I think I've finally figured out my issue with clutch slaves. I've replaced the slave 3x in the past 3 years, and it's usually been the bearing at the crux of the problem. At least, that's been the most obvious symptom.

This latest iteration though, proved there's something amiss in the bore, as when bleeding the system up, I found fluid coming out of the 2 small drain holes in the bottom of the cover. Upon taking all apart & cleaning it up, I measured the bore and felt around in there. I think when the bearings grenaded themselves, they set the slave piston off-axis, which chewed up the outer portion of the bore. Mine measures 26.4-26.6mm, so it's out-of-round at the very least. Certainly this is cause for fluid getting past the seal under pressure. Basically, the bore feels 'coned' and not cylindrical.

So my proposed solution - which I'm passing across the collective desk of Paso Knowledge here - is to get the bore milled out to accept the larger slave piston from the 906 or whatever (27.5mm). I realize this might require a slightly larger master cylinder, but maybe not? Alternative to that, what options haven't I thought of?

Sorry to hear that. The covers are becoming rare.
If the bearing seizes the piston will spin instead which will ruin the bore over a short period of time.
The 906 clutch piston has the same diameter as yours. The one of the F1 (27.95mm) has no O-ring and requires a cylinder bore with an O-ring groove.

Not sure if there`s enough meat for a steel sleeve?!

You could also try Rudy (info@duc-only.nl) maybe he has a complete cover.

This option was posted on the Paso FB group a while back. Still makes me speechless and I don`t know how that will work with the fairing but I guess it`s one way of fixing it

this is from the ducati.ms forum: http://www.ducati.ms/forums/attachments ... aulics.jpg

I'm about to bring the cover to my favorite local shop, to see what he can do. I think it possible they could sleeve it, there's plenty of meat on it still. Should it be 26mm exact, or slightly larger to accept the seal on the piston?

if the bore were 26mm it would be a fit. It will have to be a little larger than that.
I do have a spare open clutch cover. Maybe I can measure the bore tomorrow. If somebody else could do the same it would be great just to see we measure the same.
A sleeve would have to have a certain thickness not to distort when pressed it. Also it would have to have a cutout at one end or it would probably cover the fluid channels in the cover.
I`m really curious to hear if that is an option.

I have a brand new cover (in the box) and a brand new piston set the cover is 26mm the piston set juts a little bit less (2/100mm ?)

I suppose it can be rebored out to 28mm and then sleeved, I cannot see any issues in doing that.

That's good to know. I'm going to bring it to a local shop Monday morning & see what he says. The damage is minimal, but enough to leak fluid. I think I'd rather go the sleeve route than swap up to the F1 piston (thanks for clarifying, Gerhard!) I'm not sure the wall thickness would support a channel for an oil seal if I went to the larger piston.

That's one way to solve it. I mean, if it works, ok, but... Is there a turbo on that bike too? That big cone air filter looks like party of a turbo set up.

Hopefully it won't come to that for my bike.

Mine is a bit cone shaped too but still working at the moment . I have used SKF speedi sleeve before but for putting round a shaft ,don't see why you couldn't press one into a bore and they are stainless so would be longer lasting than the ally and they are nice and thin , any way you could bore and sleeve would have to be better than stock as far as durability is concerned

Haven't seen the speedi sleeve before; that's interesting. Are they deep? I'd be concerned with them being deep enough to provide length to cover the full travel of the piston's seal - but not so deep they obscure the fluid channels at the back of the bore. Going to try & sneak over to the shop today, see what they can do w/ the cover.

I did read that right: bore is 26mm; piston diameter is slightly less?

So I talked to my local shop. The owner is an extremely accurate person, and I didn't think he was going to do the job at first, because the whole thing just one big unknown to him. Anyway, I think he'll do it, but he has reservations about the size & depth of the bore in the cover. Also, he was going to use aluminum for the sleeve (since the cover is), but if there's reason to use something else (steel?) - I'll happily defer to the group's census here. Personally, I didn't particularly want to go with Al again, since it's soft enough to get damaged in the first place. What would anyone recommend for a new sleeve? Steel? Brass? (How/will they interact with the aluminum cover?)

But ultimately, before doing anything, he wants to be certain of the bore & depth. He indicated he'd bore the cylinder walls to about 1/2-thickness, re-sleeve the entire cylinder to its current depth, and then drill down the fluid fill & bleed channels through the sleeve to open those holes back up. Quoted me $140USD.

He wants to be absolutely certain of the bore dimensions. My piston measures 26mm +/- .02mm, and while the seal skirt compresses in the tangs of a micrometer, will the entire seal be able to compress enough to fit within a cylinder that just barely accepts this piston? Is 26mm the absolutely correct inside diameter of the bore, or should there be a slight variance (+.05mm? I dunno) ? Obviously, it shouldn't be much, but I don't know what to tell him, and he's not doing anything until I know exactly how wide that cylinder needs to be. He asked if I could find the original engineer's drawings & specs.

Thanks in advance, everyone who chimes in. Looking forward to getting Old Blue back on the road!

Its one of them things , if the bearing hadn't packed up and spun the whole piston ally would be fine ........but it did . If I was doing this repair I would probly go for steel sleeve , but I would def go for the later model piston assy.If the guy doing the job is a fussy bugger ..... that's a real good sign

Yeah, it is what it is; I'm just trying to determine the best way forward. And I'm definitely more interested in the fussy perfectionist than someone who's just going to wing it.

The 'later model piston' though - it's that the 907's, without a bearing? I have a new stock piston & bearing... I'd just like to fix it & forget it at this point.

But before any of that, I have to confirm the correct bore diameter of the cylinder. Is it 26mm on the nose, or how much larger to accept the piston seal?

I guess if you have a new original then use that . The later 907 type piston assy can be fitted with a deep groove ( axial load ) ball bearing ( there is a thread in the 750 faq's detailing this mod ) the idea being that the new type piston has a better sealing set up , it uses a lip seal similar to a brake cylinder seal , and the bearing can be replaced. I would think ( and Im no engineer ) that the piston would only need a few thou clearance. Sleeving brake cylinders is nothing new and I think the hardest part of doing a Paso clutch cyl would be clamping the thing down firm enough to machine accurately

maybe angelix can confirm this with his new cover.
I have a brandnew piston and a complete used cover incl piston. Both pistons measure 25.95mm, the cylinder measures 26mm.

The V-type seal Hamish is referring to has the #93040091A.