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Aug 28, 2015 4:50 pm
Aug 28, 2015 4:50 pm
Subject: Re: Brake cylinder pistons seized; how to free?
Thanks all for replies. I hadn't realised that one could still buy correct replacement cylinders. I did know about stainless sleeving, but these cylinders are pretty tolerant of some rust pitting, from experience with my V12.
The cylinders have different markings side to side, yet one at least is a perfect match in all respects to one I have off my V12, so they probably are all original.
In the end I used Julian's method with a few tweeks:
Removed boots, scraped out most of the rust with blunt pointed knife, then kitchen scourer wire wool. Then sprayed with WD40. Found a socket a nice close fit to the bore, then as Julian, in a vice, tighten, tap cylinder casing (not too hard) with hammer, retighten. Let WD40 soak overnight. Repeat again.
With one cylinder, I connected a tyre pump compressor to the bleed valve (bolt in brake fluid inlet), and one of the pistons popped out; easy to press the other out.
With the second cylinder, must have been rustier, that trick wouldn't work. Sprayed with WD40 frequently, gradually wound each piston in, until eventually, first one, then the other, freed off enough for the internal spring to return the piston. Eventually one was free enough to force out by pushing the opposing one in. By this method, although it took longer, there is no damage to the spring or seal spreaders (neither of which are supplied in seal kits).
AS an aside, I did try banging the cylinder vertically downwards on a flat steel plate, hoping that inertia and the return spring pressure might free a stuck piston...probably a forelorn hope given the light weight of the aluminium pistons. What did surprise me is that this did slightly crack the boot flange. So...don't try that!
Laurence
Laurence
Thanks all for replies. I hadn't realised that one could still buy correct replacement cylinders. I did know about stainless sleeving, but these cylinders are pretty tolerant of some rust pitting, from experience with my V12.
The cylinders have different markings side to side, yet one at least is a perfect match in all respects to one I have off my V12, so they probably are all original.
In the end I used Julian's method with a few tweeks:
Removed boots, scraped out most of the rust with blunt pointed knife, then kitchen scourer wire wool. Then sprayed with WD40. Found a socket a nice close fit to the bore, then as Julian, in a vice, tighten, tap cylinder casing (not too hard) with hammer, retighten. Let WD40 soak overnight. Repeat again.
With one cylinder, I connected a tyre pump compressor to the bleed valve (bolt in brake fluid inlet), and one of the pistons popped out; easy to press the other out.
With the second cylinder, must have been rustier, that trick wouldn't work. Sprayed with WD40 frequently, gradually wound each piston in, until eventually, first one, then the other, freed off enough for the internal spring to return the piston. Eventually one was free enough to force out by pushing the opposing one in. By this method, although it took longer, there is no damage to the spring or seal spreaders (neither of which are supplied in seal kits).
AS an aside, I did try banging the cylinder vertically downwards on a flat steel plate, hoping that inertia and the return spring pressure might free a stuck piston...probably a forelorn hope given the light weight of the aluminium pistons. What did surprise me is that this did slightly crack the boot flange. So...don't try that!
Laurence
Laurence