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Location:
Castle Hill, Sydney
Registered:
February 2004
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incredibly soft brake pedal
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Thu, 05 May 2005 07:46
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ever since i got my car put back together and running the brake pedal seems to be a hell of a lot softer than usual, you could get the brakes on full lock with a couple fingers... 
it brakes as good as usual, and all 4 wheels are locking up alright, its just REALLY soft!
i dont think its a leak or air in the system because usually your car wont brake as well with these would it?
im out of ideas, thinking about rebuilding booster and master but just wonmdering if anyone has been through this before or has any ideas what might be going on?
thanks, jesse
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Location:
Brisbane
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 08:27
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A light brake pedal means it has lots of braking assistance, ie the booster is working well. Maybe your booster wasn't hooked up properly before, and you got used to a mega-hard pedal?
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 08:30
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yeah it used to feel more like it does when the engine isnt running and theres no vacumn to the booster.
so the chance of that vacumn hose being blocked before is possible
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Location:
cambo
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 08:34
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its probably air in the system. your brakes will still work and lock up as normal, just a softer pedal. bleed the brakes, i mean it costs you $10 at most for fluid.
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 08:44
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bled them already, twice!
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 08:45
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if the vacumn hose to the brake booster was exposed/leaking what effect would that have on the pedal?
softer/harder?
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Location:
cambo
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 09:30
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harder. and possibly poor engine idle, if the car has AFM.
did you bleed in the correct order?
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Location:
Newcastle
Registered:
April 2003
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 09:37
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Did you bleed the master cyl first or just do it at the wheels?
If new pads /shoes fitted it could just be that they need to bed in.I know the pedal feels like shit in my car till the new pads bed in.
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Location:
cambo
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 10:07
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yeah that can do it, but would go away after a bit of driving. another thing: i dont know what brakes you got but if you have drums on the rear, they may need adjusting. this wont make the pedal soft or spongy, but would make the pedal need to travel a bit before the brakes work. maybe this is your problem and your mistaking pedal travel for a soft pedal.
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Location:
Sydney
Registered:
August 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 11:07
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I had troubles with the twin carb manifold. If you run your vaccuum hose to one single entry point on the manifold, and say don't use those spacers with the gap that stabilises the air between the two carb throats, there is less vaccuum. I don't run those spacers and found the pedal is hard, and put it down to only relying on one throat to provide assistance to the booster. Maybe something has changed for you in the interim that has given you better vaccuum assist?
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 11:42
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sorry i should have given more info about my setup in the first post
its the stock brake booster, a corona master cylinder, commodore front brakes, R31 skyline reae brakes
its running off twin carbies on the stock vacumn connection to the 2tg manifold.
the only other thing i can think that has changed in that area is i fixed the cam timing, its idleing HEAPS better now than it ever used to, but the problem isnt just at idle but all through the rev range.
its brakeing really dam well, it could have just been heaps hard before and its right now, but ive had second opinions and everyone thinks the brakes are REALLY light and touchy.
another thing is the booster and master were sitting in the weather for a couple weeks while i was spraying the engine bay
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and say don't use those spacers with the gap that stabilises the air between the two carb throats, there is less vaccuum
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the balance pipe from ports 1+2 and 3+4? im running one of them
[Updated on: Thu, 05 May 2005 11:44]
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Location:
cambo
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 11:51
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well poor timing previously MAY have something to do with it, giving you insuficient vacuum in the manifold meaning a hard pedal.
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Location:
Sydney
Registered:
August 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 12:12
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Yeah. If your saying it's quite touchy and light I'd say the booster is alot more effective now than before. It could be what EVO said, and have something to do with timing maybe? (whether this would have much effect on the amount of vaccuum I don't know) Or what you said about it sitting around and the booster has just fixed itself or something..........stranger things have happened. I have heard huge numbers for getting boosters reconditioned, I looked into it as I said I had the same problem, atleast yours is good now.....
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Location:
Brisbane
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 14:04
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Cam timing has a big influence on manifold vacuum at idle. Sidedraught carbs have poor vacuum to begin with, but with the cam timing out there would have been bugger-all.
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Location:
Sydney
Registered:
August 2004
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Re: incredibly soft brake pedal
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Thu, 05 May 2005 14:08
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Well there you go! Now I know what's wrong with mine. I was going to get the cam timing done soon anyway. Thanks Norbie!
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Location:
Newcastle
Registered:
April 2003
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Re: incredibly soft brake pedal
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Fri, 06 May 2005 03:31
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| jesseT18 wrote on Thu, 05 May 2005 21:42 |
sorry i should have given more info about my setup in the first post
its the stock brake booster, a corona master cylinder, commodore front brakes, R31 skyline reae brakes
its running off twin carbies on the stock vacumn connection to the 2tg manifold.
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Maybe the master cyl is the wrong size for the calipers and this has only shown up with the right manifold vacum.
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Location:
Brisbane
Registered:
November 2003
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Re: incredibly soft brake pedal
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Fri, 06 May 2005 10:12
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I'm not sure if this the phenomenon you're experiencing but could help:
" 9. A reaction disc is a small rubber disc which lives under the head of the booster output push rod. If this is lost, the brakes will be nearly uncontrollable with stopping proportional to pedal position, not pedal effort, sending you through the windscreen at the lightest touch."
I have experienced this one. quote taken from hoppers stoppers website , handy hints page.
As MJH said, is very possible it has something to do with the bore relationship of the m/cyl to the caliper pistons though.
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Sat, 07 May 2005 01:00
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yeah its definately not just me, the pedal is way to soft.
it could very easily be a part missing from booster/master, i guess ill pull em down and have a closer look
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Location:
Townsville
Registered:
February 2005
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Re: incredibly soft brake pedal
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Sat, 07 May 2005 01:09
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I find our t18 is the same, really easy to lock the fronts with barely any pressure. I think the camber and crappy tires have something to do with that.
My guess is that you had some vacuum issues previously that you have fixed.
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Membership Secretary
Location:
Sydney
Registered:
June 2002
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Re: incredibly soft brake pedal
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Thu, 12 May 2005 06:14
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I drove this car last night at the drags.
U push the pedal and nothing happens untill say the last 30% or so of travel.
In this last % of travel the pedal is very firm and the car does pull up. Mind you this was only in the staging lanes car was pulled up from 30kph or less.
Got me stumped as to what is wrong
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Location:
Adelaide, SA
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 12 May 2005 08:09
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Maybe something to do with the corona master cylinder?? The pushrod needs to actually make contact with the master cylinder piston before anything happens - could this be part of it?
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Location:
cambo
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 12 May 2005 10:00
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thats sounds VERY reasonable. sometimes when people change m/c they dont measure the PISTON ROD DEPTH. it must be the same as the orignal m/c otherwise the rod out of the booster needs to be adjusted (some are adjustable) or modified.
what did the car run?
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Location:
cambo
Registered:
May 2002
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Re: incredibly soft brake pedal
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Thu, 12 May 2005 10:20
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yeah but maybe the car you took it out of had the rod adjusted diferently, unless you used the booster from that car too? either way, take the m/c off and measure the depth of the piston to base, and measure how far the rod sticks out past the mounting point on the booster, they should be the same.
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Location:
Newcastle
Registered:
June 2004
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Re: incredibly soft brake pedal
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Thu, 12 May 2005 18:39
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I bet you have swapped the brake calipers from left to right by accident  it'll never bleed properly because the bleed screw is in the wrong position to let the air escape. Has this been checked?
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Location:
Newcastle
Registered:
April 2003
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Re: incredibly soft brake pedal
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Fri, 13 May 2005 05:20
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maybe you need to go back to the start.
get some clamps to block off each flexible hose and see how the pedal feels then.if it's still crap then you have air or other prob at the master cyl.(i'm assuming you bleed the master cyl first.)
If the pedal is nice and hard then get someone to remove the clamps one at a time and when it goes from a good feel to crap then you will find which wheel the prob will be at.
Sounds like there might be air in the system still so do this to find out where.
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Sat, 14 May 2005 08:26
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I bet you have swapped the brake calipers from left to right by accident it'll never bleed properly because the bleed screw is in the wrong position to let the air escape. Has this been checked?
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thats possible! ill check it out tomorrow
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Location:
Newcastle
Registered:
June 2004
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Re: incredibly soft brake pedal
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Tue, 17 May 2005 14:49
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How did you go with this? The lack of response means either you haven't found it yet, or it was something so obvious you don't want to tell anyone! 
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Location:
Castle Hill, Sydney
Registered:
February 2004
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Re: incredibly soft brake pedal
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Wed, 18 May 2005 07:47
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OR
ive been flat out and havent had a chance to check it yet!
im finding a hell of a lot less time for my car now since i got my licence back
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