Spongy brakes which then bind??

[Stradic]

Hi all, I'm seriously hoping someone can help.
I have an 05 X type 2.0d estate.
The other week I had a brake line fracture which meant I lost all fluid.
I took it to a high st garage who replaced the line but then struggled to get the brake fluid back through. Once they had it left me with spongy brakes, BUT after 10 miles or so my pedal gets harder and harder until the brakes bind and I can no longer move.
I took it back and after discussions bought a second hand servo and master cylinder.
These have been fitted but have made no difference. They've rebled the brakes and have now said there is nothing else they can do!
I'm convinced there is still air in the system and as it gets hot, it's expanding thus making the brakes bind.
I'm going to take it elsewhere for another rebled, but just wondered if anyone has any knowledge of this?
I've looked through the different threads, and although I can find spongy or binding I can't find them both together.

Edited by Stradic on Wednesday 13th December 21:42

[Jaguar steve]

Press the brake pedal firmly and hold for several mins with the engine running.

Does the pedal slowly sink to the floor without any fluid loss anywhere? If so I'd suspect the internal seals on the master cylinder. It'll need looking at further to confirm but my guess is that's where the fault is. Sounds like the seals are compromised allowing fluid past that then creates a hydraulic lock somewhere in the system and that's what's causing the brakes to bind on.

Test the servo by repeatedly pumping the brake pedal with the engine off to exhaust any residual vacuum. Then rest your foot lightly with consistent pressure on the brake pedal and start the engine. If the servo is OK you'll feel the pedal quickly drop slightly as the vacuum builds. If it doesn't then you've probably got a vacuum leak, but even if the servo vacuum has flailed all together that wouldn't cause the brakes to bind, it would just make pedal effort a lot harder.

It's a possibility expanding air in the system might bind the brakes but I've never come across it.

Oh... and second hand brake parts. Really?

[Sebring440]

Jaguar steve said:

I'd suspect the internal seals on the master cylinder.

But he has replaced the master cylinder.

This needs simple, steady, fault-finding. When you had the original "brake line fracture" you said that "you lost all fluid". Presumably that was not the case, and you still had brakes on either the front or rear?

Also (presumably) this locking-up fault was not present before the brake line fracture? So is the "new" brake line at fault? Has it been manufactured badly and is blocked internally?

The "brakes bind and you can no longer move". All four brakes locked? Or just the rear? Or one of the fronts? Working out which brake caliper is locking up will start to point you in the right direction.

Rare in a modern car, but not unheard of, is a brake flexible pipe failing internally. The internal rubber goes soft, swells, goes spongey, etc, etc, and will let fluid through one way, but not the other. As you can understand, this will lead to binding or completely locked brakes outboard of that flexible pipe.

It's worth considering, but I'd still be investigating why the replacement of a metal brake pipe could have caused the problem.

The theory of "expanding air" binding the brakes is not sound.

[Stradic]

Thanks for reply. It was the pipeline which runs behind the fuel tank which went. I had a brake but there was no resistance in the pedal and the brakes were pretty non existent although there was a little there. I assumed all fluid had been lost due to the fracture and the reservoir being empty (yes there was fluid in it before). I'm pretty sure it's all 4 brakes that are binding when it happens. I've taken the car to a mate today to look at and it's thrown up a fault code C1440 which looking through Google may be abs related, although I have no warnings on the dash. Could the abs pump cause this? I dont know as I'm not mechanically minded. I'm hoping when he gets to have a proper look, he will sort.

[Jaguar steve]

Sebring440 said:

Jaguar steve said:

I'd suspect the internal seals on the master cylinder.

But he has replaced the master cylinder.

This needs simple, steady, fault-finding. When you had the original "brake line fracture" you said that "you lost all fluid". Presumably that was not the case, and you still had brakes on either the front or rear?

Also (presumably) this locking-up fault was not present before the brake line fracture? So is the "new" brake line at fault? Has it been manufactured badly and is blocked internally?

The "brakes bind and you can no longer move". All four brakes locked? Or just the rear? Or one of the fronts? Working out which brake caliper is locking up will start to point you in the right direction.

Rare in a modern car, but not unheard of, is a brake flexible pipe failing internally. The internal rubber goes soft, swells, goes spongey, etc, etc, and will let fluid through one way, but not the other. As you can understand, this will lead to binding or completely locked brakes outboard of that flexible pipe.

It's worth considering, but I'd still be investigating why the replacement of a metal brake pipe could have caused the problem.

The theory of "expanding air" binding the brakes is not sound.

Yes the master cylinder has been replaced - but with a second hand one which may or may not be faulty of course, and yes I agree the expanding air scenario is highly unlikely

Fitting second hand parts is something no self respecting professional mechanic should even contemplate with saftey critical systems because when doing so they adopt the responsibility for any consequences, Quite apart from that there's the risk of jumping to false conclusions unless they are absolutely know for certain the used part is working as intended.

I doubt there's a single mechanic alive who's not been caught out by that at some time.

Clearly the original garage has wasted the OPs time and money, but at least he's appears to have found one now with the nous to read codes and hopefully the ability to repair the car properly.

[crossy67]

Expanding air or moisture will cause binding, especially if a caliper is binding and getting warm to start with.

[anonymous-user]

crossy67 said:

Expanding air or moisture will cause binding, especially if a caliper is binding and getting warm to start with.

I’m not so sure. Any moisture will be absorbed by the fluid, possibly lowering its boiling point and causing a soft pedal if it got very hot

Never heard of a system having enough air in to cause binding, it would just push fluid back to the MC.

[Sebring440]

crossy67 said:

Expanding air or moisture will cause binding, especially if a caliper is binding and getting warm to start with.

I am afraid sir, your answer is BoIIox, with a capital "B".

[crossy67]

I would have thought it would have just pushed the fluid back into the reservoir but I've seen it lock brakes up solid on two different cars. A 2000ish Astra I was driving locked the brakes whilst being driven to the point where it wouldn't move. Opened the bleed nipple, big squirt of fluid and they were free again. And an E46 did the same thing. Maybe there is more to it than that but sorting the slightly sticky calliper and a fluid change has seen the BMW right for 3 years.

Brake fluid is hydroscopic so absorbs moisture, moisture seriously reduces the boiling point of brake fluid, it expands when it boils. Same as air left in a calliper. Long shot but I've seen the moisture do this, okay, not air but not impossible and not so much bks you ignorant 2@