This article describes the process for upgrading the brakes on a Datsun 1600 from a Holden Commodore using the Girlock setup. Whilst Commodores may not be available (in large numbers) in the US the article may be of some interest generally. Perhaps the Girlock setup is available under another name!
Note: A Small amount of editing has been carried out without altering the substance of the article. This was necessary due to typos and grammar in the original article.
This article was published in Hot4s magazine.
In common with all other Japanese cars of that vintage, they had terrible brakes, in the truest sense of the word. The cars would go like stink, but stop? . . . forget it. About the only thing that went like stink in the whoa department were the pads.
They originally came out with rather kinky Sumitomo calipers with angled pads. A wacko idea if ever there was one. Many an apprentice has been reduced to tears by these examples of Ninjitsu!
So push came to shove, and enter stage left the Girlock alloy single-piston caliper. A single massive piston trying to squeeze the living daylights out of a 9 1/2 inch (244mm for those who don't understand real blokes talk) solid discs.
They worked really well until they got hot, a thing which they did with alacrity, especially when trying to stop Dattos with demon 2 Litre engines with FIA heads and other homologated goodies, not to mention the Madsuns.
The solution to this problem, if you owned a bakery, was to purchase 4-spot AP or Girling racing calipers and vented discs. If you ate crumbs, the go was to fit a pair of Commodore front calipers to both the front and rear with the appropriate discs. As most of the Dattos were doing it in the dirt, the bulk rear wheel bias was a bonus. Simply fit a bias valve and a 'juice' (read hydraulic) handbrake and you could spin the cars in their own length or nearly make them stand up on their front wheels and talk.
So to our current tale. Alan Byrn recently fitted the latest, state-of-the-art Nissan motor, an FJ20 twin-cam, to his immaculate Datsun 1600. To give the car appropriate brakes, a talk with The Professor convinced him to invest in some 10-inch ventilated discs and Commodore calipers front and rear. This formula had already been tried and proven on his brother Keith's Club Car class winning Datsun 1600.
The front conversion is simplicity in itself. Using a pair of 200B struts, a pair of 10-inch ventilated discs, bolt straight on to the original Datsun hubs. The Commodore calipers have the same bolt-mount pattern as the original Girlock calipers. A pair of 3mm shims, which are tack-welded onto the caliper mounting lugs, corrects the slight variation of the disc offset, due to it being ventilated.
The Commodore brake hose has the same thread as the Girlock ones, so it fits in just like it was made for it. If only the front brakes are being done, then there is no need to change the master cylinder, as the caliper pistons are the same size. This only applies if the master cylinder is either quite new or in good condition.
However, rear drum brakes tend to be somewhat inconsistent in a racecar. Ten-inch ventilated rear calipers had to be fitted as well. One other solution is to use original front Datto calipers (from the 200B struts) on the rear and use solid rear discs. Now for problem #1. Disc offset is absolutely critical. Too much and they foul on the trailing arm. Too little and the width of the caliper dictates that a wheel spacer must be used. Fortunately, the Prof found a disc that happens to be just right, even down to the pitch circle diameter of the wheel studs. Problem #1 solved!
Now problem #2, the really hard part. Earlier rear disc conversions on Datsun 1 600s have always mounted the caliper in such a position that it requires the car to be jacked up, or the wheel and caliper to be removed for bleeding. This is totally unsatisfactory in a racecar, as the brakes should be bled immediately before and after every meeting.
After much meditation, the Prof (a graduate of advanced three unit 'cardboard and scissors 1' at kindy) was able to devise a means of mounting the caliper in such a way that it could be bled and still clear all the other appendages that hang off a Datto trailing arm. This exercise was done on the bench with a spare trailing arm. The brackets were then trace cut, surface ground, and then drilled and tapped to suit. Problem #2 solved.
Well not quite. When Alan's 1600 arrived for the fitting session, it was found that the car had different trailing arms. They were off a 240K and these have a larger bearing housings. The carefully designed brackets didn't fit! Back to the cardboard and scissors! After some hours of hand oxy cutting, surface grinding, and drilling and tapping, a new set of brackets were fitted.
These proved to be eminently satisfactory. The calipers were then plumbed to the original hoses with new pipe and two extra short hoses. (These extra hoses are needed to allow for some 1mm sideways caliper movement as the pads wear, something that is unnecessary with the original drum set up).
Because calipers of the same piston diameter were used front and rear, a larger master cylinder was necessary. The standard cylinder is ~l6ths (20.6mm) or 7/8ths (22.2mm) depending on the model. The massive increase in piston area requires a minimum of 15/16ths (23.8mm) or preferably 1 inch (25.4 mm).
This is critical. If the master cylinder is too small, it will run out of travel before it can apply sufficient pressure. The area, hence, the volumes of fluid displaced for a given amount of travel increases with the square of the piston diameter. Beware who do your own conversions!
shows the conversion kit with mounting bracket.
Back in the early Seventies, Datsun 1600s were the rally car of choice, even to the point of some brave men putting full-house 13B rotaries in them. These cars were known as Dazdas or Madsuns, the latter being closer to the truth.