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Author Topic: Brake master cylinder  (Read 1920 times)
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Rebel Poster
Posts: 723

« on: 28 April, 2007, 10:05:36 AM »

After having completely refurbished the brakes on my Aprilia I immediately started getting problems with the wheels locking making the car immovable.The wheels all rotated fairly freely when jacked up but after only a few miles the car juddered to a halt each time.In this condition it was as if the brake pedal was welded in position with no amount of pressure depressing it even a millimetre.After 20 mins everything would miraculously and suddenly pop free  again.The breather hole was clear on the reservoir and the pedal adjustment also seemed ok.Nevertheless there was some sort pressure build up that I could not solve. Having checked everything once more the only thing left might be swollen seals causing a partial blockage of returning fluid in the master cylinder.
This was something I hadn't tackled during the brake revision due in part to foolish optimism and also because it is difficult to get at sandwiched as it is between the body and the engine.Now it couldn't be avoided any longer. One of the 3 flange mounting bolts is virtually inaccessible.One almost could believe you needed to take the engine out first to get it off! However, with a very contrived assortment of socket extensions it was finally removed with some cursing. Internal inspection of the cylinder itself revealed little to me but on taking it to a brake specialist he immediately said it should have been replaced 30 years previously......A darker shading on the upper right inside wall of the cylinder can just be made out in the photo below.Once this level of corrosion is set in, the replacement of the seals is pointless and it will just fail again, possibly with dangerous results. Sabif is the make on my second series ( lancia's own in house company I think) and the parts are not available.I considered resleeving with a stainless insert. However this can leak over time as the loctite can start to break down with brake fluid.On a single circuit car as the aprilia , failure in this regard means no brakes at all which is an experience best avoided!
To cut a long story short, I was concerned about maintaining originality but not at the expense of drivability and safety.The specialist was unwilling to fit new seals even as a temporary measure and asked me why I didn't just replace it with a new one?.I explained my desire to retain originality and the limited space available to just fit something modern.He said he could find a matching new item so having no better idea I decided to trust him (as I didn't want to risk resleeving). A week later a new master cylinder was delivered already modified by the manufacturer to fit an aprilia and is to all practical purposes identical. So it new , safe and looks original.Photos below .
« Last Edit: 28 April, 2007, 06:52:03 PM by Scarpia » Logged
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