Fulvia S1 brake callipers

[simonpen]

I have dismantled the front callipers and on each the inner piston assembly was seized and full of rust coloured gunge. The interior surface of the piston body is not smooth to the touch. They are not obviously pitted. My question is; can the new seals take a little unevenness or is it not worth the risk and it's best to replace with some new assemblies? ta

[nistri]

Without seeing the cylinder damage it is difficult to decide. If the scoring can be felt with a finger nail, it is a bad sign and calls for a new cylinder (and seals). Brake fluid should be changed every 2 y at most, in damp climate every year, also check that the steel sphere under the bleed nipple is OK, Andrea

[lancialulu]

They can be lined. If you are doing the complete brake system it might be worth considering changing to Dot5 silicon (automec) brake fluid. I run this on my S2 fulvias. Not sure if dunlop seals are different “rubber” and my react with the silicon. This fluid is long life and does not absorb water, and higher operating temperature. Having sad that I still managed to boil them going down Stelvio in a fully laden Fulvia Sport 1600 ( the road was empty so I went for it.....)

[nistri]

Relining the front cylinders can be risky as there is little metal to hone first and the interface between the new liner and the old metal might not withstand the heat generated by long and strong braking. New cylinders are readily available at moderate cost or one could fit nickel cylinders (very expensive, yet everlasting), note that Jags from the 60s fit the same cylinders, Andrea

[chriswgawne]

Based upo0n my own experiences with Dunlop front wheel cylinders for Fulvias I would always buy new.
I have had two bad experiences with bored and lined cylinders - one where fluid leaked between the lining and cylinder body and the other where the lining was pushed out by hydraulic pressure!
Neither desirable!
Chris

[Justin McArdle]

I ended up replacing all 4 sets of calipers on my 2c with new ones bought from Cavallitos. Would have saved money if I had done this in the first place! Any pitting makes the Dunlop calipers very susceptible to leakage and failure. Also, what price piece of mind?

[simonpen]

Indeed, thanks all, new ones it is.

[chriswgawne]

Absolutely Justin. Also with pitted wheel cylinders its actually possible for air to enter the wheel cylinder past the seal  on releasing brake pedal pressure without there being any fluid loss.
So one can be chasing a strange problem thinking the issue is with the master cylinder when it isn't.
Its a bit like trying to get away with old tyres - why take the risk??
Chris

[Charles Frodsham]

Interesting reading. Do the new Cavalitto cylinders come as a simple casting, or as an assembly with piston and seals?

[chriswgawne]

I have only ever had the complete assembly  from Cavalitto.
Chris

[Charles Frodsham]

Thanks.

[Jaydub]

Obviously Tim seems to have no trouble with Silicon Fluid, and you have to rely on your own experiences, but I wouldn`t recommend it at all! On more than one customer car we have had trouble with swelling seals and sticking pistons/ cylinders.
As Tim rightly said, it doesn`t absorb water and that is its problem, because on a vehicle with infrequent use, any moisture absorbed through the reservoir cap gets into the fluid and can sit in cylinders and calipers at the lowest points and cause corrosion. IMO good quality DOT 4 should be fine for normal use, or DOT 5 for more extreme use.

[lancialulu]

Obviously Tim seems to have no trouble with Silicon Fluid, and you have to rely on your own experiences, but I wouldn`t recommend it at all! On more than one customer car we have had trouble with swelling seals and sticking pistons/ cylinders.
As Tim rightly said, it doesn`t absorb water and that is its problem, because on a vehicle with infrequent use, any moisture absorbed through the reservoir cap gets into the fluid and can sit in cylinders and calipers at the lowest points and cause corrosion. IMO good quality DOT 4 should be fine for normal use, or DOT 5 for more extreme use.

maybe its because I use my cars.....that I have had no problem with silicon fluid, and maybe its because I only installed it in a totally new braking system....

[lancialulu]

Come to think of it while I was only thinking I had Silicon in my S2 Girling Fulvias, I have Silicon in my 1.3HFR (Dunlop) which has been installed at least 20 years ago and is still working fine (not that I use that car much.....).

[Sebastien]

I am sure that silicon brake fluid is a subject where you will find many strong opinions, for and against.

For any marque, be it English, Italian or German, you will find people recommending it warmly, and people that had very bad experiences : spongy pedal, problems with seals that swell, non-working master cylinders, etc….

I had a bad experience with silicon as an engineer working in defence more than 30 years ago : o-rings started swelling up when lubricated with silicon grease – we had to go back to the well known mineral grease. I remember that at the time, the type of o-ring material played a big role, as did the silicon grease used. The study was extensive, and the rework we had to do on finished components was a hassle, and a huge cost for the company. As a result I remain very cautious, and have never put silicon fluid in brake systems on my classic cars which were designed for DOT3 or DOT4.

I can also point out that when you buy wheel or master cylinders for Aurelia brakes at Cavalitto, he clearly stipulates to use DOT3, otherwise there is no warranty.