(Part 3) - Icing On The Cake
Marc continues with his excellent write
up with an R1 rear caliper swap for the Thunderace conversion.
It is a relatively simple
matter to swap out the stock Ace rear brake caliper assembly for an early model
R1 brake caliper assembly. I will be the first to state that there is
absolutely nothing wrong with using an Ace rear brake. It has superb feel, and
uses the same master cylinder as the stock FJ rear brake.
However, I could not pass up
the opportunity to add a more finished look to my bike by adding a R1 rear
caliper that matched the R1 front calipers. The end result is a rear brake
caliper assembly that not only looks great, but works every bit as good as the
stock Ace setup. Note that the R1 rear caliper pads are smaller than the Ace
pads, but are of a sintered bronze material. This is the same materials as used
on the R1 front pads, which have a reputation for great feel and long life,
without tearing up your rotors.
The following is a basic task
list of what I did to fit the R1 rear brake caliper assembly to the Thunderace
1998-2001 R1 rear brake caliper, bracket, bolts, and master cylinder.
(2) 10mm I.D. x 2mm thick aluminum washers
(1) FZS1000 (FZ1) rear brake caliper bracket
(1) Custom stainless steel braided brake hose. 30” long with 10mm banjo
fittings. One fitting is straight (at master cylinder), the other is 30
degree (at caliper)
Modification to R1 rear
brake caliper bracket – 3 mods are required to use the R1 bracket:
a) Weld on a torque arm attachment tab. This was very easy to do, although a
bit wasteful. I cut the torque arm attachment tab off of a perfectly good FZ1
rear brake caliper bracket. It was desirable to do this as the tab had the
correct OEM attachment configuration, was made of aluminum, was the correct
thickness, and provided the correct offset for the rear brake torque arm.
Preparation of the part to be welded was minimal. Simply file or grind a flat
spot on the lower right edge of the R1 bracket, and have a competent welder
TIG weld it in place.
b) Machine a relief in the
backside of the bracket to clear the rotor bolts. This was a simple lathe job,
where 5/8” wide and 0.130” deep relief was made. We got fancy and beveled the
edges to match the rotor bolt heads.
Note: I used the stock Ace rotor and bolts. This relief cut may not be
necessary if you change to a R1 rotor and bolts. But hell, then there would be
no modifying and what fun is that? The R1 rotor has already been countersunk to
provide this clearance, and uses a different, lower profile bolt. It is also
much thinner than the Ace rotor, so will not take as much heat with a big heavy
c) Center the caliper on the rotor with a washer positioned between the caliper
and bracket. I had my machinist make up some custom aluminum washers that were
10mm I.D. x 0.750 O.D. x 2mm thick.
Modification to the R1 rear
master cylinder - the R1 rear brake caliper uses a differently bored rear
master cylinder than the FJ (1/2” vs. 14mm). It is necessary to use the R1
rear master cylinder to get proper brake feel and leverage. There are 3 small
changes you will need to make when mounting an R1 rear master cylinder on your
a) The R1 master cylinder body is not threaded for attachment bolts. Easily
solved by using longer bolts through the mounting tabs, backed by lock nuts
b) The R1 master cylinder reservoir and hose is different than the FJ.
Fortunately, the R1 and FJ master cylinder reservoir and hose attach to the
master cylinder bodies in exactly the same manner. (they are both Brembo
master cylinders) Swap the FJ parts onto the R1 master cylinder.
c) The R1 master cylinder linkage is different than the FJ. Remove the R1
rod, clevis, and nut, and swap for the FJ rod, clevis, and nut.
a) Install the new R1 rear caliper bracket between wheel and right side of
swingarm. Bracket hangs below the swingarm, with torque arm tab toward the
front of the bike.
b) Attach caliper to bracket using stock bolts. Put the special 2mm spacers
between bracket and caliper.
c) Attach rear brake torque arm to caliper bracket in standard fashion, using
stock bolt, nut, and clip. The front end of the rear brake torque arm is
offset to the outside of the swingarm attachment point. Use a longer bolt and
nut. Put washers or a spacer in the clevis end to keep it from collapsing
when you tighten the bolt and nut.
d) Mount modified rear master cylinder. Attach new brake hose using new
copper crush washers. Bleed brake system and GO!
Congratulations on a job well done.
Congratulations indeed. That's
a beautiful looking bike Marc. Top job !
Marc's Ace Swingarm Installation
Marc's YZF750 Fork