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 Post subject: master cylinder rebuild - a few thoughts and my experiences
PostPosted: Thu Jun 04, 2020 7:59 pm 
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paso grand pooh-bah
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Posts: 5400
Location: southern Germany
model: 750 Paso
year: 1987
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. :drunk: ‘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).
Image

This one is trash (the edge was broken off for better visibility).
Image
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.
Image

The first step is where the O-ring sits.
Image

The second is for the white plastic disc (its high part looking outwards)
Image

Then there would be the rubber boot and on top of that the retaining ring.
Image

The PS13 is basically the same but has no retaining ring and hence no groove.
Image

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'.
Image

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.
Image

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.
Image

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.
Image

The order of parts. As already mentioned in the FAQs is:
Image

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.
Image
Image

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. :mad:
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. :banghead: 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.

Image

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
Image

and a groove in the piston.
Image

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.
Image

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:
Image

Push in a little further and insert the nail.
Image

I found a small clamp to hold the nail
Image

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.
Image

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.
Image

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.
Image

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.
Image

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.

Image


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.


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Thu Jun 04, 2020 8:58 pm 
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model: 750 Paso
year: 1989
Nice Gerhard,

Are the 2 rubber dust boots (clutch and brake side) the same?

Frank

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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 9:11 am 
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paso grand pooh-bah
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Good info there and a nice tip about the nail trick :thumbup:

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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 9:18 am 
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paso grand pooh-bah
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Frank, here're the used parts of the PS16 on the left vs. the new PS15 parts on the right.
The outer diameter of the white plastic rings is the same as is the outer diameter of the edge where the rubber boot sits. So I'm lucky and the rubber boot of the PS15 kit will fit in the PS16 m/c. The rubber boot of the PS13 rep.kit won't fit. It is smaller.
I wonder about the longer spring in the PS15 kit. The length of both pistons is identical. Maybe the depth of the cylinders isn't. I doubt the used spring set so much.


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 10:05 am 
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Gerhard,

Ok, well done!
So, if you could measure up the 16mm brake fluid seal (and maybe the 15mm aswell), ID,OD & width we could see if we can find an acceptable substitute if needed in the future ….
Just to bad that the dust seals are not sold separately (as do the radial & semiradial masters from Brembo).

The spring is hardly significant in m.h.o. it will give a little more preload but the force is not substantial compared to the applied braking force (full pull that is).

Again thanks for making this thread (series? what will be the next episode? rebuild M1R?)

Frank

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Suzuki SV1000S - 2008
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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 11:57 am 
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Good tip about the nail, that part of the procedure f sure can drive you nuts...

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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 12:06 pm 
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Quote:
we could see if we can find an acceptable substitute

Who's 'we'? :)

You know how hard it is to measure the dimensions of soft rubber parts. So keeping that in mind here are the dimensions.

PS16

Dimensions of the seal:
Height: 4,4mm
Inner diameter: 8mm (Diameter of the piston where the seal sits: 8,3mm)
Outer diameter: 16,4mm (Diameter of the piston 15,96mm)
#05424050


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 12:08 pm 
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paso grand pooh-bah
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PS15

Dimensions of the seal:
Height: 4,5mm
Inner diameter: 6,5mm (Diameter of the piston where the seal sits: 7,3mm)
Outer diameter: 15,7mm (Diameter of the piston 14,97mm)
#05424040


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 12:13 pm 
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PS15/16 rubber dust boot

Dimensions of the rubber dust boot:
Hole on the top: 4mm (diameter of the actuator pin: 4,97mm)
Bottom (outer) diameter: 22,9mm
Height: 18,3mm
Height of the bottom lip: 4mm
Thickness of the bottom lip: 2,5mm


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 05, 2020 5:28 pm 
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Thanks Gerhard,

regards,

We :thumbup:

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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Sat Jun 06, 2020 9:25 am 
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Thanks for all that effort Gerhard. I always have great difficulty finding old post on this forum so I should really take a note of all those measurements in case I ever need them.

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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Sat Jun 06, 2020 7:09 pm 
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Derek, I will add the measured dimensions to the text so in case the pictures ever are lost at least the info is still there and also link this to the FAQs.

This was my setup for polishing the cylinders. Imo you have more feeling and control holding the m/c rather than the machine. The machine should be a slow turning one. (A cordless screwdriver would work as well. A fast turning machine will heat up the part very quickly and that's not good). The chosen polishing tips just fitted into the cylinders. There's no sense in using one that's too small and 'stiring' around. The tip of the felt polishing piece was cut off so the cylinder could be polished to the bottom. No need polishing half an hour and with pressure as that would just increase the risk of making the cylinder oval. In and out 2-3 times is enough. The safest way of course is doing it by hand!
Before and after the m/c was washed thoroughly using alloy rim cleaner (as that is what I had nearby). Water alone will not wash remaining polish off! After a pass with a Q-tip and blowing it clean and dry with compressed air it’s ready to be put back together.
Do not use scratch pads or similar to clean the cylinders no matter how fine their grit is. The cylinder surface has to be (& remain) perfectly smooth.
Image
Image

PS15/16
This is the correct order of parts:
Image

Again, the seal should be fully seated on the piston. Instead of the silver disc the PS13 kit has there’s a black one which is fitted on the spring.

The actuator pin of the PS16 has a small groove (the one of the PS15 rep. kit hasn’t). The side with the groove is positioned outwards.
Image

It catches the rubber dust boot and helps pulling it outwards every time you let go of the lever.
Image

In with the retaining ring…
Image

… and on with the lever and the job is done. The assembly of the brake m/c only took a few minutes.
Image

The part numbers for the PS15 brake m/c repair kit are:
Ducati 037039340 (old number)
Ducati 037054340
Brembo 10436291
Image

Stein Dinse has stainless steel screws for the reservoir covers to replace old rusty ones. They are #10430835 and €0,50 a piece. (You can probably find some in every well sorted hardware store).
Image

Btw if needed they (SD) also have retaining ring pliers (#200002022). For €6,28 it’s close to the cheapest ones on ebay.
Image
Image

Brake cylinder paste can be found i.e. on ebay but small portions come with the rep. kits.
Image

At last the microswitch which was removed before washing the m/c. Don’t lose the tiny white spacer as it’s essential.
Image
Image
Image


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Sun Jun 07, 2020 8:50 am 
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paso grand pooh-bah
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Fantastic write up. Thanks for that Gerhard. The last motorcycle master cylinder that I rebuilt was for a bevel 900SS. It was some time ago but the procedure as I remember was more or less the same.

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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Sun Jun 07, 2020 10:22 am 
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paso grand pooh-bah
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To make this complete here some old pictures of a rear brake m/c.
Image

Below the rubber boot there’s a retainer ring. Press the piston down while removing it.
Image

It’s possible that after removal of the ring the piston won’t come out far enough to grab it. Don’t use pliers. The hole on the other end of the m/c is too small to push something through it. Instead push the piston down (ideally not with a screwdriver but w/ something w/o sharp edges) and let go. It may take a few attempts. Eventually the piston will jump up high enough you’ll be able to pull it out.
Image

The order of the parts. It may be that there’re versions with a lock ring instead of the retainer ring.
Image

The wider side of the seal is installed towards the m/c!
Image

Preparation and rebuild is the same as for the m/cs mentioned before.
For assembly press down the piston to fit the retainer (or lock) ring and apply a little bit of grease so it won’t rust.

Don’t pull out the elbow on the side unless the rubber is perished and the m/c is leaking there. It doesn’t come out that easily and using a screwdriver for levering it out (as can be seen) will leave marks. Getting it back in can also be a little struggle.
Image

The rubber dust boot. (#10.3741.10)
Image

I can't remember. What's originally on a Paso a PS11 or PS12?


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 Post subject: Re: master cylinder rebuild - a few thoughts and my experien
PostPosted: Fri Jun 12, 2020 7:01 am 
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model: 906 Paso
year: 1990
Just to add my own experience into the discussion I have had issues with incorrect size ‘lock rings with brembos’ on a couple of occasions over the last 20 years. The locking ring had insufficient interference to the bore to successfully hold the assembly in place. In the end I made my own ring on my lathe. I guessed I was just unlucky but I mention this to a friend who has done far more than me and says he has had this problem as well. Looks like brembo made up a batch of these kits with either the wrong locking ring or an incorrectly manufactured ring. Point is if this happens to you, your not special!!! Get to a lathe (or good luck with returning an opened Brake seal kit! LOL


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