GolfGTIforum.co.uk
Model specific boards => Golf mk5 => Topic started by: Paul-GTI on 30 November 2006, 16:10
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Hi,
Sometines (about 25% of the time) if I have left thr GTI standing overnight or at work, when I return the break pedal feels solid as if it has been pumped, but usually it just has its normal range of motion.
Anyone else have this?
Paul.
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It could be your brake assist working...
...if you go from gas to brake pedal real quick the car automatically over assists the brakes to give maximum braking force as it thinks your going to crash!
Does this help?
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Hi Doc,
Thanks for the reply but it dont really help as its when the car has been standing for while. I should have made it clear that it happens when you first get in before you start her up, and it is more likely to happen the longer it stands.
any more ideas?
Thanks, Paul.
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I think mine does exactly the same. get in, put your foot on it and it doesn't really move. Start the ignition and it moves down as normal? I'm pretty sure it is just normal and car kind of priming itself?
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Yup, thats exactly it. is yours intermitant like mine, or always stiff? (oo-er!!)
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:wink: not really noticed - I only drive the car at weekends really. I think if I get in the car and have only been out of it for an hour or so then it is not so stiff (!).
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surely its bound to be stiff cus the break servo is not being pressure feed from the engine cus its not running, and pedal soffens once the engine starts up and pressurises the braking system, hense why it soffens
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^^^^^^^^^^
Sounds logicl, but any idea why it only happens sometimes?
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luckily I don't know how braking systems work or even what a servo is so I assume it is all part of the engineering! :nerd:
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Hey all
I know this a GTI Forum. My ma had a Toyota Camry.
Did the same when the engine was off. Toyota told us the reason for this was because of the ABS.
When the engine is on the computer will run the breaks and control how much pressure can be applied. Thats why when you try applying the breaks without the ignition on it will be very tight and stiff because there is no feedback from the computer. If you look on older cars without ABS you can apply the breaks with or without the car running.
Vw SA says that this is normal. If the brakes are still stiff when you start the car and leave it for about 20 seconds then you should consult a dealer.
Hope this helps guys
Mike
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Hi
Did anyone ever find the solution to this?
What is actually happening is the loss of the stored vacuum in the brake servo. When the engine is switched off, the servo should be able to hold a "reserve" amount of vacuum for emergency use. This usually equals 3 full pressure activations before the reserve is extinguished. The vacuum is held by a non-return valve, either on the servo itself, on the inlet manifold (or diesel vacuum pump), or anywhere along the vacuum line.
There may be a weak point somewhere along the line, or in the non-return valve. I do know that VW and Audi often have to make quite difficult engineering decisions - obviously, they are all initially designed as left-hand drive, and then bits like steering wheel, pedals, and brake master cylinder and servo have to be swapped over. Indeed, my S4 has a completely different designed servo to the LHD models. Maybe they don't quite give it their best effort, just for us Brits, eh! :wink: :wink: :wink:
One other cause for loss of vacuum reserve - you don't happen to let young children sit in your car at home, "playing" driving like "daddy", and pumping the brake pedal!!! :smiley: :smiley:
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Haha haha I dont hav kids yet! :grin: (Good thing too)
Oh well you clearly know what yoiu are talking about. Good one