Fiat Punto Brakes Failure

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Wed 26 Dec 2001 16:30
Fiat Punto Brakes Failure - John Gilbertson
I have a 1999 (last of old model) Punto with 7,500 miles on the clock. The footbrake failed catastrophically i.e. it went flat to the floor with no prior warning. Then when I eventually managed to stop with the aid of the handbrake I was able to just pull the footbrake back. It returned to the normal working position with the brakes just as good as they were before the failure as if nothing untoward had happened! Fiat say they found no problem with the braking system, but have replaced the Master Cylinder as a 'precautionary measure'???! They won't tell me against what.

So, I wonder has anyone else had a similar problem?

Thanks, John Gilbertson.
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Thu 27 Dec 2001 15:17
Re: Fiat Punto Brakes Failure - Mark (Brazil)
Is it cable operated from the pedal ?
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Fri 28 Dec 2001 00:48
Re: Fiat Punto Brakes Failure - David W
John,

I've never had a problem exactly like yours but......

Consider when you fit a new set of brake pads. You lever back the pistons to allow room for the new pads. This leaves the new pads just a few mm from the disc. Then you get in the car and pump the pedal to bring the pads into contact with the discs.

Amazingly the pedal may go to the floor a couple of times before it goes firm again.

This can be a major shortcoming with a conventional braking system* if there is a fault......that one full stroke of the master cylinder actually moves the parts at the business end a very small distance.

It is easily possible to get in a muddle with old Land Rover brakes where the first full stroke of the pedal moves the brake cylinders out to the drums but it takes a second push to get a firm pedal and some braking action.

Just a long shot but I wonder if one of your brakes "stuck" too far in the off position so it took the full pedal travel and still nothing happened, then the second pump you gave it brought things back to normal.

A long shot?

*I refer to a conventional system because the fully powered system as fitted to Citroen Xantias and the like will still give you serious brake effort even with fluid pouring from a damaged pipe. The brake pedal just opens a high pressure valve and the system will work under fault conditions until it runs out of fluid, that in itself has a huge capacity besides a normal brake system.

David
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Fri 28 Dec 2001 20:11
Re: Fiat Punto Brakes Failure - Mark (Brazil)
Building on this, presumably if a caliper had siezed in the "off" position while not being used, and with the limited mileage of this car, I guess thats not impossible, then the symptons could have occured if that cylinder finally freed itself up and began its trek towards the disk ???

Mark (trying to give techie car answers is not easy)
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Fri 28 Dec 2001 21:07
Re: Fiat Punto Brakes Failure - steve paterson
Mark(Brazil),
A seized caliper would probably lead to noticeable brake imbalance, I'd thought of a seized wheel cylinder piston 'popping out' to meet it's shoe, but this wouldn't lead to a total brake failure, unless it happened on both sides at the same time. (assuming a diagonally split circuit). John says that the brakes have been checked and found to be OK.
Steve
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Fri 28 Dec 2001 20:38
Re: Fiat Punto Brakes Failure - John Gilbertson
Thank you all for the information. I believe I know the cause but I wanted to see if many others had suffered the same trauma, or if maybe I'm the only one to have experienced it (and lived to tell the tale!)? I have on reliable authority that the seal on the Master Cylinder reverses itself when the brake cylinder rod has been machined off-centre. So you get this sudden and catastrophic brake failure, then 5 minutes later everything is as right as rain!

I've also heard, and this also from a reliable source, that Sherpa vans a few years ago also suffered from the same disease. Ring any bells with anyone?

Thanks, John.
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Fri 28 Dec 2001 20:48
Re: Fiat Punto Brakes Failure - David W
John,

Haven't heard of this on your car but it was much talked about a while back on Astras. If you levered the brake pistons back quickly when changing pads, and without releasing a bleed nipple, then the master cylinder seals could reverse and the pedal action would be terrible.

Also I do now remember a ZX in the other month with a mysterious feel to the pedal and intermittant excessive travel. This didn't give me a 100% direction for a repair but a new master cylinder cured that.

David
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Fri 28 Dec 2001 20:01
Re: Fiat Punto Brakes Failure - steve paterson
John,
David W and myself seem to be thinking along the same lines. A badly adjusted or worn wheel bearing (on a disc brake wheel) can force the pads away from the disc, and the pistons back into the caliper. The first brake application just moves the pads towards the disc - pedal seems to go to floor.
I don't know about your Punto, but earlier Fiats had a weird back brake adjusting mechanism that always resulted in a lot of travel at the pedal. I suppose in a 'worst case' scenario, a bit of play in both front wheel bearings, and 'just' working rear brake adjusters might result in no brakes on the first application. Seems unlikely on a new car though, and equally unlikely that both both circuits in the master cylinder failed at the same time. Bit of a mystery !
Steve
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Sat 29 Dec 2001 17:07
Re: Fiat Punto Brakes Failure - John S
John

The other cause of this 'complete failure followed by apparently perfect brakes' syndrome is water contaminated brake fluid. Brake fluid is hygroscopic and absorbs moisture from the air, which is the main reason for the recommended 2 yearly change.

With hard use of the brakes this water can boil, causing a steam bubble in the system. As a result the pedal goes to the floor. Later when it's cooled down and the steam has condensed then the brakes feel fine.

Seems unlikely on a '99 car, but it's possible.

Regards

John
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