It seems my original clutch master on my '03 ST4S needs a rebuild......absolutely can't get pressure back after replacing the slave cylinder, although my spare (748, I think) master works OK. Anyway, I'm having trouble finding a seal kit. They seem to be available from KTM dealers but obviously aren't listed by Ducati model. So does anyone know the piston diameter? The number on the cylinder is 10.5056 but that doesn't mean anything to Google...... although I suspect the 10 may refer to the piston diameter. Any guidance much appreciated!
Nothing wrong with a master cylinder rebuild for safety reasons, particularly if a few years old, but did you have any symptoms prior to slave change that made you think it was on the way out? - it's possible that master bore has become "dry" and needs priming with fluid before it will work again. If this is the case, then might be easier off the bike as it can get messy. I can p.m. if need be. Alternatively, I hope someone comes up with a link for a seal kit, alternatively maybe a good condition/working s/hand unit.
Thats the one. I've just spent at least 20 minutes typing an explanetory essay but turns out I wasn't signed in any more so lkost the lot......I'll try again once the will to live returns.
Hello again Chris Following up that part number it seems to be 13mm, which seems quite large for the application. It also seems to be the same diameter as the brake master, which is called a Brembo PS3 and has a part number only a few digits different. Do you suppose that the brake and clutch masters are in fact just mirror images, only differeing in application for being on left or right bar? If so it'd simplify my life tremendously as, due to having a partially paralysed right arm, I swap the bar controls on all my bikes. Which means the master cylinders are always upside down....so I've always had to remove them from the bars and turn them over to bleed any air through the reservoirs. Until the other day when I stuck a bleed nipple banjo bolt into my spare master (from the 748 I think) and was delighted that it worked. But it would be even easier to leave the nasters on their original sides and just swap the hoses and reservoirs across ...... look better too.
Hi Indie I think you are right as it's either 12 or 13mm diameter as these were fitted to early bikes, later went to 15 or 16. There is a slight safety issue with "O" ring type union being upside down, but rear brake masters do remain leakproof in some similar applications when fitted to rear master.
Hi That's a good point but in actual fact I've yet to have a problem with the union leaking despite several years and 20k miles. Although I suppose it could be a source of air in the current gold coloured (748?) master currently in place.....that was fine initially but after a hundred odd miles on Saturday the bite point changed and neutral went awol. I bled it again at the banjo bolt, great idea and lots easier than removing and inverting the master, this morning and loads of air came out. Now feels properly solid but I'd still rather have the original back on. What I was saying in the original essay was that the Oberon slave started letting fluid past, but still worked and felt fine...I only knew because the level in the reservoir dropped, so I had it rebuilt by Oberon (same day service and a cup of coffee plus a good look at their CNC kit). But once refitted I couldn't get any pressue....tried every trick I could think of. So I dug out the spare master et voila! Steve Baily suggested that the vacuum bleeder thingie may have inverted the seal on the piston but.....? I think I may try it again, now that the bleeding banjo bolt works and makes life so much easier and if it comes back to life swap the masters back over onto their original bars. Any idea where I could find a definitive bore size for both sides?
As said, unless original cylinder showed alarming symptoms of unreliability then I would persevere with bleeding as outlined above. Either 12 or 13mm bore will work with your bike.
Righto, I'll have another go ...... still got plenty of a)time and b) 5.1 brake fluid! As a matter of interest it seems that the clutch is 13mm and the brake 16mm, so they're staying where they are. Thanks very much for your help.....beers are on me if we ever meet.
it is more difficult because there is no convenient reservoir amalgamated with the bore so the ports cannot be see easily as per the Ebay vid. I will type up a bleeding procedure for a stubborn cylinder a bit later, as might work.
