Hi guys,

My brake light switch stopped working on my front master the other day so have been going through the process of getting a new one, and I've realised that my front master seems to be a little different to other XTX masters I've seen.

Looking through the service & parts manual for my bike's model year ('05 XTX), the reservoirs in the diagrams seem to have the brake hose outlet on the front and the sight glass on the back, whereas my master has the hose outlet on the left side and the sight glass on the right, above the piston, and also has a Brembo logo on the reservoir cap and an adjustable Brembo lever.



Another thing to note is that the brake light switch in the parts manuals appears to be a clip-type, whereas the one on mine actually screws into the master assy, so I can't imagine the clip-type fitting.

I always figured this was a factory thing as it looks factory and both brake calipers on the bike are also Brembo . Maybe this master was superseded by the ones I'm seeing in parts diagrams?

Has anyone else come across one of these fitted on an XT? Any insight at all would be greatly appreciated!

That was never an OE fitment.

What you appear to have got there is a Brembo PS series master cylinder. Much better quality than the original I might add!

AFAIK the PS series master cylinders come in 10-16mm piston sizes and I'd guess that it's probably a PS11 or PS12 on your bike? They are sold by Brembo as aftermarket master cylinders, but were also fitted as standard to several KTMs, Husqvarnas and Moto Guzzis. You should be able to find a replacement switch easy enough if you search the web for Brembo PS master cylinder. I think the switch is the same regardless of what piston size it is.

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Interesting! I have to say, the lever feels spongy to me in comparison to other bikes I've fondled, but I also have to say that the braking on the front is fantastic.

One interesting thing I've just found out is that these cylinders, or very similar cylinders are used on the Yamaha R125 and WR125. Not quite the same lever, but the rest of the master looks the same, as does the switch, so I might have my answer for sourcing a switch there!



I'll have to look up the Brembo PS range then, and see if I can find any more info on them. All my searches for the Brembo master so far have come up with the racing style ones with remote reservoirs! I'll have to see if there are any model numbers hidden on the master.

I'm really curious as to why it would have been replaced though! The bike has only done 20,000 miles with two lady owners and looks like it has only done half that.

Thank you very much though, Pleiades, much, much appreciated!

It may well be that the master cylinder bore/piston is not the right size/matched to the XTX caliper and its pistons? One of the most common misconceptions with brakes is that a larger master cylinder will create more pressure. A larger master cylinder has a larger displacement, but it takes more force to create the same pressure as a smaller bore. It will effectively take more effort at the lever to create the same system pressure. The result after adding the larger master cylinder is a lever which requires more pressure to create the same amount of braking force, hence a "spongy" feel.

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Yes, that would make sense. The only other thing I can think, because of the angle the brake hose comes off the master at, there's a big high spot in the line, so it wouldn't surprise me if there's a big air bubble trapped in there. The weird thing is though, that I don't really have to use much force at all, it's almost too easy - I grabbed a handful on my first ride when I bought it, I definitely wasn't expecting it to stop as quick as it did!

Either way, I've been doing some more searching and it does appear to be the PS 11. Thank you again for that! I hope a rebuild kit won't be so hard to find if/when the time comes!

On the subject of rebuild kits, I don't suppose you'd happen to know where I could find pistons & seals for the XTX front caliper, as Yama don't seem to sell them? I've read on the forum of the XTR and XTZ calipers being the same as used on one of the BMW GS models, but I couldn't find anything about the XTX caliper.