Losing brake pressure?
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  1. #1
    Fellow Frogger!
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    Default Losing brake pressure?

    Hello Brains Trust,
    It appears my fluid pressure is disappearing in my brakes when I apply them.
    My 205gti has the mi16 motor swap but I'm fairly sure it's still the standard cylinder and booster.
    The pedal will very slowly make it's way to the floor when sitting at the lights.
    I assume it is the master cylinder leaking??-correct me if needed..
    I wouldn't mind a bit more braking power anyway so I was wondering if there were any other boosters and cylinders from other peugeot's that could be fitted instead of the standard. e.g 405 or 306?

    Thank you in advance,
    Lewis

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  2. #2
    Contented Peugeot Driver addo's Avatar
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    Bleed, bleed and bleed again. If your pedal is slowly sinking it's more likely air.

  3. #3
    1000+ Posts schlitzaugen's Avatar
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    If MC is bled correctly (and you are sure of it) and the pedal still sinks then yes, it is leaking.

    More assisting will take pedal feel away, not improve braking power. You need a bigger MC for that.
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    1000+ Posts michaelr's Avatar
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    If the pedal is sinking, but there is no fluid loss, then the most likely cause is the master cylinder. The pedal would sink with leaking callipers and brake cylinders too, but the fluid loss would be obvious. Air in the system will cause a spongy pedal, but not a progressively dropping one

    I would try a kit in the master cylinder, or new one, as the first step.
    Michael
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  5. #5
    1000+ Posts schlitzaugen's Avatar
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    True, what he said.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

  6. #6
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    Default

    Thank you!
    So what other master cylinders could I replace it with?
    Thanks again,
    Lewis

  7. #7
    1000+ Posts cam85's Avatar
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    Just get a 306 version ( I think they are 22mm ) from Dapco or the likes. Fit the correct bung to the back right outlet ( you running a single line to the back? ) and go from there. I had lots of trouble bleeding the MC and then the brakes. Was a good learning curve. Doing it again tonight! Fun fun.

    Cam
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  8. #8
    1000+ Posts schlitzaugen's Avatar
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    306

    Just ring one of the usual suspects and ask for a 306 MC with four ports, doesn't matter what model (as long as it's not ABS, I guess). They'll come with bungs to block redundant ports.

    Be sure to bleed it properly (actually, ask someone who knows how to do it to help you).

    Quote Originally Posted by cam85 View Post
    Just get a 306 version ( I think they are 22mm ) from Dapco or the likes. Fit the correct bung to the back right outlet ( you running a single line to the back? ) and go from there. I had lots of trouble bleeding the MC and then the brakes. Was a good learning curve. Doing it again tonight! Fun fun.

    Cam
    I think they are 23mm dia in fact.

    The only way I trust the MC is bled completely and the method I use is to attach brake lines to all ports (I have a stash I vandalised off a 205Si). These lines are cut short. I stick a plastic tube tightly over each one of them and the other end of the tube goes in a reservoir of fluid. I pinch all plastic lines. The MC has the fluid reservoir attached, of course. I then attach the pressure bleeding dealie I made myself (a little gizmo that applies air pressure above the brake fluid in the MC reservoir) and apply gentle pressure (tire pressure is enough). I open one plastic line at a time (release pinch) and watch the air coming out. When I am happy there are no more air bubbles, I pinch it back and open the next. This pushes fluid slow enough to fill all the space inside the MC but fast enough to push the air out of the MC. When done, I pinch the last line again, leave everything as is and replace the bungs and lines to the car lines one by one.

    I then test the MC by disconnecting the bleeding device and pumping the pedal. If any air bubbles show in the clear plastic tubes, now is the time to see them. If need be, attach the device again and give it a bit more pressure.

    It is a good idea to make sure you have no air in the car lines too (plastic tube over the end, open nipple/nipples on the respective line, push some fluid with a little bit of pressure as explained above, pinch plastic tube, leave attached until ready to connect to MC). You will need to make your own pressure bleeding device, creativity is your only limit.

    This device can in fact bleed your MC even after you attach the brake lines, because it doesn't rely on pushing fluid and then pulling it back on the upstroke. It pushes continually and consistently. Just watch the fluid level in the reservoir so it doesn't get too low. The disadvantage is that you can not visually confirm you have no air left in the MC.

    The greatest advantage of all is that this is a one-man brake servicing operation.

    Good luck.
    Last edited by schlitzaugen; 5th October 2012 at 02:55 PM.
    ACHTUNG ALLES LOOKENPEEPERS

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  9. #9
    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by schlitzaugen View Post

    I think they are 23mm dia in fact.
    most 306 are 22mm
    406 is 23.8mm

    You need to have the car pointing down hill, or raise the rear of the car, in order to overcome the bias valve easily.

    '92 205 Mi16
    '90 Mi16x4

  10. #10
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    Default He speaks the truth !

    Quote Originally Posted by michaelr View Post
    If the pedal is sinking, but there is no fluid loss, then the most likely cause is the master cylinder. The pedal would sink with leaking callipers and brake cylinders too, but the fluid loss would be obvious. Air in the system will cause a spongy pedal, but not a progressively dropping one

    I would try a kit in the master cylinder, or new one, as the first step.
    Hi
    This description is correct. If you sit with your foot on the brake with constant medium pressure and it sinks, there is a leak. Needs fixing ASAP. Try it some where not on the road. If it goes down mostly to the floor then its real bad and fix it immediately. No external leaks then it has to be the master cylinder. Leaky wheel cylinders may seal up under pressure and not sink even though they leak slightly other times. Look over the whole system.

    If there is air in the system the pedal is spongy or not real firm. However if you hold a steady pressure then it will not go down or sink. Some systems can be bitches to bleed.

    To improve the feel while testing. Turn off the engine and press the brake many times untill the vacumn has been used up. You can then just feel the straight brake system without the booster masking it. The pedal should be high and firm with no sinking. Note loose wheel bearings can cause excessive brake pedal travel also

    Putting a different master cylinder will not make the brakes "work better". The units at the wheels actually do the work. If you want reduced pedal pressure then use a smaller dia cylinder. It will proportionally increase pedal travel so do not over do it.
    jaahn

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