Pontiac Owners Club UK

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?

Could be, or air in system. Might be worth bleeding first to see if this cures it

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.

I suppose it could be...ill have to check.

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

vac. pipe shouldn't cause pedal creep

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.

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

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.

sounds like master cylinder

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?

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

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!

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

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

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.

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