corsa b spongy pedal

[bertyboy]

hi, I got a v reg corsa b that was originally a 1.2 16v. I replace the engine with a c20xe and ever since I have had really bad brakes, the pedal is spongy until around three quarters of the way down then the brakes work okay, it has done this with original brakes and cavalier 2.0 ones. I have pressure bled the brakes about 20 times and tried two different servos! Has anyone got any ideas? Thank you

[mowgli]

the first place to look is a load sensing valve(some corsas have them, some don't), if it is fitted, it will be underneath, near the rear beam.
if it is there, it might need adjusting to compensate for the lowering caused by the c20xe & any lowering springs that have been fitted, as when the rear is lowered, it cons the valve into a rear brake bias, which usually makes for crap pedal feel.

if there isn't one, then just strip the rear brakes, clean everything up, copper grease the adjusters & then put it all back together as per haynes, not forgetting to readjust the handbrake after you are sure the brakes are fully adjusted. this should improve things

[pottersrebel]

i had a similar thing with my corsa, i bled the brakes and bled them and bled them but i could still almost touch the pedal to the floor with force, it turned out the brake discs were worn to thin and under heavy pressure from the brake pedal the discs could be seen twisting. As its a stock car and i was racing the next day i just fitted almost new brake pads and i got a decent pedal, this topic has reminded me though to replace the discs over winter, whoops

[mowgli]

its also reminded me that i have been meaning to make a how to article about drilling a hole in the front face of the drum so the 'self' lol adjusters can be tweaked without stripping the brake down.

[therealnovaboy]

its also reminded me that i have been meaning to make a how to article about drilling a hole in the front face of the drum so the 'self' lol adjusters can be tweaked without stripping the brake down.

The problem with that is, eventually the shoe will wear a lip on the drum. If you keep adjusting it without removing the lip then youll get to the point where you cant get the drum off withought ripping all the brake assembly off the back plate. Your better just to get take the drum off for all the time it takes to do the job right.

[mowgli]

no, cos you can actually use my method to back the adjuster off too, so it makes drum removal a doddle.

you use a small allen key to pull the little plate back & an electrical screwdriver to turn the adjuster nut.

i'll post it up when i can, its one of those things that gm definitely should have done.

the big problem with regular drum removal is that you get brake dust onto the stub axle & grease, so you make a grinding paste which kills the bearings.

[therealnovaboy]

you use a small allen key to pull the little plate back & an electrical screwdriver to turn the adjuster nut.


I have no idea what you mean. I thought you meant flick the jagged nut on the brake as the adjuster is supposed to. Id of thought it would be a nightmare to flick it back the other way.

As you say you need to get the article up.

[mowgli]

it truly is simple... a proper old school mechanic showed me it back in the late 80's.

if you clean up the threads enough & cover them in copper slip, once the locking plate is pulled back by the allen key, the jagged nut will wind back quite easily, if you pull the handbrake on a couple of notches first

[therealnovaboy]

ah, Ive got you. I didnt know what plate you were on about.

[meritlover]

If you are saying they were fine until the engine change then it suggests to me the problem lies there. The only common part where the two components meet is the vacuum line between the servo and the manifold. Did you connect this line properly and have you fitted the NRV (or tested it)?

[Nobby]

sounds like you have buggered the master cylinder common as fook on corsas, if you push the pedal to hard when trying to bleed it flips the seals inside

[bertyboy]

Thanks for all the replies lads!
thought I would add a abit more info, I have already adjusted the load valve on rear axle then tried and was still the same so removed the load valve spring completely and was still the same.
I have also recently fitted all new rear shoes and wheel cylinders and the front are nearly new discs and pads. Also when I changed the servo twice both times I replace the whole lot including master cylinder so guess that eliminates that! I have tried fitting brake hose clamps to rear brake hoses and retried to make sure I had adjusted them wrong but was still the same.
when I fitted the engine the servo my off my car was wrong so I got some servo hose from Vauxhall and made my own including fitting the old one way valve.
I really am lost I have tried everything I can think of!!

[meritlover]

im not trying to be insulting, but is the NRV in the correct way round?

[bertyboy]

I blew through both ends and pretty sure ive got it the correct way but I will turn it round tomorrow just to make sure. I thought if it was the wrong way round the brakes don't work aswell and the pedal is hard? thanks for your help

[meritlover]

that may be the case but one mans idea of 'hard' is different to the next womans so worth a try. im only saying this as its the only thing which may have changed between the 2 engines. you should be able to suck from the servo but not blow towards it.

[meritlover]

.... I have already adjusted the load valve on rear axle then tried and was still the same so removed the load valve spring completely and was still the same.
i would imagine that would be the case. id be tempted to increse the tension of the spring (giving the effect of increased weight in the rear) i would be interested to know if it firms it up.

[reecegsi]

the first place to look is a load sensing valve(some corsas have them, some don't), if it is fitted, it will be underneath, near the rear beam.
if it is there, it might need adjusting to compensate for the lowering caused by the c20xe & any lowering springs that have been fitted, as when the rear is lowered, it cons the valve into a rear brake bias, which usually makes for crap pedal feel.

if there isn't one, then just strip the rear brakes, clean everything up, copper grease the adjusters & then put it all back together as per haynes, not forgetting to readjust the handbrake after you are sure the brakes are fully adjusted. this should improve things

Mines like this brakes are crap cars lowered how do i adjust the bias valve? Or make it better?

[meritlover]

if its mounted on the axel, release the spring tension. if its a pcv on the master cylinder then you cant without modifying it.

the brakes shouldnt be made 'worse' by the load valve. The total braking force remains the same but its just distributed differently i.e biased differently front to rear.

[mowgli]

if its mounted on the axel, release the spring tension. if its a pcv on the master cylinder then you cant without modifying it.

the brakes shouldnt be made 'worse' by the load valve. The total braking force remains the same but its just distributed differently i.e biased differently front to rear.

i once bought a mk1 astra with a load sensing valve that the spring had been knocked off. i went round a corner while braking & locked the rear..... i fixed it really quickly.


OP did you grind the lip off the brake drums or fit new drums? cos the rears will be out of adjustment if you did neither

[bertyboy]

i once bought a mk1 astra with a load sensing valve that the spring had been knocked off. i went round a corner while braking & locked the rear..... i fixed it really quickly.


OP did you grind the lip off the brake drums or fit new drums? cos the rears will be out of adjustment if you did neither


My spring is removed at the moment, I will definitely be re fitting it tomorrow after reading that! Yeah I ground the lips of the drums

[mowgli]

if there are no leaks & the self[ lol ] adjusters are tweeked up, and the spring is in the right place, then it must be master cylinder seals, or the servo leaking