why don't my rear brakes work properly?

GeX

GeX

GeX

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17 Dec 2002
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Manchester
Hi all.

Anyone offer any advice to me. My car is a FIAT Cinquecento and has PuntoGT brake system parts, namely the larger front calipers and then a rear disc conversion.

It's been on the car ~3 years. A year ago it had a new master cylinder (Cinquecento).

Just been doing some MOT checks, needed new tyres - so got them done, and whilst it was in the garage got it on the brake rollers to test all was well. But it wasn't, the rear brakes aren't really doing very much when applied via the pedal.

They work fine on the handbrake. I whipped the wheels off and had a quick look over the condition of the calipers, discs and pads but it all looked 'right'.

I can't really see what could be wrong, I did notice though that if push the brake pedal, hold it there and pull the handbrake up then I cannot 'feel' anything back through the pedal which I'm sure I could before.

All I can think to do is re bleed the rear calipers - any other suggestions, or do you reckon that'll do it?
 
it has passed with the same system before yeah, and it's a setup others use with no reported problems.

there is no adjustable proportioning valve linked into the suspension - just a statically set one near the master cylinder.
 
GeX said:
it has passed with the same system before yeah, and it's a setup others use with no reported problems.

there is no adjustable proportioning valve linked into the suspension - just a statically set one near the master cylinder.
Click to expand...

he is talking about a brake bias valve.
 
yeah, i know - which is normally found linked to the rear suspension.. alters the bias depending on rear end weight and they're prone to jamming. The one (afaik) on my car is statically set, and no moving parts.. so nothing to fail ?
 
I'd get a bias valve and remove the current static one.

Does the Punto GT have the static valve setup? If not then I bet it is that which is restricting the rears. This is due to different brake setups requiring different amounts of pressure.
 
The Bias might be all wrong now.

How much different sized are the punto calipers compared to the originals?

If it had drums on originally then you will need to change the brake bias anyway.
 
I've never felt the hand brake being applied through the pedal on rear disks, only ever on tambourines.

Sounds like a hydraulic issue to me, probably bias.
 
GeX said:
The one (afaik) on my car is statically set, and no moving arts.. so nothing to fail ?
Click to expand...

They have moving parts inside which could fail due to e.g. corrosion. Are the brake circuits split front/rear or diagonally? If the former then bleeding would certainly be a good first step.
 
afaik they are diagonally split, and if that fails i'll look at the valve.

as said though, this setup works on other cars and has worked fine on mine for ~3 years - so i know that when the valve is working, the bias is fine :)
 
A lot of cars do have different bias valves between drum and disk rear setups. Are you sure they have always been fine up until now ?
 
yes, it's never been an issue on the previous MOTs and I know around 10 other cars running the same setup.

If i hadn't increased the size of the front calipers when converting to the rear discs then it may have posed a problem.. but i did.. so it didnt :)
 
GeX said:
yes, it's never been an issue on the previous MOTs and I know around 10 other cars running the same setup.

If i hadn't increased the size of the front calipers when converting to the rear discs then it may have posed a problem.. but i did.. so it didnt :)
Click to expand...

I might be wrong, but I'd disagree.

Drums have a greater stopping force than discs. The only problem with drums is over heating and this fade.

You'll need more bias to the rear if you're using disks, more so if you've uprated the front discs.
 
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