MASTER CYLINDER UPGRADE (2011)

Nater_Potater said:

Once the caliper was re-attached to the stanchion tube, the pistons could be seen moving out with a pull on the lever, but then retract back as the lever was released! 'Last time I checked, there were no return springs in the pistons... I assumed that the new caliper seals had a good enough grip on the pistons that they were flexing everything back to battery once pressure was relaxed, rather than sliding along the piston's sides.

Click to expand...

The seals are supposed to deflect in that way to retract the pistons after brake application so the pads don't drag heavily on the disc.
The pistons should only move through the seals to compensate for pad wear.





http://mgaguru.com/mgtech/brakes/bt104.htm

As the piston moves outwards from its static position (1) the fluid seal is deflected (2). When the hydraulic pressure is released the fluid seal regains its static position, moving the piston back and providing clearance at the friction pads.

Click to expand...

dave M said:

Not wishing to appear too cynical but I suspect the makers of these kits are somewhat more wary of us owners buying the $25 overhaul kit from Kawasaki (on which they are probably based) and doing it ourselves rather than sending the unit back for a $300 overhaul!

Click to expand...

Tell me more about a $25 overhaul kit from Kawasaki, if you still have info. It certainly sounds appealing. Thanx

Anton vesely said:

Tell me more about a $25 overhaul kit from Kawasaki, if you still have info. It certainly sounds appealing. Thanx

Click to expand...

It requires the master cylinder to be machined and a (13mm bore) sleeve fitted which is where most of the cost is, unless you are thinking of doing this part of the job yourself and RGM sells the complete DIY kit for £49 GBP (no VAT to pay).

https://www.rgmnorton.co.uk/buy/mas...-with-instructions-for-all-commandos_2527.htm

https://www.rgmnorton.co.uk/csi/1245184/f/pdf/mastercylinderreline.pdf

https://www.oldbritts.com/14_061939.html

An alternative not mentioned in this thread is the resleeve kit offered by Madass on this site. It is a 13mm sleeve that just slides into the OEM MC bore without any need to re-size it...and it held there by applying a low viscosity "locktite" product. Was about $100 USD for the kit a year ago when I got mine. Works a treat.

US$60 + shipping

That kit looks great! I machined mine for the RGM kit which I got from MAP Cycles. One nice thing is that thy stock the rebuild kit for the 13mm bore. When I machined it out I kept wondering why they did not size the kit to just fit into the stock .625 (5/8") bore. I suppose it is because of the availability of metric taps in the UK. I had to purchase a 16.5mm drill bit and an 18 x 1.5mm tap to do the job. The kit threads into the machined master cylinder body and pushes hard against a neoprene seal at the back so that the pressure produced goes only into the brake line. The space around the new brass cylinder is filled with brake fluid and there is no drilling required. I hope the neoprene seal lasts a long time as well as the rest of the kit but I see no problem rebuilding it or installing a completely new kit if it needed that.

The Madass kit would potentially last longer since it does not need the neoprene seal at the back. I think it would also be easier to bleed since it does not have brake fluid around the outside of the new liner creating the potential for air bubbles. Now the only advantage I see with the RGM kit is that it is made of a high quality brass or bronze. How about it Madass? A higher quality kit with a stainless or bronze sleeve and perhaps a stainless piston. (The photo looks like aluminum.) You could offer both.

I have had bad luck with sleeving , a expensive alternative is a 13mm master cylinder sold by AN .#
06-1939/13 . A new casting with the required machined 13mm bore.

There is no metal to metal contact in the master cylinder upgrade Madass sells, look at the 2 seals where all the contact is concentrated. So you are left with corrosion as being the main wear issue, doubt alloy would be any worse than bronze and both would be helped by regular changes of brake fluid.

I machined my own components, as per this link: http://www.nocnsw.org.au/technical/commando-master-cylinder-mod
I made the sleeve out of stainless steel, and the piston out of bronze. The metal components should last forever.
Pushing that tiny drill through the stainless sleeve wall was touch and go.

Stephen Hill

Original MC bore is aluminum with the rubber seals the only contact material. My original was "workin", generating pressure, not leaking after 45 yrs. That's a pretty decent "test run". ...so I cannot see any concern for using an aluminum sleeve.

I have disassembled about 7 master cylinders with aluminum bores. The majority of them had sat with old brake fluid in them, and suffered from corrosion. Brake fluid is hygroscopic (not hydroscopic), meaning it absorbs water, hence the corrosion. If you change the brake fluid every few years, or use silicone brake fluid, corrosion in an aluminum bore is not an issue. BTW, some of those bores initially looked pretty good. But when I ran a dental pick inside them, white powdered aluminum oxides fell out, leaving grooves and small worm holes in the bore surface.

I question the notion that the rubber seals prevent contact between the piston and the bore. The brake lever slides over the end of the piston, initially at an ugly angle (radial), then latterly, at an axial angle. I doubt that the seals would counter the radial forces, particularly at the lever end of things.

Stephen Hill

If you are not hung up on authenticity you can use an aftermarket 13mm master cylinder. This would also get you your dog leg lever.
I went that way and also replaced the clumsy switch gear with chinese knock-offs of Japanese parts.
This kind of stuff is available for a fair price from Mike's XS on line.