Sitting at lights or junctions..brake pedal slowly goes down

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Sitting at lights or junctions..brake pedal slowly goes down

Post by bhm1712 » Wed Apr 09, 2014 10:09 pm

Am i right in what i think that if the brake pedal slowly finds its way to the floor when you sit at lights or a junction with the foot on the pedal then its the master cylinder leaking internally?
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by banker » Wed Apr 09, 2014 10:17 pm

Could be, or air in system. Might be worth bleeding first to see if this cures it
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Wed Apr 09, 2014 10:40 pm

cheers, will do.

Master cylinder fitted about 5 years ago so id expect it to last longer, but the car did sit for almost 2 years so that may have reduced its life?

Ill have a go at bleeding first, and then at least if its not that, the bleed nippled will be freed off enough for when i do the MC.
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Wed Apr 09, 2014 10:45 pm

I suppose it could be...ill have to check.
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by SUPERCHARGEDGTA » Wed Apr 09, 2014 11:00 pm

if there was moisture in the brake fluid then standing unused could cause rust pitting in master cylinder bore making it leak a bit
assume you have checked for leaks and fluid loss

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by SUPERCHARGEDGTA » Wed Apr 09, 2014 11:06 pm

vac. pipe shouldn't cause pedal creep

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Wed Apr 09, 2014 11:10 pm

yes i have checked for leaks and cant see anything obvious, although i have not had chance to remove the brake drums yet to see if the wheel cylinders are leaking into the drums. Thats a job for this weekend im hoping. i did replace the wheel cylinders at the same time as the MC but i know these things fail... the fluid levels are ok so im assuming that also points to no leaks.
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by SUPERCHARGEDGTA » Wed Apr 09, 2014 11:14 pm

is it worse if you slowly apply the brakes till on, than if you brake hard and hold pressure on?

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Thu Apr 10, 2014 8:37 am

Yes I believe so, if I brake hard it's hardly noticeable it's mostly when slowing down gradually to a set of lights and then waiting with the brakes on.
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by SUPERCHARGEDGTA » Thu Apr 10, 2014 11:49 am

sounds like master cylinder

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Thu Apr 10, 2014 10:12 pm

I've had a drive tonight and it's not quite like I thought - pedal generally feels vague unless I pump it, perhaps you would call it spongy. If I pump it it's fine until I come to a stop and then it goes down slowly to the bottom of the pedal stroke.

Still points to master?
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by SUPERCHARGEDGTA » Fri Apr 11, 2014 10:37 pm

dose really
spongy could be air in system, but if MC is good and level ok it shouldn't get air in it

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Fri Apr 11, 2014 10:43 pm

well you gotta love doing the master cylinder :) not messy at all!

Ill get one ordered up, if i remember it took me about 30 mins last time to pre bleed and fit the MC, and then 3 hours to bleed the brakes as the nippled were solid! hope they are easier to loosen this time!
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by SUPERCHARGEDGTA » Fri Apr 11, 2014 10:49 pm

you could try bleeding it, might be lucky and flush some muck out ;)

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by Jeff73 » Sat Apr 12, 2014 6:55 pm

if you pre bleed the master cylinder on the bench and not on the car you could be luck an not have to bleed the system or at lest not have to bleed the system to much

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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by bhm1712 » Sat Apr 12, 2014 7:47 pm

Jeff73 wrote:if you pre bleed the master cylinder on the bench and not on the car you could be luck an not have to bleed the system or at lest not have to bleed the system to much

Yes I'm going to do this, last time the master cylinder came with 2 adapters and pipes which fed back into the reservoir for bench bleeding. I hope the new one comes with those as well.
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Re: Sitting at lights or junctions..brake pedal slowly goes

Post by Jeff73 » Sat Apr 12, 2014 8:12 pm

if you pre bleed the master cylinder on the bench and not on the car you could be lucky an not have to bleed the system or at lest not have to bleed the system to much

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