Technical 2008 Fiat 500 front brake failure and imbalance

[MungoUK]

Hi,

New user here. I have decided to join as I cannot find a fix for a problem with brake system.

Long story short... My wife's 2008 Fiat 500 1.3TD has suffered a torn rubber brake hose near right hand side front brake caliper. This has been replaced by a garage with a new genuine Fiat rubber hose. The problem now is that this side will not brake - like at all... When the rubber hose it detached, the brake fluid isn't even flowing through the metal brake line that the rubber hose attaches to on the side that suffered the failure. Left side brakes fine. I am wondering what could be blocking brake fluid from getting to the left brake caliper.

I have already found that on some other brands there is a so called brake imbalance valve in the main brake servo cylinder. When pressure imbalance is detected between left and right side it trips the valve, which blocks the brake fluid on the side that was loosing pressure, so more doesn't leak. Not sure if Fiats have such thing and if so, how do you reset such valve please?

Many thanks,
Simon

 

[bugsymike]

Hi,

New user here. I have decided to join as I cannot find a fix for a problem with brake system.

Long story short... My wife's 2008 Fiat 500 1.3TD has suffered a torn rubber brake hose near right hand side front brake caliper. This has been replaced by a garage with a new genuine Fiat rubber hose. The problem now is that this side will not brake - like at all... When the rubber hose it detached, the brake fluid isn't even flowing through the metal brake line that the rubber hose attaches to on the side that suffered the failure. Left side brakes fine. I am wondering what could be blocking brake fluid from getting to the left brake caliper.

I have already found that on some other brands there is a so called brake imbalance valve in the main brake servo cylinder. When pressure imbalance is detected between left and right side it trips the valve, which blocks the brake fluid on the side that was loosing pressure, so more doesn't leak. Not sure if Fiats have such thing and if so, how do you reset such valve please?

Many thanks,
Simon

Surely if it worked correctly before the hose issue I would have thought it most likely a bit of damaged old hose debris is blocking that caliper from working.
I would have thought most garages could locate the problem and sort that.
First thing I would do is disconnect new hose from caliper and see if a good brake fluid flow at that point.
Nothing impossible but I have never heard of a system where a valve trips to cut off fluid.
What caused the fault in the first place?

 

[MungoUK]

Surely if it worked correctly before the hose issue I would have thought it most likely a bit of damaged old hose debris is blocking that caliper from working.
I would have thought most garages could locate the problem and sort that.
First thing I would do is disconnect new hose from caliper and see if a good brake fluid flow at that point.
Nothing impossible but I have never heard of a system where a valve trips to cut off fluid.
What caused the fault in the first place?

Hi,

That's the whole point. They have disconnected the rubber hose and the brake fluid does not flow through the metal brake line at all to that side. The brakes were working fine beforehand. Normally the car would veer one way if one brake wasn't working at all, like it does now, but it wasn't.

The fault was a hole in the rubber hose where it rubbed against a part near the caliper. Weird thing is when my wife felt that somethings wrong, there was a brake fluid leaking out for some 20 seconds or so, then it stopped. But the reservoir hasn't fully emptied. This is what makes me think there was a valve of some sort that got triggered and stopped the flow to that side. The mechanic says they had many Fists for that job before, but never have they experienced this symptom.

 

[John202020]

Undo the offending pipe at the abs regulator does fluid leak out when pedal pressed?

 

[bugsymike]

Also modern brake master cylinder have two pistons inside, in effect if one circuit fails you will have a poor brake pedal but it will still have some braking capability.
Unlike the 1950s LandRover recovery vehicle I went out on a customer breakdown with in the early 70s , having already gone down a very steep hill, I got to the customer and decided to swing around in the road to better work on the vehicle, touched the brakes and absolutely nothing , the pedal went to the floor and I drove over a 9 inch kerb and up a bank! That vehicle only had one brake pipe coming from the master cylinder so when a metal pipe failed instantly no brakes!
Roads were quieter in those days, I fixed the customers car and drove back to the garage using the handbrake.
Another point on your wife's car , how come the brake hose rubbing wasn't picked up at last Mot?

 

[varesecrazy]

Hi,

OK.. As you are well aware the braking system is like linked syringes

Depress one the other moves out

The volumes of fluid moving is actually VERY small

You losing a hose has pushed a Far Larger volume through the ABS unit

There Is always a chance some disturbed debris Is creating a good seal


Experience :
years ago I had a similar issue.. I had clutch failure.. Very similar to Brake failure

Pedal to the floor.. No action

The feed tube to the Slave cylinder was choked with gunk

The Slave was actually dry and rusty

It took 60+ PSI on the easibleed to shift the blockage and let fluid flow

So.. It can happen


With your 500 I believe you can Cycle the ABS with software

That may well help

 

[The Panda Nut]

Also modern brake master cylinder have two pistons inside, in effect if one circuit fails you will have a poor brake pedal but it will still have some braking capability.
Unlike the 1950s LandRover recovery vehicle I went out on a customer breakdown with in the early 70s , having already gone down a very steep hill, I got to the customer and decided to swing around in the road to better work on the vehicle, touched the brakes and absolutely nothing , the pedal went to the floor and I drove over a 9 inch kerb and up a bank! That vehicle only had one brake pipe coming from the master cylinder so when a metal pipe failed instantly no brakes!
Roads were quieter in those days, I fixed the customers car and drove back to the garage using the handbrake.
Another point on your wife's car , how come the brake hose rubbing wasn't picked up at last Mot?

This suggests that the master cylinder has failed big time, or there is now a fault in the abs pump. May be rapid loss of fluid caused debris to mover from the master cyinder into the abs and block something within. The problem must be one or the other. Has some bright spark sealed something with cling film and forgot to remove this during repair. I have also never heard of something to stop one circuit from working in such circumstances. I would start by checking fluid flows out of both ports on the master cylinder then, getting the ABS diagnosed and then tested. check alsp rear left cylinder and lines. Check for flattened section of brake line in the front right area.