I’ve spent about as much time fooling around with Toyota brakes as anyone, so here’s some collated information about it.
There are two basic types of 4 piston brakes that we’ll be dealing with: The S12+8 and the S12W.
The S12W caliper has four S12 (42.82mm) pistons. It is part number 47750-35080 (left hand) and 47730-35080 (right hand). My 240Z is fitted with S12W calipers and DBA425 rotors. This required the mounting face of the caliper to be milled 3.5mm to fit on the stock standard struts.
The S12+8 has two S12 (42.82mm) pistons, and two S8 (33.93mm) pistons. I always forget which end is supposed to squeeze more, so here’s a snippet from wilwood’s website (http://www.wilwood.com/TechTip/TechFaqs.aspx):
“Multi-piston calipers, normally with six or more pistons, have bore sizes that increase in size from front to rear.
This allows a pressure differential between the leading and trailing edge of the caliper, thus providing an even wear pattern along the entire length of the brake pad, hence it controls brake taper. This is necessary because incandescent material and debris from the leading edge of the pad is trapped between the pad and rotor; it tends to float the trailing edge of the pad off the rotor. A larger piston at the trailing edge of the pad provides more pressure to compensate for this debris buildup and keep the pad flat against the rotor.”
The S12+8 has two variants, one designed for a solid rotor, and one for a ventilated rotor. The part number for the ventilated version is 47750-60021 (left) and 47730-60021 (right). There is a non-ventilated version, but I don’t know (or care) what its part number is.
Incidentally, you can see the Toyota Electronic Parts Catalogue online here: http://www.toyodiy.com/
Both calipers are designed for a 289mm diameter, 20mm thick rotor. The offset from the mounting face of the caliper to the centre of the rotor is 30.5mm.
Another sidenote: Don’t waste time screwing around with stock or second hand master cylinders. Go to any decent brake shop and get one from a GQ Patrol. There’s two variants: One for drum brake rear, (1″ bore) and one for the disc rear (1 1/16″ bore). Neither have a residual pressure valve. You might need to bend up a new brake line, though, due to the different connection position.
My 240K is fitted with S12+8 calipers. This was difficult for me because 240K’s came with either a 2-piston or single piston stock brake. Mine was a twin piston, which meant that the mounting points are too far in to use a 4-pot brake with any decent sized rotor. I had to make adaptors.
240K-owners might notice that the caliper has been moved to the front rather than the rear. I did this by switching the struts around. This way, I get more clearance between the caliper and the steering link. Also, the load path for the braking force into the strut seemed a bit better this way.
A photo of the adaptors. They were originally meant to be plain flat and simple, but I ran into a lot of problems with offsets. I can’t think of a good way of measuring the offset required. If anyone out there has a good way, please let me know!
Here’s the caliper test-fitted to the strut.
At last, I got the damn things mounted. I had to bed up some new brake lines to do that… I might take some photos of the process and do an article on that later. I also had to use a banjo bolt because clearance was a little bit tight between the brake line and the antiroll bar at full steering lock.