International Lancia Forums

Fresh from my apparent success with the oil leak, I decided to investigate why the brakes pull slightly on a very hard stop.

First thing I noticed was that the front brake pads are worn unevenly ... this is on the Girling superduplex setup. So the pads are at an angle to the rotor, and I can easily imagine them sticking and affecting brake efficiency. And, it's an effect that would gradually appear over time, which is just what's happened.

After some Googling around, I came across this item in Huib's Fulvia Q&A section:

Sticking brakes discussion


This describes how switching the brake lines between big and small pistons caused uneven pad wear. Could it be that I have the same problem?

Out to the garage, and YES! At some point in the past, the lines from the front of the master cylinder had been connected to the top piston, and vice versa. So it looks as if that's the reason for the uneven wear.

Viva-Lancia wins again! Thanks, Huib.

Peter

The lines are confusing. Best triple check. One of the checks is blowing air through them.
The posting on the Q&A was done some years ago. Since then it sometimes crossed my mind if this is really the cause. After all, the pressure in both chambers is the same. The fluid cannot be compressed and neither can the steel plungers be compressed. It might be though that the displaced volume of the corresponding chamber is not enough when the circuits are connected the wrong way.

Good points, Huib. Yes, I triple- and quadruple-checked that the lines were indeed swapped!

My pads are worn at the bottom, just like yours. I suppose it could be a coincidence that the circuits are also swapped, but I think it's a reasonable working assumption that this somehow caused the uneven wear.

I suspect there's more than meets the eye in the design of the superduplex system. For a start, I don't see why the pistons are different sizes; as far as I know, all other multi-piston calipers have the same diameter bores.

Anyway, I'll install new pads, swap the brake lines back to their correct positions, and report back after a few thousand miles!

Peter

The only explanation I can offer for the difference in size of the pistons is that the surface area of two small pistons is now the same as the surface area of tone bigger piston. In hydraulic systems one alwasy has to think in pressure and surface area. Because there are twice as many small pistons as big pistons the displaced volume of each chamber is the same.

Since you have to take the callipers off to replace the pads, you might as well disassemble them for cleaning and check if the pistons move freely. Usually the pad chambers need cleaning from dirt and rust.

Also use new pins.

What I have never understood is the lack of a compensation hole on the second chamber of the master brake cilinder. On every other mbc I have seen there is a compensation hole in front of each seal if the plungers are in the rest position. The hole is there to connect the container with the chamber allowing expansion of fluid back into the container when becoming hot.
The S2 mbc has a hole in front of the seal on the 1st plunger but not in front of the seal on the 2nd plunger. The schematic drawing in the Concise Repair Shop Manual does show a hole in front of both seals!!! The 2nd plunger however consists of two parts which can slide over each other. You may want to check if these two parts are not stuck which often happens.
Another thing to check in the mbc is the seal on the bottom of the 2nd plunger. It should face towards the pedal as it is receiving pressure from there. It is often mounted the wrong way around which prevents pressure building up in the 1st chamber.

Many of the low cost pads on the market are of inferior quality. The Green Stuff pads from EBC are excellent.

If anybody can explain how the compensation works for the 2nd chamber I would be very happy.