Something’s Not Right…..

… and I suspected the brake master cylinder. Counsel popped by the other day and was a great help in bleeding the brakes. The Ambassador’s Daughter sat in the cockpit and did the footwork whilst Counsel and I messed about trying to get the fluid to come down the lines. Having just bled a modern system from scratch, I was a bit concerned about how long it was all taking. In the end, some vigorous pumping on the pedal seemed to do the trick and once we thought we’d got the system working, we called it a day. The following morning, I found that the brakes had almost locked themselves up. Why, I had no idea but, in order to get things moving again, I drained off some fluid through a bleed nipple and all seemed to be well again. As you know, after thinking it over, I decided that it was a problem with the brake return springs (too old and weak to push back and hold the fluid) and dashed off to a spring maker who, a couple of days later, produced a very nice return spring to pattern.

New return spring

With this fitted, things seemed a bit better but, after a few pumps on the pedal, the brakes locked up again. It was as if the fluid in the system was flowing only one way – the cylinders filling on the application of the pedal but not releasing on the return stroke and just continuing to fill to the point of, well, bursting a seal I suppose? What, I thought to myself, would happen if I stopped the flow of fluid from the reservoir so the cylinders couldn’t continue to fill up? I turned the tap off (it’s normally wired open) and voila, the brakes work perfectly. That ain’t right.

Old return spring

I’m still going ahead with the new return springs because they’re needed – all the old ones are like liquorice – and I’m going to take the master cylinder off and investigate. Luckily, the engine’s out so all this is all relatively easy stuff and the problems, though I could do without them,  have occurred at just the right moment.

New pistons

And talking of engines; the box of shiny new pistons came with their rings, not assembled, but in a separate box. Putting rings on pistons is one of the most nerve-racking jobs on a rebuild – a broken ring is a real pain. I got up early and before I went to work, settled myself at the kitchen table and read the instructions; something I wouldn’t normally need to do but, the oil control rings comprised four parts: 2 rails, a spreader and an expander, and I needed to know what went where. Well, that was me down at the first fence – I could have stayed in bed. Which was the spreader and which was the expander? The instructions didn’t say. A simple sketch would have helped. In the end, I found the information on the internet; whoever it was who took the trouble to put it up, thank you. And, I’m pleased to report that I didn’t break a single ring. Of course, I’ve yet to put the pistons in the bores and that’s the second least favourite job on  a rebuild.


6 comments on “Something’s Not Right…..

  1. Noel says:

    Nigel, Not sure what type of master cylinder you have but have you checked the brake pedal is returning far enough so the piston clears the fluid return hole? This would then let the pressure release.

    • Thanks Noel, the pedal returns all the way and there’s a bit of free play. I’m going to renew the master cylinder – I could do with one with a bigger bore anyway – because it came to me ‘new’ but secondhand.

  2. Hi Nigel,
    Re your brakes, do you have SOME play in your brake pedal? You need to leave the piston to release the return hole. Your symptoms look like it’s not the case to me. As usual I’m happy to be proved wrong!

  3. Hello Renaud, the jury’s out at the moment but will post on further investigation. I’ve got about 3/16″ play at the pedal but thanks for your suggestion – i could be getting a false reading somehow.

  4. It seems that Noel and I were on the same line. But I wonder though how you could have managed to bleed in that case? Second but, if I may, could’nt your unusual arrangement of brake mecanism -piston pushing a lever- be the problem? Maybe some springs to help the levers/cams go back to idle?

  5. Bleeding was a bit of a problem and I first suspected the return springs and have had new ones made. They haven’t made any difference to the fundamental problem but, if I disconnect the reservoir and let a bit of fluid out of one of the slave cylinders, the brakes work perfectly and continue to work perfectly – so I suspect the master cylinder is at fault. The piston pushing a lever shouldn’t have a bearing on the problem – it could be pushing a bag of carrots; it wouldn’t know any different.

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