Lucky Phil

Why? How much fucking time do you think I have in my life. I give away what I've learned here for free, you don't like my style then block my posts. You don't value or agree with the info then just ignore it. Same for anyone here, you got a problem with the delivery then don't read my posts or PM docc and get me kicked off the board. Seriously in the grand scheme of things I really don't give a shit at the end of the day. As a matter of fact I think I'm done here.

Who knows docc. The theory is the smaller pistons will move farther for a given input pressure but with less force. In reality there are seal frictional considerations to take into account. From memory it's the smaller ones that usually move first. It's not really relevant in any way that I can see. You just pump them out until the pads touch then lever them back evenly until you can force the calliper back over the disk. Phil

Using the term "I was road racing at the advent" as some form of knowledge based technical qualification is amusing. A bit like "I'm a pilot so I know the engineering technicalities of my aeroplane". Some of the least technically knowledgeable people I've ever met are motorcycle racers and pilots. There are many detailed reasons for differential pistons sizes. Some are more obvious and of greater influence and some less so. Some are mechanical, some are thermal and others chemical. They all add up to create the reasoning behind the design. As is usual when you start drilling down into the details there is rarely a simple singular answer. Phil

Yes docc you have it in reverse. I actually know this stuff and I have a calliper in my hand but you and scud might want to check some Yamaha or Honda forum or something. Phil

So you didn't believe me Scud and went looking on a Jap bike site that "seems credible" The only assumption I can make is my explanation lacks credibility Phil

The small pistons are on the leading edge scud. Phil

In "theory" docc the leading small pistons will move first due to smaller piston size and probably less seal friction due to smaller circumference but in reality there are variables at play. When the lever is pulled there will be more pressure on the trailing area of the pad due to the greater sized pistons and this compensates for the less effective friction coefficient on the trailing area of the pad due to increased disk temp compared to the leading end of the pad and "gassing" of the forward pad friction material under heavy load which reduces the effectivity of the trailing end of the pad. It's a consequence of long banana shaped pads and callipers to some degree to fit into small radial spaces created by rim size and large brake rotors. The later 4 pad design suffers less I suppose so they go back to the even piston sizes. Phil

I've been banging on about how good these things are for years after Pete recommended them. If you also don't have a spare later front timing chain cover gasket of the same style then I've been wasting my time posting about them as well. Phil

This is a new interpretation on me Scud. Piston movement is pretty much irrelevant as the pads are only a few thousands of an inch away from the disks. When you grab the brakes the actual movement of the pistons is very small. Once the pads contact the disk it's about applied pressure over area. My understanding of the original reason for differential piston size was to provide even pad wear and pad performance. The leading end of the pad experiences quite different thermal and therefore frictional conditions to the trailing end hence the differential piston size and pressure applied to the shared pad to compensate. This later calliper design uses 4 separate pads to, I suspect mitigate the original issue. It also has a central bridge over the pad slot to increase rigidity. These were the last generation of road calliper from Brembo before the Radial style calliper took over. I've never seen a Brembo design in 50 years that was a step backwards. Anyway like the majority of upgrades they usually don't stand the scrutiny of "what's absolutely necessary". I'm channelling the "American" in me with my Guzzi in that a lot of it's about "individuality" and "nobody else having one like it" However I'm also mindful of maintaining the bikes place in "its time" so upgrades such as later USD forks with radial callipers and radial master cylinders etc are not really up for consideration. Phil

They are different callipers docc. Brembo p4 34/34 with 4 individual pads as opposed to the original( pictured) 30/34 callipers with 2 pads. Phil

Yes the brake lines need to be replaces as the orientation of the Banjo is 90 deg different. These as 34/34 pistons as opposed to the original 30/34 so about a 10% difference. The original M/C should be OK. I will also see if these will work. https://www.aliexpress.com/item/4000378552965.html phil

I thought it was obvious Phil

Try telling the spell check on this site. Both are acceptable apparently, US V British differences. Phil