International Lancia Forums

After being rebuilt 5 years ago the Bonaldi booster caused the brakes to lock on again ( the original problem). Basically had enough of this and happy to sacrifice reliability/safety for originality. Hoping that someone else has been down this road and has a suggestion for a modern / generic replacement brake booster / reservoir ?

My sister has a Flavia coupe and has had the booster rebuilt maybe three times in recent years, each time only lasting 12/18 months, so I understand your frustration. It seems that here in Australia it's difficult to find someone who can rebuild these with any long term reliability.

But there is a solution. I have two Flavia berlinas and neither of them have the original booster. The Milleotto has what I think is an aftermarket PBR unit, and I think it's the VH44. If you're going to discard yours altogether, I might be interested...

I hope that helps.

Dear all,

here in Italy is possible to find new reproducted unit, available in mild steel/aluminium or full stainless steel (vacuum cylinder and pump).
This solution is not cheap but absolutely reliable, I have installed on my Flavias and Flaminia.
Feel free to contact me in PM for any further info.

Kind regards

Giovanni

If brakes are locking, I'd suspect wrong clearances in brake pedal and/or booster. My experiences have so far been, that the reputation of this system is far more problematic than reality - provided, that everything has been built and set to factory specs. One particular problem is the quality of new seals, especially the one for the pushrod in the booster. These have had a tendency to fail in some 5-6 years causing brake fluid collect in the booster. There was a small batch of better quality seals made by a German enthusiast.

BR,
Miika

Here is a description of the principle of booster function:
http://www.mgb-stuff.org.uk/servo.htm
The Duplex system in Lancia has two circuits, but the principle is same. If the brakes lock up after a while of driving, I'd suspect that the main cylinder does not get all the way back to rest position. This is likely to happen, if the clearance between main cylinder pushrod and brake pedal is too small. Another thing may be, that the pistons on brake fluid container, used for bleeding the system, push too much pressure in the system. On my Flavia their springs are located so, that they push the pistons up, but I've seen arrangement, where the pistons are pressed down by the spring, applying some pressure in the system. In case of problems, I'd try to lock these in up position to see if it has any effect.

If the brakes start to apply, eventually locking up during driving, I'm pretty sure that the issue is that the air valve has some pressure building up behind air valve piston, causing the booster to begin braking by itself. One more thing to check is the clearance of booster pushrod, though I don't think it should cause this kind of problem.

BR,
Miika