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 Post subject: Possible brake booster fault?
PostPosted: Fri Apr 06, 2018 7:58 pm 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
My trusty 95 gti which the brake master was sleeved and kitted about a year approx ago might be failing or the booster is, not sure which one. It has been good with a firm pedal for a long time but this week it has a rock hard pedal and does not have the usual pedal feel. It doesn’t want to stop. If you stomp hard as you begin to panic, something seems to give and it’s complete braking, full on through the windscreen stuff. All or nothing. But not always, most of the time. Loosing no fluid, pads still good. Vacuum tested booster, no leaks. One way valve and hose checked, right way around and no blockages. Any ideas? I have not had this problem before.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Fri Apr 06, 2018 10:38 pm 
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Joined: Fri Sep 03, 2010 10:41 am
Posts: 1413
Location: Bunya QLD 4055
If you come over I will give you another.

_________________
If "X" is an Unknown quantity, and a Spurt is a drip under pressure, then an "EXPERT" is an "Unknown Drip Under Pressure".
Why dont they just call it "Womenapause" instead.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Sat Apr 07, 2018 7:31 pm 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
Sweet, i might take you up on that. Something i noticed today was when i started this morning, normal good pedal, back out of driveway, all good still, drive down about 50m then rock hard braking again. Stayed that way untill i stoped somewhere for more than 10 minutes. Good at first then the same again untill it stops again. Any less time stopped and it was still rock hard. It has to be the booster is getting stuck after a few stomps. Probably the diafraphm still good but getting stuck on crystilized fluid. I will find out tomorrow. I will pm you pictureshowman if it looks bad, pretty sure it’s the booster. Appreciate the offer. Hopefully fixable with a cleanup.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Sun Apr 08, 2018 3:43 pm 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
The booster looks good, pretty clean inside using the finger test, everything moving like it should. Pulled the master apart and bore looks perfect and seals like new. I cant see anything wrong. With someone moving the pedal the pushrod is moving smoothly. I will drain the lines and look for blockages and re-kit master and hope for the best.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Mon Apr 09, 2018 11:12 am 
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Joined: Mon Jun 16, 2008 7:02 pm
Posts: 270
Location: Northern Beaches
I assume you have done a full (and very easy) brake booster test prior to pulling everything apart? If not sure how just google it, or refer to the Suzuki Service manual which covers the BB operation quite well. A lack of vacuum pressure will cause rock hard brakes though so if the test fails, there's your problem.

If the test is fine, then I would also check the following: are the brakes sticking (brake wheel cylinders may be freezing up), do all wheels turn freely with the car jacked up, worn/sticking pads/discs, is the master cylinder seizing up (if the BB is fine I'd be looking at this for sure), possible faulty brake proportioning valve.

Basically, start to eliminate each possible cause but google the problem as well as there is a stack of help online!

Good luck


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 Post subject: Re: Possible brake booster fault?
PostPosted: Tue Apr 10, 2018 6:08 am 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
The booster gets and holds the vacuum with no leaks as tested by a vacuum pump with a guage. Start the motor with foot on pedal sees it go down as usual but only once, hard after that for about 10 minutes. I was talking to a booster rebuiler who at first was stumped by what is is doing until i mentioned i previously drained about half a beer can of old crusty fluid from inside the booster. He thinks the control valve has had it and i am about to drop it around for a test and look at. I would rather get it fixed for good so this is never a problem again. I also thought it might be the proportioning valve but things don’t add up. I also checked my disc minimal thicknesses and they are all past the minimum now so i am up for rotors and pads once i figure this out. These current pads are ferodo street/race which where modified to suit the stock calipers so i might do that again, they hold up well when hot but create lots of brake dust which is the rotors disappearing. I got about 100 000k’s and 9 years out of them so pretty happy overall.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Fri Apr 13, 2018 7:53 am 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
The booster is stuffed and needs a few parts which are no longer available. He is trying to make the most of it but some secondhand parts would be handy so pictureshowman i will pm you soon. He said the brake fluid that leaked out if the master over the years has de-laminated the direct valve, it’s a rubber seal that is glued to a steel washer and it falls apart from the rust that the fluid made. Thats the worst bit and the diapham is a little worn as well. It’s fixable as is but better conditioned parts would be safer he tells me. If anybody else has one in reasonable condition could you let me know? Hopefully not too expensive but obviously real good means $$$.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Fri Apr 13, 2018 11:04 am 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
I am all sorted for parts now. Thanks Lawie i appreciate the donor booster, i gets me out if trouble. The rebuild guy says the rebuilt valve retested good, he thinks definately the problem. Just waiting on master kit to find out how it goes.


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 Post subject: Re: Possible brake booster fault?
PostPosted: Fri Apr 20, 2018 11:49 am 
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Joined: Tue Sep 17, 2013 7:12 pm
Posts: 229
Location: Brisbane
The rebuilt booster has fixed the problem. Awesome brakes again. Thanks to Darren and the boys at Stopmasters in Brendale. He also recommended i take out the restricted one way valve hose that goes from the manifold to the stock piping on the firewall. It’s now only using a new check valve on the booster. The revs drop a little but they work better than ever.


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