Hi,

Does anybody know which are the best brake bias valves for a Cento with Punto callipers up front, rear callipers, stock brake master cylinder and servo? Mine are dead, I won't repair them, should I buy the original valves or is there something better suited for this application?

Crikey, for a second there Rob-

I though you were talking about a cabin-adjustable racecar-style brake-bias adjuster!

sorry

Nope, I meant these two little nuggets. They are expensive to replace so maybe a different FIAT part will be good also.

They're not toooooo expensive.

I'd trust a Fiat OE part to be as good as anything else out there.. but buy something made in Europe, with a brand name you know on the box, rather than made in China with no name on it.


Ralf S.

I can buy 6 original brake masters for the price of two new valves in Poland so I'm not willing to spend that much.

Did someone try to use valve nr. 7743899 from Punto/Lancia Y/Barchetta?

You are moving massively different amounts of fluid, so standard may not be appropriate.

Pedal box is the ultimate answer.

D

You mean a swap to a Tilton-style pedal box? I don't know how would that help with the rear but it's a change I'm not willing to make.

Maaad Rob said:

You mean a swap to a Tilton-style pedal box? I don't know how would that help with the rear but it's a change I'm not willing to make.

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If you have calipers on the rear you are moving far more fluid than cylinders.

You will need to calculate the difference and make the adjustment, twice, as its a diagonal split.

You will never get a good pedal otherwise.

D

While your approach is correct engineering-wise it's somehow beyond my capabilities. For me if the car feels good and I get correct values on the rollers then it's all I'm interested in.

The pedal goes a little further down but it feels absolutely fine. I did check the braking force, front is around 2 kN, rear behaved exactly how it behaved when it had drums - unequal. I suspect the valves might be seized.

Many people swap brakes in these cars and it doesn't seem to be necessary to go into the trouble of installing pedal boxes. The Punto GT had rear disc brakes and valve nr 7751335. The same part was shared in Barchetta, Seicento, Lancia Y.



Now the rear drum cars had valve nr 7743899 again shared in Punto GT, Barchetta, Seicento and Lancia Y.



It looks the same apart from the lever that regulates the braking force. I bet it's the only difference - the minimum force is the same for both and the non-variable valve is permanently set to minimum. If a valve is good in a Punto and Seicento it should be fine in Cinquecento as well.

Could be interesting to use the adjustable ones and make them cockpit adjustable to suit what you are doing at any given time.

D

That can be achieved with an aftermarket brake bias adjuster but from what I know they only work properly in this car when set to minimum and even a small raise of brake power to the rear results in locking wheels - light rear, short wheelbase, recipe for disaster. That's not what I'm after, plus it's illegal to use on the road in Poland. I'll try the non-adjustable valves and see what results I get on the rollers.

Did you ever resolve this issue?

No, I crashed the car before I had the chance to try to make this modification. Fortunately, I bought a Punto mk1 which has these exact valves. This way I can take this car to the rollers and measure the rear axle braking force which should tell me if they in fact operate as I suspect. But before I do this I will change the drums to discs - the same setup that I have in the Cento will fit the Punto. Then I will unequivocally know if the Punto valves give the same braking force (without touching them at all). Hopefully I will do it this year.

Maaad Rob said:

No, I crashed the car before I had the chance to try to make this modification. Fortunately, I bought a Punto mk1 which has these exact valves. This way I can take this car to the rollers and measure the rear axle braking force which should tell me if they in fact operate as I suspect. But before I do this I will change the drums to discs - the same setup that I have in the Cento will fit the Punto. Then I will unequivocally know if the Punto valves give the same braking force (without touching them at all). Hopefully I will do it this year.

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I’ve held off doing the conversion as I seen the issues about the rear brake bias.

Look forward to your results.

In a Seicento? Don't even hesitate for a second and convert these drums to discs. Do it alongside 257 mm vented rotors and Punto GT calipers up front. This brake setup truly transforms the car. Now that I look at the steep downhill runs that I did I'm amazed what level of pace I was able to hold. I wouldn't even try this in my Audi.

What I try to do now is iron out tiny little problems to have the system work perfectly. The only elements I left unchanged are the valves and servo. I could buy new Cinquecento valves but they are stupidly expensive therefore I try to utilise Punto valves. I bought a run-out gauge, measured rear disc judder and there is some oscillation on the hub so that needs attention also.

This is a problem unique to my situation, it's not a universal issue of the conversion. There's no reason why you should experience the same.

Maaad Rob said:

In a Seicento? Don't even hesitate for a second and do the conversion. I wouldn't blink an eye, I'm fed up with maintaining drums. The brake setup I have now is my favorite thing in the whole car, I love it. Changing the front to 257 vented rotors and Punto GT calipers did a fantastic job.

What I try to do now is iron out tiny little problems to have the system work perfectly. The only elements I left unchanged are the valves and servo. I could buy new Cinquecento valves but they are stupidly expensive therefore I try to utilise Punto valves. I bought a run-out gauge, measured rear disc judder and there is some oscillation on the hub so that needs attention also.

This is a problem unique to my situation, it's not a universal issue of the conversion. There's no reason why you should experience the same.

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From speaking to others, it appears as if fitting an adjustable brake bias is preferable, as this would allow for adjustment regarding now having calipers.

I think it just looks so much better I think I will do it.

It simply complements the car more. If a brake bias adjuster is road legal in UK (?) then why not.

Those were broken on my cinquecento as well, the ones which I could find for cinquecento were very expensive around 60-80 pounds each, I decided to risk it and ordered some for another fiat I can't remember which one it was, either classic panda or uno since they were only 12 pounds each and they fitted and work perfectly with the factory brakes

Take a look at the pictures on page one, maybe it was one of them. I thought that Uno used just a single valve for rear brakes?

Maaad Rob said:

Take a look at the pictures on page one, maybe it was one of them. I thought that Uno used just a single valve for rear brakes?

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I think those were the ones I used, or at least they look the same, but the place where I bought them from had more pictures where it was visible that the pipe at the bottom has no exit, I don't know what it is for, its just blocked off and Im pretty sure I payed 12 pounds for them, not 20