turned it around and said should be much better. He takes it for drive and says WTF did you do brakes dont work at all. Basically with the valve the correct way it causes this reverse boosting, whereas he had it backwards which was in a way making the booster unused.
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Location:
Terrigal
Registered:
May 2002
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Re: Remote brake booster problem.
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Tue, 27 April 2004 07:10
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The booster only has 2 fittings for brake lines, an in and out I suppose..
So thats why all the T pieces have been used.
But maybe it is designed only to boost the front brakes and the rear should just run from the master cylinder.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Remote brake booster problem.
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Tue, 27 April 2004 07:18
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hmmmmm...
the booster works by having the air inside sucked out by engine vacuum. the one way valve is there to only allow air to flow in the direction of the engine.
if it was backwards, then it would only allow air, at greater pressure than in the booster, to flow toward the booster, and not out, so it would not work at all..
if it was the right way round, then air would be sucked out when the engine is not boosting, and when on boost, the one way valve should seal so that the vacuum stays in the booster..
maybe the booster has a broken diaphragm? mayeb the one way valve is leaking?
dunno... put a boost/vacuum gauge on the booster vac line, and see whats going on.. if it's pulling, and holding, vacuum, then it's a problem with the booster itself or the way the lines are hooked up....
Cya, Stewart
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Location:
Terrigal
Registered:
May 2002
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Re: Remote brake booster problem.
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Tue, 27 April 2004 07:23
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If the in and out lines on the booster cylinder were the wrong way around, do you think this might cause the reverse boosting effect?
I dont think its the one way valve as it is in a way doing its job (well not really but..), if you put it in backwards so the engine vacuum cannot draw air out of the booster the booster stops working and the brakes work but unassisted. But if you put it the correct way which allows the air to be sucked out, the brakes become almost impossible to push in.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Remote brake booster problem.
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Tue, 27 April 2004 07:34
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| TurboRA28 wrote on Tue, 27 April 2004 17:23 |
If the in and out lines on the booster cylinder were the wrong way around, do you think this might cause the reverse boosting effect?
I dont think its the one way valve as it is in a way doing its job (well not really but..), if you put it in backwards so the engine vacuum cannot draw air out of the booster the booster stops working and the brakes work but unassisted. But if you put it the correct way which allows the air to be sucked out, the brakes become almost impossible to push in.
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i think if the lines were the wrong way round, then it would be same with vac line there or not....
since it occurs when the vac line is changed, i think it's that 
i think it's the wrong way round... and maybe it's direction has been identified incorrectly.
- if it is the correct way round, the engine can draw the air out, and create vacuum in the booster. if there is boost, then it will be blocked from entering the booster.
-if it is backwards, air will be prevented from leaving the booster, so it will not work. even worse, when ther eis boost, the booster will pump up, and so have the opposite effect from that wanted, ie brakes don't work at all.
if "it's the correct way which allows the air to be sucked out" then it should work properly!!!! you WANT air to be sucked from the booster to the engine.
where is the vac line attached to on the intake tract? ont he manifold still? is it engine side or turbo side of the throttle body?
i'm still convinced that when it is backwards the brakes will work worse, sicne the booster is being pumped up...
but if it doesn't work when the 'right way around', then maybe the booster is faulty? or the OWV is faulty and not sealing against the pressure?
check the pressures 
Cya, Stewart
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Location:
Brisbane
Registered:
February 2003
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Re: Remote brake booster problem.
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Tue, 27 April 2004 07:48
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i think your first t-piece is wrong.
On my bro's old valiant ute (which had remote booster) the front disks were fed from the vac booster, and the rear brakes straight from the master.
Master cylinder:
outlet 1 -> booster
outlet 2 -> rear
Booster:
(master outlet 1 provides hydraulic push at back)
booster outlet -> t-piece
T-peice splits to front L & R
weird - but boosters are mega old territory.
If you don't like this, you have to change things over so the master Cyl only has one outlet, and the booster has two outlets (one for front, another for back) and you need a bias valve to keep suitable proportional braking between front/rear systems.
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Remote brake booster problem.
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Tue, 27 April 2004 08:50
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AT THE PEDAL SIDE
the problem with T'ing them up is that youre combining 2 different pressure rates.. i.e the front and back part of the master is often two different sizes,large for the rear if theyre drums and smaller for front with discs and even more especially with some of the later nissan ones having proportioning or partial self proportioning masters.
im guessing that by using the T youre creating some sort of fluid lock, because one large pressure is pushing against the smaller pressure, within the same loop.
this could be fixed in some instances by using one way valves but obviously you dont want to use those with a brake line for obvious reasons LOL
ultimatley im not sure that T'ing them is working for or against you so maybe thats something to look at.
AT THE REMOTE BOOSTER/MASTER END
ok again the T thing, im not sure what sort of slave your using to push the booster arm?? all the ones ive seen have been something along the lines of a clutch slave with a single line in pushing the booster arm. as far as i can tell youd only need one line from the pedal to do this, in fact if it was me .....
id look at using a clutch master, why not?? its all you really need, the only thing you have to check is that ...
A/ it provides enough fluid to push whatever slave you have at the remote end far enough to get maximum travel on the booster arm to engage the remote master the full length...
B/ it will provide and stand up to the necessary pressure to provide maximum force which i wouldnt forsee as a problem.
ok on to the booster part of things....
Stu has allready covered the basics pretty well but heres some other bits that might help...
ok.. are you using the original booster and master for the remote?? and is the pedal master the same fluid ratio? look on the side of the master youll see stuff like 13/15 or 7/11 these are the front rear split rates of the master, they refer to the bore or volume ... lets take it a step further
IF your pedal master has a better fluid rate than the remote master it will require less force and distance of pedal movement to create the same force ... soooooo
maybe there is nothing wrong with the booster, its just that your setup is exceptionally efficient at providing force.. remeber that you have lost a lot of feel with the remote if youve changed the master sizes. of course the total reverse of this scenario can also be true, in that you may require more pedal movement and force to get the same braking strength.
WARNING the above may all be bollocks but its my best guess, so modder beware
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Location:
Melbourne
Registered:
May 2002
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Re: Remote brake booster problem.
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Tue, 27 April 2004 08:56
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I really could not be bothered reading the posts so dont know if this has been discussed, have you considered that your 1 way valve is around the wrong way.
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