Brake Calliper Replacement

I had rebuilt the callipers on the 200Tdi Discovery front axle for the 109, but they are the twin-hose type connected to both hydraulic circuits.  While this would work fine on the vehicle, it would require installation of a second brake line to the front callipers, with another pair of brake hoses running from the chassis to each brake unit.

While not technically difficult, it would have been untidy and would also cost more to buy a second pair of braided hoses and all the brake line, fittings and adaptors to adapt the existing system.  As chance had it, I had access to a pair of second hand single-line callipers from a later (300Tdi, non-ABS) Discovery to rebuild with the stainless pistons I used rebuilding those earlier callipers.  They needed a clean up, being fairly well coated in deep surface rust, but once media blasted (and sprayed with red-oxide primer to prevent return of the rust), they looked to be in pretty good shape.  The pistons were all pitted and one or two seems a bit stiff.  A handful of them were really quite rusty.

There are internal differences between the single and dual-line callipers, but the casting numbers on the outside are the same.  They are identical units except in a few drillings: the single line callipers aren’t drilled for the lower nipples or the second feed line to the upper cylinders, but they have large drillings in the back of each cylinder bore to tunnel through from the lower to the upper bore.  You’ll be able to see that tunnel in the strip down photos.  So, while it would be easier to use the single circuit callipers, you could, if you wanted to, modify dual circuit cylinders to single circuit by drilling the bore connecting tunnel and fitting a bleed nipple to the redundant feed port (a blled nipple would be preferable to a blanking stud as air will be trapped in the duct between the port and the cylinder).

I’ll be adding a calliper overhaul guide to the FAQ section of the blog, so won’t go into excessive detail here, but on return of the callipers, they were stripped down to their component parts, cleaned internally and rebuilt with new seals and the Zeus stainless pistons removed from the dual-circuit callipers.  They’ll be finished in Hammerite smooth silver spray, just like the other callipers, before being fitted to the axle.

This just leaves me with the problem of mating the Discovery brake servo and master cylinder to a SIII pedal box before I do the axle swap; I don’t want to use the Defender pedal assembly as the pedal height would be wrong and the pedal would no longer match the clutch pedal.  I believe that’ll be a relatively simple mater of making an adapter plate.

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