(Mechanical genius required) Brake pedal spongey even after brake shoe adjust

Limey

1st check I'd do is the master cylinder and brake pipe joints for leakage, no point changing the fluid if it's all going to pee out again.

Good way I've found to free up the bleed nipples is a damn good scrub with a wire brush , then a toothbrush soaked in penetrating oil and leave to soak while you do other stuff.

[Deleted User]

Hi,

and when you do start bleeding, start at the wheel farthest away from master cylinder.

JooFox

Hi all, good tip on putting the wheel back on after removing the screw. I have high hopes for that one as it was leverage that I was struggling with.
I'll report back tomorrow

adouglasmhor

agrinnall wrote: »

Bit touchy this morning aren't you? If you're that good an engineer why are you having to ask what the problem is on a forum rather than just fixing it?

My dad before he retired was, an award winning civil engineer and landscape architect. He was unfortunately not in the least bit interested in mechanics unless it was soil mechanics, architectural support or drainage.

He never puts oil in a car, he has never topped up the coolant before a long journey, he once told me he thought a stone had got caught in his brakes and was making a noise (his front brake shoes were down to the metal and the discs were gouged), he calls getting repairs done for an MOT a service. He phones me to change a bulb if one goes. Being an engineer does not make you good at all engineering.

JooFox

Completely agree, I'm a qualified "engineer" and work on flying things with spinning rotors. But I work with qualified "engineers" that I wouldn't trust to change an air freshner in my car

colino

Get the car to a garage, in fact play safe for the rest of us and have them collect it.
I don't know what kind of engineering you claim to be a part of but being unable to use your eyes to look for the leak (it's a sealed system, if the reservoir was nearly empty, the system is leaking), leads me to doubt your abilities.
Brakes are both incredibly simple and important. The pipework, the calipers, or more realistically in this case, the rear cylinder needs fixed and you are bumbling around with your tinkering.
One of the few areas of car repair that I wouldn't recommend the OP picks up a Haynes manual to play with.

Joe_Horner

From your OP you're likely to have 2 separate possible problems:

The fact the fluid was "nearly empty" may or may not be a problem. Was it low before or after you replaced the front pads? And how low were the pads? As disk pads wear the fluid naturally falls in the resevoir. By the time they're worn out it can look pretty low but should come baack up to the "proper" level once they're replaced. If you top it up and then replace them, it will usually overflow as the new pads go in!

If it wasn't looking low because of the pad wear then there MUST be a leak somewhere for it too have gone down. The most likely is probably the rear cylinders as mentioned earlier. If they weep slowly then the fluid gets absorbed by the linings and / or burnt off with the heat of braking so you won't see it until you get the hubs off..

The second problem is the pedal going low. The fact it happened suddenly strongly suggests that it's a master cylinder seal failed. Unless you're talking about a pre-'75 or so car it'll have dual circuit brakes so that a failure in one circuit still lets half your brakes work. An effect of that is that, if a seal fails, the pedal will go much further to the floor but still be "hard" before you completely run out of travel.

About the only other reasons for a sudden change like that are an auto adjuster failing and letting the shoes completely clear of the drums (but then you'd have no problems getting the hubs off), a burst pipe (but then you'd be losing fluid faster than a fast tuing and have a puddle on your drive) or possibly a flexi-hose that's failed and starting balloning under pressure.

You can check the flexis by getting someone else to push the pedal hard while you watch / feel them - it'll be very obvious if they're balloning to that extent.

You'll need to get the drums off to check the rear cylinders and shoes - if you can't shift them then get a cheap 3-leg puller (should get one for less than a tenner) and wind them off with that. Hitting their edges with a big hammer while they're under pressure from the puller helps. There's a risk of damaging the drums doing this but sounds like you're planning to replace them anyway.

One point to note is, once you've replaced the rears, don't adjust them up on the handbrake cable! That will usually prevent the auto adjusters from doing their job and leave you with unreliable adjustment. Slacken the cables off and let the brakes adjust themselves up (usually by pumping the brake pedal) and only adjust the cables once the auto adjusters have worked.

JooFox

colino wrote: »

leads me to doubt your abilities.
Brakes are both incredibly simple and important.
you are bumbling around with your tinkering.
I wouldn't recommend the OP picks up a Haynes manual to play with.

Thanks Colino, as I'm sure you've deduced the leak is probably coming from the slave cylinder in the rear passenger side hub which is what I've strongly suspected.
So although I may be an engineer, I haven't yet qualified with x-ray vision so a visual inspection is not possible

Just to paint a picture for everyone, I live in a wooden shack held together by bailing twine. My transport is a cow with drum brakes on and my tools are hand crafted from driftwood collected from a beach by a druid at full moon :rotfl:
I've just bled the brake system with cat urine and I'm confident it's all fixed now as the brakes smell nice.

Here we go

Limey

:rotfl:

I have the pleasure of helping scrape up the flying things with spinny rotors when they fall out the sky.

Joe_Horner

JooFox wrote: »

Completely agree, I'm a qualified "engineer" and work on flying things with spinning rotors. But I work with qualified "engineers" that I wouldn't trust to change an air freshner in my car

I used to do that for a living and was always worried by the other qualified "engineers" who'd happily sign off on a wokka-wokka's hydraulics but weren't happy to repair their own car's brake system. Struck me as a bit like being a Microsoft programmer but unable to use a calculator (although that could explain a lot of Windows :P )