brakes playing up

[MX_Leigh]

hey all, my brakes haver recently started to lose pressure at the most random times. ever since i changed the diff in the car and bled all the lines this problem has started. the first time, luckily just as i was coming up my driveway the brake pedal went all the way to the floor and the brake warning light came on. so i bled the lines again thought nothing of it(after the first time i did it my mate forgot to put the lid on the booster amd closed the bonnet so i drove with it like that for 2 days) then it was all fine for a week until i get up to go to work in the morning and get to the end of my street to find the same problem so i left it at the mechanics for the day and they told me i need a new master cylinder. so i pick one up on the way home put it all on bleed the brake lines again, after bleeding the lines the brakes felt really stiff and had a nice feel but after 3 days they feel spongy again. is this what should happen or could there be another leak in the lines?

[VL Berlina 5speed]

check the vacum line between the booster and cylinder
make sure it isnt split or leaking
did you bleed the LH side first then the right?

[MX_Leigh]

no i did the front right to left then the rear left to right. is there a certain pattern to do it?

[Goon]

The nipples on the capliers arnt leaking??

try another bleed bro, it took me 2 go's to get mine working again..

when u replace ur booster did u make sure theres no leaks??

You dont over use ur brakes do u ???

new brake fluid??

Overall try what 5speed said.

ps. drum on the back ?.. dont worry about them..well i didnt

[MX_Leigh]

ill check the bleed nipples. and its a 5 speed so i hardly use the brakes at all. only really when im at a very low speed. i will bleed them again and hope for the best. i just dont want to be driving and suddenly have no brakes. its scary enough at low speed when it happens

[Sabbath']

no i did the front right to left then the rear left to right. is there a certain pattern to do it?

Bleed from furthest to closest.

So on a Commodore:

LHR
RHR
LHF
RHF

Checking between each that you've got sufficient fluid in the resy.

[MX_Leigh]

ok thanks everyone ill give it a go and see how it turns out. should bleeding it how i did make much of a difference and should it feel spongy or is that something else?

[HARVZ-6]

Goes the same with all braking systems.. start at the furthest point from the master cylinder and work your way in..

[jatsvl]

silly question, but are you bleeding them correctly? do you have some one helping?
the reason I ask is a mate of mine was having trouble with his brakes I asked him how he bled them and he told me by himself (gravity bleed) went around opening each bleeder until the fluid flowed freely closed it then did the next one and so on.

[MX_Leigh]

yea i am doing it correctly. pump up the brake, hold it on slowly undo the bleed nipple then tighten without taking foot off the brake, pump it up again and repeat the process until all the air out the system and its flowing fresh brake fluid