OK so as most of you know I have changed my handbrake cables and now have a very strange problem with my brakes.

While the car is stationary I push the pedal which has almost no resistance at all, but after pumping the pedal a few times it firms up to how it has should be (well nearly, will explain in a minute). However, after a few seconds the pedal resistance goes again unless i keep the pedal pressed or pump it.

Now I have changed the brake fluid, and also the reservoir cap seal was out of place, I reseated it and the pedal is rock solid when pumped as it should be. However this problem still remains I'm losing no brake fluid either

Can anyone help?

Cheers
Mark

When you changed the brake fluid did you bleed the system properly?

Yeah as far as i know. I don't think it was air in there anyway as I went through well over a litre of fluid and only a few tiny bubbles came out of the system

I've had this. I bleed the brakes on no less than 4-5 occations and the pedal still had softness. Its to do with your rear drums you need to strip them down and adjust them to tighten up the action. Don't ask me how I got it done at a garage .

Thought it was going to be something to do with that You mean the "self" adjusters that don't want to adjust themselves lol

Looks like it's rear drums off time again!

If the pedal is firm one minute and then goes soft, the chances are it does not need bleeding - if it had air in it, it would always be soft.

If the pedal goes all the way to the floor it could be that the master cylinder seals have "turned" when you pumped the brakes, so fluid is seeping past them. The seals can't cope with the length of travel the piston makes when you're bleeding the brakes.. in normal use it's a cm or less.

"Pumping" solves the problem temporarily because it re-settles the seals partially and re-fills the internal chamber with new fluid.. until it seeps past/dislodges the seals again when you apply pressure.

Sometimes the seals sort themselves out again (if you give the m/c a good whack, apparently and jiggle the brakes a bit - partially pumping them) but if not, you're looking at a new m/c.

The rear brake cylinders only push the shoes out against the drum face, so once they're out as far as necessary (shoe material almost touching the drum face) they won't be able to go any further, so it's unlikely to be a problem in the rear drum.

New m/c is about £50 or £100 depending on the type.

Ralf S.

Well what you describe is what was happening to me except I wasn't loosing fluid Brake pedal was rock hard until you turned the engine over then it would go soft or if you hold it for 30seconds it would start going soft. I bleed the brakes 3 times, check m/c for leaks there was none. I then rang a local Fiat specialist near me who said it was the drums booked it in and 45mins later it was 'tight as a nut' rock hard responsive brakes again. Im not trying to say your wrong but check the simple things first expecially if its not loosing fluid which Is what he's mentioned .

I'm going to go with Chris' idea first because i did put the adjusters all the way back in and they don't seem to have adjusted themselves back into position.

Next step is hammer > master cylinder then

How hard is a master cylinder to fit? And I'm guessing the whole hydraulic system is going to need refilling afterwards

Just to add, this problem was happening before I bled the brakes, so that has not caused this. I can't imagine seals inside the master cylinder just perish or turn for the sake of it. Will let you know how I get on

master cylinder = mess of wires, dashboard (maybe) and fluids


drum brakes are known to get stuck and not adjust, try that first, then still no avail, erm, master cylinder replacement/new seals time :yuck:

Well okay.. look at the shoes and the adjuster mechanism first... but your symptoms also sound like a worn m/c that's all.


You won't be losing fluid externally if the seals in the m/c have gone. What happens is that the when you press the brake a piston presses fluid into a dead end (the bit the brake pipes are connected to). That bit of fluid becomes isolated from the rest and is kept apart from it by the O-rings (so you can get pressure on just that part).

When the O-rings fail, the fluid being squeezed into the dead end seeps past the O-rings and is on the wrong side of the piston face. The O-rings act like the piston rings in the engine - they just seal the gap between the piston and the inner bore of the master cylinder, so any "leak" will stay inside the master cylinder, just the wrong side of the O-ring to where you want it.

When you release the brake, a spring pushes the piston back and the "dead end" is opened up to the fluid reservoir part again.

The O-rings are a tight fit on the piston and are located in grooves (again, like piston rings). As they're elastic they can flex. When you stick the brakes on the normal movement is 1cm or less. When you're bleeding the brakes it can be 5 or 6 cm. That additional movement (the O-ring is in a groove but is also trying to grip the piston) sometimes "pulls" the O-ring from its groove, especially if it's an old one.

Also, dirt in the fluid can get wedged in the O-ring and cut it, so it "leaks" (internally, I mean.. as above).

If you have to change the m/c you have to remove the fluid reservoir, unbolt the brake pipes and then unbolt the m/c from the servo unit (2 nuts). Fit the new one and then bleed the brake system. It's not toooo severe.


Ralf S.

Ok well plan is to rebuild the rear brakes with new pistons and shoes and adjust the adjuster properly.

My symptoms are identical to chris'. Engine off and the brakes are solid, but as soon as you turn the engine on the pedal goes soft unless you keep pumping

Ok so next problem...

Stripped down the drivers side drum, until i get to the brake line union which goes into the back of the cylinder. Absolutely seized! Spent 45 mins drenching it in plusgas and then undid the bolts holding the cylinder to the wheel, thinking i would be able to move the cylinder about and loosen it all up. Went at it with a spanner again and then something clicked. Great i thought, it's come undone. Wrong. Now the cylinder and the union spin on the brake line but the union is still stuck in the cylinder. How the hell am i supposed to get it off? Anyone got any tips?

Hi mate,

All i think you can really do is put bolt the cylinder back onto the back plate and that will stop it spinning and will give you more purchase to try and get it undone. Mine were stuck fast too, and then all of a sudden it just went and i punched the exhaust!

Good luck
Alan

Ralf S. said:

If the pedal is firm one minute and then goes soft, the chances are it does not need bleeding - if it had air in it, it would always be soft.

If the pedal goes all the way to the floor it could be that the master cylinder seals have "turned" when you pumped the brakes, so fluid is seeping past them. The seals can't cope with the length of travel the piston makes when you're bleeding the brakes.. in normal use it's a cm or less.

"Pumping" solves the problem temporarily because it re-settles the seals partially and re-fills the internal chamber with new fluid.. until it seeps past/dislodges the seals again when you apply pressure.

Sometimes the seals sort themselves out again (if you give the m/c a good whack, apparently and jiggle the brakes a bit - partially pumping them) but if not, you're looking at a new m/c.

The rear brake cylinders only push the shoes out against the drum face, so once they're out as far as necessary (shoe material almost touching the drum face) they won't be able to go any further, so it's unlikely to be a problem in the rear drum.

New m/c is about £50 or £100 depending on the type.

Ralf S.

Click to expand...

I agree with this. It's why I always use an Eazi Bleed.

I used an Ezibleed kit, the haynes said that's the only way to bleed a Punto with abs.

Yeah, it's pretty much the way with all of them. To be honest for £15 it's a bit of kit you can't really do without.

I had to plug the Fabia into the laptop to bleed the brakes when I changed the calipers. Bloody nightmare.

Decron said:

Yeah, it's pretty much the way with all of them. To be honest for £15 it's a bit of kit you can't really do without.

I had to plug the Fabia into the laptop to bleed the brakes when I changed the calipers. Bloody nightmare.

Click to expand...

Don't get me started about fabias and brakes lol

And the winner is...

Chris!

Changed the rear cylinders and shoes, bled the brakes and adjusted the adjusters properly and it works!

Here's a little video for you

https://www.fiatforum.com/gallery/data/1511/MOV00060.3GP

Sweet . Usually the simple things first. Whats in the vid I can't play it at work .