the brakes: Bleeding the Brembo brakes can be
a bit difficult, especially for the rear brake. To do it correctly:
- Lightly tapping on the caliper with a piece of wood or a soft hammer, in order to push out the air bubbles.
- Use a new pump oilcan and pump brake fluid from the bleeder nipple through the system usually this will build up a basic pressure so you can pump now
the fluid out the regular way.
- At least, if it doesn't work, remove the master cylinder and hold it horizontaly in one hand (with it`s feeder tube on top) with an appropriate tool push
the piston in as far as it will go an then let it return ALL THE WAY back to the shim and circlip that stops it coming out altogether. With no "pressure" in
the system it comes back slowly--some times so slowly that it doesn`t draw in a fresh charge of fluid to displace the caliper piston movement. Repeat
until the system "loads up". You can augment this method by removing the circlip and shim and (taking care not to let the piston to far out) push the piston
into the master cylinder and when it returns let it come an extra 10 mm or so (drawing that much more fluid with it to prime the system on the next push.
Because the master cylinder doesnt recharge until the piston almost bottoms out on the shim you can have a much better brake by leaving out
the circlip and the shim and controlling its "out" position with the linkage rod that pushes it during normal operation. (allow the piston to com flush with
the end of the master cylinder).
Note that the repair kits (caliper or MC) are still available at good specialist stores, a bit cheaper than brand new whole kits...
P05 Brembo calipers: Rebuilding these calipers is easy, parts are available
everywhere. Note that stainless steel/teflon coated pistons are also available,
they improve drastically the brakes.
Master cylinder ratio:
Source: Excellent site vintagebrake.com
While attending Vintage Days West, and thoroughly enjoying it, I was reminded that many of the people I had occasion to talk to, lacked an understanding of
the importance of master cylinder to wheel cylinder ratios. This critical ratio is of paramount importance in determining "feel". It has been my experience that
there is a "sweet spot" in the range. I like ratios in the 27:1 range-2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the
spectrum-firm. Ratios lower than 20:1 can result a feel so "wooden" as to have a toggle switch effect: nothing happens until the wheel locks. Disc and wheel
diameters must be taken into consideration. A 10 inch disc working against an 19" wheel just doesn't have the leverage ratio that a 13 inch disc working a 17"
wheel does. The hand lever ratio counts too: witness the adjustable master cylinders from Lockheed and Brembo.
A case in point: I had a complaint from a racer about Ferodo CP901- a compound renown for its great feel. His comment was that they worked poorly until
the wheel locked. He had been thrown on the ground twice. Intrigued, I inquired as to the application. "Yamaha RD350" he replied. A red flag went up. CP901
was not available for the 48mm Yamaha caliper. I asked "How that could that be?" He had up-graded his braking system with the 41mm Lockheed unit, but
was unaware that a master cylinder change was in order. A stock RD 350 has an already poor ratio of 18.3 :1, and with Lockheed, became an unhealthy
13.3 :1. The "sweet spot" formula said a change to a 11 or 12mm master cylinder was in order: my personal preference and recommendation would have been
an 11mm. He was able to switch to a 1/2" , and although not ideal, he was keeping the rubber side down.
For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1. I think ratios lower than 23:1
produce a lever feel so "wooden" as to have little, if any feel. Combine "low" leverage ratios with sticky pads, and unpredictable lockup is the result. The
high effort required at the lever also results in undesired input to the bars. Single piston calipers are much happier in the 14:1 to 12:1 range. Disc and
wheel diameters, as well as hand lever ratios, must be considered.
Brembo reference for Laverda: