Brembo 15mm round master cylinder rebuild

[JC85]

Is there a tutorial anywhere out there for doing this job?

[Antietam Classic Cycle]

Not that I've seen, but it's really quite simple. The piston is driven out using a length of rod inserted into the outlet. I use a suitably sized socket for pressing the new retaining ring into place during reassembly. 

[JC85]

 

Not that I've seen, but it's really quite simple. The piston is driven out using a length of rod inserted into the outlet. I use a suitably sized socket for pressing the new retaining ring into place during reassembly.

  Got it. Thanks for the tips.

[Cdn850T5NT]

Couple/three photos for discussion re this subject...











What I would like to know is, given the lip-seal design of at least one of the two brake seals - does a person NOT need something like a piston ring compressor to insert the piston in the first place?  At the very least, brake assembly paste should be used.  This is non hydrocarbon "grease" like Silglyde or the like, to ease assembly.  To my mind, using brake fluid, instead, promotes rust... as the brake fluid beyond the sealed part of the brake system ... it is hygroscopic, and will attract moisture, and will rust the parts.  Silglyde or other will not.

[Cdn850T5NT]

Incidentally, a PS15 Brembo is not exactly 15mm dia.  I think it is 15.875 mm by way of BORE, and the piston is mebe .3mm ??? less, by way of dia.  I think the cylinder is, actually, 0.625" or 5/8" bore.

[Cdn850T5NT]

BTW, I cannot see how a socket would work unless it were a very, very thin-wall socket, and I can't see how the hex form or the 12-point form inside of the socket would not foul the piston of the Master Cylinder....?  I think a thin tube of the correct dia. is needed... like the MdinaItalia one.

[Cdn850T5NT]

Tutorial:  https://www.laverdaforum.com/gallery/albums/userpics/11278/Repair_Guide_Clutch_and_Brake_Master.pdf

The fellow uses the old retaining ring, in backwards, to put the new retaining ring in place.  At least I THINK that is what is happening.  This is being done on a PS15 FRONT master... but the retaining ring system, and indeed the piston, seals, etc... ALL appear to be the same as the PS15 rear master on the Tonti Guzzi's.

[Antietam Classic Cycle]

I've done dozens with a socket as the insertion tool without a single problem of any sort. But, YMMV.

[Cdn850T5NT]

Can't argue with success.  Do you use a particularly thin-wall 12 point socket... and is it 1/2" drive?  Also, do you have to wiggle the piston to get the lip-seal to enter the bore?

[Antietam Classic Cycle]

Can't argue with success.  Do you use a particularly thin-wall 12 point socket... and is it 1/2" drive?  Also, do you have to wiggle the piston to get the lip-seal to enter the bore?

A regular old Craftsman 12-point, 3/8" drive socket. Yes, grease the seals with the supplied grease and move the piston around until the seals go into the bore.

[Cdn850T5NT]

Thx Charlie.

Also, adding a picture of the properly assembled order of the components.  Retaining ring is on the extreme LHS... over top of the stepped rubber element

[n3303j]

Incidentally, a PS15 Brembo is not exactly 15mm dia.  I think it is 15.875 mm by way of BORE, and the piston is mebe .3mm ??? less, by way of dia.  I think the cylinder is, actually, 0.625" or 5/8" bore.

Yes on the 5/8 bore. I found it odd that these were exact SAE dimensions. On the other hand it simplified sleeving the master cylinder when I had to deal with a pitted one. K&S sells seamless brass tubing to the hobby industry. Their 21/32 stock has a 5/8 bore. Ream the casting to 21/32. Loctite in an appropriate length of brass tubing and drill the cross hole  (polish off the burr). Then you are set for another 40 years.

T3 rear master cylinder was also SAE bore.

[Tusayan]

Yes on the 5/8 bore. I found it odd that these were exact SAE dimensions. On the other hand it simplified sleeving the master cylinder when I had to deal with a pitted one. K&S sells seamless brass tubing to the hobby industry. Their 21/32 stock has a 5/8 bore. Ream the casting to 21/32. Loctite in an appropriate length of brass tubing and drill the cross hole  (polish off the burr). Then you are set for another 40 years.

T3 rear master cylinder was also SAE bore.

As with wheel and handlebar diameters, it is common for brake cylinders to be sized in inches.  Also true for Japanese parts.  1/2 inch diameter for a single front disk and 5/8 inch for dual disks.

https://www.randakks.com/upgraded-front-master-cylinder-version-a-5-8-piston.html

[Cdn850T5NT]

Yes on the 5/8 bore. I found it odd that these were exact SAE dimensions. On the other hand it simplified sleeving the master cylinder when I had to deal with a pitted one. K&S sells seamless brass tubing to the hobby industry. Their 21/32 stock has a 5/8 bore. Ream the casting to 21/32. Loctite in an appropriate length of brass tubing and drill the cross hole  (polish off the burr). Then you are set for another 40 years.

T3 rear master cylinder was also SAE bore.

Excellent to know this...  I assume that the Loctite is not attacked by brake fluid...  Others like Whitepost Restorations I believe create an interference fit... but I would bet that the aluminum casting that comprises the Master is not meaty enough to allow this.

[Cdn850T5NT]

As with wheel and handlebar diameters, it is common for brake cylinders to be sized in inches.  Also true for Japanese parts.  1/2 inch diameter for a single front disk and 5/8 inch for dual disks.

https://www.randakks.com/upgraded-front-master-cylinder-version-a-5-8-piston.html

Thx for the info!  Unfortunately the link you provided does not work...

[Cdn850T5NT]

A comment re sleeving to a brass bore:  It seems to me that the OEM cylinder is anodyzed aluminum which I believe has a measure of corrosion protection by having that anodyzation (sp?).  Brass, not so much.  Critical, then, to flush brake fluid yearly, as brake fluid is hygroscopic - and will corrode the brass bore.  Do folks agree?

[Antietam Classic Cycle]

Thx for the info!  Unfortunately the link you provided does not work...

Works fine for me.

Stainless steel would have been a better choice for the sleeve and is what rebuilders normally use.

[n3303j]

Works fine for me.

Stainless steel would have been a better choice for the sleeve and is what rebuilders normally use.

Brass was what was available in the proper dimensions.
I did throw a piece of the same tube into a clear bottle of brake fluid about 10 years ago to monitor the effect of DOT 3 on the tubing. So far the tubing looks unchanged.

[Cdn850T5NT]

Excellent test.  If the brake fluid in the jar is open to the atmosphere, then any hygroscopically taken-up moisture would have done its job rotting the brass.  If no, that's great.  Mind you, it would also take oxygen to cause rot.  So, the areas of the master cylinder or the caliper bore that alternatively see air, and then see brake fluild (as piston movement occurs) - those are the ones that rot out.  So I'm not sure submerging the brass in brake fluid really is a test.  If the brake fluid gets darker as time goes on, that is corrosion-product going-in to the fluid.  If it remains more or less straw-coloured - no corrosion is occurring.