Recently I’ve been going through my spare parts boxes to see if there was something that wasn’t needed anymore or needed to be fixed. There was a PS16 brake pump, a PS15 housing and a PS13 clutch master cylinder. While the PS16 was fine, the PS15 was shot and the PS13 leaked from the lever side.
In the FAQs there’s some info about rebuilding the clutch master cylinder so my intention here is not to repeat that entirely but to share my experiences and some tips about doing it.
When tackling such a job some basic rules apply such as ‘only work in a clean environment’. Another rule which should be obvious is not to have things laying on the workbench which have nothing to do with the job at hand. In my case this was the good PS16 brake pump. While spraying some rust penetrating oil on another part some drops got on the rubber/dust boot of that pump which instantly began to deform until it tore.
‘Next project’ I figured. However, while there are repair kits for numerous Brembo clutch and brake master cylinders there’s none for the PS16 (the old type with the square fluid container). It seems the rubber boot from the PS15 kit will fit (as the only part of it) so I ordered that kit. They seem to become harder to find, at least in comparison to the last time I’ve rebuilt a master cylinder which was probably 15 years ago.
Before you go ahead and order a repair kit disassemble the master cylinder and have a close look at the cylinder wall. There are two reasons why master cylinder rebuilds fail. One is damaging the rubber lip of the seal during installation of the piston and the other is damages to the cylinder wall which will ruin the new rubber in no time. So better check.
This is how it should look (to be fair this is after polishing with Autosol).
This one is trash (the edge was broken off for better visibility).
Investing in a rebuild kit makes no sense. There’s no fixing this.
The difference between a PS15 or 16 brake m/c and a PS13 clutch m/c:
You’ll notice it at disassembly. The PS15/16 has two steps and a groove for a retaining ring.
The first step is where the O-ring sits.
The second is for the white plastic disc (its high part looking outwards)
Then there would be the rubber boot and on top of that the retaining ring.
The PS13 is basically the same but has no retaining ring and hence no groove.
Instead of a retaining ring the last part to install is a ring that is pressed into place. No idea what the correct technical term for it is so I’ll call it 'lock ring'.
To remove the old ring (after I pushed the piston out) I used some heat. Removing it with a screwdriver was then easy. I wished though I had read in the FAQs that you can fit something through the hole for the inner of the two fluid container cover screws to dent the ring and get it out this way. The hole can be seen in the first pictures at the beginning of this topic.
Continuing with the PS13 clutch mc
Before assembly find a socket nut or better a tube that will fit over the rubber boot.
Then take the disassembled m/c housing and see if you can insert it (carefully) to see if it goes in so far that it touches the first step where the white disc would sit. Check this now because if it’s a tight fit and you use a hammer to drive in the lock ring later the socket nut or tube may get stuck or worst-case scenario you’ll damage the m/c.
Also insert the piston into the boot and see if you can get the socket nut/tube over it easily. The piston should come in and out with no problems. If it gets stuck, you’ll have to look for a different tool to drive in the lock ring or you’ll damage the rubber boot when doing so.
The order of parts. As already mentioned in the FAQs is:
The seal should be fully seated on the piston of course. (This is only to show where the golden washer sits)
The lock ring has a wider side. This side should go on the rubber boot. The other way round it won’t sit correctly.
Here comes the pita part. I tried assembly similar to the description in the FAQs but then gave up before getting mad as it seemed this job requires three hands.
The problem is that the spring is longer than the cylinder is deep which means that after the piston is inserted and pressed in it needs to be held in position while somehow the other parts are installed on top of it. Then at last the piston needs to be pushed in while holding and driving in the socket nut.
If you let go the seal will pop out of the cylinder and since there’s nothing limiting the piston's travel it could tear or at least push out the rubber boot.
As so often it’s better not to force it and break something as usually the day after things will go smoothly. At least that’s my experience which confirmed itself again.
The solution is terribly simple if you look at the parts.
There’s a larger hole on the left
and a groove in the piston.
So all it needs is a nail. Find one that just fits through the hole, then file and sand the point until it is round and has no sharp edges.
Lube the piston and seal with the lube that comes with the kit or some brake cylinder lube. Push it in until you can see the groove in the piston.
Here you can see the golden washer between piston and seal:
Push in a little further and insert the nail.
I found a small clamp to hold the nail
In hindsight it is better using a nail that is as high as the fluid container or a little higher and then holding it in place by putting the cover back on. Or find an eraser or anything rubber, place it on the nail and wrap a rubber band around the fluid container to prevent the nail from falling out.
In the FAQs it says to fit the O-ring first and then install the piston. Also in the M1R manual it says to install the oil seal first and then fit the stanchion tube. That makes no sense to me. It may work for the m/c but on the fork the edge of the stanchion tube can easily damage the oil seal lip so imo the reverse order is correct.
When pressing a seal through a smaller hole it could theoretically fold. Imho install the lubed O-ring after the piston is installed. It will be a tight fit as it has to seal the mc towards the lever and one part of the O-ring will initially stick out a bit. Use a popsicle stick, lollipop stick or similar to make sure the O-ring is properly seated all around the piston. Try not to use a screw driver, dental tools or anything sharp or pointy.
If the m/c is leaking here and you're considering not to rebuild it completely but plan just to replace the O-ring (which on brake m/cs with retaining ring may be possible) do not use a random O-ring! NBR O-rings for instance are not resistant to brake fluid! No need explaining the possible consequences…
Be sure the white plastic ring sits correctly. Its job is to press against the O-ring and create a proper seal hence it’s important that it’s fully seated.
Put a very tiny bit of grease into the recess of the piston. If you put too much, the rubber boot will not unfold when you let the pulled lever go as the grease won’t allow any air to get into it.
Now I slightly lubed the outside of the boot so the socket nut would slide on and off with less risk of damaging it, installed it and drove in the lock ring.
This is were things went a little wrong for me as the clamp fell off, the nail moved and the piston came out pushing out the rubber boot. With no chance of getting it back in with the lock ring in place and having no new one (never reuse the old lock ring! Reusing retainer rings is of course ok) I put the rubber boot on top of the lock ring and used the old lock ring just to hold the rubber boot. Since it’s only a dust protection it’ll do.
On a brake m/c one would only have to remove the retaining ring and then put it back in.
The nail should be removed only after the pin and lever were installed.
The part numbers for the PS13 brake/clutch m/c repair kit are:
Brembo 10436250 (although it says 110436250 on the bag)
Ducati 000043851
Brembo 10436270
000047226
28659378
800047226
62640021A
Some are Brembo numbers, some are Ducati, some are superseeded. That's why there are so many.
Disclaimer at the end: a m/c rebuild isn’t a very difficult job but if you’re uncertain if you can do it or not better have a shop do it!
G.
