Corsa Front Brakpad replacement and master cylinder problems

[FredPluto]

Hi I have just recently replaced the front brake pads on my 12 yr old P regged 1.2 LS Corsa. since then the pedal has gone really soft and needs pumping to get the brakes working.

I did pump the brakes after fitting the new pads, but its almost like they relax back in to the caliper the next time you try the brakes after 5 minutes ?

I have searched the web and there are some suggestions that as I did not release the bleed nipples prior to pushing the caliper pistons back, that i may have rolled back the cup seals in the Master Cylinder ?

I understand the theory behind this, but find it hard to believe that it is possible as the forces needed to apply the brakes should be greater than the force of fluid pushed back through the system by a caliper clamp

If this is the case is it possible to dismantle the Master Cylinder and re-position the seals or does it need a new Master Cylinder ?

All suggestions Welcome Thank you

 

[FredPluto]

Can a mod please edit this topic title to read brake pad thankyou

 

[Burnerman]

Pushing the caliper pistons back is a perfectly acceptable method - you don't need to release the bleed nipples, although this in itself is a good thing because it keeps the nipples free and also displaces any air or dirty brake fluid that could be in there. The chances of inverting the master cylinder seals are very remote indeed.
So - when you had the old pads out - did you check to see that the caliper was free to slide on its guide pins? As they have only the one piston this is important to achieve pressure on both sides of the disc. You should bleed the brakes to see if there is any air in there, and also check the flexible rubber pipes for swelling when brake pressure is on.
A sign of master cylinder failure is that the pedal slowly reaches the floor when you keep pressure on - although no pressure at all is also a symptom. Spongy brakes, or ones that need pumping, are more of a sign of brakes needing adjustment - more usually at the back of the car where the self adjusters rarely work 100%.
If you do suspect a master cylinder fault, I wouldn't advise a rebuild but rather one from a motor factors - they are good value.
Cheers John

 

[FredPluto]

At last, I have found the problem, It was a lack of attention to detail by me

I removed the spring clips that stop the pads rattling and when I refitted them I put the ends of them forward of the flanges (they should be behind the Flanges) locking backwards at the caliper.

This small error caused the caliper pistons to be pushed back into the caliper leaving the pads loose and rattling, also then the brakes needed a quick pump to extend the pistons, which slowly were forced back into the caliper within five minutes.

I was lucky I went to someone who knows Corsa's and he identified it within seconds, the first Garage I went to wanted £220 New wheel cylinders, Master Cylinder ETC

Hope this helps all who have experienced similar and thought it was bleeding or flexy hoses

Regards
Paul