Spongy Brakes Only When Engine Is Running

[jimbobclarkie 0]

Hey guys, can anyone help

 

I have just changed both rear calipurs on my 205 1.9 gti, the break pedal is firm and acts like is supposed to when the engine is off but as soon as i start it up and i depress the pedal it is spongy and hisses on the way down. I have been through the checks on the vacume item via the haynes manual and it seems to behave appropriately, i have also bled the complete system twice, does thos mean it is the master break cylinder?

 

Cheers james

[jimbobclarkie 0]

Anyone got any ideas?

[gowmonster 2]

did you have the master cylinder off the servo vacuum unit? sounds like a leak there, IIRC the running engine should make a vacuum to make it easier to brake.

edit: just re-read that you checked this.

 

did you bled the fronts too? if it's non abs I think that the brakes work in a circuit type fashion, (nearside rear & passenger front) and ( passenger rear and nearside front)

Edited April 9, 2011 by gowmonster

[jimbobclarkie 0]

Bled the brakes in that exact order, havent had the master cylinder off the vacume as yet, i think ur rite its a leak somewhere but the odd thing is im not losing break fluid out of the resovoir

[gowmonster 2]

if your not losing fluid it must be air from the vacuum then.... maybe knocked a pipe?

[jimbobclarkie 0]

Iv only had the car a few weeks now and the breaks have been the same since iv had it, i think ur rite on the vacume, the only other thing im thinking it could be is something to do with the push rod off the break pedal.

[jimbobclarkie 0]

Ok, decided what im going to try in the following order if one dont work move onto the next

 

1. Bleed the breaks with the engine running.

2. Remove break lines from the master cylinder, plug it up and see it it still goes spongy, if so then its got to be something to do with the cylinder or the vacume servo

3. Check the push rod distance off the vacume

4. Overhaul the master cylinder

 

If all else fails take a axe and start hitting the general break areas out of fustrasion

 

Any other ideas guys?

[jimbobclarkie 0]

Hey guys im at a loss i now have no clue the vaume seems fine no holes and seals are all good, the master cylinder has no detirioration on the seals and all seems in very good knick, its only when the engine is switched on that the pedal is spongy im tearin my hair out

[gowmonster 2]

unhook the vacuum pipe entirely. then try the brakes with the engine running.

 

I don't' think you will gain anything with 1 or 4. a new MC will be in the region of £20

[jimbobclarkie 0]

The engine stalls as soon as i unhook the vacume pipe is this normal?

[jimbobclarkie 0]

Sorted, im neva bleeding a 205 again without a easy bleed kit the amount of air i got outa that system was mental, thanks to gowmonster btw believe it or not u did help

 

Thanks james